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LIBRARY 
 
 OF THE. 
 
 UNIVERSITY OF ILLINOIS 
 
CHARLES DARWIN 
 
THE 
 
 ORIGIN OF SPECIES 
 
 BY 
 
 MEANS OF NATURAL SELECTION; 
 
 OR, THE 
 
 PRESERVATION OF FAVORED RACES IN THE 
 
 STRUGGLE FOR LIFE. 
 
 By CHARLES DARWIN, M.A., F.R.S., 
 
 Author of “The Descent of Man ” etc., etc. 
 
 Reprinted from the Sixth London Edition, with all Additions and 
 
 Corrections. 
 
 A. L. BURT COMPANY, PUBLISHERS, 
 52-58 Duane Street, New York. 
 
J 
 
/ 0 
 
 CXK-4& t / & 
 
 “ But with regard to the material world, we can at least 
 go so far as this—we can perceive that events are brought 
 about not by insulated interpositions of Divine power, 
 exerted in each particular case, but by the establishment 
 of general laws.”— Whewell: Bridgewater Treatise. 
 
 “The only distinct meaning of the word * natural* is 
 stated , fixed or settled; since what is natural as much re¬ 
 quires and presupposes an intelligent agent to render it so, 
 i.e., to effect it continually or at stated times, as what is 
 supernatural or miraculous does to effect it for once.**— 
 Butler: Analogy of Revealed Religio7i . 
 
 “ To conclude, therefore, let no man out of a weak con- 
 J ceit of sobriety, or an ill-applied moderation, think or 
 maintain, that a man can search too far or be too well 
 studied in the book of God*s word, or in the book of God*s 
 o works; divinity or philosophy; but rather let men 
 d endeavor an endless progress or proficience in both.**— 
 Bacon: Advancement of Learning. 
 
AN HISTORICAL SKETCH 
 
 OP THE PROGRESS OP OPINION ON THE ORIGIN 
 
 OF SPECIES, 
 
 PREVIOUSLY TO THE PUBLICATION OF THE FIRST EDITION 
 
 OF THIS WORK. 
 
 I will here give a brief sketch of the progress of opin¬ 
 ion on the Origin of Species. Until recently the great 
 majority of naturalists believed that species were immut¬ 
 able productions, and had been separately created. This 
 view has been ably maintained by many authors. Some 
 few naturalists, on the other hand, have believed that 
 species undergo modification, and that the existing forma 
 of life are the descendants by true generation of pre exist¬ 
 ing forms. Passing over allusions to the subject in the 
 classical writers,* the first author who in modern times 
 
 *Aristotle, in his “Physicse Auscultationes ” (lib. 2, cap. 8, s. 2), 
 after remarking that rain does not fall in order to make the corn 
 grow, any more than it falls to spoil the farmer’s corn when threshed 
 out of doors, applies the same argument to organization; and adds (as 
 translated by Mr. Clair Grece, who first pointed out the passage to 
 me), “ So what hinders the different parts [of the body] from having 
 this, merely accidental relation in nature ? as the teeth, for example, 
 grow by necessity, the front ones sharp, adapted for dividing, and the 
 grinders flat, and serviceable for masticating the food; since they 
 were not made for the sake of this, but it was the result of accident. 
 And in like manner as to other parts in which there appears to exist 
 an adaptation to an end. Wheresoever, therefore, all things 
 together (that is all the parts of one whole) happened like as if they 
 were made for the sake of something, these were preserved, having 
 been appropriately constituted by an internal spontaneity; and what¬ 
 soever things were not thus constituted, perished and still perish.’ 1 
 We here see the principle of natural selection shadowed forth, but 
 how little Aristotle fully comprehended the principle, is shown by 
 his remarks on the formation of the teeth. 
 
vi 
 
 HISTORICAL SKETCH. 
 
 has treated it in a scientific spirit was Buffon. Bu- as his 
 opinions fluctuated greatly at different periods, and as he 
 does not enter on the causes or means of the transforma¬ 
 tion of species, I need not here enter on details. 
 
 Lamarck was the first man whose conclusions on the 
 subject excited much attention. This justly celebrated 
 naturalist first published his views in 1801; he much en¬ 
 larged them in 1809 in his “ Philosophic Zoologique,” and 
 subsequently, 1815, in the Introduction to his “ Ilist. Nat. 
 des Animaux sans Vertebres.” In these works he upholds 
 the doctrine that all species, including man, are descended 
 from other species. He first did the eminent service of 
 arousing attention to the probability of all change in the 
 organic, as well as in the inorganic world, being the result 
 of law, and not of miraculous interposition. Lamarck 
 seems to have been chiefly led to his conclusion on the 
 gradual change of species, by the difficulty of distinguish¬ 
 ing species and varieties, by the almost perfect gradation 
 of forms in certain groups, and by the analogy of domestic 
 productions. With respect to the means of modification, 
 he attributed something to the direct action of the phys¬ 
 ical conditions of life, something to the crossing of 
 already existing forms, and much to use and disuse, that 
 is, to the effects of habit. To this latter agency he seems 
 to attribute all the beautiful adaptations in nature; such, 
 as the long neck of the giraffe for browsing on the branches 
 of trees. But he likewise believed in a law of progressive 
 development; and as all the forms of life thus tend to 
 progress, in order to account for the existence at the 
 present day of simple productions, he maintains that such 
 forms are now spontaneously generated.* 
 
 Geoffroy Saint-Hilaire, as is stated in his “Life,” writ¬ 
 ten by his son, suspected, as early as 1795, that what we 
 call species are various degenerations of the same type. It 
 
 * I have taken the date of the first publication of Lamarck from 
 Isidore Geoffroy Saint-Hilaire’s (“ftist. Nat. Generale,” tom. ii. p t 
 405, 1859) excellent history of opinion on this subject. In this work 
 a full account is given of Buff on’s conclusions on the same subject. 
 It is curious how largely my grandfather. Dr. Erasmus Darwin, 
 anticipated the views and erroneous grounds of opinion of Lamarck 
 in his “ Zoonomia” (vol. i. pp. 500-510), published in 1794. Accord¬ 
 ing to Isid. Geoffroy there is no doubt that Goethe was an extreme 
 partisan of similar views, as shown in the introduction to a work 
 
HISTORICAL SKETCH. 
 
 Vll 
 
 was not until 1828 that he published his conviction that 
 the same forms have not been perpetuated since the origin 
 of all things. Geoffroy seems to have relied chiefly on the 
 conditions of life, or the “ monde ambiant” as the cause of 
 change. He was cautious in drawing conclusions, and did 
 not believe that existing species are now undergoing modi¬ 
 fication; and, as his son adds, “C*est done un probleme a 
 reserver enticement 4 Favenir, suppose meme que Favenir 
 doive avoir prise sur lui.” 
 
 In 1813 Dr. W. 0. Wells read before the Royal Society 
 “ An Account of a White Female, part of whose skin 
 resembles that of a Negro ; ” but his paper was not pub¬ 
 lished until his famous “ Two Essays upon Dew and Single 
 Vision ” appeared in 1818. In this paper he distinctly 
 recognizes the principle of natural selection, and this is the 
 first recognition which has been indicated; but he applies 
 it only to the races of man, and to certain characters alone. 
 After remarking that negroes and mulattoes enjoy an im¬ 
 munity from certain tropical diseases, he observes, firstly, 
 that all animals tend to vary in some degree, and, secondly, 
 that agriculturists improve their domesticated amiinals by 
 selection; and then, he adds, but what is done in this 
 latter case “ by art, seems to be done with equal efficacy, 
 though more slowly, by nature, in the formation of varie¬ 
 ties of mankind, fitted for the country which they inhabit. 
 Of the accidental varieties of man, which would occur 
 among the first few and scattered inhabitants of the middle 
 regions of Africa, some one would be better fitted than 
 others to bear the diseases of the country. This race 
 would consequently multiply, while the others would 
 decrease; not only from their inability to sustain the 
 attacks of disease, but from their incapacity of contending 
 with their more vigorous neighbors. The color of this 
 vigorous race I take for granted, from what has been 
 
 written in 1794 and 1795, but not published till long afterward be 
 bas pointedly remarked (“Goethe als Naturforscher,” von Dr. Karl 
 Meding, s. 34) that the future question for naturalists will be bow, for 
 instance, cattle got their horns and not for what they are used. It is 
 rather a singular instance of the manner in which similar views arise 
 at about the same time, that Goethe in Germany, Dr, Darwin in Eng¬ 
 land, and Geoffroy Saint-Hilaire (as we shall immediately see) in 
 France, came to the same conclusion on the origin of suedes, in the 
 years 1794-5- 
 
HISTORICAL SKETCH. 
 
 • • 9 
 
 Vlll 
 
 already said, would be dark. But the same disposition to 
 form varieties still existing, a darker and a darker race 
 would in the course of time occur: and as the darkest 
 would be the best fitted for the climate, this would at 
 length become the most prevalent, if not the only race, in 
 the particular country in which it had originated." He 
 then extends these same views to the white inhabitants of 
 colder climates. I am indebted to Mr. Rowley, of the 
 United States, for having called my attention, through Mr. 
 Brace, to the above passage of Hr. Wells* work. 
 
 The Hon. and Rev. W. Herbert, afterward Dean of 
 Manchester, in the fourth volume of the “ Horticultural 
 Transactions," 1822, and in his work on the “ Amarylli- 
 daceaa" (1837, pp. 19, 339), declares that “horticultural 
 experiments have established, beyond the possibility of 
 refutation, that botanical species are only a higher and 
 more permanent class of varieties." He extends the same 
 view to animals. The dean believes that single species of 
 each genus were created in an originally highly plastic con¬ 
 dition, and that these have produced, chiefly by inter¬ 
 crossing, but likewise by variation, all our existing species. 
 
 In 1826 Professor Grant, in the concluding paragraph 
 in his well-known paper (“Edinburgh Philosophical 
 Journal," vol. xiv, p. 283) on the Spongilla, clearly de¬ 
 clares his belief that species are descended from other 
 species, and that they become improved in the course of 
 modification. This same view was given in his Fifty-fifth 
 Lecture, published in the “ Lancet" in 1834. 
 
 In 1831 Mr. Patrick Matthew published his work on 
 “ Naval Timber and Arboriculture," in which he gives 
 precisely the same view on the origin of species as that 
 (presently to be alluded to) propounded by Mr. Wallace 
 and myself in the “Linnean Journal," and as that enlarged 
 in the present volume. Unfortunately the view was given 
 by Mr. Matthew very briefly in scattered passages in an 
 appendix to a work on a different subject, so that it re¬ 
 mained unnoticed until Mr. Matthew himself drew atten¬ 
 tion to it in the “ Gardeners* Chronicle," on April 7, 
 1860. The differences of Mr. Matthew’s views from mine 
 are not of much importance: he seems to consider that the 
 world was nearly depopulated at successive periods, and 
 then restocked; and lie gives as an alternative, that new 
 
HISTORICAL SKETCH. 
 
 in¬ 
 forms may be generated “ without the presence of any 
 mold or germ of former aggregates.” I am not sure that 
 I understand some passages; but it seems that he attributes 
 much influence to the direct action of the conditions of 
 life. He clearly saw, however, the full force of the prin¬ 
 ciple of natural selection. 
 
 The celebrated geologist and naturalist. Yon Buch, in 
 his excellent “ Description Physique des Isles Canaries” 
 (1836, p. 147), clearly expresses his belief that varieties 
 slowly become changed into permanent species, which are 
 no longer capable of intercrossing. 
 
 Rafinesque, in his “New Flora of North America,” pub¬ 
 lished in 1836, wrote (p. 6) as follows: “All species might 
 have been varieties once, and many varieties are gradually 
 becoming species by assuming constant and peculiar char¬ 
 acters;” but further on (p. 18) he adds, “except the 
 original types or ancestors of the genus.” 
 
 In 1843-44 Professor Haldeman (“ Boston Journal of 
 Nat. Hist. U. States,” vol. iv, p. 468) has ably given the 
 arguments for and against the hypothesis of the develop¬ 
 ment and modification of species: he seems to lean toward 
 the side of change. 
 
 The “Vestiges of Creation” appeared in 1844. In the 
 tenth and much improved edition (1853) the anony¬ 
 mous author says (p. 155): “The proposition determined 
 on after much consideration is, that the several series 
 of animated beings, from the simplest and oldest up to 
 the highest and most recent, are, under the providence 
 of God, the results, first, of an impulse which has been im¬ 
 parted to the forms of life, advancing them, in definite 
 times, by generation, through grades of organization ter¬ 
 minating in the highest dicotyledons and vertebrata, these 
 grades being few in number, and generally marked by in- 
 tervals of organic character, which we find to be a practi 
 cal difficulty in ascertaining affinities; second , of another 
 impulse connected with the vital forces, tending, in the 
 course of generations, to modify organic structures in ac¬ 
 cordance with external circumstances, as food, the nature 
 of the habitat, and the meteoric agencies, these being the 
 ‘ adaptations 9 of the natural theologian.” The author ap¬ 
 parently believes that organization progresses by sudden 
 leaps, but that the effects produced by the conditions of 
 
X 
 
 HISTORICAL SKETCH. 
 
 life are gradual. He argues with much force on general 
 grounds that species are not immutable productions. But 
 I cannot see how the two supposed “impulses” account in a 
 scientific sense for the numerous and beautiful coadaptations 
 which we see throughout nature; 1 cannot see that we 
 thus gain any insight how, for instance, a woodpecker has 
 become adapted to its peculiar habits of life. The work, 
 from its powerful and brilliant style, though displaying in 
 the early editions little accurate knowledge and a great 
 want of scientific caution, immediately had a very wide 
 circulation. In my opinion it has done excellent service 
 in this country in calling attention to the subject, in re¬ 
 moving prejudice, and in thus preparing the ground for 
 the reception of analogous views. 
 
 In 1846 the 'Veteran geologist M. J. d’Omalius d*Halloy 
 published in an excellent though short paper (“ Bulletins 
 de PAcad. Boy. Bruxelles,” tom. xiii, p. 581) his opinion 
 that it is more probable that new species have been pro¬ 
 duced by descent with modification than that they have 
 been separately created: the author first promulgated this 
 opinion in 1831. 
 
 Professor Owen, in 1819 (“Nature of Limbs,” p. 86), 
 wrote as follows: “ The archetypal idea was manifested 
 in the flesh under diverse such modifications, upon this 
 planet, long prior to the existence of those animal species 
 that actually exemplify it. To what natural laws or secon¬ 
 dary causes the orderly succession and progression of such 
 organic phenomena may have been committed, we, as yet, 
 are ignorant.” In his address to the British Association, 
 in 1858, he speaks (p. li) of “the axiom of the continuous 
 operation of creative power, or of the ordained becoming 
 of living things.” Further on (p. xc), after referring to 
 geographical distribution, he adds, “These phenomena 
 shake our confidence in the conclusion that the Apteryx of 
 New Zealand and the Red Grouse of England were distinct 
 creations in and for those islands respectively. Always, 
 also, it may be well to bear in mind that by the word 
 ‘creation* the ’zoologist means ‘a process he knows not 
 what.*” He amplifies this idea by adding that when such 
 cases as that of the Red Grouse are “enumerated by the 
 zoologist as evidence of distinct creation of the bird in and 
 for such islands, he chiefly expresses that he knows not 
 
HISTORICAL SKETCH\ 
 
 XL 
 
 how the Red Grouse came to be there, and there exclu¬ 
 sively; signifying also, by this mode of expressing such 
 ignorance, his belief that both the bird and the islands 
 owed their origin to a great first Creative Cause.” If we 
 interpret these sentences given in the same address, one by 
 the other, it appears that this eminent philosopher felt in 
 1858 his confidence shaken that the Apteryx and the Red 
 Grouse first appeared in their respective homes “ he knew 
 not how,” or by some process “ he knew not what.” 
 
 This address was delivered after the papers by Mr. 
 Wallace and myself on the Origin of Species, presently to 
 be referred to, had been read before the Linnean Society 
 When the first edition of this work was published, I was 
 so completely deceived, as were many others, by such 
 expressions as “ the continuous operation of creative 
 power,” that I included Professor Owen with other palaeon¬ 
 tologists as being firmly convinced of the immutability of 
 species; but it appears (“Anat. of Vertebrates,” vol. iii, 
 p. 796) that this was on my part a preposterous error. In 
 the last edition of this work I inferred, and the inference 
 still seems to me perfectly just, from a passage beginning 
 with the words “ no doubt the type-form,” etc. (Ibid., vol. 
 i, p. xxxv), that Professor Owen admitted that natural 
 selection may have done something in the formation of a 
 new species ; but this it appears (Ibid., vol. iii, p. 798) is 
 inaccurate and without evidence. I also gave some extracts 
 from a correspondence between Professor Owen and the 
 editor of the “ London Review,” from which it appeared 
 manifest to the editor as well as to myself, that Professor 
 Owen claimed to have promulgated the theory of natural 
 selection before I had done so; and I expressed my sur¬ 
 prise and satisfaction at this announcement; but as far as 
 it is possible to understand certain recently published pas¬ 
 sages (Ibid., vol. iii, p. 798) I have either partially or 
 wholly again fallen into error. It is consolatory to me 
 that others find Professor Owen’s controversial writings as 
 difficult to understand and to reconcile with each other, as 
 I do. As far as the mere enunciation of the principle of 
 natural selection is concerned, it is quite immaterial 
 whether or not Professor Owen preceded me, for both of 
 us, as shown in this historical sketch, were long ago pre¬ 
 ceded by Dr. Wells and Mr. Matthews. > 
 
HISTORICAL SKETCH. 
 
 • • 
 
 Xll 
 
 M. Isidore Geoffroy Saint-Hilaire, in his lectures deliv¬ 
 ered in 1850 (of which a Resume appeared in the “ Revue 
 et Mag. de Zoolog.," Jan., 1851), briefly gives his reason 
 for believing that specific characters “sont fixes, pour 
 chaque espece, tant qu’elle se perpetue au milieu des 
 mbmes circonstances: ils se modifient, si les circonstances 
 ambiantes viennent a changer." “En resume, Vobserva¬ 
 tion des animaux sauvages demontre deja la variability 
 limit ee des especes. Les experiences sur les animaux 
 sauvages devenus domestiques, et sur les animaux domes- 
 tiques redevenus sauvages, la demontrent plus clairement 
 encore. Ces memes experiences prouvent, de plus, que les 
 differences produites peuvent etre de valeur generique.” 
 In his “ Hist. Nat. Generate" (tom. ii, p. 430, 1859) he 
 amplifies analogous conclusions. 
 
 From a circular lately issued it appears that Dr. Freke, 
 in 1851 (“ Dublin Medical Press," p. 322), propounded 
 the doctrine that all organic beings have descended from 
 one primordial form. His grounds of belief and treat¬ 
 ment of the subject are wholly different from mine; 
 but as Dr. Freke has now (1861) published his Essay on 
 ihe “ Origin of Species by means of Organic Affinity," 
 the difficult attempt to give any idea of his views would 
 be superfluous on my part. 
 
 Mr. Herbert Spencer, in an Essay (originally pub¬ 
 lished in the “ Leader," March, 1852, and republished in 
 his “Essays," in 1858), has contrasted the theories of the 
 Creation and the Development of organic beings with 
 remarkable skill and force. He argues from the analogy 
 of domestic productions, from the changes which the em¬ 
 bryos of many species undergo, from the difficulty of dis¬ 
 tinguishing species and varieties, and from the principle of 
 general gradation, that species have been modified; and 
 he attributes the modification to the change of circum¬ 
 stances. The author (1855) has also treated Psychology 
 on the principle of the necessary acquirement of each 
 mental power and capacity by gradation. 
 
 In 1852 M. Naudin, a distinguished botanist, expressly 
 stated, in an admirable paper on the Origin of Species 
 (“Revue Horticole," p. 10^; since partly republished in 
 the “Nouvelles Archives du Museum," tom. i, p. 171), his 
 belief that species are formed in an analogous manner as 
 
historical, sketch. 
 
 • 9 C 
 
 Xlll 
 
 varieties are under cultivation ; and tlie latter process he 
 attributes to man’s power of selection. But he does not 
 show how selection acts under nature. He believes, 
 like Dean Herbert, that species, when nascent, were more 
 plastic than at present. He lays weight on what he calls 
 the principle of finality, “ puissance mysterieuse, inde- 
 termin6e; fatalite pour les uns; pour les autres volonte 
 providentielle, dont l’action incessante sur les 6tres vi- 
 vantes determine, a toutes les epoques de l’existence du 
 monde, la forme, le volume, et la duree de cliacun d’eux, 
 en raison de sa destinee dans l’ordre de choses dont il fait 
 partie. C’est cette puissance qui harmonise chaque 
 membre a Pensemble, en Pappropriant a la fonction qu’il 
 doit remplir dans Porganisme general de la nature, fonc¬ 
 tion qui est pour lui sa raison d’etre.” * 
 
 In 1853 a celebrated geologist, Count Keyserling (“Bul¬ 
 letin de la Soc. Geolog.,” 2d Ser., tom. x, p. 357), sug¬ 
 gested that as new diseases, supposed to have been caused 
 by some miasma have arisen and spread over the world, so 
 at certain periods the germs of existing species may have 
 been chemically affected by circumambient molecules of a 
 particular nature, and thus have given rise to new forms. 
 
 In this same year, 1853, Dr. Schaaffhausen published an 
 excellent pamphlet (“Verhand. des Naturhist. Vereins der 
 Preuss. Rheinlands,” etc.), in which he maintains the de¬ 
 velopment of organic forms on the earth. He infers that 
 many species have kept true for long periods, whereas a 
 few have become modified. The distinction of species he 
 explains by the destruction of intermediate graduated 
 
 *From references in Bronn’s " Untersuchungen iiber dieEnt- 
 wickelungs-Gesetze,” it appears that the celebrated botanist and 
 palaeontologist Unger published, in 1852, his belief that species 
 undergo development and modification. Dalton, likewise, in Pander 
 and Dalton’s work on Fossil Sloths, expressed, in 1821, a similar 
 belief. Similar views have, as is well known, been maintained by 
 Oken in his mystical “ Natur-Philosopliie.” From other references 
 in Godron’s work “Sur l’Espece,” it seems that Bory St. Vincent, 
 Burdach, Poiret and Fries, have all admitted that new species are 
 continually being produced. I may add, that of the thirty-four 
 authors named in this Historical Sketch, who believe in the modi- 
 cation of species, or at least disbelieve in separate acts of crea¬ 
 tion, twenty-seven have written on special branches of natural 
 history or geology. 
 
xiv 
 
 HISTORICAL SKETCH. 
 
 forms. <e Thus living plants and animals are not sepa¬ 
 rated from the extinct by new creations, but are to b© 
 regarded as their descendants through continued repro¬ 
 duction.” 
 
 A well-known French botanist, M. Lecoq, writes in 
 1854 (“Etudes sur Geograph. Bot. tom. i, p. 250), “On 
 voit que nos recherches sur la fixite ou la variation de 
 Tespece, nous conduisent directement aux idees emises 
 par deux hommes justement celebres, Geoffroy Saint- 
 Hilaire et Goethe.” Some other passages scattered through 
 M. Lecoq’s large work make it a little doubtful how far lie 
 extends his views on the modification of species. 
 
 The “ Philosophy of Creation ” has been treated in a 
 masterly manner by the Rev. Baden Powell, in his “ Essays 
 on the Unity of Worlds,” 1855. Nothing can be more 
 striking than the manner in which he shows that the intro¬ 
 duction of new species is “a regular, not a casual phenom¬ 
 enon,” or, as Sir John Herschel expresses it, “ a natural 
 in contradistinction to a miraculous process.” 
 
 The third volume of the “Journal of the Linnean 
 Society” contains papers, read July 1, 1858, by Mr. 
 Wallace and myself, in which, as stated in the introductory 
 remarks to this volume, the theory of Natural Selection is 
 promulgated by Mr. Wallace with admirable force and 
 clearness. 
 
 Yon Baer, toward whom all zoologists feel so profound a 
 respect, expressed about the year 1859 (see Prof. Rudolph 
 Wagner, “ Zoologisch-Anthropologische Untersuchungen,” 
 1861, s. 51) his conviction, chiefly grounded on the laws of 
 geographical distribution, that forms now perfectly distinct 
 have descended from a single parent-form. 
 
 In June, 1859, Professor Huxley gave a lecture before 
 the Royal Institution on the “ Persistent Types of Animal 
 Life.” Referring to such cases, he remarks, “ It is difficult 
 to comprehend the meaning of such facts as these, if we 
 suppose that each sjoecies of animal and plant, or each 
 great type of organization, was formed and placed upon the 
 surface of the globe at long intervals by a distinct act of 
 creative power; and it is 'well to recollect that such an 
 assumption is as unsupported by tradition or revelation as 
 it is opposed to the general analogy of nature. If, on the 
 other hand, we view “Persistent Types” in relation to 
 
HISTORICAL SKETCH. 
 
 XV 
 
 that hypothesis which supposes the species living at any 
 time to be the result of the gradual modification of pre¬ 
 existing species, a hypothesis which, though unproven, and 
 ' sadly damaged by some of its supporters, is yet the only 
 one to which physiology lends any countenance; their 
 existence would seem to show that the amount of modifica¬ 
 tion which living beings have undergone during geological 
 time is but very small in relation to the whole series of 
 changes which they have suffered.” 
 
 In December, 1859, Dr. Hooker published his “ Intro¬ 
 duction to the Australian Flora.” In the first part of this 
 great Work he admits the truth of the descent and modifica¬ 
 tion of species, and supports this doctrine by many original 
 observations. 
 
 The first edition of this work was published on Novem¬ 
 ber 24, 1859, and the second edition on January 7, 1860. 
 

 
CONTENTS. 
 
 Introduction 
 
 PiGS. 
 .. 1 
 
 CHAPTER I. 
 
 VARIATION UNDER DOMESTICATION. 
 
 Causes of Variability —Effects of Habit and tbe use or disuse 
 of Parts—Correlated Variation—Inheritance—Character of 
 Domestic Varieties—Difficulty of distinguishing between 
 Varieties and Species—Origin of Domestic Varieties from 
 one or more Species—Domestic Pigeons, their Differences 
 and Origin—Principles of Selection, anciently followed, 
 their Effects — Methodical and Unconscious Selection— 
 Unknown Origin of our Domestic Productions—Circum¬ 
 stances favorable to Man’s power of Selection. 6 
 
 CHAPTER II. 
 
 VARIATION UNDER NATURE. 
 
 Variability — Individual differences—Doubtful species — Wide 
 ranging, much diffused, and common species, vary most— 
 Species of the larger genera in each country vary more 
 frequently than the species of the smaller genera—Many 
 of the species of the larger genera resemble varieties in 
 being very closely, but unequally, related to each other, and 
 in having restricted ranges. 39 
 
 CHAPTER III. 
 
 STRUGGLE FOR EXISTENCE. 
 
 Its bearing on natural selection — The term used in a wide 
 sense — Geometrical ratio of increase — Rapid increase of 
 naturalized animals and plants—Nature of the checks to 
 increase —Competition universal—Effects of climate—Pro¬ 
 tection from the number of individuals—Complex relations 
 of all animals and plants throughout nature—Struggle for 
 
CONTENTS. 
 
 XVlll 
 
 life most severe between individuals and varieties of the 
 same species: often severe between species of the same 
 genus—The relation of organism to organism the most 
 important of all relations.57 
 
 CHAPTER IV. 
 
 NATURAL SELECTION; OR THE SURVIVAL OF THE FITTEST. 
 
 Natural Selection—its power compared with man’s selection— 
 its power on characters of trifling importance—its power 
 at all ages and on both sexes—Sexual Selection—On the 
 generality of intercrosses between individuals of the same 
 species—Circumstances favorable and unfavorable to the 
 results of Natural Selection, namely, intercrossing, isolation, 
 number of individuals—Slow action—Extinction caused by 
 Natural Selection—Divergence of Character, related to the 
 diversity of inhabitants of any small area and to naturaliza¬ 
 tion—Action of Natural Selection, through Divergence of 
 Character and Extinction, on the descendants from a 
 common parent — Explains the grouping of all organic 
 beings—Advance in organization—Low forms preserved— 
 Convergence of character — Indefinite multiplication of 
 species—Summary... 73 
 
 CHAPTER V. 
 
 LAWS OF VARIATION. 
 
 Effects of changed conditions — Use and disuse, combined 
 with natural selection; organs of flight and of vision— 
 Acclimatization — Correlated variation—Compensation and 
 economy of growth — False correlations — Multiple, rudi¬ 
 mentary and lowly organized structures variable — Parts 
 developed in an unusual manner are highly variable; 
 specific characters more variable than generic; secondary 
 sexual characters variable—Species of the same genus vary 
 in an analogous manner—Reversions to long-lost charac¬ 
 ters—Summary.126 
 
 CHAPTER VI. 
 
 DIFFICULTIES OF THE THEORY. 
 
 Difficulties of the theory of descent with modification— 
 Absence or rarity of transitional varieties—Transitions in 
 habits of life—Diversified habits in the same species—■ 
 Species with habits widely different from those of their 
 allies—Organs of extreme perfection—Modes of transition— 
 Cases of difficulty — Natura non facit sal turn—Organs of 
 
CONTENTS. 
 
 xix 
 
 Page. 
 
 small importance—Organs not in all cases absolutely per¬ 
 fect—The law of Unity of Type and of the Conditions of 
 Existence embraced by the theory of Natural Selection.158 
 
 CHAPTER VII. 
 
 MISCELLANEOUS OBJECTIONS TO THE THEORY OF NATURAL 
 
 SELECTION. 
 
 Longevity — Modifications not necessarily simultaneous—Modi¬ 
 fications apparently of no direct service — Progressive 
 development—Characters of small functional importance, 
 the most constant—Supposed incompetence of natural selec 
 tion to account for the incipient stages of useful structures 
 —Causes which interfere with the acquisition through 
 natural selection of useful structures—Gradations of struct¬ 
 ure with changed functions — Widely different organs in 
 members of the same class, developed from one and the 
 same source—Reasons for disbelieving in great and abrupt 
 modifications.199 
 
 CHAPTER VIII. 
 
 INSTINCT. 
 
 Jnstincts comparable with habits, but different in their 
 origin—Instincts graduated — Aphides and ants — Instincts 
 variable—Domestic instincts, their origin—Natural, instincts 
 of the cuckoo, molothrus, ostrich and parasitic bees—Slave¬ 
 making ants—Hive-bee, its cell-making instinct—Changes 
 of instinct and structure not necessarily simultaneous— 
 Difficulties of the theory of the Natural Selection of instincts 
 —Neuter or sterile insects—Summary... 242 
 
 CHAPTER IX. 
 
 HYBRIDISM. 
 
 Distinction between the sterility of first crosses and of 
 hybrids—Sterility various in degree, not universal, affected 
 by close interbreeding, removed by domestication—Laws 
 governing the sterility of hybrids—Sterility not a special 
 endowment, but incidental on other differences, not accumu¬ 
 lated by natural selection—Causes of the sterility of first 
 crosses and of hybrids—Parallelism between the effects of 
 changed conditions of life and of crossing—Dimorphism and 
 Trimorphism — Fertility of varieties when crossed and of 
 their mongrel offspring not universal—Hybrids and mon¬ 
 grels compared independently of their fertility—Summary... 277 
 
XX 
 
 CONTENTS. 
 
 CHAPTER X. 
 
 ON THE IMPERFECTION OF THE GEOLOGICAL RECORD. 
 
 PAGB. 
 
 On tlie absence of intermediate varieties at tbe present day— 
 
 On tbe nature of extinct intermediate varieties; on their 
 number—On tbe lapse of time, as inferred from tbe rate of 
 denudation and of deposition—On tbe lapse of time as esti¬ 
 mated by years—On tbe poorness of our palaeontological col¬ 
 lections—On tbe intermittence of geological formations—On 
 tbe denudation of granitic areas—On tbe absence of inter¬ 
 mediate varieties in any one formation—On tbe sudden 
 appearance of groups of species—On tbeir sudden appear¬ 
 ance in tbe lowest known fossiliferous strata—Antiquity of 
 tbe habitable eartb.312 
 
 CHAPTER XI. 
 
 ON THE GEOLOGICAL SUCCESSION OF ORGANIC BEINGS. 
 
 On tbe slow and successive appearance of new species—On 
 tbeir different rates of change — Species once lost do not 
 reappear—Groups of species follow tbe same general rules 
 in tbeir appearance and disappearance as do single species 
 —On extinction—On simultaneous changes in tbe forms 
 of life throughout tbe world—On tbe affinities of extinct 
 species to each other and to living species—On tbe state of 
 development of ancient forms—On tbe succession of tbe 
 same types within tbe same areas—Summary of preceding 
 and present chapter.343 
 
 CHAPTER XII. 
 
 GEOGRAPHICAL DISTRIBUTION. 
 
 Present distribution cannot be accounted for by differences 
 in physical conditions — Importance of barriers — Affinity 
 of tbe productions of the same continent—Centers of crea¬ 
 tion—Means of dispersal by changes of climate and of tbe 
 level of tbe land, and by occasional means—Dispersal during 
 tbe Glacial period—Alternate Glacial periods in tbe north 
 and south...373 
 
 CHAPTER XIII. 
 
 geographical distribution— continued. 
 
 Distribution of fresh-water productions — On tbe inhabitants 
 of oceanic islands—Absence of Batracbians and of terrestrial 
 Mammals—On tbe relation of tbe inhabitants of islands to 
 
CONTENTS. 
 
 xxi 
 
 Page. 
 
 those of the nearest mainland—On colonization from the 
 nearest source with subsequent modification—Summary of 
 the last and present chapter.405 
 
 CHAPTER XIV. 
 
 MUTUAL AFFINITIES OF ORGANIC BEINGS: MORPHOLOGY—EMBRY¬ 
 OLOGY—RUDIMENTARY ORGANS. 
 
 Classification, groups subordinate to groups—Natural system— 
 Rules and difficulties in classification, explained on the 
 theory of descent with modification—Classification of varie¬ 
 ties—Descent always used in classification—Analogical or 
 adaptive characters—Affinities, general, complex and radiat¬ 
 ing—Extinction separates and defines groups—Morphology, 
 between members of the same class, between parts of the 
 same individual—Embryology, laws of, explained by varia¬ 
 tions not supervening at an early age, and being inherited 
 at a corresponding age—Rudimentary organs, their origin 
 explained—Summary.428 
 
 CHAPTER XV. 
 
 RECAPITULATION AND CONCLUSION. 
 
 Recapitulation of the objections to the theory of Natural Selec¬ 
 tion—Recapitulation of the general and special circum¬ 
 stances in its favor—Causes of the general belief in the 
 immutability of species—How far the theory of Natural 
 Selection may be extended—Effects of its adoption on 
 
 the study of Natural History—Concluding remarks.476 
 
 Glossary of Scientific Terms .....507 
 
 521 
 
 Index 
 
ORIGIN OF SPECIES. 
 
 INTRODUCTION. 
 
 Wheh on board H. M. S. Beagle, as naturalist, I was 
 much struck with certain facts in the distribution of 
 the organic beings inhabiting South America, and in the 
 geological relations of the present to the past inhabitants 
 of that continent. These facts, as will be seen in the latter 
 chapters of this volume, seemed to throw some light on the 
 ' origin of species—that mystery of mysteries, as it has been 
 called by one of our greatest philosophers. On my return 
 home, it occurred to me, in 1837, that something might 
 perhaps be made out on this question by patiently accumu¬ 
 lating and reflecting on all sorts of facts which could possi¬ 
 bly have any bearing on it. After five years’ work I 
 allowed myself to speculate on the subject, and drew up 
 some short notes; these I enlarged in 1844 into a sketch of 
 the conclusions, which then seemed to me probable: from 
 that period to the present day I have steadily pursued the 
 same object. I hope that I may be excused for entering 
 on these personal details, as I give them to show that I 
 have not been hasty in coming to a decision. 
 
 My work is now (1859) nearly finished; but as it will 
 take me many more years to complete it, and as my health 
 is far from strong, I have been urged to publish this ab¬ 
 stract. I have more especially been induced to do this, as 
 Mr. Wallace, who is now studying the natural history of 
 the Malay Archipelago, has arrived at almost exactly the 
 same general conclusions that I have on the origin of 
 species. In 1858 he sent me a memoir on this subject, 
 with a request that I would forward it to Sir Charles Lyell, 
 who sent it to the Linnean Society, and it is published in the 
 third volume of the Journal of that Society. Sir C. Lyell 
 
2 
 
 INTRODUCTION. 
 
 and Dr. Hooker, who both knew of my work—the latter 
 having read my sketch of 1844—honored me by thinking 
 it advisable to publish, with Mr. Wallace’s excellent memoir, 
 some brief extracts from my manuscripts. 
 
 This abstract, which I now publish, must necessarily be 
 imperfect. I cannot here give references and authorities 
 for my several statements; and I must trust to the reader 
 reposing some confidence in my accuracy. No doubt errors 
 may have crept in, though I hope I have always been cau¬ 
 tious in trusting to good authorities alone. I can here give 
 only the general conclusions at which I have arrived, with 
 a few facts in illustration, but which, I hope, in most cases 
 will suffice. No one can feel more sensible than I do of 
 the necessity of hereafter publishing in detail all the facts, 
 with references, on which my conclusions have been 
 grounded; and I hope in a future work to do this. For 
 I am well aware that scarcely a single point is discussed in 
 this volume on which facts cannot be adduced, often ap¬ 
 parently leading to conclusions directly opposite to those 
 at which I have arrived. A fair result can be obtained 
 only by fully stating and balancing the facts and arguments 
 on both sides of eacii question; and this is here impossible. 
 
 I much regret that want of space prevents my having 
 the satisfaction of acknowledging the generous assistance 
 which I have received from very many naturalists, some 
 of them personally unknown to me. I cannot, however, 
 let this opportunity pass without expressing my deep 
 obligations to Dr. Hooker, who, for the last fifteen years, 
 has aided me in every possible way by his large stores of 
 knowledge and his excellent judgment. 
 
 In considering the origin of species, it is quite conceiv¬ 
 able that a naturalist, reflecting on the mutual affinities of 
 organic beings, on their embryological relations, their 
 geographical distribution, geological succession, and other 
 such facts, might come to the conclusion that species had 
 not been independently created, but had descended, like 
 varieties, from other species. Nevertheless, such a con¬ 
 clusion, even if well founded, would be unsatisfactoiy, until 
 it could be shown how the innumerable species, inhabit¬ 
 ing this world have been modified, so as to acquire that 
 perfection of structure and coadaptation which justly 
 excites our admiration. Naturalists continually refer to 
 
INTRODUCTION. 
 
 3 
 
 external conditions, sucli as climate, food, etc., as the only 
 possible cause of variation. In one limited sense, as we 
 shall hereafter see, this may he true; but it is preposterous 
 to attribute to mere external conditions, the structure, for 
 instance, of the woodpecker, with its feet, tail, beak and 
 tongue, so admirably adapted to catch insects under the 
 bark of trees. In the case of the mistletoe, which draws 
 its nourishment from certain trees, which has seeds that 
 must be transported by certain birds, and which has flowers 
 with separate sexes absolutely requiring the agency of cer¬ 
 tain insects to bring pollen from one flower to the other, it 
 is equally preposterous to account for the structure of this 
 parasite, with its relations to several distinct organic 
 beings, by the effects of external conditions, or of habit, or 
 of the volition of the plant itself. 
 
 It is, therefore, of the highest importance to gain a clear 
 insighi-into the means of modification and coadaptation. 
 At the commencement of my observations it seemed to me 
 probable that a careful study of domesticated animals and 
 of cultivated plants would offer the best chance of making 
 out this obscure problem. Nor have I been disappointed; 
 in this and in all other perplexing cases I have invariably 
 found that our knowledge, imperfect though it be, of vari¬ 
 ation under domestication, afforded the best and safest 
 clue. I may venture to express my conviction of the high 
 value of such studies, although they have been very com¬ 
 monly neglected by naturalists. 
 
 From these considerations, I shall devote the first chap¬ 
 ter of this abstract to variation under domestication. We 
 shall thus see that a large amount of hereditary modifica¬ 
 tion is at least possible; and, what is equally or more im¬ 
 portant, we shall see how great is the power of man in 
 accumulating by his selection successive slight variations. 
 I will then pass on to the variability of species in a state of 
 nature; but I shall, unfortunately, be compelled to treat 
 this subject far too briefly, as it can be treated properly 
 only by giving long catalogues of facts. We shall, how¬ 
 ever, be enabled to discuss what circumstances are most 
 favorable to variation. In the next chapter the strug¬ 
 gle for existence among all organic beings throughout 
 the world, which inevitably follows from the high geomet¬ 
 rical ratio of their increase, will be considered. This is 
 
4 
 
 INTRODUCTION. 
 
 « 
 
 the doctrine of Malthus, applied to the whole animal and 
 vegetable kingdoms. As many more individuals of each 
 species are horn than can possibly survive; and as, conse¬ 
 quently, there is a frequently recurring struggle for exist¬ 
 ence, it follows that any being, if it vary however slightly 
 in any manner profitable to itself, under the complex and 
 sometimes varying conditions of life, will have a better 
 chance of surviving, and thus be naturally selected. From 
 the strong principle of inheritance, any selected variety 
 will tend to propagate its new and modified form. 
 
 This fundamental subject of natural selection will be 
 treated at some length in the fourth chapter; and we shall 
 then see how natural selection almost inevitably causes 
 much extinction of the less improved forms of life, and 
 leads to what I have called divergence of character. In the 
 next chapter I shall discuss the complex and little known 
 laws of variation. In the five succeeding chapters, the 
 most apparent and gravest difficulties in accepting the 
 theory will be given: namely, first, the difficulties of tran¬ 
 sitions, or how a simple being or a simple organ can be 
 changed and perfected into a highly developed being or 
 into an elaborately constructed organ; secondly, the sub¬ 
 ject of instinct, or the mental powers of animals; thirdly, 
 hybridism, or the infertility of species and the fertility of 
 varieties when intercrossed; and fourthly, the imperfection 
 of the geological record. In the next chapter I shall con¬ 
 sider the geological succession of organic beings through¬ 
 out time; in the twelfth and thirteenth, their geographical 
 distribution throughout space; in the fourteenth, their 
 classification or mutual affinities, both when mature and 
 in an embryonic condition. In the last chapter I shall 
 give a brief recapitulation of the whole work, and a few 
 concluding remarks. 
 
 No one ought to feel surprise at much remaining as yet 
 unexplained in regard to the origin of species and varieties, 
 if he make due allowance for our profound ignorance in 
 regard to the mutual relations of the many beings which 
 live around us. Who can explain why one species ranges 
 widely and is very numerous, and why another allied species 
 has a narrow range and is rare? Yet these relations are of 
 the highest importance, for they determine the present 
 welfare and, as I believe, the future success and modifica- 
 
INTRODUCTION. 
 
 5 
 
 tion of every inhabitant of this world. Still less do we 
 know of the mutual relations of the innumerable inhab¬ 
 itants of the world during the many past geological epochs 
 in its history* Although much remains obscure, and will 
 long remain obscure, I can entertain no doubt, after the 
 most deliberate study and dispassionate judgment of which 
 I am capable, that the view which most naturalists until 
 Tecently entertained, and which I formerly entertained— 
 namely, that each species has been independently created 
 —is erroneous. I am fully convinced that species are not 
 immutable; but that those belonging to what are called the 
 same genera are lineal descendants of some other and 
 generally extinct species, in the same manner as the 
 acknowledged varieties of any one species are the descend¬ 
 ants of that species. Furthermore, I am convinced that 
 natural selection has been the most important, but not the 
 exclusive, means of modification* 
 
VARIATION UNDER DOMESTICATION. 
 
 6 
 
 CHAPTER L 
 
 VARIATION' UNDER DOMESTICATION. 
 
 Causes of Variability—Effects of Habit and tbe use or disuse of 
 Parts—Correlated Variation—Inheritance—Character of Domes¬ 
 tic Varieties—Difficulty of distinguishing between Varieties 
 and Species—Origin of Domestic Varieties from one or more 
 Species—Domestic Pigeons, their Differences and Origin— 
 Principles of Selection, anciently followed, their Effects— 
 Methodical and Unconscious Selection—Unknown Origin of 
 our Domestic Productions—Circumstances favorable to Man’s 
 power of Selection. 
 
 CAUSES OF VARIABILITY. 
 
 When we compare tbe individuals of the same variety 
 or sub-variety of our older cultivated plants and animals, 
 one of the first points~which strikes us is, that they gen¬ 
 erally differ more from each other than do the individuals , 
 of any one species or variety in a state of nature. And if 
 we reflect on the vast diversity of the plants and animals 
 which have been cultivated, and which have varied during 
 all ages under the most different climates and treatment, 
 we are driven to conclude that this^ceat varia bility is d ue 
 to our domestic pr oductions h aving be en raised under corr- 
 cUfibns o f life nbiT so u niform as, and somewhat different 
 Tron^HEImse towhich, the p a rent speci es had been exposed 
 under nature. There is, also, some probability in the view 
 propounded by Andrew Knight, that this variability may 
 be partly co nne cted with excess of food. It seems clear 
 thatorgamc beings musITbe exposed~cluring several gener¬ 
 ations to new conditions to cause any great amount of 
 variation; and that, when the organization has once begun 
 to vary, it generally continues varying for many gener¬ 
 ations. No case is on record of a variable organism ceas¬ 
 ing to vary under cultivation. Our oldest cultivated 
 plants, such as wheat, still yield new varieties: our oldest 
 
VARIATION UNDER DOMESTICATION. 
 
 domesticated animals are still capable of rapid improve¬ 
 ment or modification 
 
 As far as I am able to judge, after long attending to the 
 subject, the conditions of life appear to act in two ways— 
 directly on the whole organization or on certain parts 
 alon$ and indirectly by affecting the reproductive system. 
 With respect to the direct action, we must bear in mind 
 that in every case, as Professor Weismann has lately 
 insisted, and as I have incidently shown in my work on 
 “ Variation under Domestication,” there are two factors: 
 namely, the nature of the organism and the nature of the 
 conditions. The former seems to be much the more 
 important; for nearly similar variations sometimes arise 
 under, as far as we can judge, dissimilar conditions; and, 
 on the other hand, dissimilar variations arise under condi¬ 
 tions which appear to be nearly uniform. The effe cts on 
 the offspring ^ire,,e ither def inite or indefinite . They may 
 be considered as definite widen all or nearly all the offspring 
 of individuals exposed to certain conditions during several 
 generations are modified in the same manner. It is 
 extremely difficult to comeTttT any conclusion in regard to 
 the extent of the changes which have been thus definitely 
 induced. There can, however, be little doubt about many 
 slight changes, such as size from the amount of food, 
 color from the nature of the food, thickness of the skin 
 and hair from climate, etc. Each of the endless variations 
 which we see in the plumage of our fowls must have had 
 some efficient cause; and if the same cause were to act 
 uniformly during a long series of generations on many 
 individuals, all probably would be modified in the same 
 manner. Such facts as the complex and extraordinary 
 outgrowths which variably follow from the insertion of a 
 minute drop of poison by a gall-producing insect, shows us 
 what singular modifications might result in the case of 
 plants from a chemical change in the nature of the sap. 
 
 Indefinite variability is a much more common result of 
 changed conditions than definite variability, and has prob¬ 
 ably played a more important part in the formation of our 
 domestic races. We see indefinite variability in the end¬ 
 less slight peculiarities which distinguish the individuals 
 of the same species, and which cannot be accounted for by 
 inheritance from either parent or from some more remote 
 
VARIATION UNDER DOMESTICATION. 
 
 & 
 
 ancestor. Even strongly-marked differences occasionally 
 appear in tlio young of the same litter, and in seedlings 
 from the same seed-capsule. At long intervals of time, 
 out of millions of individuals reared in the same country 
 and fed on nearly the same food, deviations of structure so 
 strongly pronounced as to deserve to be called monstros¬ 
 ities arise; but monstrosities cannot be separated by any 
 distinct line from slighter variations. All such changes of 
 structure, whether extremely slight or strongly marked, 
 which appear among many.Jn d ividu a l s Jiving—together.— 
 m ay be considered_ _as the indefinite effects of the non dic¬ 
 tions of life on eac h indivi dual org a ni s m^ m-mearly the 
 same mannei_asJflte--chillr-effects-differeni-men- inanindefi- 
 nite manner, accordin g-i o their state of body or constit u- 
 tion. causing coughs ^or colds, rheumutism, or inflammation 
 of yarimifr-orgahsT 
 
 IVitli respect to what I have called the indirect action of 
 changed conditions, namely, through the reproductive 
 system of being affected, we may infer that variability is 
 thus induced, partly from the fact of this system being 
 extremely sensitive to any change in the conditions, and 
 partly from the similarity, as Kolreuter and others have 
 remarked, between the variability which follows from the 
 srossing of distinct species, and that which may be observed 
 with plants and animals when reared under new or unnat¬ 
 ural conditions. Many facts clearly show how eminently 
 susceptible the reproductive system is to very slight 
 changes in the surrounding conditions. Nothing is more 
 easy than to tame an animal, and few things more difficult 
 than to get it to breed freely under confinement, even when 
 the male and female unite. How many animals there are 
 which will not breed, though kept in an almost free state in 
 their native country! This is generally, but erroneously 
 attributed to vitiated instincts. Many cultivated plants 
 display the utmost vigor, and yet rarely or never seed! In 
 some few cases it has been discovered that a very 
 trifling change, such as a little more or less water at 
 some particular period of growth, will determine whether 
 or not a plant will produce seeds. I cannot here give the 
 details which I have collected and elsewhere published 
 on this curious subject; but to show how singular the 
 laws are which determine the reproduction of animals 
 
VARIATION UNDER DOMESTICATION. 
 
 9 
 
 under confinement, I may mention that carnivorous 
 animals, even from the tropics, breed in this country 
 pretty freely under confinement, with the exception of the 
 plantigrades or bear family, which seldom produce young; 
 whereas carnivorous birds, with the rarest exception, hardly 
 ever lay fertile eggs. Many exotic plants have pollen 
 utterly worthless, in the same condition as in the most 
 sterile hybrids. When, on the one hand, we see domesti¬ 
 cated animals and plants, though often weak and sickly, 
 breeding freely under confinement; and when, on the other 
 hand, we see individuals, though taken young from a state 
 of nature perfectly tamed, long-lived and healthy (of 
 which I could give numerous instances), yet having their 
 reproductive system so seriously affected by unperceived 
 causes as to fail to act, we need not be surprised at this 
 system, when it does act under confinement, acting irregu¬ 
 larly, and producing offspring somewhat unlike their 
 parents. I may add that as some organisms breed freely 
 under the most unnatural conditions—for instance, rabbits 
 and ferrets kept in hutches—showing that their reproduct¬ 
 ive organs are not easily affected; so will some animals and 
 plants withstand domestication or cultivation, and vary 
 very slightly—perhaps hardly more than in a state of 
 nature. 
 
 Some naturalists have maintained that all variations are 
 connected with the act of sexual reproduction; but this is 
 certainly an error; for I have given m another work a long 
 list of “ sporting plants,” as they are called by gardeners; 
 that is, of plants which have suddenly produced a single 
 bud with a new and sometimes widely different character 
 from that of the other buds on the same plant. These 
 bud variations, as they may be named, can be propagated 
 by grafts, offsets, etc., and sometimes by seed. They 
 ©ccur rarely under nature, but are far from rare under 
 culture. As a single bud out of many thousands produced 
 year after year on the same tree under uniform conditions, 
 has been known suddenly to assume a new character; and 
 as buds on distinct trees, growing under different con¬ 
 ditions, have sometimes yielded nearly the same variety— 
 for instance, buds on peach-trees producing nectarines, 
 and buds on common roses producing moss-roses—we 
 clearly see that the nature of the conditions is of subordi- 
 
10 
 
 VARIATION UNDER DOMESTICATION. 
 
 nate importance in comparison with the nature of the 
 organism in determining each particular form of varia¬ 
 tion; perhaps of not more importance than the nature of 
 the spark, by which a mass of combustible matter is 
 ignited, has in determining the nature of the flames. 
 
 effects of habit and of the use or disuse of parts; 
 
 CORRELATED VARIATION; INHERITANCE. 
 
 Changed habits produce an inherited effect as in the 
 period of the flowering of plants when transported from 
 one climate to another. With animals the increased 
 use or disuse of parts has had a more marked influence; 
 thus I find in the domestic duck that the bones of the 
 wing weigh less and the bones of the leg more, in 
 proportion to the whole skeleton, than do the same 
 bones in the wild duck; and this change may be 
 safely attributed to the domestic duck flying much 
 less, and walking more, than its wild parents. The 
 great and inherited development of the udders in cows 
 and goats in countries where they are habitually milked, in 
 comparison with these organs in other countries, is prob¬ 
 ably another instance of the effects of use. Not one of our 
 domestic animals can be named which has not in some 
 country drooping ears; and the view which has been sug¬ 
 gested that the drooping is due to disuse of the muscles' of 
 the ear, from the animals being seldom much alarmed, 
 seems probable. 
 
 Many laws regulate variation, some few of which can be 
 dimly seen, and will hereafter be briefly discussed. I will 
 here only allude to what may be called correlated variation. 
 Important changes in the embryo or larva will probably 
 entail changes in the mature animal. In monstrosities, the 
 correlations between quite distinct parts are very curious; 
 and many instances are given in Isidore Geoffroy St. 
 Hilaire's great work on this subject. Breeders believe that 
 long limbs are almost always accompanied by an elongated 
 head. Some instances of correlation are quite whimsical; • 
 thus cats which are entirely white and have blue eyes are 
 generally deaf; but it has been lately stated by Mr. Tait 
 that this is confined to the males. Color and constitu¬ 
 tional pecularities go together, of which many remarkable 
 
VARIATION UNDER DOMESTICATION. 
 
 11 
 
 cases could be given among animals and plants. From 
 facts collected by Heusinger, it appears that white sheep 1 
 and pigs are injured by certain plants, while dark-colored 
 individuals escape: Professor Wyman has recently com¬ 
 municated to me a good illustration of this fact; on asking 
 some farmers in Virginia how it was that all their pigs were 
 black, they informed him that the pigs ate the paint-root 
 (Lachnanthes), which colored their bones pink, and which 
 caused the hoofs of all but the black varieties to drop off; 
 and one of the “ crackers ” ( i . e. Virginia squatters) added, 
 
 “ we select the black members of a litter for raising, as 
 they alone have a good chance of living.” Hairless dogs 
 have imperfect teeth; long-haired and coarse-haired animals 
 are apt to have, as is asserted, long or many horns; pigeons 
 with feathered feet have skin between their outer toes; 
 pigeons with short beaks have small feet, and those with 
 long beaks large feet. Hence if man goes on selecting,\ 
 and thus augmenting, any peculiarity, he will almost cer-l 
 tainly modify unintentionally other parts of the structure/ 
 owing to the mysterious laws of correlation. 
 
 The results of the various, unknown, or but dimly 
 understood laws of variation are infinitely complex and 
 diversified. It is well worth while carefully to study the 
 several treatises on some of our old cultivated plants, as on 
 the hyacinth, potato, even the dahlia, etc.; and it is really 
 sui prising to note the endless points of structure and con¬ 
 stitution in which the varieties and sub-varieties differ 
 slightly from each other. The whole organization seems to 
 have become plastic, and departs in a slight degree from 
 that of the parental type. 
 
 Any variation which is not inherited is unimportant for 
 us. But the number and diversity of inheritable deviations 
 of structure, both those of slight and those of consider¬ 
 able physiological importance, are endless. Dr. Prosper 
 Lucas* treatise, in two large volumes, is the fullest 
 and the best on this subject. Ho breeder doubts how 
 strong is the tendency to inheritance; -that like pro¬ 
 duces like is his fundamental belief: doubts have 
 been thrown on this principle only by theoretical 
 writers. When any deviation of structure often appears, 
 and we see it in the father and child, we cannot tell 
 whether it may not be due to the same o&use having acted 
 
12 
 
 VARIATION UNDER DOMESTICATION. 
 
 on both; but when among individuals, apparently exposed 
 to the same conditions, any very rare deviation, due to 
 some extraordinary combination of circumstances, appeals 
 in the parent—say, once among several million individu¬ 
 als—and it reappears in the child, the mere doctrine of 
 chances almost compels us to attribute its reappearance to 
 inheritance. Every one must have heard of cases of al¬ 
 binism, prickly skin, hairy bodies, etc., appearing in 
 several members of the same family. If strange and rare de¬ 
 viations of structure are really inherited, less strange and 
 commoner deviations may be freely admitted to be inherit¬ 
 able. Perhaps the correct way of viewing the whole 
 subject would be, to look at the inheritance of every 
 character whatever as the rule, and non-inheritance as the 
 anomaly. 
 
 The Jaws gov ern in g in heritance... are for the most part 
 unknown. NcT one canTsay why the same peculiarity in 
 'different individuals of the same species, or in different 
 species, is sometimes inherited and sometimes not S 03 why 
 the child often reverts in certain characteristics to its grand¬ 
 father or grandmother or more remote ancestor; why a 
 peculiarity is often transmitted from one sex to both sexes, 
 or to one sex alone, more commonly but not exclusively to 
 the like sex. It is a fact of some importance to us, that 
 peculiarities appearing in the males of our domestic breeds 
 are often transmitted, either exclusively or in a much 
 greater degree, to the males alone. A much more im¬ 
 portant rule, which I think may be trusted, is that, at 
 whatever period of life a peculiarity first appears, it tends 
 to reappear in the offspring at a corresponding age, though 
 sometimes earlier. In many cases this could not be other¬ 
 wise; thus the inherited peculiarities in the horns of cattle 
 could appear only in the offspring when nearly mature; 
 peculiarities in the silk-worm are known to appear at the 
 corresponding caterpillar or cocoon stage. But hereditary 
 diseases and some other facts make me believe that the 
 rule has a wider extension, and that, when there is no ap¬ 
 parent reason why a peculiarity should appear at any 
 particular age, yet that it does tend to appear in the off¬ 
 spring at the same period at which it first appeared in the 
 parent. I believe this rule to be of the highest importance 
 in explaining the laws of embryology. These remarks are 
 
VARIATION UNDER DOMESTICATION. 
 
 13 
 
 of course confined to the first appearance of the peculiarity, 
 and not to the primary cause which may have acted on the 
 ovules or on the male element; in nearly the same manner 
 as the increased length of the horns in the offspring fron 
 a short-horned cow by a long-horned bull, though appear¬ 
 ing late in life, is clearly due to the male element. 
 
 Having alluded to the subject of reversion, I may here 
 refer to a statement often made by naturalists—namely, 
 that our domestic varieties, when run wild, gradually bu t 
 i nvariably revert in character to their aboriginal stocks . 
 Hence it has been argued that "nolleductions can be drawn 
 from domestic races to species in a state of nature. I have 
 in vain endeavored to discover on what decisive facts 
 the above statement has so often and so boldly been made. 
 There would be great difficulty in proving its truth: we 
 may safely conclude that very many of the most strongly 
 marked domestic varieties could not possibly live in a wild 
 state. In many cases we do not know what the aboriginal 
 stock was, and so could not tell whether or not nearly per¬ 
 fect reversion had ensued. It would be necessary, in order 
 to prevent the effects of intercrossing, that only a single 
 variety should have been tuFned loose in its new home. 
 Nevertheless, as our varieties certainly do occasionally 
 revert in some of their characters to ancestral forms, it 
 seems to me not improbable that if we could succeed in 
 naturalizing, or were to cultivate, during many gener¬ 
 ations, the several races, for instance, of the cabbage, in 
 very poor soil—in which case, however, some effect would 
 have to be attributed to the definite action of the poor 
 soil—that they would, to a large extent, or even wholly, 
 revert to the wild aboriginal stock. Whether or not the 
 experiment would succeed is not of great importance for 
 our line of argument; for by the experiment itself the 
 conditions of life are changed. If it could be shown that 
 our domestic varieties manifested a strong tendency to 
 reversion—that is, to lose their acquired characters, while 
 kept under the same conditions and while kept in a con¬ 
 siderable body, so that free intercrossing might check, by 
 blending together, any slight deviations in their structure, 
 in such case, I grant that we could deduce nothing from 
 domestic varieties in regard to species. But there is not a 
 shadow of evidence in favor of this view: to assert that we 
 
14 
 
 CHARACTER OF DOMESTIC VARIETIES, 
 
 could not breed our cart and race-horses, long and short¬ 
 horned cattle, and poultry of various breeds, and esculent 
 vegetables, for an unlimited number of generations, would 
 be opposed to all experience. 
 
 CHARACTER OF DOMESTIC VARIETIES; DIFFICULTY OF DIS¬ 
 TINGUISHING BETWEEN VARIETIES AND SPECIES; 
 ORIGIN OF DOMESTIC VARIETIES FROM ONE OR MORE 
 SPECIES. 
 
 "When we look to the hereditary varieties or races of our 
 domestic animals and plants, and compare them with 
 closely allied species, we generally perceive in each domes¬ 
 tic race, as already remarked, less uniformity of character 
 than in true species. Domestic races often have a some¬ 
 what monstrous character; by which I mean, that, 
 although differing from each other and from other species 
 of the same genus, in several trifling respects, they often 
 differ in an extreme degree in some one part, both when 
 compared one with another, and more especially when 
 compared with the species under nature to which they are 
 nearest allied. With these exceptions (and with that of 
 the perfect fertility of varieties when crossed—a subject 
 hereafter to be discussed),/domestic races of the same 
 species differ from each other in the same manner as do 
 the closely allied species of the same genus in a state of 
 nature, but the differences in most cases are less in degree. 
 This must be admitted as true, for the domestic races of 
 many animals and plants have been ranked by some com¬ 
 petent judges as the descendants of aboriginally distinct 
 species, and by other competent judges as mere varieties. 
 If any well marked distinction existed between a domestic 
 race and a species, this source of doubt would not so per¬ 
 petually recur. It has often been stated that domestic races 
 do not differ ft'om each other in characters of generic value. 
 It can be shown that this statement is not correct; but 
 naturalists differ much in determing what characters are 
 of generic value; all such valuations being at present 
 empirical. When it is exjffained how genera originate 
 under nature, it will be seen that we have no right to 
 expect often to find a generic amount of difference in our 
 domesticated races. 
 
CHARACTER OH DOMESTIC VARIETIES. 
 
 15 
 
 In attempting to estimate the amount of structural dif¬ 
 ference between allied domestic races, we are soon involved 
 in doubt, from not knowing whether they are descended 
 from one or several parent species. This point, if it could 
 be cleared up, would be interesting; if, for instance, it 
 could be shown that the greyhound, bloodhound, terrier, 
 spaniel and bull-dog, which we all know propagate their kind 
 truly, were the offspring of any single species, then such 
 facts would have great weight in making us doubt about 
 the immutability of the many closely allied natural species 
 —for instance, of the many foxes—inhabiting the different 
 quarters of the world. I do not believe, as we shall pres¬ 
 ently see, that the whole amount of difference between the 
 several breeds of the dog has been produced under domes¬ 
 tication; I believe that a small part of the difference is due 
 to their being descended from distinct species. In the case 
 of stron gly marked—races- -of—gome- other domesticated- 
 species, there is presumptive or even strong evidence that 
 all are descended from a single wil'd stock. 
 
 It has often been assumed that man has chosen for do¬ 
 mestication animals and plants having an extraordinary 
 inherent tendency to vary, and likewise to withstand 
 diverse climates. I do not dispute that these capacities 
 have added largely to the value of most of our domesticated 
 productions; but how could a savage possibly know, when 
 he first tamed an animal, whether it would vary in suc¬ 
 ceeding generations, and whether it would endure other 
 climates? Has the little variability of the ass and goose, or 
 the small power of endurance of warmth by the reindeer, 
 or of cold by the common camel, prevented their domesti¬ 
 cation? I cannot doubt that if other animals and plants, 
 equal in number to our domesticated productions, and 
 belonging to equally diverse classes and countries, were 
 taken from a state of nature, and could be made to breed 
 for an equal number of generations under domestication, 
 they would on an average vary as largely as the parent 
 species of our existing domesticated productions have 
 varied. 
 
 In the case of most of our anciently domesticated animals 
 and plants, it is not possible to come to any definite con¬ 
 clusion, whether they are descended, from one or several 
 wild species. The argument mainly relied on by those who 
 
16 
 
 CHARACTERS OF DOMESTIC VARIETIES. 
 
 believe in the multiple origin of our domestic animals is, 
 that we find in the most ancient times, on the monuments 
 of Egypt, and in the lake-habitations of Switzerland, 
 much diversity in the breeds ; and that some of these 
 ancient breeds closely resemble, or are even identical with, 
 those still existing. But this only throws far backward 
 the history of civilization, and shows that animals were 
 domesticated at a much earlier period than has hitherto 
 been supposed. The lake-inhabitants of Switzerland cul¬ 
 tivated several kinds of wheat and barley, the pea, the 
 poppy for oil and flax ; and they possessed several domesti¬ 
 cated animals. They also carried on commerce with other 
 nations. All this clearly shows, as Ileer has remarked, 
 that they had at this early age progressed considerably in 
 civilization ; and this again implies a long continued pre¬ 
 vious period of less advanced civilization, during which the 
 domesticated animals, kept by different tribes in different 
 districts, might have varied and given rise to distinct races. 
 Since the discovery of flint tools in the superficial forma¬ 
 tions of many parts of the world, all geologists believe that 
 barbarian men exsisted at an enormously remote period ; 
 and we know that at the present day there is hardly a tribe 
 so barbarous as not to have domesticated at least the dog. 
 
 The origin of most of our domestic animals will prob¬ 
 ably forever remain vague. But I may here state that, 
 looking to the domestic dogs of the whole world, I have, 
 after a laborious collection of all known facts, come to the 
 conclusion that several wild species of Canidse have been 
 tamed, and that their blood, in some cases mingled 
 together, flows in the veins of our domestic breeds. In 
 regard to sheep and goats I can form no decided opinion. 
 From facts communicated to me by Mr. Blyth, on the 
 habits, voice, constitution and structure of the humped 
 Indian cattle, it is almost certain that they are descended 
 from a different aboriginal stock from our European cattle ; 
 and some competent judges believe that these latter have 
 had two or three wild progenitors, whether or not these 
 deserve to be called species. This conclusion, as well as 
 that of the specific distinction between the humped and 
 common cattle, may, indeed, be looked upon as established 
 by the admirable researches of Professor Rutimeyer. With 
 respect to horses, from reasons which I cannot here give, I 
 
CHARACTER OF DOMESTIC VARIETIES. 
 
 17 
 
 am doubtfully inclined to believe, in opposition to several 
 authors, that all the races belong to the same species. 
 Having kept nearly all the English breeds of the fowl alive, 
 having bred and crossed them, and examined their skele¬ 
 tons, it appears to me almost certain that all are the 
 descendents of the wild Indian fowl, Gallus bankiva; and 
 this is the conclusion of Mr. Blyth, and of others who have 
 studied this bird in India. In regard to ducks and rabbits, 
 some breeds of which differ much from each other, the 
 evidence is clear that they are all descended from the 
 common duck and wild rabbit. 
 
 The doctrine of the origin of our several domestic races 
 from several aboriginal stocks, has been carried to an 
 absurd extreme by some authors. They believe that every 
 race which breeds true, let the distinctive characters be 
 ever so slight, has had its wild prototype. At this rate 
 there must have existed at least a score of species of wild 
 cattle, as many sheep, and several goats, in Europe alone, 
 and several even within Great Britain. One author believes 
 that there formerly existed eleven wild species of sheep 
 peculiar to Great Britain! When we bear in mind that 
 Britain has now not one peculiar mammal, and France but 
 few distinct from those of Germany, and so with Hungary, 
 Spain, etc., but that each of these kingdoms possesses sev¬ 
 eral peculiar breeds of cattle, sheep, etc., we must admit 
 that many domestic breeds must have originated in Europe; 
 for whence otherwise could they have been derived? So 
 it is in India. Even in the case of the breeds of the 
 domestic dog throughout the world, which I admit are 
 descended from several wild species, it cannot be doubted 
 that there has been an immense amount of inherited 
 variation; for who will believe that animals closely 
 resembling the Italian greyhound, the bloodhound, the 
 bull-dog, pug-dog, or Blenheim spaniel, etc.—so unlike 
 all wild Canidse—ever existed in a state of nature? It 
 has often been loosely said that all our races of dogs have 
 been produced by the crossing of a few aboriginal species; 
 but by crossing we can only get forms in some degree inter¬ 
 mediate between their parents; and if we account for our 
 several domestic races by this process, we must admit the 
 former existence of the most extreme forms, as the Italian 
 greyhound, bloodhound, bull-dog, etc., in the wild state. 
 
18 
 
 DOMESTIC 1 'IQ EONS. 
 
 Moreover, the possibility of making distinct races by cross¬ 
 ing has been greatly exaggerated. Many cases are on record 
 showing that a race may be modified by occasional crosses 
 if aided by the careful selection of the individuals which 
 present the desired character; but to obtain a race inter¬ 
 mediate between two quite distinct races would be very 
 difficult. Sir J, Sebright expressly experimented with 
 this object and failed. The offspring from the first cross 
 between two pure breeds is tolerably and sometimes (as I 
 have found with pigeons) quite uniform in character, and 
 every thing seems simple enough; but when these mongrels 
 are crossed one with another for several generations, hardly 
 two of them are alike, and then the difficulty of the task 
 becomes manifest. 
 
 BREEDS OF THE DOMESTIC PIGEON, THEIR DIFFERENCES 
 
 AND ORIGIN. 
 
 Believing that it is always best to study some special 
 group, I have, after deliberation, taken up domestic 
 pigeons. I have kept every breed which I could purchase 
 or obtain, and have been most kindly favored with skins 
 from several quarters of the world, more especially by the 
 Hon. Wo Elliot, from India, and by the Hon. C. Murray, 
 from Persia. Many treatises in different languages have 
 been published on pigeons, and some of them are very 
 important as being of considerable antiquity. I have 
 associated with several eminent fanciers and have been per¬ 
 mitted to join two of the London Pigeon Clubs. The 
 | diyexsityiof the breeds is something astonishing. Compare 
 the English carrier and the short-faced tumbler, and see 
 the wonderful difference in their beaks, entailing corres¬ 
 ponding differences in their skulls. The carrier, more 
 especially the male bird, is also remarkable from the won¬ 
 derful development of the carunculated skin about the 
 head; and this is accompanied by greatly elongated eyelids, 
 very large external orifices to the nostrils, and a wide gape 
 of mouth. The short-faced tumbler has a beak in outline 
 almost like that of a finch; and the common tumbler has 
 the singular inherited habit of flying at a great height in a 
 compact flock and tumbling in the air head over heels. 
 The runt is a bird of great with long massive beak 
 
DOMESTIC PIGEONS. 
 
 19 
 
 and large feet; some of the sub-breeds of runts have very 
 long necks, others very long wings and tails, others singu- 
 larly short tails. The barb is allied to the carrier, but, 
 instead of a long beak, has a very short and broad one. 
 The pouter has a much elongated body, wings and legs; 
 and its enormously developed crop, which it glories in 
 inflating, may well excite astonishment and even laughter. 
 The turbit has a short and conical beak with a line of 
 reversed feathers down the breast; and it has the habit of 
 continually expanding, slightly, the upper part of the 
 esophagus. The Jacobin has the feathers so much reversed 
 along the back of the neck that they form a hood; and it has, 
 proportionally to its size, elongated wing and tail feathers. 
 The trumpeter and laugher, as their names express, utter 
 a very different coo from the other breeds. The fantail 
 has thirty or even forty tail-feathers, instead of twelve or 
 fourteen—the normal number in all the members of the 
 great pigeon family: these feathers are kept expanded and 
 are carried so erect that in good birds the head and tail 
 touch: the oil-gland is quite aborted. Several other less 
 distinct breeds might be specified. 
 
 In the skeletons of the several breeds, the development 
 of the bo nes of th e face, in length and breadth and curva¬ 
 ture, differs en ormo usly. The shape, as well as the breadth 
 and length of the ramus of the lower jaw, varies in a highly 
 remarkable manner. The caudal and sacral vertebra vary 
 in number; as does the number of the ribs, together with 
 their relative breadth and the presence of processes. The 
 size and shape of the apertures in the sternum are highly 
 variable; so is the degree of divergence and relative size of 
 the two arms of the furcula. The proportional width of 
 the gape of mouth, the proportional length of the eye¬ 
 lids, of the orifice of the nostrils, of the tongue (not always 
 in strict correlation with the length of beak), the size of 
 the crop and of the upper part of the esophagus; the 
 development and abortion of the oil-gland; the number of 
 the primary wing and caudal feathers; the relative length 
 of the wing and tail to each other and to the body; the 
 relative length of the leg and foot; the number of scutelke 
 on the toes, the development of skin between the toes, are 
 all points of structure which are variable. The period at 
 which the perfect plumage is acquired varies, as does the 
 
20 
 
 DOMESTIC PIGEONS 
 
 state of the down with which the nestling birds are clothed 
 when hatched. The shape and size of the eggs vary. The 
 manner of flight, and in some breeds the voice and disposi¬ 
 tion, differ remarkably. Lastly, in certain breeds, the 
 males and females have come to differ in a slight degree 
 from each other. 
 
 Altogether at least a score of pigeons might be chosen 
 which, if shown to an ornithologist, and he were told that 
 they were wild birds, would certainly be ranked by him as 
 well-defined species. Moreover, I do not believe that any 
 ornithologist would in this case place the English carrier, 
 the short-faced tumbler, the runt, the barb, pouter, and 
 fantail in the same genus; more especially as in each of 
 these breeds several truly-inherited sub-breeds, or species, 
 as he would call them, could be shown him. 
 
 Great as are the differences between the breeds of the 
 pigeon, I am fully convinced that the common opinion of 
 naturalists is correct, namely, that all j tre descended from 
 the rock-pigeon (Columbia livia), mcludinguncler this 
 term several geographical races or sub-species, which differ 
 from each other in the most trifling respects. As several 
 of the reasons which have led me to this belief are in some 
 degree applicable in other cases, I will here briefly give 
 them. If the several breeds are not varieties, and have 
 not proceeded from the rock-pigeon, they must have de¬ 
 scended from at least seven or eight aboriginal stocks; for 
 it is impossible to make the present domestic breeds by the 
 crossing of any lesser number; how, for instance, could 
 a pouter be produced by crossing two breeds unless 
 one of the parent-stocks possessed the characteristic 
 enormous crop? The supposed aboriginal stocks must 
 all have been rock-pigeons, that is, they did not breed 
 or willingly perch on trees. But besides 0. livia, with 
 its geographical sub species, only two or three other 
 species of rock-pigeons are known; and these have not any 
 of the characters of the lomestic breeds. Hence the sup¬ 
 posed aboriginal stocks must either still exist in the coun¬ 
 tries where they were originally domesticated, and yet be 
 unknown to ornithologists; and this, considering their 
 size, habits and remarkable characters, seems improbable; 
 or they must have become extinct in the wild state. But 
 birds breeding on precipices, and good flyers, are unlikely 
 
DOMESTIC PIGEONS. 
 
 21 
 
 to be exterminated; and the common rock-pigeon, which 
 has the same habits with the domestic breeds, has not been 
 exterminated even on several of the smaller British islets, 
 or on the shores of the Mediterranean. Hence the sup¬ 
 posed extermination of so many species having similar 
 habits with the rock-pigeon seems a very rash assumption. 
 Moreover, the several above-named domesticated breeds 
 have been transported to all parts of the world, and, there¬ 
 fore, some of them must have been carried back again into 
 their native country; but not one has become wild or feral, 
 though the dovecot-pigeon, which is the rock-pigeon in a 
 very slightly altered state, has become feral in several 
 places. Again, all recent experience shows that it is diffi¬ 
 cult to get wild animals to breed freely under domestica¬ 
 tion; yet on the hypothesis of the multiple origin of our 
 pigeons, it must be assumed that at least seven or eight 
 species were so thoroughly domesticated in ancient times 
 by half-civilized man as to be quite prolific under confine¬ 
 ment. 
 
 An argument of great weight, and applicable in several 
 other cases, is, that the above-specified breeds, though 
 agreeing generally with the wild rock-pigeon in constitu¬ 
 tion, habits, voice, coloring, and in most parts of their 
 structure, yet are certainly highly abnormal in other parts; 
 we may look in vain through the whole great family of Col- 
 umbidse for a beak like that of the English carrier, or that 
 of the short-faced tumbler, or barb; for reversed feathers 
 like those of the Jacobin; for a crop like that of the pouter; 
 for tail-feathers like those of the fantail. Hence it must 
 be assumed, not only that half-civilized man succeeded in 
 thoroughly domesticating several species, but that he in¬ 
 tentionally or by chance picked out extraordinarily abnor¬ 
 mal species; and further, that these very species have since 
 all become extinct or unknown. So many strange contin¬ 
 gencies are improbable in the highest degree. 
 
 Some facts in regard to the coloring of pigeons well de¬ 
 serve consideration. The rock-pigeon is of a slaty-blue, 
 with white loins; but the Indian sub-species, 0. interme¬ 
 dia of Strickland, has this part bluish. The tail has a ter¬ 
 minal dark bar, with the outer feathers externally edged at 
 the base with white. The wings have two black bars. 
 Some semi-domestic breeds, and some truly wild breeds. 
 
22 
 
 DOMESTIC PIGEON’S. 
 
 Lave, besides the two black bars, the wings checkered with 
 black. * These several marks do not occur together in any 
 other species of the whole family. Now, in every one of the 
 domestic breeds, taking thoroughly well-bred birds, all the 
 above marks, even to the white edging of the outer tail- 
 feathers, sometimes concur perfectly developed. More¬ 
 over, when birds belonging to two or more distinct breeds 
 are crossed, none of which are blue or have any of the 
 above-specified marks, the mongrel offspring are very 
 apt suddenly to acquire these characters. To give 
 one instance out of several which I have observed: 
 I crossed some white fantails, which breed very 
 true, with some black barbs—and it so happens that 
 blue varieties of barbs are so rare that I never heard of an 
 instance in England; and the mongrels were black, brown 
 and mottled. I also crossed a barb with a spot, which is a 
 white bird with a red tail and red spot on the forehead, 
 and which notoriously breeds very true; the mongrels were 
 dusky and mottled. I then crossed one of the mongrel 
 barb-fantails with a mongrel barb-spot, and they produced 
 a bird of as beautiful a blue color, with the white loins, 
 double black wing-bar, and barred and white-edged tail- 
 feathers, as any wild rock-pigeon ! We can understand 
 these facts, on the well-known principle of reversion to 
 ancestral characters, if all the domestic breeds are de¬ 
 scended from the rock-pigeon. But, if we deny this, we 
 must make one of the two following highly improbable 
 suppositions. Either, first, that all the several imagined 
 aboriginal stocks were colored and marked like the rock- 
 pigeon, although no other existing species is thus colored 
 and marked, so that in each separate breed there might be 
 a tendency to revert to the very same colors and markings. 
 Or, secondly, that each breed, even the purest, has within 
 a dozen, or at most within a score, of generations, been 
 crossed by the rock-pigeon: I say within a dozen or twenty 
 generations, for no instance is known of crossed descend¬ 
 ants reverting to an ancestor of foreign blood, removed by 
 a greater number of generations. In a breed which has 
 been crossed only once the tendency to revert to any 
 character derived from such a cross will naturally become 
 less and less, as in each succeeding generation there will be 
 less of the foreign blood; but when there has been no cross. 
 
DOMESTIC PIGEONS. 
 
 23 
 
 and there is a tendency in the breed to revert to a character 
 which was lost during some former generation, this 
 tendency, for all that we can see to the contrary, may be 
 transmitted undiminished for an indefinite number of gen¬ 
 erations. These two distinct cases of reversion are often 
 confounded together by those who have written on in¬ 
 heritance. 
 
 Lastly, the hybrids or mongrels from between all the 
 breeds of the pigeon are perfectly fertile, as I can state 
 from my own observations, purposely made, on the most 
 distinct breeds. Now, hardly any cases have been ascer¬ 
 tained with certainty of hybrids from two quite distinct 
 species of animals being perfectly fertile. Some authors 
 believe that long-continued domestication eliminates this 
 strong tendency to sterility in species. From the history 
 of the dog, and of some other domestic animals, this con¬ 
 clusion is probably quite correct, if applied to species 
 closely related to each other. But to extend it so far as to 
 suppose that species, aboriginally as distinct as carriers, 
 tumblers, pouters, and fantails now are, should yield off¬ 
 spring perfectly fertile inter se, would be rash in the 
 extreme. 
 
 From these several reasons, namely, the improbability 
 of man having formerly made seven or eight supposed 
 species of pigeons to breed freely under domestication—• 
 these supposed species being quite unknown in a wild state, 
 and their not having become anywhere feral—these species 
 presenting certain very abnormal characters, as compared 
 with all other Columbidae, though so like the rock-pigeon 
 in most respects—the occasional reappearance of the blue 
 color and various black marks in all the breeds, both when 
 kept pure and when crossed—and lastly, the mongrel off¬ 
 spring being perfectly fertile—from these several reasons, 
 taken together, we may safely conclude that all our 
 domestic breeds are descended from the rock-pigeon or 
 Columbae livia with its geographical sub-species. 
 
 In favor of this view, I may add, firstly, that the wild 
 C. livia has been found capable of domestication in Europe 
 and in India; and that it agrees in habits and in a great 
 number of points of structure with all the domestic breeds. 
 Secondly, that although an English carrier or a short¬ 
 faced tumbler differs immensely in certain characters from 
 
u 
 
 DOMESTIC PIGEONS ,. 
 
 the rock-pigeon, yet that by comparing the several sub¬ 
 breeds of these two races, more especially those brought 
 from distant countries, we can make, between them and 
 the rocL-pigeon, an almost perfect series; so we can in 
 some other cases, but not with all the breeds. Thirdly, 
 those characters which are mainly distinctive of each breed 
 are in each eminently variable, for instance, the wattle and 
 length of beak of the carrier, the shortness of that of the 
 tumbler, and the number of tail-feathers in the fantail; 
 and the explanation of this fact will be obvious when we 
 treat of selection. Fourthly, pigeons have been watched 
 and tended with the utmost care and loved by many 
 people. They have been domesticated for thousands of 
 years in several quarters of the world; the earliest known 
 record of pigeons is in the fifth ^Egyptian dynasty, about 
 3000 B.c., as was pointed out to me by Professor Lepsius; 
 but Mr. Birch informs me that pigeons are given in a bill 
 of fare in the previous dynasty. In the time of the 
 Romans, as we hear from Pliny, immense prices were given 
 for pigeons; “nay, they are come to this pass, that they 
 can reckon up their pedigree and race.” Pigeons were 
 much valued by Akber Khan, in India, about the year 
 1600; never less than 20,000 pigeons were taken with the 
 court. “ The monarchs of Iran and Turan sent him some 
 very rare birds;” and, continues the courtly historian, 
 “His Majesty, by crossing the breeds, which method was 
 never practiced before, has improved them astonishingly.” 
 About this same period the Dutch were as eager about 
 pigeons as were the old Romans. The paramount impor¬ 
 tance of these considerations in explaining the immense 
 amount of variation which pigeons have undergone, will 
 likewise be obvious when we treat of selection. We shall 
 then, also, sec how it is that the several breeds so often 
 have a somewha . monstrous character. It is also a most 
 favorable circumstance for the production of distinct 
 breeds, hat male and female pigeons can be easily mated 
 for life; and thus different breeds can be kept together in 
 the same aviary. 
 
 I have discussed the probable origin of domestic pigeons 
 at some, yet quite insufficient, length; because when I first 
 kept pigeons and watched the several kinds, well knowing 
 haw truly they breed, ^ foit fully as much difficulty in 
 
SELECTION BY MAN. 
 
 25 
 
 believing that since they had been domesticated they had 
 all proceeded from a common parent, as any naturalist 
 could in coming to a similar conclusion in regard to the 
 many species of finches, or other groups of birds, in 
 nature. One circumstance has struck me much; namely, 
 that nearly all the breeders of the various domestic 
 animals and the cultivators of plants, with whom I 
 have conversed, or whose treatises I have read, are 
 firmly convinced that the several breeds to which each 
 has attended, are descended from so many aboriginally dis¬ 
 tinct species. Ask, as I have asked, a celebrated raiser of 
 Hereford cattle, whether his cattle might not have de¬ 
 scended from Long-horns, or both from a common parent- 
 stock, and he will laugh you to scorn. I have never met a 
 pigeon, or poultry, or duck, or rabbit fancier, who was not 
 fully convinced that each main breed was descended from a 
 distinct species. Van Mons, in his treatise on pears and 
 applet, shows how utterly he disbelieves that the several 
 sorts, for instance a Ribston-pippin or Codlin-apple, could 
 ever have proceeded from the seeds of the same tree. In¬ 
 numerable other examples could be given. The explana¬ 
 tion, I think, is simple: from long-continued study they 
 are strongly impressed with the differences between the 
 several races; and though they well know that each race 
 varies slightly, for they win their prizes by selecting such 
 slight differences, yet they ignore all general arguments, 
 and refuse to sum up in their minds slight differences 
 accumulated during many successive generations. May 
 not those naturalists who, knowing far less of the 
 laws of inheritance than does the breeder, and know¬ 
 ing no more than he does of the intermediate links in the 
 long lines of descent, yet admit that many of our domestic 
 races are descended from the same parents—may they not 
 learn a lesson of caution, when they deride the idea of 
 species in a state of nature being lineal descendants of other 
 species? 
 
 PRINCIPLES OF SELECTION ANCIENTLY FOLLOWED, AND 
 
 THEIR EFFECTS. 
 
 Let ns now briefly consider the steps by which domestic 
 races have been produced, either from one or from several 
 
26 
 
 SELECTION BY MAN 
 
 allied species. Some effect may be attributed to the direct 
 and definite action of the external conditions of life, and 
 some to habit; but he would be a bold man who would ac¬ 
 count by such agencies for the differences between a dray 
 and race-horse, a greyhound and bloodhound, a carrier and 
 tumbler pigeon. One of the most remarkable features in 
 our domesticated races is that we see in them adaptation, 
 not indeed to the animal's or plant's own good, but to 
 man’s use or fancy. Some variations useful to him have 
 probably arisen suddenly, or by one step; many botanists, 
 for instance, believe that the fuller’s teasel, with its hooks, 
 which can not be rivaled by any mechanical contrivance, 
 is only a variety of the wild Dipsacus; and this amount of 
 change may have suddenly arisen in a seedling. So it has 
 probably been with the turnspit dog; and this is known to 
 have been the case with the ancon sheep. But when we 
 compare the dray-horse and race-horse, the dromedary and 
 camel, the various breeds of sheep fitted either for culti¬ 
 vated land or mountain pasture, with the wool of one 
 breed good for one purpose, and that of another breed for 
 another purpose; when we compare the many breeds of 
 dogs, each good for man in different ways; when we com¬ 
 pare the game-cock, so pertinacious in battle, with other 
 breeds so little quarrelsome, with “ everlasting layers" 
 which never desire to sit, and with the bantam so small and 
 elegant; when we compare the host of agricultural, culi¬ 
 nary, orchard and flower-garden races of plants, most useful 
 to man at different seasons and for different purposes, or so 
 beautiful in his eyes, we must, I think, look further than 
 to mere variability. We can not suppose that all the 
 breeds were suddenly produced as perfect and as useful as 
 we now see them; indeed, in many cases, we know that 
 this has not been their histoiy. The key is man's power of 
 accumulative selection: nature gives successive variations; 
 man adds them up in certain directions useful to him. In 
 this sense he may be said to have made for himself useful 
 breeds. 
 
 The great power of this principle of selection is not 
 hypothetical. It is certain that several of our eminent 
 breeders have, even within a single lifetime, modified to a 
 large extent their breeds of cattle and sheep. In order 
 fully to realize what they have done it is almost necessary 
 
SELECTION BT MAN. 
 
 27 . 
 
 to read several of the many treatises devoted to this sub¬ 
 ject, and to inspect the animals. Breeders habitually 
 speak of an animal's organization as something plastic, 
 which they can model almost as they please. If I had 
 ' space I could quote numerous passages to this effect from 
 highly competent authorities. Youatt, who was probably 
 better acquainted with the works of agriculturists than 
 almost any other individual, and who was himself a very 
 good judge of animals, speaks of the principle of selection 
 as “that which enables the agriculturist, not only to 
 modify the character of his flock, but to change it 
 altogether. It is the magician's wand, by means of which 
 he may summon into life whatever form and mold he 
 pleases." Lord Somerville, speaking of what breeders 
 have done for sheep, says: “It would seem as if they had 
 chalked out upon a wall a form perfect in itself, and then 
 had given it existence." In Saxony the importance of the 
 principle of selection in regard to merino sheep is so fully 
 recognized that men follow it as a trade: the sheep are 
 placed on a table and are studied, like a picture by a con¬ 
 noisseur; this is done three times at intervals of months, 
 and the sheep are each time marked and classed, so that 
 the very best may ultimately be selected for breeding. 
 
 What English breeders have actually effected is proved 
 by the enormous prices given for animals with a good ped¬ 
 igree; and these have been exported to almost every 
 quarter of the world. The improvement is by no means 
 generally due to crossing different breeds; all the best 
 breeders are strongly opposed to this practice, except some¬ 
 times among closely allied sub-breeds. And when a cross 
 has been made, the closest selection is far more indispen¬ 
 sable even than in ordinary cases. If selection consisted 
 merely in separating some very distinct variety and breed¬ 
 ing from it, the principle would be so obvious as hardly to 
 be worth notice; but its importance consists in the great 
 effect produced by the accumulation in one direction, 
 during successive generations, of differences absolutely 
 inappreciable by an uneducated eye—differences which I 
 for one have vainly attempted to appreciate. Not one man 
 in a thousand has accuracy of eye and judgment sufficient 
 to become an eminent breeder. If gifted with these qual¬ 
 ities, and he studies his subject for years, and devotes his 
 
28 
 
 SELECTION BY MAN. 
 
 lifetime to it with indomitable perseverance, he will suc¬ 
 ceed, and may make great improvements; if he wants any 
 of these qualities, he will assuredly fail. Few would read- 
 ily believe in the natural capacity and years of practice 
 requisite to become even a skillful pigeon-fancier. 
 
 The same principles are followed by horticulturists; but 
 the variations are here often more abrupt. ~No one sup¬ 
 poses that our choicest productions have been produced by 
 a single variation from the aboriginal stock. We have 
 proofs that this has not been so in several cases in which 
 exact records have been kept; thus, to give a very trifling 
 instance, the steadily increasing size of the common goose¬ 
 berry may be quoted. We see an astonishing improvement 
 in many florists’ flowers, when the flowers of the present 
 day are compared with drawings made only twenty or 
 thirty years ago. When a race of plants is once pretty well 
 established, the seed-raisers do not pick out the best plants, 
 but merely go over their seed-beds, and pull up the 
 “ rogues,” as they call the plants that deviate from the 
 proper standard. With animals this kind of selection is, 
 in fact, likewise followed; for hardly any one is so careless 
 as to breed from his worst animals. 
 
 In regard to plants, there is another means of observing 
 the accumulated effects of selection—namely, by comparing 
 the diversity of flowers in the different varieties of the same 
 species in the flower-garden; the diversity of leaves, pods, 
 or tubers, or whatever part is valued, in the kitchen-garden, 
 in comparison with the flowers of the same varieties; and 
 the diversity of fruit of the same species in the orchard, in 
 comparison with the leaves and flowers of the same set of 
 varieties. See how different the leaves of the cabbage are, 
 and how extremely alike the flowers; how unlike the flow¬ 
 ers of the heartsease are, and how alike the leaves; how 
 much the fruit of the different kinds of gooseberries differ 
 in size, color, shape and hairyness, and yet the flowers pre¬ 
 sent very slight differences. It is not that the varieties 
 which differ largely in some one point do not differ at all 
 in other points; this is hardly ever—I speak after careful 
 observation—perhaps never, the case. The law of corre¬ 
 lated variation, the importance of which should never be 
 overlooked, will insure some dif erences; but, as a general 
 rule, it cannot be doubted that the continued selection of 
 
UNCONSCIOUS SELECTION. 
 
 29 
 
 slight variations, either in the leaves, the flowers, or the 
 fruit, will produce races differing from each other chiefly 
 in these characters. 
 
 It may be objected that the principle of selection has 
 been reduced to methodical practice for scarcely more than 
 three-quarters of a century; it has certainly been more at¬ 
 tended to of late years, and many treatises have been pub¬ 
 lished on the subject; and the result has been, in a corre¬ 
 sponding degree, rapid and important. But it is very far 
 from true that the principle is a modern discovery. I could 
 give several references to works of high antiquity, in which 
 the full importance of the principle is acknowledged. In 
 rude and barbarous periods of English history choice ani¬ 
 mals were often imported, and laws were passed to prevent 
 their exportation: the destruction of horses under a certain 
 size was ordered, and this may be compared to the 
 “ roguing" of plants by nurserymen. The principle of 
 selection I find distinctly given in an ancient Chinese ency¬ 
 clopedia. Explicit rules are laid down by some of the 
 Koman classical writers. From passages in Genesis, it is 
 clear that the color of domestic animals was at that early 
 period attended to. Savages now sometimes cross their 
 dogs with wild canine animals, to improve the breed, and 
 they formerly did so, as is attested by passages in Pliny. 
 The savages in South Africa match their draft cattle by 
 color, as do some of the Esquimaux their team of dogs. 
 Livingstone states that good domestic breeds are highly 
 valued by the negroes in the interior of Africa who have 
 not associated with Europeans. Some of these facts do 
 not show actual selection, but they show that the breeding 
 of domestic animals was carefully attended to in ancient 
 times, and is now attended to by the lowest savages. It 
 would, indeed, have been a strange fact, had attention not 
 been paid to breeding, for the inheritance of good and bad 
 qualities is so obvious. 
 
 UNCONSCIOUS SELECTION. 
 
 At the present time, eminent breeders try by methodical 
 selection, with a distinct object in view, to make a new 
 strain or sub-breed, superior to anything of the kind in the 
 country. But, for our purpose, a form of selection, which 
 may be called unconscious, and which results from every 
 
30 
 
 UNCONSCIOUS SELECTION. 
 
 one trying to possess and breed from the best individual 
 animals, is more important. Thus, a man who intends 
 keeping pointers naturally tries to get as good dogs as he can, 
 and afterward breeds from his own best dogs, but he has 
 no wish or expectation of permanently altering the breed. 
 Nevertheless we may infer that this process, continued 
 during centuries, would improve and modify any breed, in 
 the same way as Bakewell, Collins, etc., by this very same 
 process, only carried on more methodically, did greatly 
 modify, even during their lifetimes, the forms and qualities 
 of their cattle. Slow and insensible changes of this kind 
 can never be recognized unless actual measurements or care¬ 
 ful drawings of the breeds in question have been made long 
 ago, which may serve for comparison. In some cases, how¬ 
 ever, unchanged, or but little changed, individuals of the 
 same breed exist in less civilized districts, where the breed 
 has been less improved. There is reason to believe that 
 King Charles 5 spaniel has been unconsciously modified to a 
 large extent since the time of that monarch. Some highly 
 competent authorities are convinced that the setter is 
 directly derived from the spaniel, and has probably been 
 slowly altered from it. It is known that the English 
 pointer has been greatly changed within the last century, 
 and in this case the change has, it is believed, been chiefly 
 effected by crosses with the foxhound; but what concerns 
 us is, that the change has been effected unconsciously and 
 gradually, and yet so effectually that, though the old 
 Spanish pointer certainly came from Spain, Mr. Borrow 
 has not seen, as I am informed by him, any native dog in 
 Spain like our pointer. 
 
 By a similar process of selection, and by careful training, 
 English race-horses have come to surpass in fleetness and size 
 the parent Arabs, so that the latter, by the regulations for 
 the Goodwood Races, are favored in the weights which they 
 carry. Lord Spencer- and others have shown how the 
 cattle of England have increased in weight and in early 
 maturity, compared with the stock formerly kept in this 
 country. By comparing the accounts given in various old 
 treatises of the former and present state of carrier and 
 tumbler pigeons in Britain, India and Persia, we can trace 
 the stages through which they have insensibly passed, and 
 come to differ so greatly from the rock-pigeon. 
 
UNCONSCIOUS SELECTION. 
 
 31 
 
 Youatt gives an excellent illustration of the effects of a 
 course of selection which may be considered as unconscious, 
 in so far that the breeders could never have expected, or 
 even wished, to produce the result which ensued—namely, 
 the production of the distinct strains. The two flocks of 
 Leicester sheep kept by Mr. Buckley and Mr. Burgess, as 
 Mr. Youatt remarks, “ Have been purely bred from the 
 original stock of Mr. Bakewell for upward of fifty years. 
 There is not a suspicion existing in the mind of any one at 
 all acquainted with the subject that the owner of either of 
 them has deviated in any one instance from the pure blood 
 of Mr. Bake well’s flock, and yet the difference between the 
 sheep possessed by these two gentlemen is so great that 
 they have the appearance of being quite different varieties.” 
 
 If there exist savages so barbarous as never to think of 
 the inherited character of the offspring of their domestic 
 animals, yet any one animal particularly useful to them, 
 for any special purpose, would be carefully preserved 
 during famines and other accidents, to which savages are 
 so liable, and such choice animals would thus generally 
 leave more offspring than the inferior ones; so that in this 
 case there would be a kind of unconscious selection going 
 on. We see the value set on animals even by the bar-1 
 barians of Tierra del Fuego, by their killing and devouring l 
 their old women, in times of dearth, as of less value than * 
 their dogs. 
 
 In plants the same gradual process of improvement 
 through the occasional preservation of the best individuals, 
 whether or not sufficiently distinct to be ranked at their 
 first appearance as distinct varieties, and whether or not 
 two or more species or races have become blended together 
 by crossing, may plainly be recognized in the increased size 
 and beauty which we now see in the varieties of the hearts¬ 
 ease, rose, pelargonium, dahlia and other plants, when 
 compared with the older varieties or wdth their parent- 
 stocks. Ho one would ever expect to get a first-rate hearts¬ 
 ease or dahlia from the seed of a wild plant. No one 
 would expect to raise a first-rate melting pear from the 
 seed of the wild pear, though he might succeed from a 
 poor seedling growing wild, if it had come from a garden- 
 stock. The pear, though cultivated in classical times, 
 appears, from Pliny’s description, to have been a fruit of 
 
32 
 
 UNCONSCIOUS SELECTION. 
 
 very inferior quality. I have seen great surprise expressed 
 in horticultural works at the wonderful skill of gardeners 
 in having produced such splendid results from such poor 
 materials; but the art has been simple, and, as far as the 
 final result is concerned, has been followed almost uncon¬ 
 sciously. It lias consisted in always cultivating the best 
 known variety, sowing its seeds, and, when a slightly better 
 variety chanced to appear, selecting it, and so onward. 
 But the gardeners of the classical period, who cultivated 
 the best pears which they could procure, never thought* 
 what splendid fruit we should eat; though we owe our 
 excellent fruit in some small degree to their having naturally 
 chosen and preserved the best varieties they could any¬ 
 where find. 
 
 A large amount of change, thus slowly and uncon¬ 
 sciously accumulated, explains, as I believe, the well- 
 known fact, that in a number of cases we cannot 
 recognize, and therefore do not know, the wild parent- 
 stocks of the plants which have been longest cultivated 
 in our flower and kitchen gardens. It it has taken 
 centuries or thousands of years to improve or modify most 
 of our plants up to their present standard of usefulness to 
 man, we can understand liow it is that neither Australia, 
 the Cape of Good Hope, nor any other region inhabited by 
 quite uncivilized man, has afforded us a single plant worth 
 culture. It is not that these countries, so rich in species, 
 do not by a strange chance possess the aboriginal stocks of 
 any useful plants, but that the native plants have not been 
 improved by continued selection up to a standard of per¬ 
 fection comparable with that acquired by the plants in 
 countries anciently civilized. 
 
 In regard to the domestic animals kept by uncivilized 
 man, it should not be overlooked that they almost always 
 have to struggle for their own food, at least during certain 
 seasons. And in two countries very differently circum¬ 
 stanced, individuals of the same species, having slightly 
 different constitutions or structure, would often suc¬ 
 ceed better in the one country than in the other; 
 and thus by a process of “natural selection,” as 
 will hereafter be more fully explained, two sub¬ 
 breeds might be formed. This, perhaps, partly 
 explains why the varieties kept by savages, as has been 
 
UNCONSCIOUS SELECTION. 
 
 33 
 
 remarked by some authors, have more of the character of 
 true species than the varieties kept in civilized countries. 
 
 On the view here given of the important part which 
 selection by man has played, it becomes at once obvious, 
 how it is that our domestic races show adaptation in their 
 structure or in their habits to man's wants or fancies. We 
 can, I think, further understand the frequently abnormal 
 character of our domestic races, and likewise their differ¬ 
 ences being so great in external characters, and relatively 
 so slight in internal parts or organs. Man can hardly 
 select, or only with much difficulty, any deviation of 
 structure excepting such as is externally visible; and 
 indeed he rarely cares for what is internal. He can never 
 act by selection, excepting on variations which are first 
 given to him in some slight degree by nature. No man 
 would ever try to make a fantail till he saw a pigeon with 
 a tail developed in some slight degree in an unusual 
 manner, or a pouter till he saw a pigeon with a crop of 
 somewhat unusual size; and the more abnormal or unusual 
 any character was when it first appeared, the more likely 
 it would be to catch his attention. But to use such an ex¬ 
 pression as trying to make a fantail is, I have no doubt, in 
 most cases, utterly incorrect. The man who first selected 
 a pigeon with a slightly larger tail, never dreamed what the 
 descendants of that pigeon would become through long- 
 continued, partly unconscious and partly methodical, selec¬ 
 tion. Perhaps the parent-bird of all fantails had only 
 fourteen tail-feathers somewhat expanded, like the present 
 Java fantail, or like individuals of other and distinct 
 breeds, in which as many as seventeen tail-feathers have 
 been counted. Perhaps the first pouter pigeon did not in¬ 
 flate its crop much more than the turbit now does 
 the upper part of its esophagus—a habit which is disre¬ 
 garded by all fanciers, as it is not one of the points of the 
 breed. 
 
 Nor let it be thought that some great deviation of struc¬ 
 ture would be necessary to catch the fancier’s eye: he per¬ 
 ceives extremely small differences, and it is in human 
 nature to value any novelty, however slight, in 
 one’s own possession. Nor must the value which would 
 formerly have been set on any slight differences in the 
 individuals of the same species, be judged of by the value 
 
34 CIRCUMSTANCES FA VORABLE TO SELECTION. 
 
 which is now set on them, after several breeds have fairly 
 been established. It is known that with pigeons many 
 slight variations now occasionally appear, but these are re* 
 jected as faults or deviations from the standard of per¬ 
 fection in each breed. The common goose has not given 
 rise to any marked varieties; hence the Toulouse and the 
 common breed, which differ only in color, that most fleet¬ 
 ing of characters, have lately been exhibited as distinct at 
 our poultry shows. 
 
 These views appear to explain what has sometimes been 
 noticed, namely, that we know hardly anything about the 
 origin or history of any of our domestic breeds. But, in 
 fact, a breed, like a dialect of a language, can hardly be 
 said to have a distinct origin. A man preserves and breeds 
 from an individual with some slight deviation of structure, 
 or takes more care than usual in matching his best animals, 
 and thus improves them, and the improved animals slowly 
 spread in the immediate neighborhood. But they will as 
 yet hardly have a distinct name, and from being only 
 slightly valued, their history will have been disregarded. 
 When further improved by the same slow and gradual 
 process, they will spread more widely, and will be recog¬ 
 nized as something distinct and valuable, and will then 
 probably first receive a provincial name. In semi-civilized 
 countries, with little free communication, the spreading of 
 a new sub-breed would be a slow process. As soon as the 
 points of value are once acknowledged, the principle, as I 
 have called it, of unconscious selection will always tend— 
 perhaps more at one period than at another, as the breed 
 rises or falls in fashion—perhaps more in one district than 
 in another, according to the state of civilization of the in¬ 
 habitants—slowly to add to the characteristic features of 
 the breed, whatever they may be. But the chance will bo 
 infinitely small of any record having been preserved of such 
 slow, varying and insensible changes. 
 
 CIRCUMSTANCES FAVORABLE TO MAN’S POWER OF SELEC¬ 
 TION. 
 
 I will now say a few words on the circumstances, favor¬ 
 able or the reverse, to man’s power of selection. A high 
 degree of variability is obviously favorable, as freely giving 
 
CIRCUMSTANCES FAVORABLE TO SELECTION. 35 
 
 the materials for selection to work on; not that mere in¬ 
 dividual differences are not amply sufficient, with extreme 
 care, to allow of the accumulation of a large amount of 
 modification in almost any desired direction. But as 
 variations manifestly useful or pleasing to man appear only 
 occasionally, the chance of their appearance will be much 
 increased by a large number of individuals being kept. 
 Hence, number is of the highest importance for success. 
 On this principle Marshall formerly remarked, with respect 
 to the sheep of part of Yorkshire, “As they generally 
 belong to poor people, and are mostly in small lots , they 
 never can be improved.” On the other hand, nurserymen, 
 from keeping large stocks of the same plant, are generally 
 far more successful than amateurs in raising new and 
 valuable varieties. A large number of individuals of an 
 animal or plant can be reared only where the conditions for its 
 propagation are favorable. When the individuals are scanty 
 all will be allowed to breed, whatever their quality may be, 
 and this will effectually prevent selection. But probably the 
 most important element is that the animal or plant should 
 be so highly valued by man, that the closest attention is 
 paid to even the slightest deviations in its qualities or 
 structure. Unless such attention be paid nothing can be 
 effected. I have seen it gravely remarked, that it was 
 most fortunate that the strawberry began to vary just when 
 gardeners began to attend to this plant. Ho doubt the 
 strawberry had always varied since it was cultivated, but 
 the slight varieties had been neglected. As soon, however, 
 as gardeners picked out individual plants with slightly 
 larger, earlier or better fruit, and raised seedlings from 
 them, and again picked out the best seedlings and bred 
 from them, then (with some aid by crossing distinct species) 
 those many admirable varieties of the strawberry were 
 raised which have appeared during the last half-century. 
 
 With animals, facility in preventing crosses is an im¬ 
 portant element in the formation of new races—at least, 
 in a country which is already stocked with other races. In 
 this respect inclosure of the land plays a part. Wander¬ 
 ing savages or the inhabitants of open plains rarely possess 
 more than one breed of the same species. Pigeons can be 
 mated for life, and this is a great convenience to the fancier, 
 for thus many races may be improved and kept true. 
 
36 CIRCUMSTANCES FA VORABLE TO SELECTION. 
 
 though mingled in the same aviary; and this circumstance 
 must have largely favored the formation of new breeds. 
 Pigeons, I may add, can be propagated in great numbers 
 and at a very quick rate, and inferior birds may be freely 
 rejected, as when killed they serve for food. On the other 
 hand, cats, from their n octnral rambling habits, can not 
 be easily matched, and, although so much valued by 
 women and children, we rarely see a distinct breed long 
 kept up; such breeds as we do sometimes see are almost 
 always imported from some other country. Although I 
 do not doubt that some domestic animals vary less than 
 others, yet the rarity or absence of distinct breeds of the 
 cat, the donkey, peacock, goose, etc., may be attributed in 
 main part to selection not having been brought into play: 
 in cats, from the difficulty in pairing them; in donkeys, 
 from only a few being kept by poor people, and little atten¬ 
 tion paid to their breeding; for recently in certain parts of 
 Spain and of the United States this animal has been sur¬ 
 prisingly modified and improved by careful selection; in 
 peacocks, from not being very easily reared and a large 
 stock not kept: in geese, from being valuable only for two 
 purposes, food and feathers, and more especially from no 
 pleasure having been felt in the display of distinct breeds; 
 but the goose, under the conditions to which it is exposed 
 when domesticated, seems to have a singularly inflexible 
 organization, though it has varied to a slight extent, as I 
 have elsewhere described. 
 
 Some authors have maintained that the amount of varia¬ 
 tion in our domestic productions is soon reached, and can 
 never afterward be exceeded. It would be somewhat rash 
 to assert that the limit has been attained in any one case; 
 for almost all our animals and plants have been greatly im¬ 
 proved in many ways within a recent period; and this im¬ 
 plies variation. It would be equally rash to assert that 
 characters nowfincreased to their utmost limit, could not, 
 after remaining fixed for many centuries, again vary under 
 new conditions of life. No doubt, as Mr. Wallace has re¬ 
 marked with much truth, a limit will be at last reached. 
 For instance, there must be a limit to the fleetness of any 
 terrestrial animal, as this will be determined by the fric¬ 
 tion to be overcome, the weight of the body to be carried, 
 and the power of contraction in the muscular fibers. But 
 
CIRCUMSTANCES FAVORABLE TO SELECTION. 37 
 
 what concerns us is that the domestic varieties of the same 
 species differ from each other in almost every character, 
 which man has attended to and selected, more than do the 
 distinct species of the same genera. Isidore Geoffroy St. 
 Hilaire has proved this in regard to size, and so it is with 
 color, and probably with the length of hair. With respect 
 to fleetness, which depends on many bodily characters. 
 Eclipse was far fleeter, and a dray-horse is comparably 
 stronger, than any two natural species belonging to the same 
 genus. So with plants, the seeds of the different varieties 
 of the bean or maize probably differ more in size than do 
 the seeds of the distinct species in any one genus in the 
 same two families.' The same remark holds good in regard 
 to the fruit of the several varieties of the plum, and still 
 more strongly with the melon, as well as in many other 
 analogous cases. 
 
 To sum up on the origin of our domestic races of ani¬ 
 mals and plants. Changed conditions of life are of the 
 highest importance in causing variability, both by acting 
 directly on the organization, and indirectly by affecting the 
 reproductive system. It is not probable that variability is 
 an inherent and necessary contingent, under all circum¬ 
 stances. The greater or less force of inheritance and 
 reversion determine whether variations shall endure. 
 Variability is governed by many unknown laws, of which 
 correlated growth is probably the most important. Some¬ 
 thing, but how much we do not know, may be attributed 
 to the definite action of the conditions of life. Some, per¬ 
 haps a great, effect may be attributed to the increased use 
 or disuse of parts. The final result is thus rendered 
 infinitely complex. In some cases the intercrossing of 
 aboriginally distinct species appears to have played an 
 important part in the origin of our breeds. When several 
 breeds have once been formed in any country, their occa 
 sional intercrossing, with the aid of selection, has, no 
 doubt, largely aided in the formation of new sub-breeds; 
 but the importance of crossing has been much exaggerated, 
 both in regard to animals and to those plants which are 
 propagated by seed. With plants which are temporarily 
 propagated by cuttings, buds, etc., the importance of cross¬ 
 ing is immense; for the cultivator may here disregard the 
 extreme variability both ©£ hybrids and of mongrels, and 
 
 
38 CIRCUMSTANCES FAVORABLE TO SELECTION. 
 
 the sterility of hybirds; but plants not propagated by seed 
 are of little importance to us, for their endurance is only 
 temporary. Over all these causes of change, the accumu¬ 
 lative action of selection, whether applied methodically 
 and quickly, or unconsciously and slowly, but more 
 efficiently, seems to have been the predominant power. 
 
 
VARIATION UNDER NATURE, 
 
 CHAPTER II. 
 
 VARIATION UNDER NATURE. 
 
 Variability —Individual differences—Doubtful species—Wide rang, 
 ing, much diffused, and common species, vary most—Species of 
 tbe larger genera in each country vary more frequently than 
 the species of the smaller genera—Many of the species of tli9 
 larger genera resemble varieties in being very closely, but un¬ 
 equally, related to each. other, and in having restricted ranges. 
 
 Before applying the principles arrived at in the last 
 chapter to organic beings in a state of nature, we must 
 briefly discuss whether these latter are subject to any 
 variation. To treat this subject properly, a long catalogue 
 of dry facts ought to be given; but these I shall reserve for 
 a future work. Nor shall I here discuss the various defini¬ 
 tions which have been given of the term species. No one 
 definition has satisfied all naturalists; yet every naturalist 
 knows vaguely what he means when he speaks of a species. 
 Generally the term includes the unknown element of s 
 distinct act of creation. The term “variety” is almost 
 equally difficult to define; but here community of descent 
 is almost universally implied, though it can rarely be 
 proved. We have also what are called monstrosities; but 
 they graduate into varieties. By a monstrosity I presume 
 is meant some considerable deviation of structure, gener¬ 
 ally injurious, or not useful to the species. Some authors 
 use the term “variation” in a technical sense, as implying 
 a modification directly due to the physical conditions of 
 life; and “variations” in this sense are supposed not to be 
 inherited; but who can say that the dwarfed condition of 
 shells in the brackish waters of the Baltic, or dwarfed 
 plants on Alpine summits, or the thicker fur of an animal 
 from far northward, would not in some cases be inherited 
 for at least a few generations? And in this case I presume 
 that the form would be called a. variety. 
 
INDIVIDUAL DIFFERENCES. 
 
 It may be doubted whether sudden and considerable 
 deviations of structure, such as we occasionally see in our 
 domestic productions, more especially with plants, are ever 
 permanently propagated in a state of nature. Almost 
 every part of every organic being is so beautifully related 
 to its complex conditions of life that it seems as improbable 
 that any part should have been suddenly produced peifect, 
 as that a complex machine should have been invented by 
 man in a perfect state. Under domestication monstrosi¬ 
 ties sometimes occur which resemble normal stiuctures in 
 widely different animals. Thus pigs have occasionally been 
 bom with a sort of proboscis, and if any wild species of the 
 same genus had naturally possessed a proboscis, it might 
 have been argued that this had appeared as a monstrosity, 
 but I have as yet failed to find, after diligent search, cases 
 of monstrosities resembling normal structures in nearly 
 allied forms, and these alone bear on the question. If 
 monstrous forms of this kind ever do appear in a state ot 
 nature and are capable of reproduction (which is riot 
 always the case), as they occur rarely and singly, then- 
 preservation would depend on unusually favorable circum¬ 
 stances. They would, also, during the first and succeeding 
 venerations cross with the ordinary form, and thus then 
 abnormal character would almost inevitably be lost. Hut 
 I shall have to return in a future chapter to the preserva¬ 
 tion and perpetuation of single or occasional variations. 
 
 INDIVIDUAL DIFFERENCES. 
 
 The many slight differences which appear in the offspring 
 from the same parents, or which it may be presumed have 
 thus arisen, from being observed in the individuals of the 
 same species inhabiting the same confined locality, may be 
 called individual differences. No one supposes that all 
 the individuals of the same species are cast in the same 
 .actual mold. These individual differences aie of the 
 /(highest importance for us, for they are often inherited, as 
 (must be familiar to every one; and they thus afford mate- 
 I rials for natural selection to act on and accumulate, m the 
 / same manner as man accumulates in any given diiection 
 I individual differences in his domesticated pioductions. 
 i These xndividual differences generally affect what naturalists 
 
INDIVIDUAL DIFFERENCES. 
 
 41 
 
 consider unimportant parts; but I could show, by a long 
 catalogue of facts, that parts which must be called important, 
 whether viewed under a physiological or classificatory point 
 of view, sometimes vary in the individuals of the same 
 species. I am convinced that the most experienced natu¬ 
 ralist would be surprised at the number of the cases of 
 variability, even in important parts of structure, which he 
 could collect on good authority, as I have collected, during 
 a course of years. & It should be remembered that systema- 
 tists are far from being pleased at finding variability in 
 important characters, and that there are not many men 
 who will laboriously examine internal and important 
 organs, and compare them in many specimens of the same 
 species. It would never have been expected that the 
 branching of the main nerves close to the great central 
 ganglion of an insect would have been variable in the same 
 species; it might have been thought that changes of this 
 nature could have been effected only by slow degrees; yet 
 Sir J. Lubbock has shown a degree of variability in these 
 main nerves in Coccus, which may almost be compared to 
 the irregular branching of the stem of a tree. This philo¬ 
 sophical naturalist, I may add, has also shown that the 
 muscles in the larvas of certain insects are far from uni¬ 
 form. Authors sometimes argue in a circle when they 
 state that important organs never vary; for these same 
 authors practically rank those parts as important (as some 
 few naturalists have honestly confessed) which do not vary; 
 and, under this point of view, no instance will ever be 
 found of an important part varying; but under any other 
 point of view many instances assuredly can be given* 
 
 There is one point connected with individual differences 
 which is extremely perplexing : I refer to those genera 
 which have been called “ protean” or “ polymorphic,” in 
 which species present an inordinate amount of variation. 
 With respect to many of these forms, hardly two naturalists 
 agree whether to rank them as species or as varieties. We 
 may instance Rubus, Rosa, and Hieracium among plants, 
 several genera of insects and of Brachiopod shells. In 
 most polymorphic genera some of the species have fixed 
 and definite characters. Genera which are polymorphic in 
 one country seem to be, with a few exceptions, polymorphic 
 in other countries, and likewise, judging from Brachiopod 
 
42 
 
 INDIVIDUAL DIFFERENCES. 
 
 shells, at former periods of time. These facts are ver> 
 perplexing, for they seem to show that this kind of varia¬ 
 bility is independent of the conditions of life. I am in¬ 
 clined to suspect that we see, at least in some of these 
 polymorphic genera, variations which are of no service or 
 disservice to the species, and which consequently have not 
 been seized on and rendered definite by natural selection, 
 as hereafter to be explained. 
 
 * Individuals of the same species often present, as is 
 I known to every one, great differences of structure, in- 
 I dependency of variation, as in the two sexes of various 
 ) animals, in the two or three castes of sterile females or 
 workers among insects, and in the immature and larval 
 states of many of the lower animals. / There are, also, cases 
 of dimorphism and trimorphism, both with animals and 
 plants. Thus, Mr. Wallace, who has lately called attention 
 to the subject, has shown that the females of certain 
 species of butterflies, in the Malayan Archipelago, reg¬ 
 ularly appear under two or even three conspicuously dis¬ 
 tinct forms, not connected by intermediate varieties. Fritz 
 Muller has described analogous but more extraordinary 
 cases with the males of certain Brazilian Crustaceans: thus, 
 the male of a Tanais regularly occurs under two distinct 
 forms; one of these has strong and differently shaped 
 pincers, and the other has antennae much more abundantly 
 furnished with smelling-hairs. Although in most of these 
 cases, the two or three forms, both with animals and plants, 
 are not now connected by intermediate gradations, it is 
 probable that they were once thus connected. Mr. Wallace, 
 for instance, describes a certain butterfly which presents in 
 the same island a great range of varieties connected by in¬ 
 termediate links, and the extreme links of the chain closely 
 resemble the two forms of an allied dimorphic species in¬ 
 habiting another part of the Malay Archipelago. Thus 
 also with ants, the several worker-castes are generally quite 
 distinct; but in some cases, as we shall hereafter see, the 
 castes are connected together by finely graduated varieties. 
 So it is, as I have myself observed, with some dimorphic 
 plants. It certainly at first appears a highly remarkable 
 fact that the same female butterfly should have the power 
 of producing at the same time three distinct female forms 
 and a male; and that an hermaphrodite plant shouM pro- 
 
DOUBTFUL SPECIES. 43 
 
 nhrorlulT the ® am . e seed-capsule three distinct herma- 
 p nodite foims, bearing three different kinds of females and 
 three or even six different kinds of males. Nevertheless 
 these cases are only exaggerations of the common fact that 
 
 P roduoes , offspring of two sexes which some- 
 times differ from each other in a wonderful manner. 
 
 DOUBTFUL SPECIES. 
 
 The forms which possess in some considerable degree 
 
 to* other Ct fo ° f Speoles > but which “e so closely similar 
 to other forms or are so closely linked to them bv 
 
 rank'Them 1r U r tl0 i nS ’ tbat natnralists do not like to 
 most 11? species, are in several respects the 
 , r nnpoitant for us. We have every reason to 
 
 fm e n that many ° f these do «btful and closely allied 
 
 lon™time^ e fo Peim£ i nently 1 „ etained their character for a 
 f P ®’ fo1 , as Io >ig, as far as we know, as have good 
 
 unffe bv® ,r CleS - , Pl ; actica11 ^ w hen a naturalist § can 
 unite by means of intermediate links any two forms he 
 
 common 6 but & <? & ?- riety t °, f the otb er ; ranking the most 
 ““ OD ’ ll ‘ sometimes the one first described as the 
 
 diffienltv i- h i T he n l he variet y- But cases of great 
 in deohW WI notbere enumerate, sometimes arise 
 m deciding whether or not to rank one form as a variety 
 
 of another, even when they are closely connected Vmtel 
 
 / | late J ll “ ks ’. nor will the commonly assumed ^hybrid 
 
 cnftv Tu t l6 mtermedlate forms always remove the diffi¬ 
 culty. in veiy many cases. However, one form is ranked 
 
 WeTctaallv h an0t t er ’ ? 0t i b !T ae the iuformediate links 
 nave actually been found, but because analogy leads the 
 
 exist^or mav ^g 1086 , ^ they do nof somewhere 
 
 for the e^t, J n?’f exlsted i and here a wide door 
 for the cntiy of doubt and conjecture is opened. 
 
 l nce ’. m determining whether a form should be ranked j 
 
 “ or * vai ’iety, the opinion of naturalists having » 
 
 to foflow dg We * “ f 'I lde ex P eidenoe seems the only guidf 
 to follow. We must, however, in many cases, decide bv a 
 
 kT?n° nty °. f natllra t|sts, for few well-marked and well- 
 
 as sned^hv i e M Can f be named Whicb have Bot been ra nked 
 as species by at least some competent -judges. 
 
 dhat varieties of this doubtful nature are far f*om 
 
44 
 
 DOUBTFUL SPECIES. 
 
 uncommon cannot be disputed. Compare the several floras 
 of Great Britain, of France, or of the United States, drawn 
 up by different botanists, and see what a surprising num¬ 
 ber of forms have been ranked by one botanist as good 
 species, and by another as mere varieties. Mr. H. C. 
 Watson, to whom I lie under deep obligation for assistance 
 of all kinds, has marked for me 182 British plants, which 
 are generally considered as varieties, but which have all 
 been ranked by botanists as species; and in making this 
 list he has omitted many trifling varieties, but which never¬ 
 theless have been ranked by some botanists as species, and 
 he has entirely omitted several highly polymorphic genera. 
 Under genera, including the most polymorphic forms, Mr. 
 Babington gives 251 species, whereas Mr. Bentham gives 
 only 112—a difference of 139 doubtful forms! Among 
 animals which unite for each birth, and which are highly 
 locomotive, doubtful forms, ranked by one zoologist as a 
 species and by another as a variety, can rarely be found 
 within the same country, but are common in separated 
 areas. How many of the birds and insects in North 
 America and Europe, which differ very slightly from each 
 other, have been ranked by one eminent naturalist as un¬ 
 doubted species, and by another as varieties, or, as they 
 are often called, geographical races! Mr. Wallace, in 
 several valuable papers on the various animals, especially 
 on the Lepidoptera, inhabiting the islands of the great 
 Malayan Archipelago, shows that they may be classed under 
 four heads, namely, as variable forms, as local forms, as 
 geographical races or sub-species, and as true representa¬ 
 tive species. The first or variable forms vary much within 
 the limits of the same island. The local forms are moder¬ 
 ately constant and distinct in each separate island; but 
 when all from the several islands are compared together, 
 the differences are seen to be so slight and graduated that 
 it is impossible to define or describe them, though at the 
 same time the extreme forms are sufficiently distinct. 
 The geographical races or sub-species are local forms 
 completely fixed and isolated; but as they do not 
 differ from each other by strongly marked and 
 important characters, <( There is no possible test but 
 individual opinion to determine wffiich of them shall be 
 considered as species and which as varieties.” Lastly, 
 
DOUBTFUL SPECIES. 
 
 45 
 
 representative species fill the same place in the natural 
 economy of each island as do the local forms and sub¬ 
 species; but as they are distinguished from each other by a 
 greater amount of difference than that between the local 
 forms and sub-species, they are almost universally ranked 
 by naturalists as true species. Nevertheless, no certain 
 criterion can possibly be given by which variable forms, 
 local forms, sub-species and representative species can be 
 recognized. 
 
 Many years ago, when comparing, and seeing others com¬ 
 pare, the birds from the closely neighboring islands of the 
 Galapagcs Archipelago, one with another, and with those 
 from the American mainland, I was much struck how en¬ 
 tirely vague and arbitrary is the distinction between species 
 and varieties. On the islets of the little Maderia group 
 there are many insects which are characterized as 
 varieties in Mr. Wollaston’s admirable work, but which 
 would certainly be ranked as distinct species by many en¬ 
 tomologists. Even Ireland has a few animals, now gen¬ 
 erally regarded as varieties, but which have been ranked as 
 species by some zoologists. Several experienced ornitholo¬ 
 gists consider our British red grouse as only a strongly 
 marked race of a Norwegian species, whereas the greater 
 number rank it as an undoubted species peculiar to Great 
 Britain. A wide distance between the homes of two doubt¬ 
 ful forms leads many naturalists to rank them as distinct 
 species; but what distance, it has been well asked, will suf¬ 
 fice if that between America and Europe is ample, will that 
 between Europe and the Azores, or Maderia, or the Cana¬ 
 ries, or between the several islets of these small archipelagos, 
 be sufficient? 
 
 Mr. B. D. Walsh, a distinguished entomologist of the 
 United States, has described what he calls Phytophagic 
 varieties and Phytophagic species. Most vegetable-feeding 
 insects live on one kind of plant or on one group of plants; 
 some feed indiscriminately on many kinds, but do not in 
 consequence vary. In several cases, however, insects 
 found living on different plants, have been observed by 
 Mr. Walsh to present in their larval or mature state, or in 
 both states, slight, though constant differences in color, 
 size, or in the nature of their secretions. In some instances 
 the males alone, in other instances, both males and females. 
 
46 
 
 DOUBTFUL SPE0IE8. 
 
 have been observed thus to differ in a slight degree. When 
 the differences are rather more strongly marked, and when 
 both sexes and all ages are affected, the forms are ranked 
 by all entomologists as good species. But no observer can 
 determine for another, even if he can do so for himself, 
 which of these Phytophagic forms ought to be called 
 species and which varieties. Mr. Walsh ranks the forms 
 which it may be supposed would freely intercross, as varie¬ 
 ties; and those which appear to have lost this power, as 
 species. As the differences depend on the insects having 
 long fed on distinct plants, it can not be expected that 
 intermediate links connecting the several forms should 
 now be found. The naturalist thus loses his best guide in 
 determining whether to rank doubtful forms as varieties 
 or species. This likewise necessarily occurs with closely 
 allied organisms, which inhabit distinct continents or 
 islands. When, on the other hand, an animal or plant 
 ranges over the same continent, or inhabits many islands in 
 the same archipelago, and presents different forms in the 
 different areas, there is always a good chance that inter¬ 
 mediate forms will be discovered which will link together 
 the extreme states; and these are then degraded to the 
 rank of varieties. 
 
 Some few naturalists maintain that animals never pre¬ 
 sent varieties; but then these same naturalists rank the 
 slightest difference as of specific value; and when the same 
 identical form is met with in two distant countries, or in 
 two geological formations, they believe that two distinct 
 species are hidden under the same dress. The term 
 species thus comes to be a mere useless abstraction, imply¬ 
 ing and assuming a separate act of creation. It is certain 
 that many forms, considered by highly competent judges 
 to be varieties, resemble species so completely in character 
 that they have been thus ranked by other highly compe¬ 
 tent judges. But to discuss whether they ought to be 
 called species or varieties, before any definition of these 
 terms has been generally accepted, is vainly to beat the air*. 
 
 Many of the cases of strongly marked varieties or doubt¬ 
 ful species well deserve consideration; for several interest¬ 
 ing lines of argument, from geographical distribution, 
 analogical variation, hybridism, etc., have been brought to 
 bear in the attempt to determine their rank; but space 
 
. DOUBTFUL SPECIES. 
 
 47 
 
 does not here permit me to discuss them. Close investiga¬ 
 tion, in many cases, will no doubt bring naturalists to agree 
 how to rank doubtful forms. Yet it must be confessed 
 that it is in the best known countries that we find the 
 greatest number of them. I have been struck with the 
 fact that if any animal or plant in a state of nature be 
 highly useful to man, or from any cause closely attracts 
 his attention, varieties of it will almost universally be 
 found recorded. These varieties, moreover, will often be 
 ranked by some authors as species. Look at the common 
 oak, how closely it has been studied; yet a German author 
 makes more than a dozen species out of forms, which are 
 almost universally considered by other botanists to be vari¬ 
 eties; and in this country the highest botanical authorities 
 and practical men can be quoted to show that the sessile 
 and pedunculated oaks are either good and distinct species 
 or mere varieties. 
 
 I may here allude to a remarkable memoir lately pub¬ 
 lished by A. de Candolle, on the oaks of the whole world. 
 No one ever had more ample materials for the discrimina¬ 
 tion of the species, or could have worked on them with 
 more zeal and sagacity. He first gives in detail all the many 
 points of structure which vary in the several species, and 
 estimates numerically the relative frequency of the vari¬ 
 ations. He specifies above a dozen characters which may 
 be found varying even on the same branch, sometimes 
 according to age or development, sometimes without 
 any assignable reason. Such characters are not of course 
 of specific value, but they are, as Asa Gray has remarked 
 in commenting on this memoir, such as generally enter 
 into specific definitions. De Candolle then goes on to 
 say that he gives the rank of species to the forms that 
 differ by characters never varying on the same tree, and 
 never found connected by intermediate states. After 
 this discussion, the result of so much labor, he 
 emphatically remarks: “ They are mistaken, who 
 repeat that the greater part of our species are clearly 
 limited, and that the doubtful species are in a feeble 
 minority. This seemed to be true, so long as a genus was 
 imperfectly known, and its species were founded upon a 
 few specimens, that is to say, were provisional. Just as 
 we come to know them better, intermediate forms flow in, 
 
48 
 
 DOUBTFUL SPECIES. 
 
 and doubts as to specific limits augment.” He also adds 
 that it is the best known species which present the greatest 
 number of spontaneous varieties and sub-varieties. Thus 
 Quercus robur has twenty-eight varieties, all of which, 
 excepting six, are clustered round three sub-species, 
 namely Q. pedunculata, sessiliflora and pubescens. The 
 forms which connect these three sub-species are compara¬ 
 tively rare; and, as Asa Gray again remarks, if these con¬ 
 necting forms which are now rare were to become totally 
 extinct the three sub-species would hold exactly the same 
 relation to each other as do the four or five provisionally 
 admitted species which closely surround the typical Quer¬ 
 cus robur. Finally, De Candolle admits that out of the 300 
 species, which will be) enumerated in his Prodromus as 
 belonging to the oak family, at least two-thirds are provis¬ 
 ional species, that is, are not known strictly to fulfil the 
 definition above given of a true species. It should be 
 added that De Candolle no longer believes that species 
 are immutable creations, but concludes that the derivative 
 theory is the most natural one, “ and the most accordant 
 with the known facts in palaeontology, geographical 
 botany and zoology, of anatomical structure and classific¬ 
 ation.” 
 
 When a young naturalist commences the study of a 
 group of organisms quite unknown to him he is at first 
 much perplexed in determining what differences to consider 
 as specific and what as varietal; for he knows nothing of 
 the amount and kind of variation to which the group is 
 subject; and this shows, at least, how very generally there 
 is some variation. But if he confine his attention to one 
 class within one country he will soon make up his mind 
 how to rank most of the doubtful forms. His general ten¬ 
 dency will be to make many species, for he will become 
 impressed, just like the pigeon or poultry fancier before 
 alluded to, with the amount of difference in the forms 
 which he is continually studying; and he has little general 
 knowledge of analogical variation in other groups and in 
 other countries by which to correct his first impressions. 
 As he extends the range of his observations he will meet 
 with more cases of difficulty; for he will encounter a 
 greater number of closely allied forms. But if his obser¬ 
 vations be widely extended he will in the end generally be 
 
DOUBT*uL SPECIES. 
 
 49 
 
 able to make up his own mind; but he will succeed in this 
 at the expense of admitting much variation, and the truth 
 of this admission will often be disputed by other natural¬ 
 ists. When he comes to study allied forms brought from 
 countries not now continuous, in which case he cannot 
 hope to find intermediate links, he will be compelled to 
 trust almost entirely to analogy, and his difficulties will 
 rise to a climax. 
 
 Certainly no clear line of demarcation has as yet been 
 drawn between species and sub-species—that is, the forms 
 which in the opinion of some naturalists come very near 
 to, but do not quite arrive at, the rank of species; or, 
 again, between sub-species and well-marked varieties, or 
 between lesser varieties and individual differences. These 
 differences blend into each other by an insensible series; 
 and a series impresses the mind with the idea of an actual 
 passage. 
 
 Hence I look at individual differences, though of small 
 interest to the systematist, as of the highest importance 
 for us, as being the first steps toward ^such slight varieties 
 as are barely thought worth recording in works on natural 
 history. And I look at varieties which are in any degree 
 more distinct and permanent, as steps toward more 
 strongly marked and permanent varieties; and at the lat¬ 
 ter, as leading to sub-species, and then to species. The 
 passage from one stage of difference to another may, in 
 many cases, be the simple result of the nature of the 
 organism and of the different physical conditions to which it 
 has long been exj)osed; but with respect to the more im¬ 
 portant and adaptive characters, the passage from one stage 
 of difference to another may be safely attributed to the 
 cumulative action of natural selection, hereafter to be ex¬ 
 plained, and to the effects of the increased use or disuse of 
 parts. A well-marked variety may therefore be called an 
 incipient species; but whether this belief is justifiable must 
 be judged by the weight of the various facts and considera¬ 
 tions to be given throughout this work. 
 
 It need not be supposed that all varieties or incipient 
 species attain the rank of species. They may become ex¬ 
 tinct, or they may endure as varieties for very long periods, 
 as has been shown to be the case by Mr. Wollaston with 
 the varieties of certain fossil land-shells in Madeira, and 
 
50 
 
 DOMINANT SPECIES VARY MOST. 
 
 with plants by Gaston cle Saporta. If a variety were to 
 flourish so as to exceed in numbers the parent species, it 
 would then rank as the species, and the species as the 
 variety; or it might come to supplant and exterminate the 
 parent species; or both might co-exist, and both rank as 
 independent species. But we shall hereafter return to this 
 subject. 
 
 ui From these remarks it will be seen that I look at the 
 term species as one arbitrarily given, for the sake of con¬ 
 venience, to a set of individuals closely resembling each 
 other, and that it does not essentially differ from the term 
 variety, which is given to less distinct and more fluctuating 
 forms. The term variety, again, in comparison with mere 
 individual differences, is also applied arbitrarily, for con¬ 
 venience sake. 
 
 WIDE-RANGING, MUCH DIFFUSED, AND COMMON SPECIES 
 
 VARY MOST. 
 
 Guided by theoretical considerations, I thought that 
 some interesting results might be obtained in regard to the 
 nature and relations of the species which vary most, by 
 tabulating all the varieties in several well-worked floras. 
 At first this seemed a simple task; but Mr. II. C. Watson, 
 to whom I am much indebted for valuable advice and 
 assistance on this subject, soon convinced me that there 
 were many difficulties, as did subsequently Dr. Hooker, 
 even in stronger terms. I shall reserve for a future work 
 the discussion of these difficulties, and the tables of the 
 proportional numbers of the varying species. Dr. Hooker 
 permits me to add that after having carefully read my 
 manuscript, and examined the tables, he thinks that the 
 following statements are fairly well established. The whole 
 subject, however, treated as it necessarily here is with much 
 brevity, is rather perplexing, and allusions cannot be 
 avoided to the “struggle for existence,” “divergence of 
 character,” and other questions, hereafter to be discussed. 
 
 Alphonso de Candolle and others have shown that 
 
 I plants which have very wide ranges generally present 
 varieties; and this might have been expected, as they are 
 exposed to diverse physical conditions, and as they come 
 into competition (which, as we shall hereafter see, is an 
 equally or more important circumstance) with different 
 
SPECIES OF LARGER GENERA VARIABLE. 51 
 
 sets of organic beings. But my tables further show that, 
 in any limited country, the species which are the most 
 common, that is abound most in individuals, and the 
 species which are most widely diffused within their own 
 country (and this is a different consideration from wide 
 range, and to a certain extent from commonness), oftenest 
 give rise to varieties sufficiently well-marked to have been 
 recorded in botanical works. Hence it is the most flourish¬ 
 ing, or, as they may be called, the dominant species—those 
 which range widely, are the most diffused in their own 
 country, and are the most numerous in individuals—which 
 oftenest produce well-marked varieties, or, as I consider 
 them, incipient species. And this, perhaps, might have 
 been anticipated; for, as varieties, in order to become in 
 any degree permanent, necessarily have to struggle with the 
 other inhabitants of the country, the species which are 
 already dominant will be the most likely to yield offspring, 
 which, though in some slight degree modified, still inherit 
 those advantages that enabled their parents to become 
 dominant over their compatriots. In these remarks on 
 predominence, it should be understood that reference is 
 made only to the forms which come into competition with 
 each other, and more especially to the members of the 
 same genus or class having nearly similar habits of life. 
 With respect to the number of individuals or commonness 
 of species, the comparison of course relates only to the 
 members of the same group. One of the higher plants 
 may be said to be dominant if it be more numerous in 
 individuals and more widely diffused than the other plants 
 of the same country, which live under nearly the same 
 conditions. A plant of this kind is not the less dominant 
 because some conferva inhabiting the water or some para¬ 
 sitic fungus is infinitely more numerous in individuals, 
 and more widely diffused. But if the conferva or parasitic 
 fungus exceeds its allies in the above respects, it will then 
 be dominant within its own class. 
 
 SPECIES OF THE LARGER GENERA IN EACH COUNTRY 
 VARY MORE FREQUENTLY THAN THE SPECIES OF THE 
 SMALLER GENERA. 
 
 If the plants inhabiting a country, as described in any 
 Flora, be divided into two equal masses, all those in the 
 
52 
 
 SPECIES OF LARGER GENERA VARIABLE. 
 
 larger genera (i. e ., those including many species) being 
 placed on one side, and all those in the smaller genera on 
 the other side, the former will be found to include a.some¬ 
 what larger number of the very common and much diffused 
 or dominant species. This might have been anticipated, 
 for the mere fact of many species of the same genus in- 
 habiting any country, shows that there is something in^ 
 the organic or inorganic conditions of that country favor¬ 
 able to the genus; and, consequently, we might have ex¬ 
 pected to have found in the larger genera, or those includ¬ 
 ing many species, a larger proportional number of dominant 
 species. But so many causes tend to obscure this result, that 
 I am surprised that my tables show even a small majority 
 on the side of the larger genera. I will here allude to only 
 two causes of obscurity. Fresh water and salt-loving 
 plants generally have very wide ranges and are much dif¬ 
 fused, but this seems to be connected with the nature of 
 the stations inhabited by them, and has little or no relation 
 to the size of, the genera to which the. species belong. 
 Again, plants low in the scale of organization are generally 
 much more widely diffused than plants higher in the scale; 
 and here again there is no close relation to the size of the 
 genera. The cause of lowly organized plants ranging 
 widely will be discussed in our chapter on Geographical 
 Distribution. 
 
 From looking at (species as only strongly marked and 
 well-defined varieties,; I was led to anticipate that the 
 species of the larger genera in each country would oftener 
 present varieties, than the species of the smaller genera; 
 for wherever many closely related species {i.e., species.of 
 the same genus) have been formed, many varieties or incip¬ 
 ient species ought, as a general rule, to be now forming. 
 Where many large trees grow, we expect to find saplings. 
 Where many species of a genus have been formed through 
 variation, circumstances have been favorable for variation; 
 and hence we might expect that the circumstances would 
 generally still be favorable to variation. On the other 
 hand, if we look at each species as a special act of creation, 
 there is no apparent reason why more varieties should 
 occur in a group having many species, than in one having 
 
 few. # I 
 
 To test the truth of this anticipation I have arranged 
 
SPECIES OF LARGER GENERA . 
 
 53 
 
 che plants of twelve countries, and the coleopterous insects 
 of two districts, into two nearly equal masses, the species 
 of the larger genera on one side, and those of the smaller 
 genera on the other side, and it has invariably proved to be 
 the case that a larger proportion of the species on the side 
 of the larger genera presented varieties, than on the side of 
 the smaller genera. Moreover, the species of the large 
 genera which present any varieties, invariably present a 
 larger average number of varieties than do the species of 
 the small genera. Both these results follow when another 
 division is made, and when all the least genera, with from 
 only one to four species, are altogether excluded from the 
 tables. These facts are of plain signification on the view 
 that species are only strongly marked and permanent 
 varieties; for wherever many species of the same genus 
 have been formed, or where, if we may use the expression, 
 the manufactory of species has been active, we ought 
 generally to find the manufactory still in action, more 
 especially as we have every reason to believe the process of 
 manufacturing new species to be a slow one. And this 
 certainly holds true if varieties be looked at as incipient 
 species; for my tables clearly show, as a general rule, that, 
 wherever many species of a genus have been formed, the 
 species of that genus present a number of varieties, that is, 
 of incipient species, beyond the average. It is not that all 
 large genera are now varying much, and are thus increasing 
 in the number of their species, or that no small genera are 
 now varying and increasing; for if this had been so, it 
 would have been fatal to my theory; inasmuch as geology 
 plainly tells us that small genera have in the lapse of time 
 often increased greatly in size; and that large genera have 
 often come to their maxima, decline, and disappeared. 
 All that we want to show is, that where many species of a 
 genus have been formed, on an average many are still 
 forming; and this certainly holds good. 
 
 MANY OF THE SPECIES INCLUDED WITHIN THE LARGER 
 GENERA RESEMBLE VARIETIES IN BEING VERY CLOSELY, 
 BUT UNEQUALLY, RELATED TO EACH OTHER, AND IN 
 HAVING RESTRICTED RANGES. 
 
 There are other relations between the species of large 
 
54 
 
 SPECIES OF LARGER GENERA. 
 
 genera and their recorded varieties which deserve notice. 
 We have seen that there is no infallible criterion by which 
 to distinguish species and well-marked varieties; and when 
 intermediate links have not been found between doubtful 
 forms, naturalists are compelled to come to a determination 
 by the amount of difference between them, judgingby anal¬ 
 ogy whether or not the amount suffices to raise one or both to 
 the rank of species, j Hence the amount of difference is one 
 very important criterion in settling whether two forms 
 should be ranked as species or varieties. Now Fries has 
 remarked in regard to plants, and Westwood in regard to 
 insects, that in large genera the amount of difference 
 between the species is often exceedingly small. I have 
 endeavored to test this numerically by averages, and, as far 
 as my imperfect results go, they confirm the view. I have 
 also consulted some sagacious and experienced observers, 
 and, after deliberation, they concur in this view. In this 
 respect, therefore, the species of the larger genera resemble 
 varieties, more than do the species of the smaller genera. 
 Or the case may be put in another way, and it may be said, 
 that in the larger genera, in which a number of varieties or 
 I incipient species greater than the average are now manu- 
 l facturing, many of the species already manufactured still 
 : to a certain extent resemble varieties, for they differ from 
 each other by less than the usual amount of difference. 
 
 Moreover, the species of the larger genera are related to each 
 other, in the same manner as the varieties of anyone species 
 are related to each other. No naturalist pretends that all 
 the species of a genus are equally distinct from each other; 
 they may generally be divided into sub-genera, or sections, 
 or lesser groups. As Fries has well remarked, little 
 groups of species are generally clustered like satellites 
 around other species. And what are varieties but groups 
 of forms, unequally related to each other, and clustered 
 round certain forms—that is, round their parent species. 
 Undoubtedly there is one most important point of differ¬ 
 ence between varieties and species, namely, that the 
 'amount of difference between varieties, when compared 
 with each other or with their parent species, is much less 
 .than that between the species of the same genus. But when 
 we come to discuss the principle, as I call it, of divergence 
 of character, we shall see bow this may be explained, and 
 
55 
 
 RESEMBLE VARIETIES. 
 
 how the lesser differences between varieties tend to increase 
 into the greater differences between species. 
 
 There is one other point which is worth notice. Varie¬ 
 ties generally have much restricted ranges. This state¬ 
 ment is indeed scarcely more than a truism, for, if a 
 vanetv were found to have a wider range than that 
 ot its supposed parent species, their denominations 
 would be reversed But there is reason to believe 
 that, the species which are very closely allied to other 
 species, and m so far resemble varieties, often have much 
 restricted ranges.. For instance, Mr. H. C. Watson has 
 marked for me m the well-sifted London catalogue of 
 Fiants (4th edition) sixty-three plants which are therein 
 ianked as species, but which he considers as so closelv 
 allied to other species as to be of doubtful value: these 
 sixty-three reputed species range on an average over 6.9 
 of the provinces into which Mr. Watson has divided 
 Lieat Britain. Now, in this same catalogue, fifty- 
 three acknowledged varieties are recorded, and these 
 range over 7.7 provinces; whereas, the species to which 
 ™ net l es Mong range over 14.3 provinces. So 
 that the acknowledged varieties have nearly the same 
 restricted average range, as have the closely allied forms, 
 marked for me by Mr. Watson as doubtful species, but 
 which are almost universally ranked by British botanists 
 as good and true species. 
 
 SUMMARY. 
 
 Finally, varieties cannot be distinguished f»om species, 
 --except, first, by the discovery of. intermediate linking’ 
 forms; and, secondly, by a certain indefinite amount of 
 difference between them; for two forms, if differing very 
 little are generally ranked as varieties, notwithstanding 
 that they cannot be closely connected; but the amount of 
 difference considered necessary to give to any two forms 
 the rank of species cannot be defined. In genera havino- 
 more than the average number of species in any country, 
 tne species of . these genera have more than the average 
 number of varieties. In large genera the species are apt 
 to be closely but unequally allied together, forming little 
 dusters round other species. Species very closely allied to 
 
56 
 
 RESEMBLE VARIETIES. 
 
 other species apparently have restricted ranges. In all 
 these respects the species of large genera present a strong 
 analogy with varieties. And we can clearly understand 
 these analogies, if species once existed as varieties, and 
 thus originated; whereas, these analogies are utterly inex¬ 
 plicable if species are independent creations. 
 
 We have also seen that it is the most flourishing or domi¬ 
 nant species of the larger genera within each class which 
 on an average yield the greatest nurffber of varieties; and 
 varieties, as we shall hereafter see, tend to become con¬ 
 verted into new and distinct species. Thus the larger 
 genera tend to become larger; and throughout nature the 
 forms of life which are ^ow dominant tend to become still 
 more dominant by leaving many modified and dominant 
 descendants. But, by steps hereafter to be explained,, the 
 larger genera also tend to break up into smaller genera. 
 And thus, the forms of life throughout the universe be¬ 
 come divided into groups subordinate to groups. 
 
STRUGGLE FOR EXISTENCE. 
 
 57 
 
 CHAPTER III. 
 
 STRUGGLE FOR EXISTENCE. 
 
 Its bearing on natural selection—The term used in a wide sense— 
 Geometrical ratio of increase—Rapid increase of naturalized 
 animals and plants—Nature of the checks to increase—Com¬ 
 petition universal—Effects of climate—Protection from the 
 number of individuals—Complex relations of all animals and 
 plants throughout nature—Struggle for life most severe between 
 individuals and varieties of the same species: often severe 
 between species of the same genus—The relation of organism 
 to organism the most important of all relations. 
 
 Before entering on the subject of this chapter I must 
 make a few preliminary remarks to show how the struggle 
 for existence bears on natural selection. It has been seen 
 in the last chapter that among organic beings in a state of 
 nature there is some individual variability: indeed I am 
 not aware that this has ever been disputed. It is imma¬ 
 terial for us whether a multitude of doubtful forms be 
 called species or sub-species or varieties; what rank, for 
 instance, the two or three hundred doubtful forms of 
 British plants are entitled to hold, if the existence of any 
 well-marked varieties be admitted. But the mere exist¬ 
 ence of individual variability and of some few well-marked 
 varieties, though necessary as the foundation for the work, 
 helps us but little in understanding how species arise in 
 nature. How have all those exquisite adaptations of one 
 part of the organization to another part, and to the condi¬ 
 tions of life and of one organic being to another being, 
 been perfected? We see these beautiful co-adaptations 
 most plainly in the woodpecker and the mistletoe; and only 
 a little less plainly in the humblest parasite which clings to 
 the hairs of a quadruped or feathers of a bird; in the 
 structure of the beetle which dives through the water; in 
 the plumed seed which is wafted by the gentlest breeze; in 
 
55 
 
 STRUGGLE FOR EXISTENCE. 
 
 short, we see beautiful adaptations everywhere and in every 
 part of the organic world. 
 
 Again, it may be asked, how is it that varieties, which I 
 have called incipient species, become ultimately converted 
 into good and distinct species, which in most cases 
 obviously differ from each other far more than do the 
 varieties of the same species? How do those groups of 
 species, which constitute what are called distinct genera 
 and which differ from each other more than do the species 
 of the same genus, arise? All these results, as we shall 
 more fully see in the next chapter, follow from the struggle 
 for life. Owing to this struggle, variations, however slight 
 and from whatever cause proceeding, if they be in any 
 degree profitable to the individuals of a species, in their 
 infinitely complex relations to other organic beings and 
 to their physical conditions of life, will tend to the 
 preservation of such individuals, and will generally be 
 inherited by the offspring. The offspring, also, will 
 thus have a better chance of surviving, for, of the many 
 individuals of any species which are periodically born, 
 but a small number can survive. I have called this 
 | principle, by which each slight variation, if useful, is 
 1 preserved, by the term natural selection, in order to 
 linark its relation to man's power of selection. But the 
 expression often used by Mr. Herbert Spencer, of the Sur¬ 
 vival of the Fittest, is more accurate, and is sometimes 
 * equally convenient. We have seen that man by selection 
 can certainly produce great results, and can adapt organic 
 beings to his own uses, through the accumulation of slight 
 but useful variations, given to him by the hand of Nature. 
 But Natural Selection, we shall hereafter see, is a power 
 incessantly ready for action, and is as immeasurably superior 
 to man's feeble efforts as the works of Nature are to those 
 of Art. 
 
 We will now discuss in a little more detail the struggle 
 for existence. In my future work this subject will be 
 treated, as it well deserves, at greater length. The elder 
 De Candolle and Lyell have largely and philosophically 
 shown that all organic beings are exposed to severe compe¬ 
 tition. In regard to plants, no one has treated this sub¬ 
 ject with more spirit and ability than W. Herbert, Dean 
 of Manchester, evidently the result of his great horticul- 
 
STRUGGLE FOR EXISTENCE. 
 
 59 
 
 tural knowledge. Nothing is easier than to admit in 
 words the truth of the universal struggle for life‘s or nrP re 
 difficult—at least I found it so—than constantly to b&B’ 
 this conclusion in mind. Yet unless it be thoroughly en-\ 
 grained in the mind, the whole economy of nature, with 
 every fact on distribution, rarity, abundance, extinction, 
 and variation, will be dimly seen or quite misunderstood. 
 We behold the face of nature bright with gladness, we 
 often see superabundance of food; we do not see or we 
 forget that the birds which are idly singing round us 
 mostly live on insects or seeds, and are thus constantly 
 destroying life; or we forget how largely these songsters, 
 or their eggs, or their nestlings, are destroyed by birds and 
 beasts of prey; we do not always bear in mind, that, 
 though food may be now superabundant, it is not so at all 
 seasons of each recurring year. 
 
 THE TERM, STRUGGLE FOR EXISTENCE, USED IH A LARGE 
 
 SEHSE. 
 
 I should premise that I use this term in a large and 
 metaphorical sense, including dependence of one being on 
 another, and including (which is more important) not 
 only the life of the individual, but success in leaving prog¬ 
 eny. Two canine animals, in. a time of dearth, may be 
 truly said to struggle with each other which shall get food 
 and live. But a plant on the edge of a desert is said to 
 struggle for life against the drought, though more prop¬ 
 erly it should be said to be dependent on the moisture. A 
 plant which annually produces a thousand seeds, of which 
 only one of an average comes to maturity, may be more 
 truly said to struggle with the plants of the same and other 
 kinds which already clothe the ground. The mistletoe is 
 dependent on the apple and a few other trees, but can 
 only in a far-fetched sense be said to struggle with these 
 trees, for, if too many of these parasites grow on the same 
 tree, it languishes and dies. But several seedling mistle¬ 
 toes, growing close together on the same branch, may more 
 truly be said to struggle with each other. As the mistle¬ 
 toe is disseminated by birds, its existence depends on them; 
 and it may metaphorically be said to struggle with other 
 fruit-bearing plants, in tempting the birds to devour 
 
CO GEOMETRICAL RATIO OF INCREASE. 
 
 thus disseminate its seeds. In these several senses, which 
 pass into each other, I use for convenience sake the gen¬ 
 eral term of Struggle for Existence. 
 
 GEOMETRICAL RATIO OF INCREASE. 
 
 — A struggle for existence inevitably follows from the high 
 rate at which all organic beings tend to increase. Every 
 being, which during its natural lifetime produces several 
 eggs or seeds, must suffer destruction during some period 
 of its life, and during some season or occasional year, 
 otherwise, on the principle of geometrical increase, its 
 numbers would quickly become so inordinately great that 
 no country could support the product. Hence, as more 
 individuals are produced than can possibly survive, there 
 must in every case be a struggle for existence, either one in¬ 
 dividual with another of the same species, or with the 
 individuals of distinct species, or with the physical con¬ 
 ditions of life. It is the doctrine of Malthus applied with 
 manifold force to the whole animal and vegetable king¬ 
 doms; for in this case there can be no artificial increase of 
 food, and no prudential restraint from marriage. Although 
 some species may be now increasing, more or less rapidly, 
 in numbers, all can not do so, for the world would not hold 
 them. 
 
 There is no exception to the rule that every organic 
 being naturally increases at so high a rate, that, if not 
 destroyed, the earth would soon be covered by the progeny 
 of a single pair. Even slow-breeding man has doubled in 
 twenty-five years, and at this rate, in less than a thousand 
 years, there would literally not be standing-room for his 
 progeny. Linnaeus has calculated that if an annual plant 
 produced only two seeds—and there is no plant so unpro¬ 
 ductive as this—and their seedlings next year produced 
 two, and so on, then in twenty years there would be a 
 million plants. The elephant is reckoned the slowest 
 breeder of all known animals, and I have taken some pains to 
 estimate its probable minimum rate of natural increase; it 
 will be safest to assume that it begins breeding when thirty 
 years old, and goes on breeding till ninety years old, 
 bringing forth six young in the interval, and surviving till 
 one hundred years old; if this be so, after a period of from 
 
GEOMETRICAL RATIO OF INCREASE. 61 
 
 740 to 750 years there would be nearly nineteen million 
 elephants alive descended from the first pair. 
 
 But we have better evidence on this subject than mere 
 theoretical calculations, namely, the numerous recorded 
 cases of the astonishingly rapid increase of various animals 
 in a state of nature, when circumstances have been favor 
 able to them during two or three following seasons. Still 
 more striking is the evidence from our domestic animals of 
 many kinds which have run wild in several parts of the 
 world; if the statements of the rate of increase of slow- 
 breeding cattle and horses in South America, and latterly 
 in Australia, had not been well authenticated, they would 
 have been incredible. So it is with plants; cases could be 
 given of introduced plants which have become common 
 throughout whole islands in a period of less than ten years. 
 Several of the plants, such as the cardoon and a tall thistle, 
 which are now the commonest over the wide plains of La 
 Plata, clothing square leagues of surface almost to the ex¬ 
 clusion of every other plant, have been introduced from 
 Europe; and there are plants which now range in India, as 
 I hear from Dr. Falconer, from Cape Comorin to the 
 Himalaya, which have been inported from America since 
 its discovery. In such cases, and endless others, could be 
 given, no one supposes, that the fertility of the animator 
 plants has been suddenly and temporarily increased in any 
 sensible degree. The obvious explanation is that the con¬ 
 ditions of life have been highly favorable, and that there 
 has consequently been less destruction of the old and 
 young and that nearly all the young have been enabled to 
 breed. Their geometrical ratio of increase, the result of 
 which never fails to be surprising, simply explains their 
 extraordinarily and rapid increase and wide diffusion in their 
 new homes. 
 
 In a state of nature almost every full-grown plant an¬ 
 nually produces seed, and among animals there are very 
 few which do not annually pair. Hence we may confi¬ 
 dently assert that all plants and animals are tending to in¬ 
 crease at a geometrical ratio—that all would rapidly stock 
 every station in which they could anyhow exist-r-and that 
 this geometrical tendency to increase must be checked by 
 destruction at some period of life. Our familiarity with 
 the larger domestic animals tends,, I think, to mislead us; 
 
62 
 
 GEOMETRICAL RATIO OF INCREASE. 
 
 we see no great destruction falling on them, but we do not 
 keep in mind that thousands are annually slaughtered for 
 food, and that in a state of nature an equal number would 
 have somehow to be disposed of. 
 
 The only difference between organisms which annually 
 produce eggs or seeds by the thousand, and those which 
 produce extremely few, is, that the slow breeders would re¬ 
 quire a few more years to people, under favorable condi¬ 
 tions, a whole district, let it be ever so large. The condor 
 lays a couple of eggs and the ostrich a score, and yet in the 
 same country the condor may be the more numerous of the 
 two. The Fulmar petrel lays but one egg, yet it is be¬ 
 lieved to be the most numerous bird in the world. One 
 fly deposits hundreds of eggs, and another, like the hippo- 
 bosca, a single one. But this difference does not determine 
 how many individuals of the two species can be supported 
 in a district. A large number of eggs is of some im¬ 
 portance to those species which depend on a fluctuating 
 amount of food, for it allows them rapidly to increase in 
 number. But the real importance of a large number of 
 eggs or seeds is to make up for much destruction at some 
 period of life; and this period in the great majority of 
 cases is an early one. If an animal can in any way protect 
 its own eggs or young, a small number may be produced, 
 and yet the average stock be fully kept up; but if many 
 eggs or young are destroyed, many must be produced or 
 the species will become extinct. It would suffice to keep 
 up the full number of a tree, which lived on an average 
 for a thousand years, if a single seed were produced once 
 in a thousand years, supposing that this seed were never 
 destroyed and could be insured to germinate in a fitting 
 place; so that, in all cases, the average number of any an¬ 
 imal or plant depends only indirectly on the number of its 
 eggs or seeds. 
 
 In looking at Nature, it is most necessary to keep the 
 foregoing considerations always in mind—never to forget 
 that every single organic being may be said to be striving 
 to the utmost to increase in numbers; that each lives by a 
 struggle at some period of its life; that heavy destruction 
 inevitably falls either on the young or old during each gen¬ 
 eration or at recurrent intervals. Lighten any check, mit¬ 
 igate the destruction ever so little, and the number of the. 
 species will almost instantaneously increase to any amount 
 
NATURE OF THE CHECKS TO INCREASE. [t 
 NATURE OF THE CHECKS TO INCREASE. 
 
 The causes which check the natural tendency of each 
 species to increase are most obscure. Look at the most 
 vigorous species; by as much as it swarms in numbers, by 
 so much will it tend to increase still further. We know 
 not exactly what the checks are even in a single instance. 
 Nor will this surprise any one who reflects how ignorant 
 we are on this head, even in regard to mankind, although 
 so incomparably better known than any other animal. 
 This subject of the checks to increase has been ably treated 
 by several authors, and I hope in a future work to discuss 
 it at considerable length, more especially in regard to the 
 feral animals of South America. Here I will make only a 
 few remarks, just to recall to the reader’s mind some*of the 
 chief points. Eggs or very young animals seem generally 
 to suffer most, but this is not invariably the case. With 
 plants there is a vast destruction of seeds, but from some 
 observations which I have made it appears that the seed¬ 
 lings suffer most from germinating in ground already 
 thickly stocked with other plants. Seedlings, also, are 
 destroyed in vast numbers by various enemies; for instance, 
 on a piece of ground three feet long and two wide, dug and 
 cleared, and where there could be no choking from other 
 plants, I marked all the seedlings of our native weeds as 
 they came up, and out of 357 no less than 295 were de¬ 
 stroyed, chiefly by slugs and insects. If turf which has 
 long been mown, and the case would be the same with turf 
 closely browsed by quadrupeds, be let to grow, the more 
 vigorous plants gradually kill the less vigorous, though 
 fully grown plants; thus out of twenty species grown on a 
 little plot of mown turf (three feet by four) nine species 
 perished, from the other species being allowed to grow up 
 freely. 
 
 The amount of food for each species, of course, gives 
 the extreme limit to which each can increase; but very fre¬ 
 quently it is not the obtaining food, but the serving as prey 
 to other animals, which determines the average number of 
 a species. Thus, there seems to be little doubt that the 
 stock of partridges, grouse and hares on any large estate 
 depends chiefly on the destruction of vermin. If not one 
 head of game were shot during the next twenty years in 
 
£ 
 
 NATURE OF THE CHECKS To INCREASE. 
 
 England, and, at the same time, if no vermin were de- 
 stroyed, there would, in all probability, be less game than 
 at present, although hundreds of thousands of game 
 animals are now annually shot. On the other hand, 
 in some cases, as with the elephant, none are destroyed by 
 beasts of prey; for even the tiger in India most rarely dares 
 to attack a young elephant protected by its dam. 
 
 Climate plays an important part in determining the 
 average numbers of a species, and periodical seasons of ex¬ 
 treme cold or drought seem to be the most effective of all 
 k checks. I estimated (chiefly from the the greatly reduced 
 numbers of nests in the spring) that the winter of 1854-5 
 destroyed four-fifths of the birds in my own grounds; and 
 this is a tremendous destruction, when we remember that 
 ten per cent, is an extraordinarily severe mortality from 
 epidemics with man. The action of climate seems at first 
 sight to be quite independent of the struggle for existence; 
 
 dmt in so far as climate chiefly acts in reducing food, 
 jit brings on the most severe struggle between the indi¬ 
 viduals, whether of the same or of distinct species, which 
 subsist on the same kind of food. Even when climate, 
 for instance, extreme cold, acts directly, it will be the least 
 vigorous individuals, or those which have got least food 
 through the advancing winter, which will suffer the most. 
 When we travel from south to north, or from a damp 
 region to a dry, we invariably see some species gradually 
 getting rarer and rarer, and finally disappearing; and the 
 change of climate being conspicious, we are tempted to 
 attribute the whole effect to its direct action. But this is 
 a false view; we forget that each species, even where it 
 most abounds, is constantly suffering enormous destruc¬ 
 tion at some period of its life, from enemies or from com¬ 
 petitors for the same place and food; and if these enemies 
 or competitors be in the least degree favored by any slight 
 change of climate, they will increase in numbers; and as 
 each area is already fully stocked with inhabitants, the 
 other species must decrease. When we travel southward 
 and see a species decreasing in numbers, we may feel sure 
 that the cause lies quite as much in other species being 
 i favored, as in this one being hurt. So it is when we 
 travel northward, but in a somewhat lesser degree, for 
 the number of species of all kinds, and, therefore of 
 
NATURE OF THE CHECKS TO INCREASE. 
 
 65 
 
 competitors, decreases northward, or in ascending a mount- 
 
 I ain, we far oftener meet with stunted forms, due to the 
 directly injurious action of climate, than we do in proceed¬ 
 ing southward or in descending a mountain. When we 
 reach the Arctic regions, or snow-capped summits, or abso¬ 
 lute deserts, the struggle for life is almost exclusively with 
 the elements. 
 
 I That climate acts in main part indirectly by favoring 
 other species we clearly see in the prodigious number of } 
 plants which in our gardens can perfectly well endure our 
 climate, but which never become naturalized, for they 
 cannot compete with our native plants nor resist destruc¬ 
 tion by our native animals. 
 
 When a species, owing to highly favorable circumstances, 
 increases inordinately in numbers in a small tract, epidem - 
 ics—at least, this seems generally to occur with our game 
 animals—often ensue; and here we have a limiting check 
 independent of the struggle for life. But even some of 
 these so-called epidemics appear to be due to parasitic 
 worms, which have from some cause, possibly in part 
 through facility of diffusion among the crowded animals, 
 but disproportionally favored: and here comes in a sort of 
 1 struggle between the parasite and its prey. 
 
 On the other hand, in many cases, a large stock of indi¬ 
 viduals of the same species, relatively to the numbers of its 
 . enemies, is absolutely necessary for its preservation. Thus 
 we can easily raise plenty of corn and rape-seed, etc., in 
 our fields, because the seeds are in great excess compared 
 with the number of birds which feed on them; nor can the 
 birds, though having a superabundance of food at this one 
 season, increase in number proportionally to the supply of 
 seed, as their numbers are checked during the winter; but 
 any one who has tried knows how troublesome it is to get 
 seed from a few wheat or other such plants in a garden; I 
 have in this case lost every single seed. ' This view of the 
 necessity of a large stock of the same species for its preser¬ 
 vation, explains, I believe, some singular facts in nature 
 such as that of very rare plants being sometimes extremely 
 abundant, in the few spots where they do exist; and that 
 of some social plants being social, that is abounding in 
 individuals, even on the extreme verge of their range. For 
 in such cases, we may believe, that a plant could exist only 
 
66 
 
 STRUGGLE FOR EXISTENCE, 
 
 where the conditions of its life were so favorable that many 
 could exist together, and thus save the species from utter 
 destruction. I should add that the good effects of inter¬ 
 crossing, and the ill effects of close interbreeding, no 
 doubt come into play in many of these cases; but I will not 
 here enlarge on this subject. 
 
 COMPLEX RELATIONS OF ALL ANIMALS AND PLANTS TO 
 EACH OTHER IN THE STRUGGLE FOR EXISTENCE. 
 
 Many cases are on record showing how complex and unex¬ 
 pected are the checks and relations between organic beings, 
 which have to struggle together in the same country. I 
 will give only a single instance, which, though a simple 
 one, interested me. In Staffordshire, on the estate of a 
 relation, where I had ample means of investigation, there 
 was a large and extremely barren heath, which had never 
 been touched by the hand of man; but several hundred 
 acres of exactly the same nature had been inclosed twenty- 
 five years previously and planted with Scotch fir. The change 
 in the native vegetation of the planted part of the heath 
 was most remarkable, more than is generally seen in pass¬ 
 ing from one quite different soil to another: not only the 
 proportional numbers of the lieath-plants were wholly 
 changed, but twelve species of plants (not counting grasses 
 and carices) flourished in the plantations, which could not 
 be found on the heath. The effect on the insects must 
 have been still greater, for six insectivorous birds were very 
 common in the plantations, which were not to be seen on 
 the heath; and the heath was frequented by two or three 
 distinct insectivorous birds. Here we see how potent has 
 been the effect of the introduction of a single tree, nothing 
 whatever else having been done, with the exception of the 
 land having been inclosed, so that cattle could not enter. 
 But how important an element inclosure is, I plainly saw 
 near Farnham, in Surrey. Here there are extensive heaths, 
 with a few clumps of old Scotch firs on the distant hill¬ 
 tops: within the last ten years large spaces have been 
 inclosed, and self-sown firs are now springing up in multi¬ 
 tudes, so close together that all cannot live.. When I 
 ascertained that these young trees had not been sown or 
 planted I was so much surprised at their numbers that I 
 
STRUGGLE FOR EXISTENCE. 
 
 67 
 
 went to several points of view, whence I could examine 
 hundreds of acres of the uninclosed heath, and literally I 
 could not see a single Scotch fir, except the old planted 
 clumps. But on looking closely between the stems of the 
 heath, I found a multitude of seedlings and little trees 
 which had been perpetually browsed down by the cattle. 
 In one square yard, at a point some hundred yards distant 
 from one of the old clumps, I counted thirty-two little 
 trees; and one of them, with twenty-six rings of growth, 
 had, during many years tried to raise its head above the 
 stems of the heath, and had failed. No wonder that, as 
 soon as the land was inclosed, it became thickly clothed 
 with vigorously growing young firs. Yet the heath was so 
 extremely barren and so extensive that no one would ever 
 have imagined that cattle would have so closely and effec¬ 
 tually searched it for food. 
 
 Here we see that cattle absolutely determine the 
 existence of the Scotch fir; but in several parts of the 
 world insects determine the existence of cattle. Perhaps 
 Paraguay offers the most curious instance of this; for here 
 neither cattle nor horses nor dogs have ever run wild, 
 though they swarm southward and northward in a feral 
 state; and Azara and Rengger have shown that this is 
 caused by the greater number in Paraguay of a certain fly, 
 which lays its eggs in the navels of these animals when 
 first born. The increase of these flies, numerous as they 
 are, must be habitually checked by some means, probably 
 by other parasitic insects. Hence, if certain insectivorous 
 birds were to decrease in Paraguay, the parasitic insects 
 would probably increase; and this would lessen the num¬ 
 ber of the navel-frequenting flies—then cattle and horses 
 would become feral, and this would certainly greatly alter 
 (as indeed I have observed in parts of South America) the 
 vegetation: this again would largely affect the insects; and 
 this, as we have just seen in Staffordshire, the insectivor¬ 
 ous birds, and so onward in ever-increasing circles of com¬ 
 plexity. Not that under nature the relations will ever be 
 as simple as this. Battle within battle must be continually 
 recurring with varying success; and yet in the long-run 
 the forces are so nicely balanced that the face of nature 
 remains for long periods of time uniform, though assuredly 
 the merest trifle would give the victory to one organic 
 
68 
 
 STRUGGLE FOR EXISTENCE. 
 
 being over another. Nevertheless, so profound is our 
 ignorance, and so high our presumption, that we marvel 
 when we hear of the extinction of an organic being; and 
 as we do not see the cause, we invoke cataclysms to deso¬ 
 late the world, or invent laws on the duration of the forms 
 /of life! 
 
 f I am tempted to give one more instance showing how 
 ' plants and animals, remote in the scale of nature, are 
 bound together by a web of complex relations. I shall 
 , hereafter have occasion to show that the exotic Lobelia 
 folgens is never visited in my garden by insects, and con¬ 
 sequently, from its peculiar structure, never sets a seed. 
 Nearly all our orchidaceous plants absolutely require the 
 visits of insects to remove their pollen-masses and thus to 
 fertilize them. I find from experiments that Bumble-bees 
 are almost indispensable to the fertilization of the hearts¬ 
 ease (Yiolo tricolor), for other bees do not visit this flower. 
 I have also found that the visits of bees are necessary for the 
 fertilization of some kinds of clover; for instance twenty 
 heads of Dutch clover (Trifolium repens) yielded 2,290 
 seeds, but twenty other heads, protected from bees, produced 
 not one. Again, 100 heads of red clover (T. pratense) 
 produced 2,700 seeds, but the same number of protected 
 heads produced not a single seed. Humble-bees alone 
 visit red clover, as other bees cannot reach the nectar. It 
 has been suggested that moths may fertilize the clovers; 
 but I doubt whether they could do so in the case of the 
 red clover, from their weight not being sufficient to depress 
 the wing petals. Hence we may infer as highly probable 
 that, if the whole genus of humble-bees became extinct or 
 very rare in England, the heartsease and red clover would 
 become very rare, or wholly disappear. The number of 
 humble-bees in any district depends in a great measure 
 upon the number of field-mice, which destroy their combs 
 and nests; and Colonel Newman, who has long attended to 
 the habits of humble-bees, believes that “more than two- 
 thirds of them are thus destroyed all over England.” 
 Now the number of mice is largely dependent, as every 
 one knows, on the number of cats; and Colonel Newman 
 says, “ Near villages and small towns I have found the 
 nests of humble-bees more numerous than elsewhere,which 
 I attribute to the number of cats that destroy the mice.” 
 
3TTUGGLE FOB EXISTENCE. 
 
 69 
 
 Hence it is quite Credible that the presence of a feline 
 animal in large numbers in a district might determine, 
 through the intervention first of mice and then of bees, 
 the frequency of certain flowers in that district! 
 
 In the case of every species, many different checks, act¬ 
 ing at different periods of life, and during different seasons 
 or years, probably come into play; some one check or some 
 few being generally the most potent; but all will concur in 
 determining the average number, or even the existence of 
 the species. In some cases it can be shown that widely 
 different checks act on the same species in different dis¬ 
 tricts. When we look at the plants and bushes clothing 
 an entangled bank, we are tempted to attribute their pro¬ 
 portional numbers and kinds to what we call chance. But 
 how false a view is this! Every one has heard that when 
 an American forest is cut down, a very different vegetation 
 springs up; but it has been observed that ancient Indian 
 ruins in the Southern United States, which must formerly 
 have been cleared of trees, now display the same beautiful 
 diversity and proportion of kinds as in the surrounding 
 virgin forests. What a struggle must have gone on during 
 long centuries between the several kinds of trees, each 
 annually scattering its seeds by the thousand; what war 
 between insect and insect—between insects, snails and 
 other animals with birds and beasts of prey—all striving to 
 increase, all feeding on each other, or on the trees, their 
 seeds and seedlings, or on the other plants which first 
 clothed the ground and thus checked the growth of the 
 trees. Throw up a handful of feathers and all fall to the 
 ground according to definite laws; but how simple is the 
 problem where each shall fall compared to that of the 
 action and reaction of the innumerable plants and animals 
 which have determined, in the course of centuries, the 
 proportional numbers and kinds of trees now growing on 
 the old Indian ruins! 
 
 The dependency of one organic being on another, as of a 
 parasite on its prey, lies generally between beings remote 
 in the scale of nature. This is likewise sometimes the 
 case with those which may be strictly said to struggle with 
 each other for existence, as in the case of locusts and grass- 
 feeding quadrupeds. But the struggle will almost invari¬ 
 ably be most severe between the individuals of the same 
 
70 
 
 STRUGGLE FOR EXISTENCE. 
 
 Bpecies, for they frequent the same districts, require the 
 same food, and are exposed to the same dangers. In the 
 case of varieties of the same species, the struggle will 
 generally be almost equally severe, and we sometimes see 
 the contest soon decided: for instance, if several varieties 
 of wheat be sown together and the mixed seed be resown, 
 some of the varieties which best suit the soil or climate, 
 or are naturally the most fertile, will beat the others 
 and so yield more seed, and will consequently in a 
 few years supplant the other varieties. To keep up a 
 mixed stock of even such extremely close varieties as 
 the variously colored sweet peas, they must be each 
 year harvested separately, and the seed then mixed 
 in due proportion, otherwise the weaker kinds will 
 steadily decrease in number and disappear. So again 
 with the varieties of sheep; it has been asserted that certain 
 mountain varieties will starve out other mountain varieties, 
 so that they cannot be kept together. The same result 
 has followed from keeping together different varieties of 
 the medicinal leech. It may even be doubted whether the 
 varieties of any of our domestic plants or animals have so 
 exactly the same strength, habits, and constitution, that 
 the original proportions of a mixed stock (crossing being 
 prevented) could be kept up for half-a-dozen generations, 
 if they were allowed to struggle together, in the same mari¬ 
 ner as beings in a state of nature, and if the seed or young 
 were not annually preserved in due proportion 
 
 STRUGGLE FOR LIFE MOST SEVERE BETWEEN - INDIVIDUALS 
 AND VARIETIES OF THE SAME SPECIES. 
 
 As the species of the same genus usually have, though 
 by no means invariably, much similarity in habits and 
 constitution, and always in structure, the struggle will 
 generally be more severe between them, if they come into 
 ' competition with each other, than between the species 
 of distinct genera. We see this in the recent extension 
 over parts of the United States of one species of swallow 
 having caused the decrease of another species. The recent 
 increase of the missel-thrush in parts of Scotland has caused 
 the decrease of the song-thrush. How frequently we hear 
 of one species of rat taking the place of another species 
 
„ STRUGGLE FOR EXISTENCE. 
 
 n 
 
 under the most different climates! In Russia the small 
 Asiatic cockroach has everywhere driven before it its great 
 congener. In Australia the imported hive-bee is rapidly 
 exterminating the small, stingless native bee. One species 
 of charlock has been known to supplant another species; 
 and so in other cases. We can dimly see why the com¬ 
 petition should be most severe between allied forms, which 
 fill nearly the same place in the economy of nature; but 
 probably in no one case could we precisely say why one 
 species has been victorious over another in the great battle 
 of life. 
 
 A corollary of the highest importance may be deduced 
 from the foregoing remarks, namely, that the structure of 
 every organic being is related, in the most essential yet 
 often hidden manner, to that of all the other organic 
 beings, with which it comes into competition for food or 
 residence, or from which it has to escape, or on which it 
 preys. This is obvious in the structure of the teeth and 
 talons of the tiger; and in that of the legs and claws of the 
 parasite which clings to the hair on the tiger’s body. But 
 in the beautifully plumed seed of the dandelion, and in 
 the flattened and fringed legs of the water-beetle, the re¬ 
 lation seems at first confined to the elements of air and 
 water. Yet the advantage of the plumed seeds no doubt 
 stands in the closest relation to the land being already 
 thickly clothed with other plants, so that the seeds may 
 be widely distributed and fall on unoccupied ground. In 
 the water-beetle, the structure of its legs, so well adapted 
 for diving, allows it to compete with other aquatic insects, 
 to hunt for its own prey, and to escape serving as prey to 
 other animals. 
 
 The store of nutriment laid up within the seeds of many 
 plants seems at first sight to have no sort of relation to 
 other plants. But from the strong growth of young plants 
 produced from such seeds, as peas and beans, when sown 
 m the midst of long grass, it may be suspected that the 
 chief use of the nutriment in the seed is to favor the growth 
 of the seedlings, while struggling with other plants growing 
 vigorously all around. 
 
 Look at a plant in the midst of its range! Why does it 
 not double or quadruple its numbers? We know that it 
 can perfectly well withstand a little more heat or cold. 
 
STRUGGLE FOR EXISTENCE. 
 
 72 
 
 H ' 
 
 dampness or dryness, for elsewhere it ranges into slightly 
 hotter or colder, damper or drier districts. In this case we 
 can clearly see that if we wish in imagination to give the 
 plant the power of increasing in numbers, we should have 
 to give it some advantage over its competitors, or over the 
 animals which prey on it. On the confines of its geo¬ 
 graphical range, a change of constitution with respect to 
 climate would clearly be an advantage to our plant; but we 
 have reason to believe that only a few plants or animals 
 range so far, that they are destroyed exclusively by the 
 rigor of the climate. Not until we reach the extreme con¬ 
 fines of life, in the Arctic regions or on the borders of an 
 utter desert, will competition cease. The land may be ex¬ 
 tremely cold or dry, yet there will be competition between 
 some few species, or between the individuals of the same 
 species, for the warmest or dampest spots. 
 
 Hence we can see that when a plant or animal is placed 
 in a new country, among new competitors, the conditions 
 of its life will generally be changed in an essential manner, 
 although the climate may be exactly the same as in its 
 former home. If its average numbers are to increase in 
 its new home, we should have to modify it in a different 
 way to what we should have had to do in its native 
 country; for we should have to give it some advantage 
 over a different set of competitors or enemies. 
 
 It is good thus to try in imagination to give any one species 
 an advantage over another. Probably in no single instance 
 should we know what to do. This ought to convince us of 
 our ignorance on the mutual relations of all organic beings; 
 ji conviction as necessary, as it is difficult to acquire. All 
 that we can do is to keep steadily in mind that each or¬ 
 ganic being is striving to increase in a geometrical ratio; 
 that each, at some period of its life, during some season of 
 the year, during each generation, or at intervals, has to 
 struggle for life and to suffer great destruction. When we 
 reflect on this struggle we may console ourselves with the 
 full belief that the war of nature is not incessant, that ho 
 fear is felt, that death is generally prompt, and that the 
 vigorous, the healthy and the happy survive and multiply. 
 
NATURAL SELECTION. 
 
 73 
 
 CHAPTER IV. 
 
 NATURAL SELECTION; OR THE SURVIVAL OF THE FITTEST. 
 
 Natural Selection—its power compared witli man’s selection—its 
 power on characters of trifling importance—its power at all ages 
 and on both sexes—Sexual Selection—On the generality of inter¬ 
 crosses between individuals of the same species—Circumstances 
 favorable and unfavorable to the results of Natural Selection, 
 namely, intercrossing, isolation, number of individuals—Slow 
 action—Extinction caused by Natural Selection—Divergence of 
 Character, related to the diversity of inhabitants of any small 
 area and to naturalization—Action of Natural Selection, through 
 Divergence of Character and Extinction, on the descendants 
 from a common parent—Explains the grouping of all organic 
 beings—Advance in organization—Low forms preserved—Con¬ 
 vergence of character—Indefinite multiplication of species— 
 Summary. 
 
 How will the struggle for existence, briefly discussed in 
 the last chapter, act in regard to variation? Can the prin¬ 
 ciple of selection, which we have seen is so potent in the 
 hands of man, apply unde r pat jura? I think we shall 
 see that it can act most efficiently. Let the endless 
 number of sliglit variations and individual differences 
 occurring in our domestic productions, and, in a lesser 
 degree, in those under nature, be borne in mind; as well as 
 the strength of the hereditary tendency. Under domesti¬ 
 cation, it may truly be said that the whole organization 
 becomes in some degree plastic. But the variability, which 
 we almost universally meet with in our domestic produc¬ 
 tions is not directly produced, as Hooker and Asa Gray 
 have well remarked, by man; he can neither originate 
 varieties nor prevent their occurrence; he can only pre¬ 
 serve and accumulate such as do occur. Unintentionally 
 he exposes organic beings to new and changing conditions 
 of life, and variability ensues; but similar changes of con¬ 
 ditions might and do occur under nature. Let it also be 
 
^ NATURAL SELECTION\ 
 
 borne in mind how infinitely complex and close-fitting are 
 the mutual relations of all organic beings to each other 
 and to their physical conditions of life; and consequently 
 what infinitely varied diversities of structure might bo of 
 use to each being under changing conditions of life. Can 
 it then be thought improbable, seeing that vanations 
 useful to man have undoubtedly occurred, that other 
 variations useful in some way to each being in the gieat 
 and complex battle of life, should occur in the course of 
 many successive generations? If such do occur, can we 
 doubt (remembering that many more individuals aie bom 
 than can possibly survive) that individuals having any ad- 
 vantage, however slight, over others, would have the best 
 chance of surviving and procreating their kind. On the 
 other hand, we may feel sure that any variation m the least 
 degree injurious would be rigidly, destroyed. This preser¬ 
 vation of farm-able individual differences and variations, 
 and the destruction of those which are rajunpus, I ^ ave 
 called Natural Selection, or the .Survival of the fittest. 
 Variations neither useful nor injurious would not be affected 
 by natural selection, and would be left either a fluctuati g 
 element, as perhaps we see in certain polymorphic s P eclc > 
 or would ultimately become fixed, owing to the nature of 
 the organism and the nature of the conditions. 
 
 Several writers have misapprehended or objected to the 
 term Natural Selection. Some have even imagined that 
 natural selection induces variability, whereas, it implies 
 only the preservation of such variations as arise and aie 
 beneficial to the being under its conditions of life No 
 one objects to agriculturists speaking of the potent effects 
 of man’s selection; and in this case the individual differ¬ 
 ences given by nature, which man for some object selects 
 must of necessity first occur. Others have, objected, that 
 the term selection implies conscious choice in the animals 
 which become modified; and it has even been urged that, 
 as plants have no volition, natural selection is not applica¬ 
 ble to them! In the literal sense of the word, no doubt, 
 natural selection is a false term; but who ever objected to 
 chemists speaking of the elective affinities of the vanous 
 elements?—and yet an acid cannot strictly be said to elect 
 the base with which it in preference combines. It has 
 been said that I speak of natural selection as an active 
 
NATURAL SELECTION. 
 
 75 
 
 power or Deity; but who objects to an author speaking of 
 the attraction of gravity as ruling the movements of the 
 planets? Every one knows what is meant and is implied 
 by such metaphorical expressions; and they are almost 
 necessary for brevity. So again it is difficult to avoid peN 
 sonifying the word Nature; but I mean by nature, only 
 the aggregate action and product of many natural laws, 
 and by laws the sequence of events as ascertained by us. 
 With a little familiarity such superficial objections will be 
 forgotten. 
 
 We shall best understand the probable course of natural 
 selection by taking the case of a country undergoing some 
 slight physical change, for instance, of climate. The pro¬ 
 portional numbers of its inhabitants will almost immedi¬ 
 ately undergo a change, and some species will probably be¬ 
 come extinct. We may conclude, from what we have seen 
 of the intimate and complex manner in which the inhabi¬ 
 tants of each country are bound together, that any change 
 in the numerical proportions of the inhabitants, independ¬ 
 ently of the change of climate itself, would seriously affect 
 the others. If the country were open on its borders, new 
 forms would certainly immigrate, and this would likewise 
 seriously disturb the relations of some of the former inhab¬ 
 itants. Let it be remembered how powerful the influence 
 of a single introduced tree or mammal has been shown to 
 be. But in the case of an island, or of a country partly 
 surrounded by barriers, into which new and better adapted 
 forms could not freely enter, we should then have places in 
 the economy of nature which would assuredly be better filled 
 up if some of the original inhabitants were in some man¬ 
 ner modified; for, had the area been open to immigration, 
 these same places would have been seized on by intruders. 
 In such cases, slight modifications, which in any way 
 favored the individuals of any species, by better adapting 
 them to their altered conditions, would tend to be pre¬ 
 served; and natural selection would have free scope for the 
 work of improvement. 
 
 We have good reason to believe, as shown in the first 
 chapter, that changes in the conditions of life give a ten¬ 
 dency to increased variability; and in the forgoing cases 
 the conditions have changed, and this would manifestly be 
 favorable to natural selection, by affording a better chance 
 
76 NATURAL SELECTION 
 
 of the occurrence of profitable variations. Unless such 
 occur, natural selection can do nothing. Under le 
 term of " variations,” it must never he forgotten that 
 mere individual differences are included.. .As man 
 can produce a great result with his domestic animals and 
 plants by adding up in any given direction individual dif¬ 
 ferences, so could natural selection, but far more easily 
 from having incomparably longer time for action JNor 
 do I believe that any great physical change, as of climate, 
 or any unusual degree of isolation, to check immigration, is 
 necessary in order that new and unoccupied places should 
 be left for natural selection to fill up by improving some 
 of the varying inhabitants. For as all the inhabitants of 
 each country are struggling together with nicely balanced 
 forces, extremely slight modifications m the structure or 
 habits of one species would often give it an advantage over 
 others- and still further modifications of the same kind 
 would often still further increase the advantage, as long as 
 the species continued under the same conditions ot me 
 and profited by similar means of subsistence and. defence. 
 
 ^STo country can be named in which all the native inhab¬ 
 itants are now so perfectly adapted to each other and to 
 the physical conditions under which they live, that none 
 of them could be still better adapted or improved; for in 
 all countries the natives have been so far conquered by 
 naturalized productions that they have allowed some for¬ 
 eigners to take firm possession of the land. And as for¬ 
 eigners have thus in every country beaten some of the 
 natives, we may safely conclude that the natives might 
 have been modified with advantage, so as to have better 
 
 resisted the intruders. , . 
 
 As man can produce, and certainly has produced, a great 
 result by his methodical and unconscious means of selec¬ 
 tion, what may not natural selection effect? Man can act 
 only on external and visible characters; Nature, if I may 
 be allowed to personify the natural preservation or survival; 
 of the fittest, cares nothing for. appearances, except in so 
 far as they are useful to any being. She can act on every 
 internal organ, on every shade of constitutional difference 
 on the whole machinery of life. Man selects only for his 
 own o-oocl; Nature only for that of the bein^ which she 
 tends. Every selected character is fully exercised by liei, 
 
NATURAL SELECTION. 
 
 77 
 
 as is implied by the fact of their selection. Man keeps the 
 natives of many climates in the same country. He seldom 
 exercises each selected character in some peculiar and fit¬ 
 ting manner; he feeds a long and a short-beaked pigeon on 
 the same food; he does not exercise a long-backed or long- 
 legged quadruped in any peculiar manner; he exposes 
 sheep with long and short wool to the same climate; does 
 not allow the most vigorous males to struggle for the 
 females; he does not rigidly destroy all inferior animals, 
 but protects during each varying season, as far as lies in 
 his power, all his productions. He often begins his selec¬ 
 tion bv some half-monstrous form, or at least by some mod¬ 
 ification prominent enough to catch the eye or to be 
 plainly useful to him. Under nature^the slightest differ¬ 
 ences of structure or constitution may well turn the nicely 
 balanced scale in the struggle for life, and so be preserved. 
 How fleeting are the wishes and efforts of man! How 
 short his time, and consequently how poor will be his 
 results, compared with those accumulated by Nature 
 during whole geological periods! Can we wonder, then, 
 that Nature’s productions should be far “truer” in char¬ 
 acter than man’s productions; that they should be infinitely 
 better adapted to the most complex conditions of life, 
 and should plainly bear the stamp of far higher workman¬ 
 ship? 
 
 It may metaphorically be said that natural selection 
 is daily and hourly scrutinizing, throughout the world, the 
 slightest variations; rejecting those that are bad, preserv- j 
 ing and adding up all that are good; silently and insen¬ 
 sibly working, whenever and wherever opportunity offers , 
 at the improvement of each organic being in relation to its 
 organic and inorganic conditions of life. We see nothing 
 of these slow changes in progress, until the hand of time 
 has marked the lapse of ages, and then so imperfect is our 
 view into long-past geological ages that we see only that 
 the forms of life arq now different from what they formerly j 
 were. 
 
 In order that any great amount of modification should 
 be effected in a species, a variety, when once formed 
 must again, perhaps after a long interval of time, 
 vary or present individual differences of the same favorable 
 nature as before; and these must again be preserved, and 
 
78 
 
 NATURAL SELECTION. 
 
 so onward, step by step. Seeing that individual differences 
 of the same kind perpetually recur, this can hardly be con¬ 
 sidered as an unwarrantable assumption. But whether it 
 is true, we can judge only by seeing how far the bypotlie- 
 sis accords with and explains the general phenomena of 
 nature. On the other hand, the ordinary belief that the 
 amount of possible variation is a strictly limited quantity, 
 
 is likewise a simple assumption. , * 
 
 Although natural selection can act only through and for 
 .the good°of each being, yet characters and structures, 
 
 \which we are apt to consider as of very trifling importance, 
 ‘may thus be acted on. When we see leaf-eating insects 
 green, and bark-feeders mottled-gray; the alpine ptarmigan 
 white in winter, the red grouse the color of heathei, we 
 must believe that these tints are of service to these buds 
 and insectr in preserving them from danger. Grouse, if 
 not destroyed at some period of their lives, would lncieaso 
 in countless numbers; they are known to suffer barge y 
 from birds of prey; and hawks are guided by eyesight to 
 their prey—so much so that on parts of the continent per¬ 
 sons are warned not to keep white pigeons, as being the 
 most liable to destruction. Hence natural selection mig 1 
 / be effective in giving the proper color to each kind ol 
 ' grouse, and in keeping that color when once acquired 
 true and constant. Nor ought we to think that the oc¬ 
 casional destruction of an animal of any particular color 
 would produce little effect; we should remember how 
 essential it is in a flock of white sheep to destroy a lamb 
 with the faintest trace of black. We have seen how the 
 color of hogs, which feed on the “pamt-root in Virginia 
 determines whether they shall live or die. In plants the 
 down on the fruit and the color of the flesh are consideied 
 by botanists as characters of the most trifling importance; 
 vet we hear from an excellent horticulturist. Downing, 
 that in the United States that smooth-skinned fruits suffer 
 far more from a beetle, a Curcuho, than those with down, 
 that purple plums suffer far more from a certain disease 
 than yellow plums; whereas another disease attacks yellow- 
 fleshed peaches far more those with other colored 
 flesh. If, with all the aids of art, these slight differ¬ 
 ences make a great difference in cultivating the several 
 varieties, assuredly, in a state of nature, where the trees 
 
NATURAL SELECTION. 
 
 79 
 
 would have to struggle with other trees and with a host of 
 enemies, such differences would effectually settle which 
 variety, whether a smooth or downy, a yellow or a purple- 
 fleshed fruit, should succeed. 
 
 In looking at many small points of difference between 
 species, which, as far as our ignorance permits us to judge, 
 seem quite unimportant, we must not forget that climate, 
 food, etc., have no doubt produced some direct effect. It 
 is also necessary to bear in mind that, owing to the law of 
 correlation, when one part varies and the variations are 
 accumulated through natural selection, other modifica¬ 
 tions, often of the most unexpected nature, will ensue. 
 
 As we see that those variations which, under domesti¬ 
 cation, appear at any particular period of life, tend to 
 reappear in the offspring at the same period; for instance, 
 in the shape, size and flavor of the seeds of the many 
 varieties of our culinary and agricultural plants; in the 
 caterpillar and cocoon stages of the varieties of the silk¬ 
 worm; in the eggs of poultry, and in the color of the down 
 of their chickens; in the horns of our sheep and cattle 
 when nearly adult; so in a state of nature natural selection 
 will be enabled to act on and modify organic beings at any 
 age, by the accumulation of variations profitable at that 
 age, and by their inheritance at a corresponding age. If it 
 profit a plant to have its seeds more and more widely dis¬ 
 seminated by the wind, I can see no greater difficulty in 
 this being effected through natural selection, than in the 
 cotton-planter increasing and improving by selection the 
 down in the pods on his cotton-trees. Natural selection 
 may modify and adapt the larva of an insect to a score of 
 contingencies, wholly different from those which concern 
 the mature insect; and these modifications may effect, 
 through correlation, the structure of the adult. So, con¬ 
 versely, modifications in the adult may affect the structure 
 of the larva; but in all cases natural selection will insure 
 that they shall not be injurious: for if they were so. the 
 species would become extinct. 
 
 Natural selection will modify the structure of the young 
 in relation to the parent and of the parent in relation to 
 the young. In social animals it will adapt the structure of 
 each individual for the benefit of the whole community; 
 if the community profits by the selected change. "What 
 
NATURAL SELECTION\ 
 
 80 
 
 natural selection cannot do, is to modify the structure of 
 one species, without giving it any advantage, for the good 
 of another species; and though statements to this effect 
 may be found in works of natural. history, I cannot find 
 one case which will bear investigation. A structure used 
 only once in an animal's life, if of high importance to 
 it, might be modified to any extent by natural selection; 
 for instance, the great jaws possessed by certain insects, 
 used exclusively for opening the cocoon—or the hard tip to 
 the beak of unhatched birds, used for breaking the eggs. 
 It has been asserted, that of the best short-beaked tumbler- 
 pigeons a greater number perish in the egg than are able to 
 get out of it; so that fanciers assist in the act of hatching. 
 Now, if nature had to make the beak of a full-grown pigeon 
 very short for the bird's own advantage, the process of 
 modification would be very slow, and there would be simul¬ 
 taneously the most rigorous selection of all the young birds 
 within the egg, which had the most powerful and hardest 
 beaks, for all with weak beaks would inevitably perish; or, 
 more delicate and more easily broken shells might be 
 selected, the thickness of the shell being known to vary 
 like every other structure. 
 
 It may be well here to remark that with all beings there 
 must be much fortuitous destruction, which can have 
 little or no influence on the course of natural selection. 
 For instance, a vast number of eggs or seeds are 
 annually devoured, and these could be modified through 
 natural selection only if they varied in some manner 
 which protected them from their enemies. Yet many of 
 these eggs or seeds would perhaps, if not destroyed, have 
 yielded individuals better adapted to their conditions of 
 life than any of those which happened to survive. So 
 again a vast number of mature animals and plants, whether 
 or not they be the best adapted to their conditions, must 
 be annually destroyed by accidental causes, which would 
 not be in the least degree mitigated by certain changes of 
 structure or constitution which would in other ways be 
 beneficial to the species. But let the destruction of the adults 
 be ever so heavy, if the number which can exist in any dis¬ 
 trict be not wholly kept down by such causes—or again let 
 the destruction of eggs or seeds be so great that onl} r a 
 hundredth or a thousandth part are developed—yet of 
 
SEXUAL SELECTION ,. 
 
 81 
 
 those which do survive, the best adapted individuals, sup- 
 I posing that there is any variability in a favorable direction, 
 
 I will tend to propagate their kind in larger numbers than 
 I the less well adapted. If the numbers be wholly kept 
 u down by the causes just indicated, as will often have been 
 the case, natural selection will be powerless in certain ben¬ 
 eficial directions; but this is no valid objection to its effi¬ 
 ciency at other times and in other ways; for we are far 
 from having any reason to suppose that many species ever 
 undergo modification and improvement at the same time 
 in the same area. 
 
 SEXUAL SELECTION - . 
 
 Inasmuch as peculiarities often appear under domestica¬ 
 tion in one sex and become hereditarily attached to that 
 sex, so no doubt it will be under nature. Thus it is ren¬ 
 dered possible for the two sexes to be modified through 
 natural selection in relation to different habits of life, as is 
 sometimes the case; or for one sex to be modified in rela¬ 
 tion to the other sex, as commonly occurs. This leads me 
 to say a few words on what I have called sexual selection. 
 This form of selection depends, not on a struggle for exist- 
 tence in relation to other organic beings or to external 
 conditions, but on a struggle between the individuals of 
 one sex, generally the males, for the possession of the other 
 sex. The result is not death to the unsuccessful competi¬ 
 tor, but few or no offspring. Sexual selection is, there¬ 
 fore, less rigorous than natural selection. Generally, the 
 most vigorous males, those which are best fitted for their 
 places in nature, will leave most progeny. But in many 
 cases victory depends not so much on general vigor, a son 
 having special weapons, confined to the male sex. A horn¬ 
 less stag or spurless cock would have a poor chance of 
 leaving numerous offspring. Sexual selection, by always 
 allowing the victor to breed, might surely give indomitable 
 courage, length of spur and strength to the wing to strike 
 in the spurred leg, in nearly the same manner as does the 
 brutal cockfighter by the careful selection of his best cocks. 
 How low in the scale of nature the law of battle descends 
 I know not; male alligators have been described as fight¬ 
 ing, bellowing and whirling round, like Indians in a war- 
 dance, for the possession of the females; male salmons have 
 
82 
 
 SEXUAL SELECTION. 
 
 been observed fighting all day long; male stag-beetles 
 sometimes bear wounds from the huge mandibles of other 
 males; the males of certain hymenopterous insects have 
 been frequently seen by that inimitable observer M* 
 Fabre, fighting for a particular female who sits by, an ap¬ 
 parently unconcerned beholder of the struggle, and then 
 retires with the conqueror. The war is, perhaps, severest 
 between the males of polygamous animals, and these seem 
 oftenest provided with special weapons. The males of 
 carnivorous animals are already well armed; though to 
 them and to others, special means of defence may be 
 given through means of sexual selection, as the mane of 
 the lion, and the hooked jaw to the male salmon; for the 
 shield may be as important for victory as the sword or 
 spear. 
 
 Among birds, the contest is often of a more peaceful 
 character. All those who have attended to the subject, 
 believe that there is the severest rivalry between the males 
 of many species to attact, by singing, the females. The 
 rock-thrush of Guiana, birds of paradise, and some others, 
 congregate, and successive males display with the most 
 elaborate care, and show off in the best manner, their 
 gorgeous plumage; they likewise perform strange antics 
 before the females, which, standing by as spectators, at 
 last choose the most attractive partner. Those who have 
 closely attended to birds in confinement well know that 
 they often take individual preferences and dislikes: thus 
 Sir R. Heron has described how a pied peacock was emi¬ 
 nently attractive to all his hen birds. I cannot here enter 
 on the necessary details; but if man can in a short time 
 give beauty and an elegant carriage to his bantams, accord¬ 
 ing to his standard of beauty, I can see no good reason to 
 doubt that female birds, by selecting, during thousands of 
 generations, the most melodious or beautiful males, accoid- 
 to their standard of beauty, might produce a marked 
 effect. Some well-known laws, with respect to the pumage 
 of male and female birds, in comparison with the plumage 
 of the young, can partly be explained through the action 
 of sexual selection on variations occurring at different 
 ages, and transmitted to the males alone or to both sexes 
 at corresponding ages; but I have not space here to enter 
 on this subject. '' 
 
SEXUAL SELECTION. go 
 
 of^nvVnim^fjn.vp 1 ^ 6 ’ tbat when tbe ma,es and females 
 
 01 anj_ ani mal have the same general habits of life W 
 
 jhffer .n structure, color, or Srnament, such differences 
 
 have been mainly caused by sexual selection- that is bv 
 
 individual males having had, in successh^generatLs 7 
 
 some slight advantage over other males, in their weapons' 
 
 means of defense, or charms, which they have transmitted 
 
 o th w mate offspring alone. Yet, I wonld noWteh to 
 
 attnbute all sexual differences to this agency: for we see 
 
 attachedbTthc m„T alS peo "! iarities arisin g and becoming 
 attacned to the male sex, which apparently have not been 
 
 thf brTasf ofTh^ by m i n * The tuft of hair on 
 
 and itifdn?Lf h t n 1 l tUr -x ey - C00k cannot be of any use, 
 and it is doubtful whether it can be ornamental in the eves 
 
 of the female bird; indeed, had the tuft appeared under 
 
 domestication it would have been called a monstrosity. 
 
 illustrations op the action of natural selection 
 
 OR, THE SURVIVAL OP THE FITTEST 
 
 tionbcts 6 1 mnst^V? cIear . h ? w > as 1 Relieve, natural selec- 
 non acts, 1 must beg permission to give one or two imam 
 
 nary illustrations. Let us take the case of a wolf which 
 
 preys on various animals, securing some bv craft some bv 
 
 strength, and some by fleetness; and let “us suppose that 
 
 the fleetest prey, a deer for instance, had from any change 
 
 m the country increased in numbers or 
 
 ye'ar whl de t C he ea wo1f in n \ mb ® r % durin g ^at season of the 
 year wlien the wolf was hardest pressed for food Under 
 
 he^ best Cn chance Ce of he 8Wi - f, ? St and slimmest "'°'lves 
 tne pest ciiance of surviving, and so be preserved or 
 
 selected, provided always that they retained streno-j-L f n 
 
 master their prey at this or some ofhei- period of thl v a 
 
 when they were compelled to prey on other animals I can 
 
 see no more reason to doubt that this would be the resnft 
 
 than that man should be able to improve the fleetness of his 
 
 grevhounds by careful and methodical selection or by that 
 
 kind of unconscious selection which follows from each man 
 
 ifvirw tv ke n P 4 1 6 b T St d0gS without any thought of mod- 
 »*"* tbe breed - 1 may add that, according to Mr 
 
 p f ? e -’u t U e are two varieties of the wolf inhabiting the 
 Gatskili Mountains, in the United States, one with a fight 
 
84 illustrations of tub action 
 
 srevViound-like form, which pursues deer, and the other 
 more bulky, with shorter legs, which more frequently 
 
 attacks the shepherd s flocks. ...... t 
 
 It should be observed that in the above illustration, I 
 speak of the slimmest individual wolves, and not of any 
 single strongly marked variation having been preserved. 
 In former editions of this work I sometimes spoke as if 
 this latter alternative had frequently occurred. I saw lie 
 great importance of individual differences, and this led 
 me fully to discuss the results of unconscious selection by 
 man, which depends on the preservation of all the more or 
 less valuable individuals, and on the destruction of the 
 worst. I saw, also, that the preservation m a state ot 
 nature of any occasional deviation of structure, such as a 
 monstrosity, would be a rare event; and that, if at hist 
 preserved, it would generally be lost by suosequent inter¬ 
 crossing with ordinary individuals. Nevertheless, unti 
 reading an able and valuable article in the “ North British 
 Review” (1867), I did not appreciate how rarely single 
 variations, whether slight or strongly marked, could be 
 perpetuated. The author takes the case of a pair ot am- 
 £ producing during their lifetime two hundred 
 offspring, of which, from various causes of destruction, 
 only two on an average survive to pro-create their kmc. 
 This is rather an extreme estimate for most of the higher 
 animals but by no means so for many of _ the lower organ¬ 
 isms He then shows that if a single individual were born, 
 which varied in some manner, giving it twice as good a 
 chance of life as that of the other individuals, yet the 
 chances would be strongly against its survival. Supposing 
 it to survive and to breed, _ and that half its yoi g 
 inherited the favorable variation; still, as the Reviewer 
 o-oes on to show, the young would have only a slightly 
 better chance of surviving and breeding; and this chance 
 would go on decreasing in the succeeding generations. 
 The -justice of these remarks cannot, I think, be 
 disuuted If, for instance, a bird of some kind could 
 procure its food more easily by having its beak curved, 
 and if one were born with its beak strongly curved, 
 and which consequently flourished, nevertheless them 
 would be a very poor chance of this one individual perpet¬ 
 uating its kind to the exclusion of the common form; but 
 
 
OF NATURAL SELECTION 85 
 
 there can hardly be a doubt, judging by what we see taking 
 place under domestication, that this result would follow 
 fiom the preservation during many generations of a laro-e 
 numbei of individuals with more or less strongly curved 
 beaks, and from the destruction of a still larger number 
 with the straightest beaks. 
 
 It should not, however, be overlooked that certain 
 rather strongly marked variations, which no one would 
 lank as mere individual differences, frequently recur 
 owmg to a similar organization being similarly acted on—- 
 ol which fact numerous instances could be given with our 
 domestic productions. In such cases, if the varying indi¬ 
 vidual did not actually transmit to its offspring its "newly-' 
 acquired character, it would undoubtedly transmit to them 
 as ong as the existing conditions remained the same, a 
 still stronger tendency to vary in the same manner. There 
 can also be little doubt that the tendency to vary in the 
 same manner has often been so strong that all the individ¬ 
 uals of the same species have been similarly modified with- 
 fche , aid 1 of an y foi 'm of selection. Or only a third, 
 
 1 0 3* dentil part of the individuals may have been thus 
 affected, of which fact several instances could be given. 
 Thus Grraba estimates that about one-fifth of the guille¬ 
 mots in the Faroe Islands consist of a variety so well 
 marked, that it was formerly ranked as a distinct species 
 under the name of Uria lacrymans. In cases of this kind, 
 it the vaiiation were of a beneficial nature, the original 
 form would soon be supplanted by the modified form 
 through the survival of the fittest. 9 
 
 . ^ ie fects of intercrossing in eliminating variations of 
 all kinds, I shall have to recur; but it maybe here remarked 
 that most.animals and plants keep to their proper homes, 
 and do not needlessly wander about; we see this even with 
 migratory birds, which almost always return to the same 
 spot. Consequently each newly-formed variety would gen¬ 
 erally be at first local, as seems to be the common rule with 
 varieties in a state of nature; so that similarly modified.indi- 
 viduals would soon exist in a small body together and 
 would often breed together. If the new variety were suc¬ 
 cessful in its battle for life, it would slowly spread from a 
 central district, competing with and conquering the un¬ 
 changed individuals ou the margins of an ever-increasing 
 circle* 
 
86 ILL USTRA TIONS OF THE ACTION 
 
 It may be worth while to give another and more complex 
 illustration of the action of natural selection. Certain 
 plants excrete sweet juice, apparently for the sake of elim¬ 
 inating something injurious from the sap: this is effected, 
 for instance, by glands at the base of the stipules m some 
 Leguminosse, and at the backs of the leaves of the common 
 laurel. This juice, though small m quantity, is greedily 
 sought by insects; but their visits do not m.any way ben¬ 
 efit the plant. Now, let us suppose that the juice or nectar 
 was excreted from the inside of the flowers of a ceitarn 
 number of plants of any species. Insects m seeking the 
 nectar would get dusted with pollen, and would often 
 transport it from one flower to another. The flowers of 
 two distinct individuals of the same species would thus get 
 crossed; and the act of crossing, as can be fully proved, 
 gives rise to vigorous seedlings, which consequently would 
 have the best chance of flourishing and surviving. ie 
 plants which produced flowers with the largest glands or 
 nectaries, excreting most nectar, would oftenest be visited 
 by insects, and would oftenest be crossed; and so in the 
 long-run would gain the upper hand and form a local 
 variety. The flowers, also, which had their stamens and 
 pistils placed, in relation to the size and habits of the par¬ 
 ticular insect which visited them, so as to favor in any 
 decree the transportal of the pollen, would likewise be 
 favored. We might have taken the case of insects visiting 
 flowers for the sake of collecting pollen instead of nectar; 
 and as pollen is formed for the sole purpose of fertilization, 
 its destruction appears to be a simple loss to the plant; yet 
 if a little pollen were carried, at first occasionally and then 
 habitually, by the pollen-devouring insects from flower to 
 flower, and a cross thus effected, although nine-tenths of 
 the pollen were destroyed it might still be a great gain to 
 the plant to be thus robbed; and the individuals which 
 produced more and more pollen, and had larger anthers, 
 
 would be selected. , 
 
 When our plant, by the above process long continued, 
 
 had been rendered highly attractive to insects, they would, 
 unintentionally on their part, regularly carry pollen from 
 flower to flower; and that they do this effectually I cou c 
 easily show by many striking facts. I will give only one, 
 as likewise illustrating one step in the separation of the 
 
OF NATURAL SELECTION. 37 
 
 sexes of plants. Some holly-trees bear only male flowers 
 which have four stamens producing a rather small quan¬ 
 tity of pollen, and a rudimentary pistil; other holly-trees 
 bear only female flowers; these have a full-sized pistil, and 
 four stamens with shrivelled anthers, in which not a grain 
 of polen can be detected. Having found a female tree 
 exactly sixty yards from a male tree, I put the stigmas of 
 twenty flowers, taken from different branches, under the 
 nncioscope, and on all, without exception, there were a few 
 pollen-grains, and on some a profusion. As the wind had 
 set for several days from the female to the male tree, the 
 pollen could not thus have been carried. The weather 
 had been cold and boisterous and therefore not favorable 
 to bees, nevertheless every female flower which I examined 
 had been effectually fertilized bv the bees, which had flown 
 irorn tree to tree in search of nectar. But to return to 
 our imaginary case; as soon as the plant had been ren¬ 
 dered so highly attractive to insects that pollen was regu¬ 
 larly carried from flower to flower, another process might 
 commence. No naturalist doubts the advantage of what 
 has been called the “ physiological division of labor;” hence 
 we may believe that it would be advantageous to a plant to 
 produce stamens alone in one flower or on one whole plant 
 and pistils alone in another flower or on another plant! 
 
 * V? nts unc ^ e . r culture and placed under new conditions 
 01 life, sometimes the male organs and sometimes the 
 female organs become more or less impotent; now if we 
 suppose this to occur in ever so slight a degree under 
 nature, then, as pollen is already carried regularly from 
 flowei to flower, and as a more complete separation of the 
 sexes of our plant would be advantageous on the principle 
 of the division of labor, individuals with this tendency 
 more and more increased, would be continually favored or 
 selected, until at last a complete separation of the sexes 
 might be effected. It would take up too much space to 
 show the various steps, though dimorphism and other 
 means, by which the separation of the sexes in plants of 
 various kinds is apparently now in progress; but I may 
 add that some of the species of holly in North America 
 are according to Asa Gray, in an exactly intermediate 
 condition, or, as he expresses it, are more or less dioeciously 
 polygamous. J 
 
Sg ILLUSTRATIONS OF THE ACTION 
 
 Let us now turn to the nectar-feeding insects; we may 
 suppose the plant, of which we have been slowly increasing 
 the nectar by continued selection, to be a common plant; 
 and that certain insects depended in mam part on its 
 nectar foi food. I could give many facts showing how 
 anxious bees are to save time: for instance, their habit o 
 cuttino- holes and sucking the nectar at the bases of ceitain 
 dowers, which with a very little more trouble they can enter 
 by the mouth. Bearing such facts in mind, it maybe believed 
 that under certain circumstances individual differences m 
 the curvature or length of the probocis, etc., too slight to e 
 appreciated by us, might profit a bee or other insect so 
 that certain individuals would be able to obtain then food 
 more quickly than others; and thus the communities to 
 which they belonged would dourish and throw off many 
 swarms inheriting the same peculiarities. -The tubes of 
 the corolla of the common red or incarnate clovers (irito- 
 liurn pratense and incarnatum) do not on a hasty glance 
 appear to differ in length; yet the hive-bee can easily suck 
 the nectar out of the incarnate clover, but not out of the 
 common red clover, which is visited by humble-bees alone, 
 so that whole delds of the red clover offer m vam an abun¬ 
 dant supply of precious nectar to the. hive-bee. That this 
 nectar is much liked by the hive-bee is certain; for I have 
 repeatedly seen, but only in the autumn, many hive-bees 
 sucking the dowers through holes bitten m the base of the 
 tube by humble-bees. The difference in the length of the 
 corolla in the two kinds of clover, which determines the 
 visits of the hive-bee, must be very tndmg; for I have been 
 assured that when red clover has been mown the dowers 
 of the second crop are somewhat smaller, and that these 
 are visited by many hive-bees. I do not know whether 
 this statement is accurate; nor whether another published 
 statement can be trusted, namely, that the Ligurian bee, 
 which is generally considered a mere variety of the com¬ 
 mon hive-bee, and which freely crosses with it, is able to 
 reach and suck the nectar of the red clover. Thus, in a 
 country where this kind of clover abounded, it might oe 
 a great advantage to the hive-bee to have a slightly longer 
 or differently constructed proboscis. On the other hand, 
 as the fertility of this clover absolutely depends on bees vis¬ 
 iting the dowers, if humble-bees were to become rare m any 
 
OF NATURAL SELECTION. 
 
 So 
 
 country, it might be a great advantage to the plant to have 
 a shorter or more deeply divided corolla, so that the hive- 
 bees should be enabled to suck its flowers. Thus I can un¬ 
 derstand how a dower and a bee might slowly become, 
 either simultaneously or one after the other, modified and 
 adapted to each other in the most perfect manner, by 
 the continued preservation of all the individuals which 
 presented slight deviations of structure mutually favorable 
 to each other. 
 
 I am well aware that this doctrine of natural selection, 
 exemplified in the above imaginary instances, is open to 
 the same objections which were first urged against Sir 
 Charles Lyelfis noble views on “ the modern changes of 
 the earth, as Illustrative of geology;” but we now seldom 
 hear the agencies which we see still at work, spoken of as 
 trifling or insignificant, when used in explaining the excava¬ 
 tion of the deepest valleys or the formation of long lines of 
 inland cliffs. Natural selection acts only by the preserva¬ 
 tion and accumulation of small inherited modifications, 
 each profitable to the preserved being; and as modern geol¬ 
 ogy has almost banished such views as the excavation of a 
 great valley by a single diluvial wave, so will natural selec¬ 
 tion banish the belief of the continued creation of new or¬ 
 ganic beings, or of any great and sudden modification in 
 their structure. 
 
 ON THE INTERCROSSING OF INDIVIDUALS. 
 
 I must here introduce a short digression. In the case of 
 animals and plants with separated sexes, it is of course ob¬ 
 vious that two individuals must always (with the ex¬ 
 ception of the curious and not well understood cases of 
 parthenogenesis) unite for each birth; but in the case of 
 hermaphrodites this is far from obvious. Nevertheless 
 there is reason to believe that with all hermaphrodites two 
 individuals, either occasionally or habitually, concur for 
 the reproduction of their kind. This view was long ago 
 doubtfully suggested by Sprengel Knight and Kolreuter. 
 We shall presently see its importance; but I must here 
 Sreat the subject with extreme brevity, though I have the 
 materials prepared for an ample discussion. All vertebrate 
 animals, all insects and some other large groups of animals. 
 
90 
 
 ON THE INTERCROSSING 
 
 pair for each birth. Modern research has much diminished 
 the number of supposed hermaphrodites and of real herma¬ 
 phrodites a large number pair; that is, two individuals regu¬ 
 larly unite for reproduction, which is all that concerns us. 
 But still there are many hermaphrodite animals which cer¬ 
 tainly do not habitually pair, and a vast majority of plants 
 are hermaphrodites. What reason, it may be. asked, is 
 there for supposing in these cases that two individuals ever 
 concur in reproduction? As it is impossible here to enter 
 on details, I must trust to some general considerations 
 alone. 
 
 In the first place, I have collected so large a body of 
 facts, and made so many experiments, showing, in accord¬ 
 ance with the almost universal belief of breeders, that with 
 animals and plants a cross between different varieties, or 
 between individuals of the same variety but of another 
 strain, gives vigor and fertility to the offspring; and on 
 the other hand, that close interbreeding diminishes vigor 
 and fertility; that these facts alone incline me to believe 
 that it is a general law of nature that no organic being 
 fertilizes itself for a perpetuity of generations; but that a 
 cross with another individual is occasionally—perhaps at 
 long intervals of time—indispensable. 
 
 On the belief that this is a law of nature, we can, I 
 think, understand several large classes of facts, such as 
 the following, which on any other view are inexplicable. 
 Every hybridizer knows how unfavorable exposure to wet 
 is to the fertilization of a flower, yet what a multitude of 
 flowers have their anthers and stigmas fully exposed to the 
 weather 1 If an occasional cross be indispensable, notwith¬ 
 standing that the plant’s own anthers and pistil stand so 
 near each other as almost to insure self-fertilization, the 
 fullest freedom for the entrance of pollen from another in¬ 
 dividual will explain the above state of exposure of the 
 organs. Many flowers, on the other hand, have their 
 organs of fructification closely inclosed, as in the great 
 papilionaceous or pea-family; but these almost invariably 
 present beautiful and curious adaptations in relation to the 
 visits of insects. So necessary are the visits of bees to 
 many papilionaceous flowers, that their fertility is greatly 
 diminished if these visits be prevented. Eow, it is scarcely 
 possible for insects to fly from flower to flower, and not to 
 
OF INDIVIDUALS. 
 
 fil 
 
 carry pollen from one to tlie other, to the great good of the 
 plant. Insects act like a camel-hair pencil, and it is suffi¬ 
 cient, to insure fertilization, just to touch with the same 
 brush the anthers of one flower and then the stigma of 
 another; but it must not be supposed that bees would thus 
 produce a multitude of hybrids between distinct species; 
 for if a plant’s own pollen and that from another species 
 are placed on the same stigma, the former is so prepotent 
 that it invariably and completely destroys, as has" been 
 shown by Gartner, the influence of the foreign pollen. 
 
 "W hen the stamens of a flower suddenly spring toward 
 the pistil, or slowly move one after the other toward 
 it, the contrivance seems adapted solely to ensure self- 
 fertilization; and no doubt it is useful for this end: but 
 the agency of insects is often required to cause the stamens 
 to spring forward, as Kolreuter has shown to be the case 
 with the barberry; and in this very genus, which seems to 
 have a special contrivance for self-fertilization, it is well 
 known that, if closely-allied forms or varieties are planted 
 near each other, it is hardly possible to raise pure seedlings, 
 so largely do they naturally cross. In numerous other 
 cases, far from self-fertilization being favored, there are 
 special contrivances which effectually prevent the stigma 
 receiving pollen from its own flower, as I could show from 
 the works of Sprengel and others, as well as from my own 
 observations: for instance, in Lobelia fulgens, there is 
 a really beautiful and elaborate contrivance by which all 
 the infinitely numerous pollen-granules are swept out of 
 the conjoined anthers of each flower, before the stigma of 
 that individual flower is ready to receive them; and as this 
 flower is never visited, at least in my garden, by insects, it 
 never sets a seed, though by placing pollen from one flower 
 on the stigma of another, I raise plenty of seedlings. 
 Another species of Lobelia, which is visited by bees, seeds 
 freely in my garden. In very many other cases, though 
 there is no special mechanical contrivance to prevent the 
 stigma receiving pollen from the same flower, yet, as 
 Sprengel, and more recently Hildebrand and others have 
 shown, and as I can confirm, either the anthers burst 
 before the stigma is ready for fertilization, or the stigma is 
 ready before the pollen of that flower is ready, so that these 
 so-named dichogamous plants have in fact separated sexes. 
 
92 
 
 ON THE INTERCROSSING 
 
 and must habitually be crossed. So it is with the recipro¬ 
 cally dimorphic and trimorphic plants previously alluded 
 to. How strange are these facts! How strange that the 
 pollen and stigmatic surface of the same flower, though 
 placed so close together, as if for the very purpose of self- 
 fertilization, should be in so many cases mutually useless 
 to each other? How simply are these facts explained on 
 i the view of an occasional cross with a distinct individual 
 i being advantageous or indispensable! . , 
 
 If several varieties of the cabbage, radish, onion and of 
 some other plants, be allowed to seed near each other, a 
 large majority of the seedling thus raised turn out, as 1 
 founds mongrels: for instance, I raised 233 seedling cab¬ 
 bages from some plants of different varieties growing near 
 each other, and of these only 78 were true to their kind 
 and some even of these were not perfectly true. Yet the 
 pistil of each cabbage-flower is surrounded not only by its 
 own six stamens but by those of the many other flowers on 
 the same plant; and the pollen of each flower readily gets 
 on its stigma without insect agency; for I have found that 
 plants carefully protected from insects produce the lull 
 number of pods. How, then, comes it that such a vast 
 number of the seedlings are mongrelized?. It must arise 
 from the pollen of a distinct variety having a prepotent 
 effect over the flower's own pollen; and that this is part ot 
 the general law of good being derived from the intercross¬ 
 ing of distinct individuals of the same species. When dis¬ 
 tinct species are crossed the case is reversed, for a plant s 
 own pollen is almost always prepotent over foreign pollen; 
 but to this subject we shall return in a future chapter. 
 
 In the case of a large tree covered with innumerable 
 flowers, it may be objected that pollen could seldom be 
 carried from tree to tree, and at most only from flower 
 to flower on the same tree; and flowers on the same tree 
 can be considered as distinct individuals only in a limited 
 sense. I believe this objection to be valid, but that nature 
 has largely provided against it by giving to trees a stiong 
 tendency to bear flowers with separated sexes. W hen the 
 sexes are separated, although the male and female floweis 
 may be produced on the same tree, pollen must be regu¬ 
 larly carried from flower to flower; and this will give 
 a better chance of pollen being occasionally carried from 
 
of mmviD uals : 
 
 93 
 
 tree to tree. That trees belonging to all orders have their 
 sexes more often separated than other plants, I find to be 
 the case in this country; and at my request Dr. Hooker 
 tabulated the trees ©f New Zealand, and Dr. Asa Gray, 
 those of the United States, and the result was as I antici¬ 
 pated. On the other hand. Dr. Hooker informs me that 
 the rule does not hold good in Australia: but if most of 
 the Australian trees are dichogamous, the same result 
 would follow as if they bore flowers with separated sexes. 
 I have made these few remarks on trees simply to call 
 attention to the subject. 
 
 Turning for a brief space to animals: various terrestrial 
 species are hermaphrodites, such as the land-mollusca and 
 earth-worms; but these all pair. As yet I have not found 
 a single terrestrial animal which can fertilize itself. This 
 remarkable fact, which offers so strong a contrast with ter¬ 
 restrial plants, is intelligible on the view of an occasional 
 cross being indispensible; for owing to the nature of the 
 fertilizing element there are no means, analogous to the 
 action of insects and of the wind with plants, by which an 
 occasional cross could be effected with terrestrial animals 
 without the concurrence of two individuals. Of aquatic 
 animals, there are many self-fertilizing hermaphrodites; 
 but here the currents of water offer an obvious means for 
 an occasional cross. As in the case of flowers, I have as 
 yet failed, after consultation with one of the highest 
 authorities, namely. Professor Huxley, to discover a single 
 hermaphrodite animal with the organs of reproduction^ 
 perfectly enclosed that access from without, and the occa¬ 
 sional influence of a distinct individual, can be shown to 
 be physically impossible. Cirripedes long appeared to me 
 to present, under this point of view, a case of great diffi¬ 
 culty; but I have been enabled, by a fortunate chance, to 
 prove that two individuals, though both of self-fertilizing 
 hermaphrodites, do sometimes cross. 
 
 It must have struck most naturalists as a strange anomaly 
 that, both with animals and plants, some species of the 
 same family and even of the same genus, though agreeing 
 closely with each other in their whole organization, are 
 hermaphrodites, and some unisexual. But if, in fact, all 
 hermaphrodites do occasionally intercross, the difference 
 between them and unisexual species is, as far as function 
 is concerned, ver/ siWl. 
 
94 
 
 CIRCUMSTANCES FAVORABLE TO THE 
 
 From these several considerations and from the many 
 special facts which I have collected, but which I am 
 unable here to give, it appears that with animals and 
 plants an occasional intercross between distinct individuals 
 is a very general, if not universal, law of nature. 
 
 CIRCUMSTANCES FAVORABLE FOR THE PRODUCTION OF 
 NEW FORMS THROUGH NATURAL SELECTION. 
 
 This is an extremely intricate subject. A great amount 
 « 4 )f variability, under which term individual differences are 
 always included, will evidently be favorable. A large num- 
 *»ber of individuals, by giving a better chance within any 
 given period for the appearance of profitable variations, 
 will compensate for a lesser amount of variability in each 
 individual, and is, I believe, a highly important element of 
 success. Though nature grants long periods of time for 
 the work of natural selection, she does not grant an indefi¬ 
 nite period, for as all organic beings are striving to seize on 
 each place in the economy 01 nature, if any one species 
 does not become modified and improved in a corresponding 
 degree with its competitors it will be exterminated. Unless 
 favorable variations be inherited by some at least of the 
 offspring, nothing can be effected by natural selection. 
 The tendency to reversion may often check or prevent the 
 work; but as this tendency has not prevented man from 
 forming by selection numerous domestic races, why should 
 it prevail against natural selection? 
 
 In the case of methodical selection, a breeder selects for 
 some definite object, and if the individuals be allowed freely 
 to intercross, his work will completely fail. But when 
 many men, without intending to alter the breed, have a 
 nearly common standard of perfection, and all try to pro¬ 
 cure and breed from the best animals, improvement surely 
 but slowly follows from this unconscious process of selec¬ 
 tion, notwithstanding that there is no separation of selected 
 individuals. Thus it will be under nature; for within a 
 confined area, with some place in the natural polity not 
 perfectly occupied, all the individuals varying in the right 
 direction, though in different degrees, will tend to be pre¬ 
 served. But if the area be large, its several districts will 
 almost certainly present different conditions of life; and 
 
95 
 
 RESULTS OF NATURAL SELECTION. 
 
 then, if the same species undergoes modification in differ¬ 
 ent districts, the newly formed varieties will intercross on 
 the confines of each. But we shall see in the sixth chap¬ 
 ter that intermediate varieties, inhabiting intermediate dis¬ 
 tricts, will in the long run generally be supplanted by one 
 of the adjoining varieties. Intercrossing will chiefly affect 
 those animals which unite for each birth and wander 
 much, and which do not breed at a very quick rate. 
 Hence with animals of this nature, for instance birds, 
 varieties will generally be confined to separated countries; 
 and. this I find to be the case. With hermaphrodite or¬ 
 ganisms which cross only occasionally, and likewise with 
 animals which unite for each birth, but which wander lit¬ 
 tle and can increase at a rapid rate, a new and improved 
 variety might be quickly formed on any one spot, and 
 might there maintain itself in a body and afterward 
 spread, so that the individuals of the new variety would 
 chiefly cross together. On this principle nurserymen 
 always prefer saving seed from a large body of plants, as 
 the chance of intercrossing is thus lessened. 
 
 Even with animals, which unite for each birth, and which 
 do not propagate rapidly, we must not assume that free in¬ 
 tercrossing would always eliminate the effects of natural 
 selection; for I can bring forward a considerable body of 
 facts showing that within the same area two varieties of 
 the same animal may long remain distinct, from haunting 
 different stations, from. breeding at slightly different 
 seasons, or from the individuals of each variety preferring 
 to pair together. 
 
 / Intercrossing plays a very important part in nature by 
 keeping the individuals of the same species, or of the 
 -same variety, true and uniform in character. It will 
 obviously thus act far more efficiently with those animals 
 which unite for each birth; but, as alread}' - stated, we 
 have reason to believe that occesional intercrosses take 
 place with all animals and plants. Even if these take 
 place only at long intervals of time, the young thus pro¬ 
 duced will gain so much in vigor and fertility over the 
 offspring from long-continued self-fertilization, that they 
 will have a better chance of surviving and propagating their 
 kind; and thus in the long-run the influence "of crosses, 
 even at rare intervals, will be great. With respect to or- 
 
90 
 
 CIRCUMSTANCES FA VORABLE TO THE 
 
 ganic beings extremely low in tlie scale, which do not 
 propagate sexually, nor conjugate, and which cannot pos¬ 
 sibly intercross, uniformity of character can be retained 
 by them under the same conditions of life, only through 
 the principle of inheritance, and through natural selection 
 which will destroy any individuals departing from the 
 proper type. If the conditions of life change and the form 
 undergoes modification, uniformity of character can be 
 given to the modified offspring, solely by natural selection 
 preserving similar favorable variations. 
 a Isolation also is an important element in the modifica- 
 I tion of species through natural selection. In a confined or 
 isolated area, if not very large, the organic and inorganic 
 conditions of life will generally be almost uniform; so that 
 natural selection will tend to modify all the varying indi¬ 
 viduals of the same species in the same manner. Inter¬ 
 crossing with the inhabitants of the surrounding districts, 
 will also be thus prevented. Moritz Wagner has lately pub¬ 
 lished an interesting essay on this subject, and has sho^n 
 that the service rendered by isolation in preventing crosses 
 between newly-formed varieties is probably greater even than 
 I supposed. But from reasons already assigned I can by no 
 means agree with this naturalist, that migration and isola¬ 
 tion are necessary elements for the formation of new species. 
 The importance of isolation is likewise great in prevent¬ 
 ing, after any physical change in the conditions, such as 
 of climate, elevation of the land, etc., the immigration of 
 better adapted organisms; and thus new places in the 
 natural economy of the district will be left open to be 
 filled up by the modification of the old inhabitants. Lastly, 
 isolation will give time for a new variety to be improved at 
 a slow rate; and this may sometimes be of much import¬ 
 ance. If, however, an isolated area be very small, either 
 from being surrounded by barriers, or from having very 
 peculiar physical conditions, the total number of the in¬ 
 habitants will be small; and this will retard the production 
 of new species through natural selection, by decreasing the 
 chances of favorable variations arising. 
 
 The mere lapse of time by itself does nothing, either for 
 or against natural selection. I state this because it has 
 been erroneously asserted that the element of time has 
 been assumed by me to play an all-important part in modi- 
 
RESULTS OF NATURAL SELECTION. 97 
 
 species, as if all the forms of life were necessarily 
 undergoing change through some innate law. Lapse of 
 fime is only so far important, and its importance in this 
 respect is great, that it gives a better chance of beneficial 
 variations arising and of their being selected, accumulated, 
 and fixed. It likewise tends to increase the direct action 
 of the physical conditions of life, in relation to the consti¬ 
 tution of each organism. 
 
 If we turn to nature to test the truth of these remarks, 
 and look at any small isolated area, such as an oceanic 
 island, although the number of species inhabiting it is 
 small, as we shall see in our chapter on Geographical Dis¬ 
 tribution; yet of these species a very large proportion are 
 endemic,—that is, have been produced there and nowhere 
 else in the world. Hence an oceanic island at first sight 
 seems to have been highly favorable for the production of 
 new species. But we may thus deceive ourselves, for to 
 ascertain whether a small isolated area, or a large open 
 area like a continent, has been most favorable for "the pro¬ 
 duction of new organic forms, we ought to make the com¬ 
 parison within equal times; and this we are incapable of 
 doing. 
 
 # Although isolation is of great importance in the produc¬ 
 tion of new species, on the whole I am inclined to believe 
 * that largeness of area is still more important, especially for 
 the production of species which shall prove capable of 
 enduring for a long period, and of spreading widely. 
 
 • Throughout a great and open area, not only will there be 
 I a better chance of favorable variations, arising from the 
 I large number of individuals of the same species there sup- 
 | ported, but the conditions of life are much more complex 
 from the large number of already existing species; and if 
 some of these many species become modified and improved, 
 others will have to'be improved in a corresponding degree, or 
 they will be exterminated. Each new form, also, as soon as 
 it has been much improved, will be able to spread over the 
 open and continuous area, and will thus come into competi¬ 
 tion with many other forms. Moreover, great areas, though 
 now continuous, will often, owing to former oscillations of 
 level, have existed in a broken condition; so that the good 
 effects of isolation will generally, to a certain extent, have 
 concurred. Finally. I conclude that, although small 
 
98 CIRCUMSTANCES FA VORABLE TO THE 
 
 isolated areas have been in some respects highly favorable 
 for the production of new species, yet that the course ot 
 modification will generally have been more rapid on large 
 areas; and what is more important, that the new forms 
 produced on large areas, which already have been victor¬ 
 ious over many competitors, will be those that will spread 
 ' most widely, and will give rise to the greatest numbei of 
 new varieties and species. They will thus play a more 
 important part in the changing history of the oiganic 
 
 world. . .. , 
 
 In accordance with this view, we can, perhaps, under¬ 
 stand some facts which will be again alluded to m our 
 chapter on Geographical Distribution; for instance, the 
 fact of the productions of the smaller continent of Austra¬ 
 lia now yielding before those of the larger JEuropaso-Asiatic 
 area. Thus, also, it is that continental productions have 
 everywhere become so largely naturalized on islands. 
 On a small island, the race for life will have been less 
 severe, and there will have been less modification and less 
 extermination. Hence, we can understand how it is that 
 the flora of Maderia, according to Oswald ITeer, resembles 
 to a certain extent the extinct tertiary flora of Hurope. 
 All fresh water basins, taken together, make a small aiea 
 compared with that of the sea or of the luud. 
 sequently, the competition between freshwater productions- 
 will have been less severe than elsewhere, new forms will 
 have been then more slowly produced, and old forms more 
 slowly exterminated. And it is in fresh water basins that 
 we find seven genera of Ganoid fishes, remnants of a once 
 preponderant order: and in fresh water we find some of the 
 most anomalous forms now known in the world as the 
 Ornithorhynchus and Lepidosiren, which, like fossils, con¬ 
 nect to a certain extent orders at present widely sundered 
 in the natural scale. These anomalous forms may be 
 called living fossils; they have endured to the present day, 
 from having inhabited a confined area, and from having 
 been exposed to less varied, and therefore less severe, com- 
 
 To sum up, as far as the extreme intricacy of the subject 
 permits, the circumstances favorable and unfavorable for 
 \ the production of new species through natural selection. 
 
 \ 1 conclude that for terrestrial productions a large contx- 
 
RESULTS OF NATURAL SELECTION. 99 
 
 nexital area, which has undergone many oscillations of 
 level, will have been the most favorable for the production 
 of many new forms of life, fitted to endure for a Ions’ time 
 and to spread widely. While the area existed as a'conti¬ 
 nent the inhabitants.will have been numerous in individu¬ 
 als and kinds, and will have been subjected to severe com¬ 
 petition. . \\ hen converted by subsistance into large 
 separate islands there will still have existed many indi¬ 
 viduals of the same species on each island: intercrossing 
 on the confines of the range of each new species will have 
 been checked: after physical changes of any kind immigra- 
 tion wdl have been prevented, so that new places in the 
 polity of each island wifi have had to be filled up by the 
 modification of the old inhabitants; and time will have 
 been allowed for the varieties in each to become well modi¬ 
 fied and perfected. When, by renewed elevation, the 
 islands were reconverted into a continental area, there will 
 again have been very severe competition; the most favored 
 or improved varieties will have been enabled to spread* 
 there will have been much extinction of the less improved 
 l°i’fs and the relative proportional numbers of the various 
 inhabitants of the reunited continent will again have been 
 changed; and again there will have been a fair field for 
 natural selection to improve still further the inhabitants 
 and thus to produce new species. 
 
 ^-^4? r^ural selection generally acts with extreme slow¬ 
 ness 1 fully admit. It can act only when there are places 
 u } the natural polity of a district which can be better occu¬ 
 pied by the modification of some of its existing inhabitants. 
 Ifiq occurrence of such places will often depend on physi- 
 cal changes, which generally take place very slowly, and 
 on the immigration of better adapted forms being pre- 
 
 ^ some ^ ew ^ke old inhabitants become modi¬ 
 fied the mutual relations of others will often be disturbed* 
 and this will create new places, ready to be filled up by 
 better adapted forms; but all this will take place very 
 Although all the individuals of the same species 
 difler m some slight degree from each other, it would often 
 be long befyre differences of the right nature in various 
 parts of the organization might occur. The result would 
 °tt* greatly retarded by free intercrossing. Many will 
 excj aim that these several causes are amply sufficient to 
 
100 EXTINCTION BT NATURAL SELECITON. 
 
 neutralize the power of natural selection. _ I do not believe 
 so But I do believe that natural selection will generally 
 act very slowly, only at long intervals of time, and only on 
 a few of the inhabitants of the same region. I further 
 believe that these slow, intermittant results accord well 
 with what geology tells us of the rate and manner at which 
 the inhabitants of the world have changed. 
 
 Slow though the process of selection may be, if feeble 
 man can do much by artificial selection, I can see no limit 
 to the amount of change, to the beauty and complexity of 
 the coadaptations between all organic beings, one with 
 another and with their physical conditions of life, which 
 may have been affected in the long course of time through 
 nature’s power of selection, that is by the survival of the 
 fittest. 
 
 EXTINCTION CAUSED BY NATURAL SELECTION. 
 
 This subject will be more fully discussed in our chap¬ 
 ter on Geology; but it must here be alluded to from 
 being intimately connected with natural selection. Nat¬ 
 ural selection acts solely through the preservation of vari¬ 
 ations in some way advantageous, which consequently en¬ 
 dure Owing to the high geometrical rate of inciease of 
 all organic beings, each area is already fully stocked with 
 inhabitants; and it follows from this, that as the favored 
 forms increase in number, so, generally, will the less fa¬ 
 vored decrease and become rare. Rarity, as geology tells 
 us, is the precursor to extinction. We can see that any 
 form which is represented by few individuals will run a 
 (rood chance of utter extinction, during great fluctuations 
 m the nature or the seasons, or from a temporary increase 
 ir the number of its enemies. But we may go further than 
 this" for, as new forms are produced, unless we admit that 
 specific forms can go cn indefinitely increasing in number, 
 many old forms must become extinct. That the number 
 of specific forms has not indefinitely increased, geology 
 plainly tells us; and we shall presently attempt to show 
 why it is that the number of species throughout the world 
 has not become immeasurably gi eat. . 
 
 We have seen that the species which are most numer¬ 
 ous in individuals have the best chance of producing favor- 
 
DIVERGENCE OF CHARACTER. lw 
 
 able variations within any given period. We have evi¬ 
 dence of this, m the facts stated in the second chapter 
 
 ®k”j ,ng 18 l w common and diffused or dominant 
 
 species which offer the greatest number of recorded vari¬ 
 eties. Hence,_ rare species will be less quickly modified or 
 improved within any given period; they will consequently 
 be beaten in the race for life by the modified and improved 
 descendants of. the commoner species. 
 
 Prom these several considerations I think it inevitably 
 follows, that as new species in the course of time are 
 formed through natural selection, others will become rarer 
 and rarer, and finally extinct. The forms which stand in 
 closest competition with those undergoing modification 
 and improvement, will naturally suffer most. And we 
 have seen in the chapter on the Struggle for Existence 
 that it is the most closely-allied forms,—varieties of the 
 same species, and species of the same genus or related 
 
 from ha^ng nearly the same structure, 
 constitution and habits, generally come into the severest 
 competition with each other consequently, each new vari¬ 
 ety or species, during the progress of its formation, will 
 generally press hardest on its nearest kindred, and tend to 
 exterminate them. We see the same process of extermina¬ 
 tion among_ our domesticated productions, through the 
 selection of improved forms by man. Many curious in¬ 
 stances could be given showing how quickly new breeds of 
 cattle, sheep and other animals, and varieties of flowers 
 take the place of older and inferior kinds. In Yorkshire’ 
 it is historically known that the ancient black cattle were 
 displaced by the long-horns, and that these “ were swept 
 
 t,3 by - f th t s“ rns ” (I < l l,ote the vvorcls <>f »» agricul- 
 tuial wnter) as if by some murderous pestilence.” 
 
 divergence of character. 
 
 yhe principle, which I have designated by this term, is 
 importance, and explains, as I believe, several im¬ 
 portant facts. In the first place, varieties, even strongly 
 marked ones, though having somewhat of the charac- 
 ter of species—as is shown by the hopeless doubts 
 
 many cases how to rank them—yet certainly differ 
 m less from each other than do good and distinct 
 
DIVERGENCE OF CHARACTER . 
 
 102 
 
 species. Nevertheless according to my view, varieties are 
 species in the process of formation, or are, as I have called 
 them, incipient species. How, then, does the lesser differ¬ 
 ence between varieties become augmented into the greater 
 difference between species? I hat this does habitually 
 happen, we must infer from most of the innumerable 
 species throughout nature presenting well-marked differ¬ 
 ences; whereas varieties, the supposed prototypes and 
 parents of future well-marked species, present slight and 
 ill-defined differences. Mere chance, as we may call it, 
 might cause one variety to differ in some character from its 
 parents, and the offspring of this variety again to differ 
 from its parent in the very same character and in a greater 
 degree; but this alone would never account for so habitual 
 and large a degree of difference as that between the species 
 of the same genus. 
 
 As has always been my practice, I have sought light on 
 this head from our domestic productions. We shall here 
 find something analogous. It will be admitted that the 
 production of races so different as short-horn and Here¬ 
 ford cattle, race and cart horses, the several breeds of 
 pigeons, etc., could never have been effected by the mere 
 chance accumulation of similar variations during many 
 successive generations. In practice, a fancier is, foi in¬ 
 stance, struck by a pigeon having a slightly shorter beak; 
 another fancier is struck by a pigeon having a rather longer 
 beak; and on the acknowledged principle that “ fanciers 
 do not and will not admire a medium standard, but like 
 extremes,” they both go on (as has actually occurred with 
 the sub-breeds of the tumbler-pigeon) choosing and breed¬ 
 ing from birds with longer and longer beaks, or with 
 shorter and shorter beaks. Again, we may suppose that 
 at an early period of history, the men of one nation or dis¬ 
 trict required swifter horses, while those of another re¬ 
 quired stronger and bulkier horses. The early differences 
 would be very slight; but, in the course of time, from the 
 continued selection of swifter horses in the one case, and 
 of stronger ones in the other, the differences would become 
 greater, and would be noted as forming two sub-breeds. 
 Ultimately after the lapse of centuries, these s-ub-breeds 
 would become converted into two well-established and dis¬ 
 tinct breeds. As the differences became greater, the in- 
 
DIVERGENCE OF CHARACTER. 103 
 
 ferior animals with intermediate characters, being neither 
 very swift nor very strong, would not have been used for 
 breeding, and will thus have tended to disappear. Here, 
 then, we see in man s productions the action of what may bei 
 called the principle of divergence, causing differences, at! 
 first barely appreciable, steadily to increase, and the breeds 
 to diverge in character, both from each other and from 
 their common parent. 
 
 But, how, it may be asked, can any analogous principle 
 apply in nature? I believe it can and does apply most 
 efficiently (though it was a long time before I saw how), 
 from the simple circumstance that the more diversified the 
 descendants from any one species become in structure, 
 constitution and habits, by so much will they be better 
 enabled to seize on many and widely diversified places in 
 
 the polity of nature, and so be enabled to increase in 
 numbers. 
 
 . We can clearly discern this in the case of animals with 
 simple habits. Take the case of a carnivorous quadruped, 
 of which the number that can be supported in any country 
 has long ago arrived at its full average. If its natural 
 power of increase be allowed to act, it can succeed in in¬ 
 creasing (the country not undergoing any change in con¬ 
 ditions) only by its varying descendants seizing on places 
 at present occupied by other animals: some of them, for 
 instance, being enabled to feed on new kinds of prey, 
 either dead or alive; some inhabiting new stations, climb¬ 
 ing trees, frequenting water, and some perhaps becoming 
 less carnivorous. The more diversified in habits and 
 structure the descendants of our carnivorous animals 
 become, the more places they will be enabled to occupy. 
 What applies to one animal will apply throughout all time 
 to all animals—that is, if they vary—for otherwise natural 
 selection can effect nothing. So it will be with plants. It 
 has been experimentally proved, that if a plot of ground 
 be sown with one species of grass, and a similar plot be 
 sown with several distinct genera of grasses, a greater 
 number of plants and a greater weight of dry herbage can 
 be raised in the latter than the former case. The same has 
 been found to hold good when one variety and several mixed 
 varieties of wheat have been sown on equal spaces of 
 ground. Hence, if any one species of grass were to go on 
 
104 
 
 DIVERGENCE OF CHARACTER. 
 
 varying, and the varieties were continually selected which 
 differed from each other in the same manner, though in a 
 very slight degree, as do the distinct species and genera of 
 grasses, a greater number of individual plants of this 
 species, including its modified descendants, would succeed 
 in living on the same piece of ground. And we know that 
 each species and each variety of grass is annually sowing 
 almost countless seeds; and is thus striving, as it may be 
 said, to the utmost to increase in number. Consequently, 
 in the course of many thousand generations, the most dis¬ 
 tinct varieties of any one species of grass would have the 
 best chance of succeeding and of increasing in numbers, 
 and thus of supplanting the less distinct varieties; and 
 varieties, when rendered very distinct from each other, 
 take the rank of species. 
 
 The truth of the principle that the greatest amount of 
 life can be supported by great diversification of structure, 
 is seen under many natural circumstances. In an extremely 
 small area, especially if freely open to immigration, and 
 ^diere the contest between individual and individual must 
 be very severe, we always find great diversity in its inhabi¬ 
 tants. For instance, I found that a piece of turf, three 
 feet by four in size, which had been exposed for many 
 years to exactly the same conditions, supported twenty 
 species of plants, and these belonged to eighteen genera 
 and to eight orders, which shows how much these plants 
 .differed from each other. So it is with the plants and 
 insects on small and uniform islets: also in small ponds of 
 fresh water. Farmers find that they can raise more food 
 by a rotation of plants belonging to the most different 
 orders: nature follows what may be called a simultaneous 
 rotation. Most of the animals and plants which live close 
 round any small piece of ground, could live on it (suppos¬ 
 ing its nature not to be in any way peculiar), and may be 
 said to be striving to the utmost to live there; but, it is 
 seen, that where they come into the closest competition, the 
 advantages of diversification of structure, with the accom¬ 
 panying differences of habit and constitution, determine 
 that the inhabitants, which thus jostle each other most 
 closely, shall, as a general rule, belong to what we call 
 different genera and orders. 
 
 The same principle is seen in the naturalization of 
 

 DIVEllGENGE OF G1IA UAGTER. > q ~ 
 
 plants through man’s agency in foreign lands It might 
 Imve been expected that the plants which would uc- 
 ceed in becoming naturalized in any land would generally 
 have been closely allied to the indigenes; for these ! 
 
 “wKuntv at Tt aS Created “ d ada P‘«d for 
 
 nected^ that n^tLv 1 u“ ,g , ht . als0 ’ P erha P s - have been ex- 
 pccted that natuialized plants would have belonged to a 
 
 thlifnew 8 h 1 o 0 m e es eSP B la t 11 H adapted - to certain sta ‘ ions in 
 eir new homes. But the case is very different- ami 
 
 Alph. de Candolle has well remarked, in his great ami 
 
 p rt'ioi allv n! lat floras g‘T by naturalfzafion^ prl 
 poitionally with the number of the native genera ami 
 
 species, far more in new genera than in new species To 
 
 give a single instance: in the last edition of Dr P Asa Grav’s 
 
 Manual of the Flora of the Northern United States’’ 2G0 
 
 natuialized plants are enumerated, and these belong- to TG 2 
 
 genera We thus see that these natu rai zed pal are of 
 
 a highly diversified nature. They differ moreover to f 
 
 arge extent, from the indigenes, for out of the ] 62 
 
 LlSous fnd 6 ^ n ° ', eSS thau 100 ^era a « not there 
 to tlfo ’ d th ,“ sa lai 'ge proportional addition is made 
 to the genera now hving in the United States. 
 
 By considenng the nature of the plants or animals which 
 have m any country struggled successfully with the indi- 
 f®" es ’ a ",f la V° there become naturalized, we may gain 
 0In ®, c T ru( ^ e lf ^ ea in what manner some of the natfvp^ 
 
 o7eftheD e compatZf fi6d 1 ^ to gain an “dvantege 
 
 diversification of P strnct ; a " d W ® m ? y at least infer thit 1 
 uiveisincation ot structure, amounting to new generic dif ' 
 
 ferences, would be profitable to them. § / 
 
 inhabitan d ts a of ta t g he same reg^Ts^M fait “ tf he 
 
 of the physiological dTvSIl'ta W nil^ oi-ZsoVhe 
 
 Mihie Edwards ? l ] b ^ Ct S0 well elSatl by 
 
 . N ° Physiologist doubts that a stomach 
 adapted to digest vegetable matter alone or flesh Xne 
 
 d “° St nu "triment from these substances. So h! the 
 
 eapableof there sulVoidifnilmseuls? 1 ’ A sefoflnfmals® 
 with their organization but little diversified, could hardly 
 
106 
 
 RESULT OF THE ACTION 
 
 compete with a set more perfectly le Austahan 
 
 It may be doubted, for instance, whether the Australian 
 
 mammals which are divided into groups differing but 
 little from each other, and feebly representing, as Mr. 
 Waterhouse and others have remarked, our carnivoious, 
 ruminant and rodent mammals, could Buccessfully com¬ 
 pete with these well-developed orders. In the Australian 
 mammals, we see the process of diversification in an eaily 
 and incomplete stage of development. 
 
 the probable effects of the ACTI0 ^ p 0F r // R T ^ 
 
 SELECTION THROUGH DIVERGENCE OP' 
 
 and extinction, on the descendants of a com¬ 
 mon ANCESTOR. 
 
 After the foregoing discussion, which has been much 
 compressed, we may Lame that the modified descendants 
 of any one species will succeed so much the better as tl ey 
 become more 1 diversified in structure and axethus.enabled 
 to encroach on places occupied by other beings. Now let 
 us see how thif principle "of benefit being derived from 
 divergence of character, combined with the pnnciples ol 
 natural selection and of extinction, tends to act. ,. 
 
 The accompanying diagram will aid us m understanding 
 this rather perplexing subject. Let A to L represent the 
 species of a genus large in its own country; these species are 
 supposed to°resemble each other in unequal degrees, as is 
 so generally the case in nature, and as is represented 
 in the diagram by the letters standing at unequal distances. 
 
 I have said a la,|e genus, because as we saw in the second 
 chapter, on an average more species vary in larg g 
 than in small genera; and the varying species of the huge 
 p-enera present a greater number of varieties. \Ve hav , 
 flso, seen that the species, which are the commonest and 
 most widely diffused, vary more than do the raie ana 
 restricted species. Let (A) be a common, widelj-diffused, 
 and varying species, belonging to a genus large . { 
 
 country. The branching and diverging dotted lines ol 
 unequal lengths proceeding from (A), may represent its 
 offspring. The variations are supposed to be 
 Sttemely shfht, but of the most diversified nature; they 
 are not Supposed all to appear simultaneously, but often 
 
OF NATURAL SELECTION. 107 
 
 after long intervals of time; nor are they all supposed to 
 endure for equal periods. Only those variations which are 
 m some way profitable will be preserved or naturally 
 selected. And here the importance of the principle of 
 benefit derived from divergence of character comes in: for 
 this will generally lead to the most different or divergent 
 variations (represented by the outer dotted lines) beino- 
 preserved and accumulated by natural selection. When a 
 dotted line reaches one of the horizontal lines, and is there 
 marked by a small numbered letter, a sufficient amount of 
 vaiiation is supposed to have been accumulated to form it 
 into a fairly well marked variety, such as would be thought 
 worthy of record m a systematic work. 
 
 The intervals between the horizontal lines in the dia¬ 
 gram, may represent each a thousand or more generations. 
 Atter a thousand generations, species (A) is supposed to 
 have produced two fairly well marked varieties, namely 
 a and m These two varieties will generally still be 
 exposed to the same conditions which made their parents 
 variable, and the tendency to variability is in itself hered¬ 
 itary; consequently they will likewise tend to vary, and 
 commonly m nearly the.same manner as did their parents. 
 Moreover these two varieties, being only slightly modified 
 
 inis, will tend to inherit those advantages which made 
 their parent (A) more numerous than most of the other 
 inhabitants of the same country; they will also partake of 
 tnqse more general advantages which made the genus to 
 which the parent species belonged, a large genus in its own 
 country. And all these circumstances are favorable to the 
 production of new varieties. 
 
 If, then these two varieties be variable, the most 
 divergent of their variations will generally be preserved 
 during the next thousand generations. And after this 
 interval, variety a is supposed in the diagram to have pro¬ 
 duced variety a 2 , which will, owing to the principle of 
 divergence differ more from (A) than did variety a 1 . 
 Variety m is supposed to have produced two varieties, 
 namely m and 5 2 differing from each other, and more 
 considerably from their common parent (A). We may 
 continue the process by similar steps for any length of 
 ime; some of the varieties, after each thousand genera¬ 
 tions, producing only a single variety, but in a more and 
 
108 
 
 RESULT OF THE ACTION 
 
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OF NATURAL SELECTION. 
 
 109 
 
 XIV 
 
 .XIII 
 
 
110 
 
 RESULT OF THE ACTION 
 
 more modified condition, some producing two or three 
 varieties, and some failing to produce any. Ihus the 
 varieties or modified descendants of the common parent 
 m will generally go on increasing m number and diverg¬ 
 ing’in character. In the diagram the process is repre¬ 
 sented up to the ten-thousandth generation, and under a 
 condensed and simplified form up to the fourteen-thous- 
 
 andtli generation. a-l j. 
 
 But 1 must here remark that I do not suppose that the 
 process ever goes on so regularly as is represented m the 
 diagram, though in itself made somewhat irregular nor 
 that it goes on continuously; it is far more probable that 
 each form remains for long periods unaltered, and then 
 again undergoes modification. Nor do I suppose that the 
 most divergent varieties are invariably preserved: a medium 
 form may often long endure, and may or may not produce 
 more than one modified descendant; for natural selection 
 will always act according to the nature of the places which 
 are either unoccupied or not perfectly occupied by other 
 beings; and this will depend on infinitely complex rela¬ 
 tions But as a general rule, the more diversified m struc¬ 
 ture the descendants from any one species can be rendered, 
 the more places they will be enabled to seize on, and the 
 more their modified progeny will increase.. In our diagram 
 the line of succession is broken at regular intervals by small 
 numbered letters marking the successive forms which have 
 become sufficiently distinct to be recorded as varieties. But 
 these breaks are imaginary, and might have been mserte 
 anvwhere, after intervals long enough to allow the accumu¬ 
 lation of a considerable amount of divergent variation. 
 
 As all the modified descendents from a common and 
 ■widely-diffused species, belonging to a large genus, will 
 tend to partake of the same advantages which made their 
 parent successful in life, they will generally go on multi¬ 
 plying in number as well as diverging m character this 
 is represented in the diagram by the several divergent 
 branches proceeding from (A).. The modified offspring 
 from the later and more highly improved branches m the 
 lines of descent, will, it is probable, often take the place 
 of and so destrov, the earlier and less improved branches: 
 this is represented in the diagram by some of the lower 
 branches not reaching to the upper horizontal lines, in 
 
OF NATURAL SELECTION . 
 
 Ill 
 
 some cases no doubt the process of modification will be 
 confined to a single line of descent, and the number of 
 modified descendants will not be increased; although the 
 amount of divergent modification may have been augmented. 
 This case would be represented in the diagram, if all the 
 lines proceeding from (A) were removed, excepting that 
 f 1 om to a i0 . In the same way the English racehorse 
 and English pointer have apparently both gone on slowly 
 diverging in character from their original stocks, without 
 either having given off any fresh branches or races. 
 
 After ten thousand generations, species (A) is supposed 
 to have produced three forms, and m 10 , which, 
 
 from having diverged in character during the successive 
 generations, will have come to differ largely, but perhaps 
 unequally, from each other and from their common parent. 
 If we suppose the amount of change between each hori¬ 
 zontal line in our diagram to be excessively small, these 
 three forms may still be only well-marked varieties; but 
 we have only to suppose the steps in the process of modi¬ 
 fication to be more numerous or greater in amount, to 
 convert these three forms into doubtful or at least into 
 well-defined species. Thus the diagram illustrates the 
 steps by which the small differences distinguishing varieties 
 are increased into the larger differences distinguishing 
 species. By continuing the same process for a greater 
 number of generations (as shown in the diagram in "a con¬ 
 densed and simplified manner), we get eight species, marked 
 by the letters between a 14 and m 14 , all descended from 
 (A). Thus, as I believe, species are multiplied and genera 
 are formed. 
 
 . a large genus it is probable that more than one spe¬ 
 cies would vary. In the diagram I have assumed that a 
 second species (I) has produced, by analogous steps, after 
 ten thousand generations, either two well-marked varieties 
 (w 10 and z 10 ) or two species, according to the amount of 
 change supposed to be represented between the horizontal 
 lines. After fourteen thousand generations, six new spe¬ 
 cies, marked by the letters n 14 to z 14 , are supposed to 
 have been produced. In any genus, the species which are 
 already very different in character from each other, will 
 generally tend to produce the greatest number of modified 
 descendants; for these will have the best chance of seizing 
 
112 RESULT OF THE ACTION 
 
 or new and widely different places in the polity of nature; 
 hence in the diagram I have chosen the extreme species 
 ( \ i and the nearly extreme species (I), as those whicl 
 have largely varied, and have given rise to new varieties 
 and suedes The other nine species (marked by capital 
 fotteXTour original genus, may for long but unequal 
 neriods continue to transmit unaltered descendants, and 
 this is shown in the diagram by the dotted lines unequa y 
 
 F S E to,;i’g“« process oi „oai«c,ti.n rep^cntoi » 
 
 fully stocked country natural selection necessari y ac s j 
 l he selected form having some advantage in the snuggle 
 for life oter other forms, there will be a constant tendency 
 in the improved descendants of anyone species to supplant 
 and Exterminate in each stage of descentUen-pi^ece^o^ 
 and their original progenitor. For it s ion Id be:r<ame 
 bered that the competition will geneially be most seveie 
 between those forms which are most nearly related to each 
 other in habits, constitution and structure. Hence all th 
 intermediate forms between the earlier and latei states, 
 that is between the less and more unproved states of 
 the same species, as well as the original parent specms 
 itself will generally tend to become extinct, bo it pioba 
 blv will be with many whole collateral lines of descent, 
 winch will be conquered by later and improved lines. , 
 
 however, the modified offspring of a . cieS ^ g ® f t 
 some distinct country, or become quickly adapted to 
 son e quite new station, in which offspring and progen¬ 
 itor do not come into competition, both may continue to 
 
 eX Tf' then our diagram be assumed to represent a consid¬ 
 erable* amount of modification, species (A) and all the 
 earlier varieties will have become extinct, being 1 enlaced b) 
 eight new species («“ to and species (I) will be le- 
 
 reared bv six (n u to z u ) new species. . . 1 , 
 
 1 But we may go further than this. The original species of 
 
 our genus were supposed to resemble each other m unequal 
 
 degrees as is so generally the case in nature; species ( A) being 
 
 more nearly related to B, C and D than to the other spe¬ 
 cies; and species (I) more to G, H, K, L than to the o iei - 
 
OF NATURAL SELECTION. 
 
 11? 
 
 These two species (A and I) were also supposed to be very 
 coni m on and widely diffused species, so that they must 
 originally have had some advantage over most of the other 
 species of the genus. Their modified descendants, four¬ 
 teen in number at the fourteen-thousandth generation, will 
 probably have inherited some of the same advantages; 
 they have also been modified and improved in a diversified 
 manner at each stage of descent, so as to have become 
 adapted to many related places in the natural economy of 
 their country. It seems, therefore, extremely probable that 
 they will have taken the places of, and thus exterminated, 
 not only their parents. (A) and (I), but likewise some of 
 the original species which were most nearly related to their 
 parents. Hence very few of the original species will have 
 transmitted offspring to the fourteenth thousandth genera¬ 
 tion.. We may suppose that only one (F) of the two 
 species (E and F) which were least closely related to the 
 other nine original species, has transmitted descendants to 
 this late stage of descent. 
 
 The new species in our diagram, descended from the 
 original eleven. species, will now be fifteen in number. 
 Owing to the divergent tendency of natural selection, the 
 extreme amount of difference in character between species 
 a u and z u will be much greater than that between the 
 most distinct of the original eleven species. The new 
 species, moreover, will be allied to each other in a widely 
 different manner. Of the eight descendants from (A) the 
 three marked a u , q u , p u , will be nearly related from 
 having recently branched off from a 10 ; b u and/ 14 , from hav¬ 
 ing diverged at an earlier period from a 5 , will be in some 
 degree distinct from the three first-named species; and 
 lastly, o u , e u and m u , will be nearly related one to the 
 other, but, from having diverged at the first commence¬ 
 ment of the process of modification, will be widely differ¬ 
 ent from the. other five species, and may constitute a sub¬ 
 genus or a distinct genus. 
 
 The six descendants from (I) will lorm two sub-genera 
 or genera. But as the original species (I) differed largely 
 from (A), standing nearly at the extreme end of the 
 original genus, the six descendants from (I) will, owing to 
 inheritance alone, differ considerably from the eight de¬ 
 scendants from (A); the two groups, moreover, are sup- 
 
114 
 
 RESULT OF TEE ACTION 
 
 posed to have gone on diverging in different directions. 
 The intermediate species, also (and this is a very import¬ 
 ant consideration), which connected the original species 
 (A) and (I), have all become, except (F), extinct, and 
 have left no descendants. Hence the six new species de¬ 
 scended from (I), and the eight descendants fiom (A), 
 will have to be ranked as very distinct genera, 01 even as 
 distinct sub-families. 
 
 Thus it is, as I believe, that two or more genera are 
 produced by descent with modification, from two or more 
 species of the same genus. And the two or more parent- 
 species are supposed to be descended from some one species 
 of an earlier genus. In our diagram this is indicated by the 
 broken lines beneath the capital letters, converging m sub¬ 
 branches downward toward a single point; this point rep- 
 resents a species, the supposed progenitor of oui seveial 
 new sub-genera and genera. 
 
 It is worth while to reflect for a moment on the charac¬ 
 ter of the new species F 14 , which is supposed not to have 
 diverged much in character, but to have retained the torm 
 of (F) either unaltered or altered only in a slight degree. 
 In this case its affinities to the other fourteen new; species 
 will be of a curious and circuitous nature. Being de¬ 
 scended from a form that stood between. the parent- 
 species (A) and (I), now supposed to be extinct and un¬ 
 known, it will be in some degree intermediate m character 
 between the two groups descended from these two species. 
 But as these two groups have gone on diverging in charac¬ 
 ter from the type of their parents, the new species (f ) 
 will not be directly intermediate between them, but rather: 
 between types of the two groups; and every naturalist 
 will be able to call such cases before his mind. . 
 
 In the diagram each horizontal line has. hitherto been 
 supposed to represent a thousand generations., but each 
 mav represent a million or more generations; it may also 
 represent a section of the successive strata of the earth s 
 crust including extinct remains. We shall, when we come 
 to our chapter on geology, have to refer again to this sub- 
 iect, and I think we shall then see that the diagram throws 
 lio-ht on the affinities of extinct beings, which, though 
 generally belonging to the same orders, families or genera, 
 W'ith those now living, yet are often, in some degree, intei- 
 
OF NATURAL SELECTION. n~ 
 
 mediate in character between existing erorms* anri mn 
 understand this fact, for the extinc 
 
 dirergedTe^sJ 18 ^ the branehin S of descend 
 
 nollxpWdTo thefn 1 ^ r ® P f Ce8S ° f mod >fication, as 
 now explained, to the formation of genera alone If in 
 
 diagram, we suppose the amount of change represented 
 by each successive group of diverging dotted lines to be 
 great, the forms marked «» to pf those marked V and 
 / , and those marked o 11 to m u , will form three verv dis¬ 
 tinct genera. We shall also have two very distinct genera 
 descended from ( I} , differing widely from tlL descendants o? 
 i- . .?. se two & r ° u P s of genera will thus form two clis- 
 
 s-ent modifier 1- ° rdei ’ S ’ ao ? ordin g to the amount of diver- 
 fram And the°two lPP0S f be re P resent ed in the dia- 
 from two sneets .7il V l*?” 1 , 108 * or orders > are descended 
 nosfd to K f 51 °i' lgmal genns > and these are sup- 
 Snknown form? fr ° m SOme sti11 raore ancient aid 
 
 We have seen that in each country it is the species be 
 longing to the larger genera which oftenest present varie 
 ties or incipient species. This, indeed, might have been 
 pected, for, as natural selection acts through one form 
 
 existence 0 "?? ad ,T aut ?? e over other forms in the struggle for 
 existence, it will chiefly act on those which already have 
 
 some advantage; and the largeness of any group shows that 
 
 its species have inherited from a common ancestor some 
 
 advantage in common. Hence, the stri?gg“fo? the PrT 
 
 duction of new and modified descendants will mainlv lie 
 
 between the larger groups which are all trying to increase 
 
 n number. One large group will slowly conquer anotlm? 
 
 of' further varStion ^ ? U - mber ’ “ d tlu,s lesse “ its chance 
 w“Inn th li d improvement. Within the same 
 mr ge the later and more highly Derfeofprl 
 
 groups, from branching out and seizing on many new 
 
 ln , * he 'P oll ty of nature, will constantly tend to sup- 
 P ant and destroy the earlier and less improved subgroups 
 
 peaf a Looktog 6 to gr ?? P % an t d sub -S rou PS wil1 finaUy disfpl 
 pear, booking to the future, we can predict thnt iha 
 
 groups of organic beings which are now large and trium 
 
 phant, and which are least broken up, that is which W 
 
 as yet suffered least extinction, will, for a long period, con? 
 
116 
 
 ON THE DEGREE TO WHICH 
 
 tinue to increase. But which groups will ultimately pre. 
 vail no man can predict; for we know that many groups, 
 formerly most extensively developed, have now become ex¬ 
 tinct. Looking still more remotely to the future, we may 
 predict that, owing to the continued and steady increase of 
 the larger groups, a multitude of smaller groups will be- 
 come utterly extinct, and leave no modified descendants; 
 and consequently that, of the species living at any one 
 period, extremely few will transmit descendants to a 
 remote futurity. I shall have to return to this subject m the 
 chapter on classification, but I may add that as, according 
 to this view, extremely few of the more ancient species 
 have transmitted descendants to the present day, and, as 
 all the descendants of the same species form a class, we 
 can understand how it is that there exist so few classes in 
 each main division of the animal and vegetable kingdoms. 
 Although few of the most ancient species have Jett modi¬ 
 fied descendants, yet, at remote geological periods, the 
 earth may have been almost as well peopled with species ot 
 many genera, families, orders and classes, as at the present 
 
 time. 
 
 ON THE DEGREE TO WHICH ORGANIZATION TENDS TO 
 
 ADVANCE. 
 
 Natural selection acts exclusively by the preservation and 
 accumulation of variations, which are'beneficial under the 
 organic and inorganic conditions to which each creatine is 
 1 exposed at all periods of life. The ultimate result is that 
 \ each creature tends to become more and more improved 
 in relation to its conditions. This improvement inevitably 
 deads to the gradual advancement of the organization ot 
 the greater number of living beings throughout the won . 
 But here we enter on a very intricate subject, for natural¬ 
 ists have not defined to each other’s satisfaction what is 
 meant by an advance in organization. Among the verte- 
 brata the degree of intellect and an approach in structure 
 to man clearly come into play. It might be thought that 
 the amount of change which the various parts and organs 
 pass through in their development from embryo to 
 maturity would suffice as a standard of > comparison; but 
 there are cases, as with certain parasitic crustaceans, iu 
 
ORGANIZATION TENDS TO ADVANCE. 117 
 
 which several parts of the structure become less perfect, so 
 that the mature animal cannot be called higher than its 
 larva. Von Baer s standard seems the most widely appli¬ 
 cable and the best, namely, the amount of differentiation of 
 
 1 i u 0 . same or & anic being, in the adult state, as I 
 should be inclined to add, and their specialization for 
 different functions; or, as Milne Edwards would express it, 
 ne completeness of the division of physiological labor. 
 But we shall see how obscure this subject is if we look for 
 instance, to fishes,, among which some naturalists rank 
 those as highest which, like the sharks, approach nearest 
 to amphibians; while other naturalists rank the common 
 ony or teleostean fishes as the highest, inasmuch as they 
 are most strictly fish-like, and differ most from the other 
 vertebrate classes. We see still more plainly the obscurity 
 0 the subject by turning to plants, among which the 
 standard of intellect is of course quite excluded; and here 
 some botanists rank those plants as highest which have 
 every organ, as sepels, petals, stamens and pistils, fully 
 developed m each flower; whereas other botanists, probably 
 with more truth, look at the plants which have their 
 
 several organs much modified and reduced in number as 
 the highest. 
 
 If we take as the standard of high organization, the 
 amount of differentiation and specialization of the several 
 organs m each being when adult (and this will include the 
 advancement of the brain for intellectual purposes), 
 natural selection clearly leads toward this standard: for 
 all physiologists admit that the specialization of organs 
 inasmuch as in this state they perform their functions 
 better, is an advantage to each being; and hence the 
 accumulation of variations tending toward specialization 
 is within the scope of natural selection. On the other 
 hand, we can see, bearing in mind that all organic beings 
 are striving to increase at a high ratio and to seize on 
 every unoccupied or less well occupied place in the 
 economy of nature, that it is quite possible for natural 
 selection gradually to fit a being to a situation in which 
 several organs would be superfluous or useless: in such 
 cases there would be retrogression in the scale of organiza¬ 
 tion. Whether organization on the whole has actually ad¬ 
 vanced from the remotest geological periods to the present 
 
11S ON THE DEGREE TO ' tUICH 
 
 day will be more conveniently discussed in our chapter on 
 
 But°it may be objected that if all organic beings thu 
 tend to rise in the scale, bow is it that throughout the 
 world a multitude of the lowest forms still exist; and how 
 is it that in each great class some forms are far moie 
 highly developed than others? Why have not the moie 
 highly developed forms every where supplanted and extei- 
 m mated the lower? Lamarck.who believed.man innate 
 and inevitable tendency toward perfection m all organic 
 beino-s seems to have felt this difficulty so strongly that he 
 was Ted to suppose that new and simple forms are continu¬ 
 ally being produced by spontaneous generation. Science 
 has not as yet proved the truth of this belief, whatever the 
 future may reveal. On our theory the continued existence 
 of lowly organisms offers no difficulty; for natural selec¬ 
 tion, or the survival of the fittest, does not necessarily in¬ 
 clude progressive development—it only takes advantage o 
 f such variations as arise and are beneficial to each creature 
 ‘ under its complex relations of life. And it may be askec 
 what advantage, as far as we can see, would it be to an l 
 fusorian animalcule—to an intestinal worm—or even to an 
 earth-worm, to be highly organized. Ii it were no advan¬ 
 tage, these forms would be left, by natural selection, un¬ 
 improved or but little improved, and might remain for in¬ 
 definite ages in their present lowly condition. And geo.- 
 oo-y tells us that some of the lowest forms, as the infusoria 
 and rhizopods, have remained for an enormous penod m 
 nearly their present state. But to suppose that-mostof the 
 manv now existing low forms have not m the least ad 
 vanned since the "first dawn of life would be extremely 
 raslr for every naturalist who has dissected some of the 
 beings now ranked as very low in the scale, must have been 
 struck with their really wondrous and beautiful organiza- 
 
 j • 
 
 ^Nearly the same remarks are applicable, if we look to the 
 different grades of organization within the same giea 
 group; for instance, in the vertebrata to the co-existence 
 of mammals and fish—among mammalia, to the co-exist¬ 
 ence of man and the ormthorhynchus—among fishes, to 
 the co-existence of the shark and thelancelet (Amphioxus) 
 which latter fish in the extreme simplicity of its structure 
 
ORGANIZATION TENDS TO ADVANCE. X19 
 
 approaches the invertebrate classes. But mammals and 
 fish hardly come into competition with each other; the ad¬ 
 vancement of the whole class of mammals, or of certain 
 members in this class, to the highest grade would not lead 
 to their taking the place of fishes. Physiologists believe 
 that the brain.must be bathed by wa#*m blood to be highly 
 active, and this requires aerial respiration; so that warm¬ 
 blooded mammals when inhabiting the water lie under a 
 disadvantage in having to come continually to the surface 
 to breathe. With fishes, members of the shark family 
 would not tend to supplant the lancelet; for the lancelet, 
 as I hear from Fritz Muller, has as sole companion and 
 competitor on the barren sandy shore of South Brazil, an 
 anomalous annelid. The three lowest orders of mam¬ 
 mals, namely, marsupials, edentata, and rodents, co-exist 
 in South America in the same region with numerous 
 monkeys, and probably interfere little with each other. 
 Although organization, on the whole, may have advanced 
 and be still advancing throughout the world, yet the scale 
 will always present many degrees of perfection; for the 
 high advancement of certain whole classes, or of certain 
 members of each class, does not at all necessarily lead to 
 the extinction of those groups with which they do not enter 
 into close competition. In some cases, as we* shall here¬ 
 after see, lowly organized forms appear to have been pre¬ 
 served to the present day, from inhabiting confined or 
 peculiar stations, where they have been subjected to less 
 severe competion, and where their scanty numbers have re¬ 
 tarded the chance of favorable variations arising. 
 
 Finally, I believe that many lowly organized*forms now"' 
 exist throughout the.world, from various causes. In some * 
 cases variations or individual differences of a favorable 
 nature may never have arisen for natural selection to act 
 on and accumulate. In no case, probably, has time suf¬ 
 ficed for the utmost possible amount of development. In 
 some, few cases there has been what we must call retro¬ 
 gression or organization. But the main cause lies in the 
 fact that under very simple conditions of life a high organi¬ 
 zation would be of no service,—possibly would be of actual 
 disservice, as being of a more delicate nature, and more 
 liable to be put out of order and injured. J 
 
 Looking to the first dawn of life, when all organic beings. 
 
120 
 
 COVERGENCE OF CHARACTER. 
 
 as we may believe, presented the simplest structure, liow, 
 it has been asked, could the first step in the advancement 
 or differentiation of parts have arisen? Mr. Herbert 
 Spencer would probably answer that, as soon as simple 
 unicellular organism came by growth or division to be 
 compounded of several cells, or became attached to any 
 supporting surface, his law “ that homologous units ot 
 any order become differentiated in proportion as their rela¬ 
 tions to incident forces become different would come 
 into action. But as we have no facts to guide us, specula¬ 
 tion on the subject is almost useless. It is, however, an 
 error to suppose that there would be no struggle for exi& - 
 ence, and, consequently, no natural selection, until many 
 forms had been produced: variations m a single species 
 inhabiting an isolated station might, be beneficial, anu 
 thus the whole mass of individuals might be modified, or 
 two distinct forms might arise. But, as I remarked toward 
 the close of the introduction, no one ought to feel surprise 
 at much remaining as yet unexplained on the origin ot 
 species, if we make due allowance for our profound ignor¬ 
 ance on the mutual relations of the inhabitants ot the 
 world at the present time, and still more so during pas 
 
 ages. 
 
 COFTVERGEFTCE OF CHARACTER. 
 
 Mr. H. C. Watson thinks that I have overrated the im¬ 
 portance of divergence of character (in which, however, he 
 apparently believes), and that convergence, as it may . be 
 called, has likewise played a part. If two species belonging 
 to two distinct though allied genera, had both produced a 
 laro-e number of new and divergent forms, it is conceivable 
 that these might approach each other so closely that they 
 would have all to be classed under the same genus; and 
 thus the descendants of two distinct genera would converge 
 into one. But it would in most cases be extremely rash to at¬ 
 tribute to convergence a close and general similarity of sti uct- 
 ure in the modified descendants of widely distinct forms. 
 The shape of a crystal is determined solely by the molecular 
 forces, and it is not surprising that dissimilar substances 
 should sometimes assume the same form; but with organic 
 beings we should bear in mind that the. form of each de- 
 J pends on an infinitude of complex relations, namely on the 
 
COVERGENCE OF CHARACTER. 
 
 121 
 
 variations which have arisen, these being due to causes far too 
 intricate to be followed out—on the nature of tlie variations 
 which have been preserved or selected, and this depends on 
 the surrounding physical conditions, and in a still higher de- 
 , gree on the surrounding organisms with which each being has 
 ; come into competition—and lastly, on inheritance (in itself a 
 fluctuating element) from innumerable progenitors, all of 
 which have had their forms determined through equally com- 
 Jplex relations. It is incredible that the descendants of two 
 organisms, which had originally differed in a marked man¬ 
 ner, should ever afterward converge so closely as to lead 
 to a near approach to identity throughout their whole 
 organization. If this had occurred, we should meet with 
 the same form, independently of genetic connection, re¬ 
 curring in widely separated geological formations; and the 
 balance of evidence is opposed to any such an admission. 
 
 Mr. Watson has also objected that the continued action 
 of natural selection, together with divergence of character, 
 would tend to make an indefinite number of specific forms. 
 As far as mere inorganic conditions are concerned, it seems 
 probable that a sufficient number of species would soon 
 become adapted to all considerable diversities of heat, 
 moisture, etc.; but I fully admit that the mutual relations 
 of organic beings are more important; and as the number 
 of species in any country goes on increasing, the organic 
 conditions of life must become more and more complex. 
 Consequently there seems at first no limit to the amount of 
 profitable diversification of structure, and therefore no 
 limit to the number of species which might be produced. 
 We do not know that even the most prolific area is fully 
 stocked with specific forms: at the Cape of Good Hope and 
 in Australia, which support such an astonishing number of 
 species, many European plants have become naturalized. 
 But geology shows us, that from an early part of the ter¬ 
 tiary period the number of species of shells, and that from 
 the middle part of this same period, the number of mam¬ 
 mals has not greatly or at all increased. What then checks 
 an indefinite increase in the number of species? The 
 amount of life (I do not mean the number of specific 
 forms) supported on an area must have a limit, depending 
 so largely as it does on physical conditions; therefore, if 
 an area be inhabited by verv many species, each or nearly 
 
SUMMARY . 
 
 122 
 
 each species will be represented by few individuals; and 
 such species will be liable to extermination from accidental 
 fluctuations in the nature of the seasons or in the number 
 of their enemies. The process of extermination in such 
 cases would be rapid, whereas the production of new species 
 must always be slow. Imagine the extreme case of as many 
 species as individuals in England, and the first severe winter 
 or very dry summer would exterminate thousands on thou¬ 
 sands of species. Rare species, and each species will become 
 rare if the number of species in any country becomes in¬ 
 definitely increased, will, on the principle often explained, 
 present within a given period few favorable variations; con¬ 
 sequently, the process of giving birth to new specific foims 
 would thus be retarded." When any species becomes very 
 rare, close interbreeding will help to exterminate it; authors 
 have thought that this comes into play in accounting foi 
 the deterioration of the aurochs in Lithuania, of red deer 
 in Scotland and of bears in Norway, etc. Lastly, and this 
 I am inclined to think is the most important element, a 
 dominant species, which has already beaten many compet¬ 
 itors in its own home, will tend to spread and supplant 
 many others. Alph. de Candolle has shown that those 
 species which spread widely tend generally to spread very 
 widely, consequently they will tend to supplant and exter¬ 
 minate several species in several areas, and thus check the 
 inordinate increase of specific forms throughout the world. 
 Dr. Hooker has recently shown that in the southeast cor¬ 
 ner of Australia, where, apparently, there are many in¬ 
 vaders from different quarters of the globe, the endemic 
 Australian species have been greatly reduced in number. 
 How much weight to attribute to these several considera¬ 
 tions I will not pretend to say; but conjointly they must 
 limit in each country the tendency to an indefinite aug¬ 
 mentation of specific forms. 
 
 SUMMARY OF CHAPTER. 
 
 If under changing conditions of life organic beings pre¬ 
 sent individual differences in almost every part of their 
 structure, and this cannot be disputed; if there be, owing 
 to their geometrical rate of increase, a severe struggle for 
 life at some age, season or year ; and this certainly cannot 
 
SUMMARY. 
 
 123 
 
 be disputed; then, considering the infinite complexity of 
 the relations of all organic beings to each other and to their 
 conditions of life, causing an infinite diversity in structure, 
 constitution and habits, to be advantageous to them, it 
 would be a most extraordinary fact if no variations had 
 ever occurred usefu l to each being’s own welfare, in the 
 sa me manner a s^nnuiX-variations have oonnrmTuseful to 
 man. But if _variations, useful to any organic fining eve r 
 occur, assuredly individuals thus characterized will have 
 the_best_chance of being preserve d iiTthe sti-mro-lo for life: 
 a nd from the strong principle of inheritancS . these w7)j 
 tend to ,. produce offs pring similarly characterized. This 
 prmgi&le o f preservation 1 or the survival of the fit - 
 jgs'BA —ixat.LiJLiaX^^ It leads ftTThe im¬ 
 
 provement of each creaturem relation to its organic and in¬ 
 organic conditions of life,; and consequently, in most cases, 
 to what must be regarded as an advance in organization. 
 Nevertheless, low and simple forms will long endnrn if wql l 
 fitted for their simple conditions of life . 
 
 Natural selection, on the principle of qualities being in- 
 hented at corresponding ages, can modify th e ~_egg. seecT or 
 easily as the adult. Among many animals sexual 
 selection will have given its aid to ordinary selection by 
 assuring to the most vigorous and best adapted males the 
 greatest number of offspring. Sexual selection will also 
 give characters useful to the males alone in their struggles 
 or rivalry with other males; and these characters will be 
 transmitted to one se*. or to both sexes, according to the 
 form of inheritance which prevails. 
 
 Whether natural selection has really thus acted in 
 adapting the various forms of life to their several condi¬ 
 tions and stations, must be judged by the general tenor 
 and balance of evidence given in the following chapters. 
 But we have already seen how it entails extinction; and 
 how largely extinction has acted in the worlds history, 
 geology plainly declares. Natural selection, also , l ead s 
 to divergence,of — character: "for the mnro nro-Mm'p. beings 
 diverge in structure, habits and constitution, by so much 
 the more can a large number be supported on the area, of 
 which we see proof by looking to the inhabitants of any 
 small spot, and to the productions naturalized in foreign 
 lands. Therefore, during the modification of the descend- 
 
,., 4 SUMMART. 
 
 ants of any one spec if- an d during the incess a nt straggle of 
 a Tf artftnifts to increase liTlmmbers/tKe ^S L re div e rsifie d the 
 
 .—-in th« battle lor hie. thus the StmUl (tTHerences ills 
 I ' inonisTiin TTarieties ofthe same species, steadily tend to 
 increase, till they equal the greater differences between 
 species of the same genus, or even of distinct genera. 
 
 1 Wo have seen that it is the common, the widely diffused 
 and widely ranging species, belonging to the larger genei a 
 within each class, which vary most; and these tend to 
 transmit to their modified offspring that superiority which 
 
 now makes them dominant in their divert 
 
 ural selection, as has just been remarked, lgad s to divei 
 
 once of character. andto 
 
 improved and inte rmediate forms of life. On these pun 
 5 ^rtra-5atKr5^TEe affimties, aSOHe generally well 
 
 prnles the nature ot tne affinities, anc. — 0 
 defined distinctions between the 
 beino-s in each class throughout the world, may De 
 explained. It is a truly wonderful fact—the wonder of 
 which we are apt to overlook from familiarity—that all 
 
 animals and all plants throughout a11 time 
 should he related^to each other in groups, subordinate to 
 groups, in the manner which we everywhere behold- 
 . namely varieties of the same species most closely related, 
 species of the same genus less closely and mgj 
 forming sections and sub-genera, species of distinct genera 
 much less closely related, and genera related in different 
 degrees forming" sub-families, families, orders,, sub-classes 
 and Blasses Idio several subordinate groups in any class 
 cannot be ranked in a single file, but seen clustered round 
 points and these round other points, and so on m almost 
 endless cycles. If species had been independently created 
 no explanation would have been possible of this kind of class 
 ification; but it is explained through inheritance and the 
 complex action of natural selection, entailing extinction 
 and divergence of character, as we have seen illustrated m 
 
 simile largely speaks the truth. The green and budding 
 twigs may S represent existing species; and those produced 
 during former years may represent fc^long.succession 
 
SUMMARY. 
 
 125 
 
 of extinct species. At each period of growth all the grow¬ 
 ing twigs have tried to branch out on all sides, and to over¬ 
 top and kill the surrounding twigs and branches, in the 
 same manner as species and groups of species have at all 
 times overmastered other species in the great battle for life. 
 The limbs divided into great branches, and these into lesser 
 and lesser branches, were themselves once, when the tree 
 'Was young, budding twigs; and this connection of the 
 former and present buds by ramifying branches may well 
 represent the classification of all extinct and living species 
 in groups subordinate to groups. Of the many twigs 
 which flourished when the tree was a mere bush, only two 
 or three, now grown into great branches, yet survive and 
 bear the other branches; so with the species which lived 
 during long-past geological periods, very few have left 
 living and modified descendants. From the first growth 
 of the tree, many a limb and branch has decayed and 
 diopped off; and these fallen branches of various sizes 
 may represent those whole orders, families and genera 
 which have now no living representatives, and which are 
 known to us only in a fossil state. As we here and 
 there see a thin, straggling branch springing from a fork 
 low down in a tree, and which by some chance has been 
 favored and is still alive on its summit, so we occasionally 
 see. an. animal like the Ornithorhynchus or Fepidosiren, 
 which in some small degree connects by its affinities two 
 large branches of life, and which has apparently been 
 saved from fatal competition by having inhabited a pro¬ 
 tected station.. As buds give.llse.by growth to fresh burls . 
 ai l4 these, if jigQr ous^ branch out and overto p on a l l sides 
 
 it has 
 
 W with th a -great Tree of Life, which fills with if a "^ 
 and bro ken ^ranches the crust of t he ea rth, and covers th e 
 fiS S ^ce ever-branching and beautiful ramifications. 
 
126 
 
 LAWS OF VARIATION. 
 
 CHAPTER V. 
 
 LAWS OF VARIATION. 
 
 Effects of changed conditions—Use and disuse combined with 
 natural selection; organs of flight and of vision-Acclimatisa- 
 t i on —Correlated variation—Compensation and economy ot 
 trrowth—False correlations—Multiple, rudimentary and lowly 
 organized structures variable—Parts developed in an unusual 
 maimer are highly variable: specific characters more variable 
 than generic; secondary sexual characters variable—Species ot 
 the same genus vary in an analogous manner Reveisions to 
 long-lost characters—Summary. 
 
 I have hitherto sometimes spoken as if the variations 
 so common and multiform with organic beings under do¬ 
 mestication, and in a lesser degree with those under nature 
 —were due to chance. This, of course is a wholly incorrect 
 expression, but it serves to acknowledge plainly oui igno- 
 ranee of the cause of each particular variation. home 
 authors believe it to be as much the function of the repro¬ 
 ductive system to produce individual differences, 01 slight 
 deviations of structure, as to make the child like its parents. 
 But the fact of variations and monstrosities occurring 
 much more frequently under domestication than under 
 nature, and the greater variability of species having wide 
 ranges than of those with restricted ranges, lead to the con¬ 
 clusion that variability is generally related to the conditions 
 of life to which each species has been exposed duung sev¬ 
 eral successive generations. In the first chapter I at¬ 
 tempted to show that changed conditions act in two ways, 
 directly on the whole organization or on certain parts alone, 
 and indirectly through the reproductive system. > In all cases 
 there are two factors, the nature of the organism, which 
 is much the most important of the two, and the nature of 
 the conditions. The direct action of changed conditions 
 leads to definite or indefinite results. In the latter case the 
 organization seems to become plastic, and we ha\e much 
 
LAWS OF VARIATION. 
 
 127 
 
 fluctuating variability. In tlie former case the nature of 
 the organism is such that it yields readily, when subjected 
 to certain conditions, and all, or nearly all, the individuals 
 become modified in the same way. 
 
 It is very difficult to decide how far changed conditions, 
 such as of climate, food, etc., have acted in a definite 
 manner. There is reason to believe that in the course of 
 time the effects have been greater than can be proved by 
 clear evidence. But we may safely conclude that the 
 innumerable complex co-adaptations of structure, which 
 we see throughout nature between various organic beings, 
 .cannot be attributed simply to such action. In the follow- 
 I ing cases the conditions seem to have produced some slight 
 definite effect: E. Forbes asserts that shells at their 
 southern limit, and when living in shallow water, are more 
 brightly colored than those of the same species from 
 further north or from a greater depth; but this certainly 
 does not always hold good. Mr. Gould believes that birds 
 of the same species are more brightly colored under a clear 
 atmosphere, than when living near the coast or on islands; 
 and Wollaston is convinced that residence near the sea 
 affects the colors of insects. Moquin-Tandon gives a list 
 of plants which, when growing near the sea-shore, have 
 their leaves in some degree fleshy, though not elsewhere 
 fleshy. These slightly varying organisms are interesting 
 in as far as they present characters analogous to those pos¬ 
 sessed by the species which are confined to similar condi¬ 
 tions. 
 
 When a variation is of the slightest use to any being, we 
 cannot tell how much to attribute to the accumulative 
 action of natural selection, and how much to the definite 
 action of the conditions of life. Thus, it is well known 
 to furriers that animals of the same species have thicker 
 and better fur the further north they live; but who can 
 tell how much of this difference may be due to the warmest 
 clad individuals having been favored and preserved during 
 many generations, and how much to the action of the 
 severe climate? For it would appear that climate has some 
 direct action on the hair of our domestic quadrupeds. 
 
 Instances could be given of similar varieties being pro¬ 
 duced from the same species under external conditions 
 ©f life as different as can well be conceived; and, on th,8 
 
128 
 
 EFFECTS OF USE AND DISUSE. 
 
 other hand, of dissimilar varieties being produced under 
 apparently the same external conditions. Again, innumer¬ 
 able instances are known to every naturalist, of species 
 keeping true, or not varying at all, although living under 
 the most opposite climates. Such considerations as these 
 incline me to lay less weight on the direct action of the 
 surrounding conditions, than on a tendency to vary, due 
 to causes of which we are quite ignorant. 
 
 In one sense the conditions of life may be said, not only 
 to cause variability, either directly or indirectly, but like¬ 
 wise to include natural selection, for the conditions 
 determine whether this or that variety shall survive. But 
 when man is the selecting agent, we clearly see that the 
 two elements of change are distinct; variability is in some 
 manner excited, but it is the will of man which accumu¬ 
 lates the variations in certain direction; and it is this latter 
 agency which answers to the survival of the fittest under 
 nature. 
 
 EFFECTS OF THE INCREASED USE AND DISUSE OF PARTS, AS 
 \ CONTROLLED BY NATURAL SELECTION. 
 
 From the facts alluded to in the first chapter, I think 
 there can be no doubt that use in our domestic animals has 
 strengthened and enlarged certain parts, and disuse dimin¬ 
 ished 0 them; and that such modifications are inherited. 
 Under free nature we have no standard of comparison by 
 which to judge of the effects of long-continued use or 
 disuse, for we know not the parent-forms; but many 
 animals possess structures which can be best explained by 
 the effects of disuse. As Professor Owen has remarked, 
 there is no greater anomaly in nature than a bird that cannot 
 fly; yet there are several in this state. The logger-headed 
 duck of South America can only flap along the surface 
 of the water, and has its wings in nearly the same condition 
 as the domestic Aylesbury duck; it is a remarkable fact 
 that the young birds, according to Mr. Cunningham, can 
 fly, while the adults have lost this power. As the larger 
 ground-feeding birds seldom take flight except to escape 
 danger, it is probable that the nearly wingless condition of 
 several birds, now inhabiting or which lately inhabited 
 several oceanic islands, tenanted by no beasts of prey, has 
 
EFFECTS OF USE AND DISUSE. 
 
 129 
 
 been caused by disuse. The ostrich indeed inhabits con¬ 
 tinents, and is exposed to danger from which it cannot 
 escape by flight, but it can defend itself, by kicking its 
 enemies, as efficiently as many quadrupeds. We may 
 believe that the progenitor of the ostrich genus had habits 
 like those of the bustard, and that, as the size and weight 
 of its body were increased during successive generations, 
 its legs were used more and its wings less, until they be¬ 
 came incapable of flight. 
 
 Kirby has remarked (and I have observed the same fact) 
 that the anterior tarsi, or feet, of many male dung-feeding 
 beetles are often broken off; he examined seventeen speci¬ 
 mens in his own collection, and not one had even a relic 
 left. In the Onites apelles the tarsi are so habitually lost 
 that the insect has been described as not having them. In 
 some other genera they are present, but in a rudimentary 
 condition. In the Ateuchus or sacred beetle of the Egyp¬ 
 tians, they are totally deficient. The evidence that acci¬ 
 dental mutilations can be inherited is at present not de¬ 
 cisive^ but the remarkable cases observed by Brown-Sequard 
 in guinea-pigs, of the inherited effects of operations, 
 should make us cautious in denying this tendency. Hence, 
 it will perhaps be safest to look at the entire absence of the 
 anterior tarsi in Ateuchus, and their rudimentary con¬ 
 dition in some other genera, not as cases of inherited mu¬ 
 tilations, but as due to the effects of long continued disuse; 
 for as many dung-feeding beetles are generally found with 
 their tarsi lost, this must happen early in life; therefore 
 the tarsi cannot be of much importance or be much used 
 by these insects. 
 
 In some cases we might easily put down to disuse 
 modifications of structure which are wholly, or mainly due 
 to natural selection. Mr. Wollaston has discovered the 
 remarkable fact that 200 beetles, out of the 550 species (but 
 more are now known) inhabiting Maderia, are so far defi¬ 
 cient in wings that they cannot fly; and that, of the 
 twenty-nine endemic genera, no less than twenty-three 
 have all their species, in this condition! Several facts,— 
 namely, that beetles in many parts of the world are fre¬ 
 quently blown to sea and perish; that the beetles in Maderia, 
 as observed by Mr. Wollaston, lie much concealed, until 
 the wind lulls and the sun shines; that the proportion of 
 
130 EFFECTS OF USE AND DISUSE. 
 
 wingless beetles is larger on the exposed Desertas than in 
 Maderia itself; and especially the extraordinary fact, so 
 strongly insisted on by Mr. W ollaston, that certain large 
 groups'of beetles, elsewhere excessively numerous, which 
 absolutely require the use of their wings, are here almost 
 entirely absent. These several considerations make me be¬ 
 lieve that the wingless condition of so many Maderia 
 beetles is mainly due to the action of natural selection, 
 combined probably with disuse. For during many succes¬ 
 sive generations each individual beetle which new least, 
 either from its wings having been ever so little less per¬ 
 fectly developed or from indolent habit, will have had the 
 best chance of surviving from not being blown out to sea; 
 and, on the other hand, those beetles which most readily 
 took to flight would oftenest have been blown to sea, and 
 thus destroyed. 
 
 The insects in Maderia which are not ground-feeders, 
 and which, as certain flower-feeding coleopteia and 
 lepidoptera, must habitually use their wings to gain their 
 subsistence, have, as Mr. Wollaston suspects,, tlieii wings 
 not at all reduced, but even enlarged. This is quite com- 
 patable with the action of natural selection. For when 
 a new insect first arrived on the island, the tendency of 
 nature 1 selection to enlarge or to reduce the wings, would 
 depend on whether a greater number of individuals were 
 saved by successfully battling with the winds, or by giving 
 up the attempt and rarely or never flying. As with 
 mariners shipwrecked near a coast, it would have been 
 better for the good swimmers if they had been able to swim 
 still further, whereas it would have been better for the 
 swimmers if they had not been able to swim at all and had 
 stuck to the wreck. 
 
 The eyes of moles and of some burrowing rodents are 
 rudimentary in size, and in some cases are quite co\eied 
 by skin and fur. This state of the eyes is probably due to 
 gradual reduction from disuse, but aided peibaps by 
 natural selection. In South America, a burrowing rodent, 
 the tuco-tuco, or Otenomys, is even more subterranean in 
 its habits than the mole; and I was assured by a Spaniard, 
 who had often caught them, that they were frequently 
 blind. One which I kept alive was certainly in this con¬ 
 dition, the cause, as appeared on dissection, having been 
 
EFFECTS OF USE AND DISUSE. 131 
 
 inflammation of the nictitating 1 membrane. As frequent 
 inflammation of the eyes mast be injurious to any animal, 
 and as eyes are certainly not necessary to animals having 
 subteiianean habits, a reduction in their size, with the 
 adhesion of the eyelids and growth of fur over them, 
 might in such case be an ad vantage; and if so, natural 
 selection would aid the effects of disuse. 
 
 It is well known that several animals, belonging to the 
 most different classes, which inhabit the caves of Carniola 
 and Kentucky, are blind. In some of the crabs the 
 foot-stalk for the eyes remains, though the eye is gone* 
 th .e stand for the telescope is there, though the telescope 
 with its glasses has been lost. As it is difficult to imag¬ 
 ine that eyes, though useless, could be in any way injurious 
 to animals living in darkness, their loss may be attributed 
 to disuse. In one of the blind animals, namely, the cave- 
 rat (Eeotoma), two of which were captured by Professor 
 Silliman at above half a mile distance from the mouth of 
 the cave, and therefore not in the profoundest depths, the 
 eyes were lustrous and of large size; and these animals, as 
 I am informed by Professor Silliman, after having been ex¬ 
 posed foi about a month to a graduated light, acquired a 
 dim perception of objects. 
 
 It is difficult to imagine conditions of life more similar 
 than deep limestone caverns under a nearly similar climate; 
 so that, in accordance with the old view of the blind ani¬ 
 mals having been separately created for the American and 
 European caverns, very close similarity in their organiza¬ 
 tion and affinities might have been expected. This is cer¬ 
 tainly not the case if we look at the two whole faunas; and 
 with lespect to the insects alone, Schiodte has remarked: 
 “We are accordingly prevented from considering the entire 
 phenomenon in any other light than something purely 
 local, and the similarity which is exhibited in a few forms 
 between the Mammoth Cave (in Kentucky) and the caves 
 m Carniola, otherwise than as a very plain expression of 
 that analogy which subsists generally between the fauna 
 of Europe and of Korth America.” On my view we must 
 suppose that American animals, having in most cases ordi- 
 luny powers of vision, slowly migrated by successive gener¬ 
 ations from the outer world into the deeper and deeper re¬ 
 cesses of the Kentucky caves, as did European animals into 
 
132 effects of use and disuse. 
 
 the caves of Europe. We have some evidence of this gra- 
 dation of habit; for, as Schiodte remarks: “ We accord- 
 ino-lv look upon the subterranean faunas as small raminca- 
 tions which have penetrated into the earth from the geo¬ 
 graphically limited faunas of the adjacent tracts, and 
 which as they extended themselves into darkness, have 
 been accommodated to surrounding circumstances Ani¬ 
 mals not far remote from ordinary forms, prepare the tran¬ 
 sition from light to darkness. Next follow those that aie 
 constructed for twilight; and last of all, those destined for 
 total darkness, and whose formation is quite pecmiar. 
 These remarks of Schiodte’s, it should be undeistocr, 
 apply not to the same, but to distinct species. By the 
 tune^ that an animal had reached, after numberless 
 venerations, the deepest recesses, disuse will on tins 
 fiew have more or less perfectly obliterated its eyes 
 and natural selection will often have effected other 
 changes, such as an increase in the length of the 
 antennae or palpi, as a compensation for blindness. 
 Notwithstanding such modifications, we might expect stil 
 to see in the cave-animals of America, affinities to the othei 
 inhabitants of that continent, and m those of Europe to 
 the inhabitants of the European continent. And this is the 
 case with some of the American cave-animals, as I heai liom 
 Professor Dana; and some of the European cave-insects are 
 very closely allied to those of the surrounding country It 
 would be difficult to give any rational explanation of the 
 affinities of the blind cave-animals to the other inhabit¬ 
 ants of the two continents on the ordinary view of their 
 'independent creation. That several of the inhabitants of the 
 caves of the Old and New Worlds should be closely related, 
 we might expect from the well-known relationship of most ol 
 their other productions. As a blind species of Bathyscia 
 is found in abundance on shady rocks far from caves, the 
 loss of vision in the cave species of this one genus has piob- 
 ably had no relation to its dark habitation; for it is natu¬ 
 ral'that an insect already deprived of vision should readily 
 become adapted to dark caverns. Another blind genus 
 (Anophthalmus) offers Ins remarkable peculiarity, that the 
 species, as Mr. Murray observes, have not as yet been found 
 anywhere except in caves; yet those which inhabit the 
 several caves of Europe and America are distinct; but it is 
 
A CCLIMA TIZA TION, 
 
 133 
 
 possible that the progenitors of these several species, while 
 they were furnished with eyes, may formerly have ranged 
 over both continents, and then have become extinct, ex¬ 
 cepting in their present secluded abodes. Far from feeling 
 surprise that some of the cave-animals should be very 
 
 S n i 0m fii° US A ^gassiz has remarked in regard to the blind 
 hsh, the Amblyopsis, and as is the case with the blind 
 Proteus with reference to the reptiles of Europe, I am only 
 surprised that more wrecks of ancient life have not been 
 preserved, owing to the less severe competition to which 
 the scanty inhabitants of these dark abodes will have been 
 
 ACCLIMATIZATION. 
 
 Habit is hereditary with plants, as in the period of 
 flowering m the time of sleep, in the amount of rain 
 requisite for seeds to germinate, etc., and this leads me to 
 say a few words, on acclimatization. As it is extremely 
 common for distinct species belonging to the same genus 
 to inhabit hot and cold countries, if it be true that all the 
 species of the same genus are descended from a single 
 parent-form, acclimatization must be readily effected dur¬ 
 ing a long course of descent. It is notorious that each 
 species is adapted to the climate of its own home: species 
 from an arctic or even from a temperate region cannot 
 endure a tropical climate, or conversely. So again, many 
 succulent plants cannot endure a damp climate. But the 
 degree of adaptation of species to the climates under which 
 they live is often overrated. We may infer this from our 
 .fiequent inability to predict whether or not an imported 
 ant will endure our climate, and from the number of 
 plants and animals brought from different countries which 
 are here. perfectly healthy. We have reason to believe 
 that species in a state of nature are closely limited in their 
 ranges by the competition of other organic beings quite as 
 much as, or more than, by adaptation to particular climates. 
 But whether or not this adaptation is in most cases very 
 close, we have evidence with some few plants, of their be"- 
 coming, to a certain extent, naturally habituated to differ¬ 
 ent temperatures; that is, they become acclimatized: thus 
 the pmes and rhododendrons, raised from seed collected 
 
ACC LIMA LIZA LION. 
 
 134 
 
 bv Dr Hooker from the same species growing at different 
 heights on the Himalayas, were found to possess in this 
 country different constitutional powers of resisting co d. 
 Mr Thwaites informs me that he has observed similar 
 facts in Ceylon; analogous observations have been made 
 by Mr H. C. Watson on European species of plants 
 brought from the Azores to England; and I could give 
 other cases. In regard to animals, several authentic 
 instances could be adduced of species haying largely 
 extended, within historical times, their range from warmer 
 to colder latitudes, and conversely; but we do not posi¬ 
 tively know that these animals were strictly adapted to 
 their native climate, though in all ordinary cases we 
 assume such to be the case; nor do we know that they 
 have subsequently become specially acclimated to their 
 new homes, so as to be better fitted for them than they 
 
 were at first. , 
 
 As we may infer that our domestic animals were origin¬ 
 ally chosen by uncivilized man because they were useful, 
 and because they bred readily under confinement, and not 
 because they were subsequently found capable ot lai- 
 extended transportation, the common and extraordinary 
 capacity in our domestic animals of not only withstanding 
 the most different climates, but of being perfectl) fertile 
 (a far severer test) under them, may be used as an argument 
 that a large proportion of other animals now m a state ot 
 nature could easily be brought to bear widely different 
 climates. We must not, however, push the foregoing 
 argument too far, on account of the probable origin ox 
 some of our domestic animals from several wild stocks; the 
 blood, for instance, of a tropical and arctic wolf may per¬ 
 haps be mingled in our domestic breeds. 1 he rat and 
 mouse cannot be considered as domestic animals, but they 
 have been transported by man to many parts of the world, 
 and now have a far wider range than any other rodent; tor 
 they live under the cold climate of Faroe in the north and 
 of the Falklands in the south, and on many an island m 
 the torrid zones. Hence adaptation to any special climate 
 may be looked at as quality readily grafted on an innate 
 wide flexibility of constitution, common to most animals. 
 On this view, the capacity of enduring the most different 
 climates by man himself and by his domestic animals, and 
 
A CCLIMA TIZA TTChV. 135 
 
 the fact of the extinct elephant and rhinoceros having for¬ 
 merly endured a glacial climate, whereas the living species 
 are now all tropical or sub-tropical in their habits, ought 
 not to be looked at as anomalies, but as examples of a very 
 common flexibility of constitution, brought, under peculiar 
 circumstances, into action. r 
 
 How much of the acclimatization of species to any 
 peculiar climate is due to mere habit, and how much to the 
 natural selection of varieties having different innate con¬ 
 stitutions, and how much to both means combined, is an 
 obscure question. That habit or custom has some influ¬ 
 ence, I must believe, both from analogy and from the in¬ 
 cessant advice given in agricultural works, even in the 
 ancient Encyclopedias of China, to be very cautious in 
 transporting animals from one district to another. And 
 as it is not likely that man should have succeeded in select- 
 mg so many breeds and sub-breeds with constitutions 
 specially fitted for their own districts, the result must, I 
 think, be due to habit. On the other hand, natural selec- 
 iou would inevitably tend to preserve those individuals 
 which were born with constitutions best adapted to any 
 country which they inhabited. In treatises on many kinds 
 ot cultivated plants, certain varieties are said to with¬ 
 stand certain climates better than others; this is strik- 
 lngly shown in works on fruit-trees published in the United 
 states, m which certain varieties are habitually recom¬ 
 mended for the northern and others for the southern states: 
 and as most of these varieties are of recent origin, they can 
 not owe thrnr constitutional differences to habit. The case 
 o he Jerusalem artichoke, which is never propagated in 
 ngland by seed, and of which, consequently, new varieties 
 lave not been produced, has even been advanced, as prov¬ 
 ing that acclimatization cannot be effected, for it is now as 
 tender as ever it was! The case, also, of the kidney-bean 
 Has been often cited for a similar purpose, and with much 
 greater weight; but until some one will sow, during a score 
 ox generations, his kidney-beans so (early that a very large 
 proportion are destroyed by frost, and then collect seed 
 irom the few survivors, with care to prevent accidental 
 crosses, and then again get seed from these seedlings, with 
 the same precautions, the experiment cannot be said to 
 have been tried. Nor let it be supposed that differences in 
 
136 
 
 CORRELATED VARIATION. 
 
 the constitution of seedling kidney-beans never appear, for 
 an account has been published how much more hardy some 
 seedlings are than others; and of this fact I have myself 
 observed striking instances. 
 
 On the whole, we may conclude that habit, or use and 
 disuse, have, in some cases, played a considerable part in 
 the modification of the constitution and structure; but 
 that the effects have often been largely combined with, and 
 sometimes overmastered by, the natural selection of innate 
 variations. 
 
 CORRELATED VARIATION. 
 
 I mean by this expression that the whole organization is 
 so tied together, during its growth and development, that 
 when slight variations in any one part occur and are accu¬ 
 mulated through natural selection, other parts become 
 modified. This is a very important subject, most 
 imperfectly understood, and no doubt wholly different 
 classes of facts may be here easily confounded together. 
 We shall presently see that simple ‘ inheritance often gives 
 the false appearance of correlation. One of the most 
 obvious real cases is. that variations of structure arising in 
 the young or larvae naturally tend to affect the structure of 
 the mature animal. The several parts which are homo¬ 
 logous, and which, at an early embryonic period, are 
 identical in structure, and which are necessarily exposed to 
 similar conditions, seem eminently liable to vary in a like 
 manner: we see this in the right and left sides of the 
 body varying in the same manner; in the front and hind 
 legs, and even in the jaws and limbs, varying together, 
 for the lower jaw is believed by some anatomists to be 
 homologous with the limbs. These tendencies, I do not 
 doubt, may be mastered more or less completely by natural 
 selection; thus a family of stags once existed with an 
 antler only on one side; and if this had been of any great 
 use to the breed, it might probably have been rendered per¬ 
 manent by selection. 
 
 Homologous parts, as has been remarked by some authors, 
 tend to cohere; this is often seen in monstrous plants: 
 and nothing is more common than the union of homolo¬ 
 gous parts in normal structures, as in the union of the 
 
CORRELATED VARIATION, 
 
 13 ? 
 
 petals into a tube. Hard parts seem to affect the form of 
 adjommg soft parts; it is believed by some authors that 
 with birds the diversity in the shape of the pelvis causes 
 the remarkable diversity in the shape of their kidneys. 
 Otheis believe that the shape of the pelvis in the human 
 n l { °™ er lnll uences by pressure the shape of the head of the 
 child. In snakes, according to Schlegel, the form of the 
 body and the manner of swallowing determine the position 
 an m/ orm ,°^ several of the most important viscera. 
 
 Ihe nature of the bond is frequently quite obscure. M. Is ,t 
 Geoffroy St. Hilaire has forcibly remarked that certain mal- 
 cqnformations frequently, and that others rarely, coexist 
 without our being able to assign any reason. What can 
 be more singular than the relation in cats between com¬ 
 plete whiteness and blue eyes with deafness, or between 
 the tortoise-shell color and the female sex; or in 
 pigeons, between their feathered feet and skin betwixt the 
 outer toes, or between the presence of more or less down on 
 the young pigeon when first hatched, with the future color 
 Jr 1 T or again, the relation between the hair and 
 
 the teeth m the naked Turkish dog, though here no doubt 
 homology comes into play? With respect to this latter 
 case of correlation, I think it can hardly be accidental that 
 the. two orders of mammals which are most abnormal in 
 their dermal covering, viz., cetacea (whales) and edentata 
 (aimadilloes, scaly ant-eaters, etc.), are likewise on the 
 whole the most abnormal in their teeth, but there are so 
 many exceptions to this rule, as Mr. Mivart has remarked, 
 that it has little value. 
 
 know of no case better adapted to show the importance 
 ot the laws of correlation and variation, independently of 
 utility, and therefore of natural selection, than that of the 
 aitterence between the outer and inner flowers in some 
 compositous and umbelliferous plants. Everyone is 
 familiar with the difference between the ray and central 
 florets of, for instance, the daisy, and this difference is 
 often accompanied with the partial or complete abortion of 
 the reproductive organs. But in some of these plants the 
 seeds also differ in shape and sculpture. These differences 
 have sometimes been attributed to the pressure of the in- 
 volucra on the florets, or to their mutual pressure, and the 
 shape of the seeds m the ray florets of some composite 
 
138 
 
 CORRELATED VARIATION. 
 
 countenances this idea; but with the umbelliferse it is by 
 no means, as Dr. Hooker informs me, the species with the 
 densest heads which most frequently differ m their inner 
 and outer flowers. It might have been thought that the 
 development of the ray-petals, by drawing nourishment 
 from the reproductive organs causes their aboition, but 
 this can hardly be the sole cause, for m some composite 
 the seeds of the outer and inner florets differ, without any 
 difference in the corolla. Possibly these seveial differ¬ 
 ences may be connected with the different flow of nutn- 
 ment toward the central and external flowers. We know, 
 at least, that with irregular flowers those nearest to the 
 axis are most subject to peloria, that is to become abnormally 
 symmetrical. I may add, as an instance of this fact, and 
 as a striking case of correlation, that in many pelargoniums 
 the two upper petals in the central flower of the truss often 
 lose their patches of darker color; and when this occurs, 
 the adherent nectary is quite aborted, the central flower 
 thus becoming peloric or regular. When the color is 
 absent from only one of the two upper petals, the nectary 
 is not quite aborted but is much shortened. 
 
 With respect to the development of the corolla, bpren- 
 gel’s idea that the ray-florets serve to attract insects, whose 
 agency is highly advantageous, or necessary for the fertili¬ 
 zation of these plants, is highly probable; and if so, nat- 
 ural selection may have come into play. But with respect 
 to the seeds, it seems impossible that their differences m 
 shape, which are not always correlated with any difference 
 in the corolla, can be in any way beneficial; yet m the um¬ 
 belliferse these differences are of such apparent importance 
 
 __the seeds being sometimes orthospermous in the exterior 
 
 flowers and ccelospermous in the central flowers—that the 
 elder De Candolle founded his main divisions in the order 
 on such characters. Hence modifications of structure, 
 viewed by systematists as of high value, may he who y 
 due to the laws of variation and correlation, without 
 being, as far as we can judge, of the slightest service to the 
 
 S ^Ve may often falsely attribute to correlated variation 
 structures which are common to whole groups of species, 
 and which in truth are simply due to inheritance; for an 
 ancient progenitor may have acquired through natuiai 
 
COMPENSATION AND ECONOMY OF GROWTH. 139 
 
 selection some one modification in structure, and, after 
 thousands of generations, some other and independent 
 modification; and these two modifications, having been 
 transmitted to a whole group of descendants with diverse 
 habits, would naturally be thought to be in some necessary 
 manner correlated. Some other correlations are apparently 
 due to the manner in which natural selection can alone 
 act. For instance, Alph. de Candolle has remarked that 
 winged seeds are never found in fruits which do not open- 
 1 should explain this rule by the impossibility of seeds 
 gradually becoming winged through natural selection, 
 unless the capsules were open; for in this case alone could 
 the seeds, which were a little better adapted to be wafted 
 
 by the wind, gain an advantage over others less well fitted 
 lor wide dispersal. 
 
 COMPENSATION - AND ECONOMY OF GROWTH. 
 
 The elder Gfeoffroy and Goethe propounded, at about the 
 same time, their law of compensation or balancement of 
 growth; or, as Goethe expressed it, “in order to spend on 
 one side, nature is forced to economize on the other side.” 
 1 think this holds true to a certain extent with our domes¬ 
 tic productions: if nourishment flows to one part or organ 
 m excess, it rarely flows, at least in excess, to another part: 
 lius it is difficult to get a cow to give much milk and to 
 fatten readily. The same varieties of the cabbage do not 
 yieid abundant and nutritious foliage and a copious supply 
 of oil-bearing seeds. # When the seeds in our fruits become 
 atrophied, the fruit itself gains largely in size and quality. 
 In our poultry, a large tuft of feathers on the head is gen-✓ 
 erally accompanied by a diminished comb, and a large 
 beard by diminished wattles. With species in a state of 
 nature it can hardly be maintained that the law is of uni- 
 vmsal application; but many good observers, more espe¬ 
 cially botanists, believe in its truth. I will not, however 
 here give any instances, for I see hardly any way of distin¬ 
 guishing between the effects, on the one hand, of a part 
 Ging largely developed through natural selection and 
 another and adjoining part being reduced by the same pro¬ 
 cess or oy disuse, and, on the other hand, the actual with¬ 
 drawal of nutriment from one part owing to the excess of 
 growth in. another and adjoining part. 
 
1 40 MULTIPLE AND R UDIMENTAR T 
 
 I suspect, also, that some of the cases of compensation 
 which have been advanced, and likewise some other facts, 
 may be merged under a more general principle, namely, 
 that natural selection is continually trying to econo¬ 
 mize every part of the organization. If under changed 
 conditions of life a structure, before useful, becomes less 
 useful, its diminution will be favored, for it will profit the 
 individual not to have its nutriment wasted m building up 
 a useless structure. I can thus only understand a fact with 
 which I was much struck when examining cirnpedes, and 
 of which many analogous instances could be given: namely, 
 that when a cirripede is parasitic within another cirnpede 
 and is thus protected, it loses more or less completely its 
 own shell or carapace. This is the case with the ma.e 
 Ibla, and in a truly extraordinary manner with the 1 roteo- 
 lepas: for the carapace in all other cirnpedes consists ot 
 the three highly important anterior segments of the head 
 enormously developed, and furnished with great nerves 
 and muscles; but in the parasitic and protected Jrioteole- 
 pas, the whole anterior part of the head is reduced to the 
 merest rudiment attached to the bases of the piehensilo 
 antennae. Now the saving of a large and complex struc¬ 
 ture, when rendered superfluous, would be a decided ad¬ 
 vantage to each successive individual of the species; for m 
 the struggle for life to which every animal is exposed, each 
 would have a better chance of supporting itself, by less 
 
 nutriment being wasted. , . ,, , 
 
 Thus, as I believe, natural selection will tend m the long 
 run to reduce any part of the organization, as soon as it 
 becomes, through changed habits, superfluous, without by 
 any means causing some other part to be largely devel¬ 
 oped in a corresponding degree. And conversely, that 
 natural selection may perfectly well succeed in laigely de¬ 
 veloping an organ without requiring as a necessary com¬ 
 pensation the reduction of some adjoining part. 
 
 MULTIPLE, RUDIMENTARY, AND LOWLY-ORGANIZED STRUC¬ 
 TURES ARE VARIABLE. 
 
 It seems to be a rule, as remarked by Is. Geoffroy Sfc. 
 Hilaire, both with varieties and species, that when any part 
 or organ is repeated many times in the same individual (as 
 
STRUCTURES VARIABLE. 141 
 
 the vertebrae in snakes, and the stamens in polyandrous 
 flowers) the number is variable; whereas the same part or 
 organ, when it occurs in lesser numbers, is constant. The 
 same author, as well as some botanists, have further re¬ 
 marked that multiple parts are extremely liable to vary 
 in structure. As ‘‘vegetable repetition," to use Professor 
 . en s expression, is a sign of low organization, the fore- 
 gomg statements accord with the common opinion of natu¬ 
 ralists, that beings which stand low in the scale of nature 
 are more variable than those which are higher. I presume 
 that lowness here means that the several parts of the 
 oiganization have been but little specialized for particular 
 functions; and as long as the same part has to perform 
 diversified work, we can perhaps see why it should remain 
 variable, that is, why natural selection should not have 
 preserved or rejected each little deviation of form so care- 
 uny as when the part has to serve for some one special 
 purpose. In the same way that a knife which has to cut 
 all sorts of things may be of almost any shape; while a tool 
 for some particular purpose must be of some particular 
 shape. .Natural selection, it should never be forgotten 
 can act solely through and for the advantage of each being* 
 Rudimentary parts, as is generally admitted, are apt to 
 be highly vanable. We shall have to recur to this subject* 
 and I will here only add that their variability seems to re¬ 
 sult from their uselessness, and consequently from natural 
 
 selection having had no power to check deviations in their 
 structure. 
 
 A PART DEVELOPED IN ANY SPECIES IN AN EXTRAORDI¬ 
 NARY DEGREE OR MANNER, IN COMPARISON WITH THE 
 SAME PART IN ALLIED SPECIES, TENDS TO BE HIGHLY 
 VARIABLE. 
 
 Several years ago I was much struck by a remark to the 
 above effect made by Mr. Waterhouse. Professor Owen, 
 also, seems to have come to a nearly similar conclusion! 
 It is hopeless to attempt to convince any one of the truth 
 of the above proposition without giving the long array of 
 facts which I have collected, and which cannot possibly bo 
 
 I n "1 . , I can only state my conviction that it is 
 a lute of high generality. I am aware of several causes of 
 
143 UNUSUALLY DEVELOPED PARTS 
 
 error, but I hope that I have made due allowances fot 
 them. It should be understood that the rule by no means 
 applies to any part, however unusually developed, unless 
 it be unusually developed in one species or m a few species 
 in comparison with the same part in many closely allied 
 species/ Thus, the wing of the bat is a most abnormal 
 structure in the class of mammals, but the rule would not 
 apply here, because the whole group of bats possesses 
 wings; it would apply only if some one species had wings 
 developed in a remarkable manner m comparison with the 
 other species of the same genus. The rule applies very 
 strongly in the case of secondary sexual characters, when 
 displayed in any unusual manner. The term, secondary 
 sexual* characters, used by Hunter, relates to characters 
 which are attached to one sex, but are not directly con¬ 
 nected with the act of reproduction. The rule applies to 
 males and females; but more rarely to the females, as they 
 seldom offer remarkable secondary sexual characters. 1 ie 
 rule being so plainly applicable in the case of secondary 
 sexual characters, may be due to the great variability of 
 these characters, whether or not displayed m any unusual 
 manner—of which fact I think there can be little doubt. 
 But that our rule is not confined to secondary sexual char¬ 
 acters is clearly shown in the case of hermaphrodite cirn- 
 pedes; I particularly attended to Mr. Waterhouse s remark, 
 while investigating this order, and I am fully convinced 
 that the rule almost always holds good. 1 shall, m a 
 future work, give a list of all the more remarkable cases. 
 
 I will here give only one, as it illustrates the rule in its 
 largest application. The opercular valves of sessile cirn- 
 pedes (rock barnacles) are, in every sense of the word, very 
 important structures, and they differ extremely little even 
 in distinct genera; but in the several species of one genus, 
 Pyrgoma, these valves present a marvellous amount ot 
 diversification; the homologous valves, in the different 
 species being sometimes wholly unlike m shape; and the 
 amount of variation in the individuals of the same species 
 is so great that it is no exaggeration to state tnat the 
 varieties of the same species differ more from each other in 
 the characters derived from these important organs, than 
 do the species belonging to other distinct genera. 
 
 As with birds the individuals of the same species, m- 
 
HIGHLY VARIABLE. 
 
 143 
 
 habiting the same country, vary extremely little, I have 
 particularly attended to them; and the rule certainly seems 
 to hold good m this class. I cannot make out that it 
 applies to > plants, and this would have seriously shaken mv 
 belief m its truth had not the great variability in plants 
 made it particularly difficult to compare their relative de¬ 
 grees of variability. 
 
 When we see any part or organ developed in a remark¬ 
 able degree or manner in a species, the fair presumption is 
 that it is of high importance to that species: nevertheless 
 
 1S , , In , , th , IS case eminently liable to variation. Why 
 should this be so? On the view that each species has been 
 independently created, with all its parts as we now see 
 them, 1 can see no explanation. But on the view that 
 groups of species are descended from some other species 
 and have been modified through natural selection, I think 
 we can obtain some light. First let me make some pre¬ 
 liminary remarks. If, in our domestic animals, any part 
 °' te "I 110 ’ 6 an ™ a l be neglected, and no selection be ap¬ 
 plied, that part (for instance, the comb in the Dorking 
 fowl) or the whole breed will cease to have a uniform 
 character: and the breed may be said to be degenerating. 
 In rudimentary organs, and in those which have been but 
 little specialized for any particular purpose, and perhaps 
 m polymorphic groups, we see a nearly parallel case; for in 
 such cases natural selection either has not or cannot have 
 come into full play, and thus the organization is left in a 
 fluctuating condition. But what here more particularly 
 concerns us is, that those points in our domestic animals, 
 which at the present time are undergoing rapid change bv 
 continued selection are also eminently liable to variation. 
 .Look at the individuals of the same breed of the pigeon 
 and see what a prodigious amount of difference there is in 
 the beaks of tumblers, in the beaks and wattle of carriers 
 in the carriage and tail of fantails, etc., these being the 
 points now mainly attended to by English fanciers. Even 
 in the same sub-breed, as in that of the short-faced tumbler 
 , 1S notoriously difficult to breed nearly perfect birds, many 
 departing widely from the standard. There may truly be 
 said to be a constant struggle going on between, on the 
 one hand, the tendency to reversion to a less perfect state, 
 as well as an innate tendency to new variations, and, on 
 
144 UNUSUALLY DEVELOPED PARTS 
 
 the other hand, the power of steady selection to keep L 2 
 breed true. In the long run selection gains the day, 
 and we do not expect to fail so completely as to breed a 
 bird as coarse as a common tumbler pigeon from a good 
 short-faced strain. But as long as selection is lapidly 
 going on, much variabilit} 7 in the parts undergoing modi¬ 
 fication may always be expected. 
 
 Now let us turn to nature. When a part has been 
 developed in an extraordinary manner in any one species, 
 compared with the other species of the same genus, we 
 may conclude that this part has undergone an extraordinary 
 amount of modification since the period when the several 
 species branched off from the common progenitor of the 
 o’enus. This period will seldom be remote in any extreme 
 degree, as species rarely endure for more than one geolog¬ 
 ical period. An extraordinary amount, of modification 
 implies an unusually large and long-continued amount of 
 variability, which has continually been accumulated by 
 natural selection for the benefit of the species. But as the 
 variability of the extraordinarily developed part or organ 
 has been so great and long-continued, within a period 
 not excessively remote, we might, as a general rule, still 
 expect to find more variability in such paits than in 
 other parts of the organization which have remained for 
 a much longer period nearly constant. And this, I am 
 convinced, is the case. That the struggle between nat¬ 
 ural selection on the one hand, and the tendency to 1 ever¬ 
 sion and variability on the other hand, will in the course 
 of time cease5 and that the most abnormally developed 
 organs may be made constant, I see no reason to doubt. 
 Hence, when an organ, however abnormal it may be, has 
 been transmitted in approximately the same condition to 
 many modified descendants, as in the case of the wing of 
 the bat, it must have existed, according to our theory, for 
 an immense period in nearly the same state \ and thus it 
 has come not to be more variable than any other structure. 
 It is only in those cases in which the modification has been 
 comparatively recent and extraordinarily great that we 
 ouo-ht to find the generative variability, as it may be 
 called, still present in a high degree. For in this case the 
 variability will seldom as yet have been fixed by the con¬ 
 tinued selection of the individuals varying in the required 
 

 HIGHLY VARIABLE. 
 
 145 
 
 manner and degree, and by tlie continued rejection of those 
 tending to revert to a former and less modified condition. 
 
 SPECIFIC CHARACTERS MORE VARIABLE THAN GENERIC 
 
 CHARACTERS. 
 
 The principle discussed under the last heading may be 
 applied to our present subject. It is notorious that spe¬ 
 cific characters are more variable than generic. To ex¬ 
 plain by a simple example what is meant: if in a large 
 genus of plants some species had blue flowers and some 
 had red, the color would be only a specific character, and 
 no one would be surprised at one of the blue species vary¬ 
 ing into red, or conversely; but if all the species had blue 
 flowers, the color would become a generic character, and 
 its variation would be a more unusual circumstance. I 
 have chosen this example because the explanation which 
 most naturalists would advance is not here applicable, 
 namely, that specific characters are more variable than gen¬ 
 eric, because they are taken from parts of less physiological 
 importance than those commonly used for classing genera. 
 
 I believe this explanation is partly, yet only indirectly, 
 true; I shall, however, have to return to this point in the 
 chapter on Classification. It would be almost superfluous 
 to adduce evidence in support of the statement, that ordi- * 
 nary specific characters are more variable than generic; 
 but with respect to important characters, I have repeatedly 
 noticed in works on natural history, that when an author 
 remarks with surprise that some important organ or part, 
 which is generally very constant throughout a large group 
 of species, differs considerably in closely allied species, it is 
 often variable in the individuals of the same species. And 
 this fact shows that a character, which is generally of gen¬ 
 eric value, when it sinks in value and becomes only of spe¬ 
 cific value, often becomes variable, though its physiological 
 importance may remain the same. Something of the same 
 kind applies to monstrosities: at least Is. Geoffrov St. 
 Hilaire apparently entertains no doubt, that the more an 
 organ normally differs in the different species of the same 
 group, the more subject it is to anomalies in the individ¬ 
 uals. 
 
 On the ordinary view of each species having been inde- 
 
146 SECONDARY SEXUAL CHARACTERS VARIABLE. 
 
 pendently created, why should that part of the struc¬ 
 ture, which differs from the same part in other 
 independently created species of the same genus, be more 
 variable than those parts which are closely alike in the 
 several species? I do not see that any explanation can be 
 given. But on the view that species are only strongly 
 marked and fixed varieties, we might expect often to find 
 them still continuing to vary in those parts of their struc¬ 
 ture which have varied within a moderately recent period, 
 and which have thus come to differ. Or to state the case 
 in another manner: the points in which all the species of a 
 genus resemble each other, and in which they differ from 
 allied genera, are called generic characters; and these char¬ 
 acters may be attributed to inheritance from a common 
 progenitor, for it can rarely have happened that natural selec¬ 
 tion will have modified several distinct species, fitted to 
 more or less widely different habits, in exactly the same 
 manner: and as those so-called generic characters have been 
 inherited from before the period when the several species 
 first branched off from their common progenitor, and sub¬ 
 sequently have not varied or come to differ in any degree, 
 or only in a slight degree, it is not probable that they 
 should vary at the present day. On the other hand, the 
 points in which species differ from other species of the 
 same genus are called specific characters; and as these 
 specific characters have varied and come to differ since the 
 period when the species branched off from a common 
 progenitor, it is probable that they should still often be in 
 some degree variable—at least more variable than those 
 parts of the organization which have for a very long period 
 remained constant. 
 
 SECONDARY SEXUAL CHARACTERS VARIABLE. 
 
 1 think it will be admitted by naturalists, without my 
 entering on details, that secondary sexual characters are 
 highly variable. It will also be admitted that species of 
 the same group differ from each other more widely in their 
 secondary sexual characters, than in other parts of their 
 organization: compare, for instance, the amount of differ¬ 
 ence between the males of gallinaceous birds, in which 
 secondary sexual characters are strongly displayed, with 
 
SECONDARY SEXUAL CHARACTERS VARIABLE. U7 
 
 nflhZZ °f dif ? e r®° ce between the females. The cause 
 . , gmal variability of these cliaracters is not mani 
 fest; but we can see why they should not have been Z- 
 i end as constant and uniform as others, for they are ac 
 cumulated by sexual selection, which is less X Z Z 
 action than ordinary selection, as it does not entail death 
 
 WwZ g ir S fe ' Vel ' ofe P ri “g to «« less favored males’ 
 Whatever the cause may be of the variability of secondary 
 
 tfon will h hTve e had aS a* h? J *"* hig Z variabfe > sexual selec- 
 non will Have had a wide scope for action, and mav thus 
 
 have succeeded m giving to the species of ihe sameCr 
 respect? 1, am ° Unt of dlfierenc e in these than in otlJr 
 
 . b ’ 3 a remarkable fact, that the secondary differences 
 between the two sexes of the same species are ZZX 
 displayed m the very same parts of the organization in 
 Of “hi B ftTf 188 -?/ tl;e Sa - me :Vns differ fro,teach othe 
 
 Of .his fact I will give in illustration the two first in 
 
 fZnZhnlVZts?° StaU f ? n . my list; and as the dif- 
 
 relation can hardly be accidentalVheT^ 1 natnr ^ th 2 
 
 S b "‘, “ ,lle Ei| s w »-*> "'«i- 
 
 nomber liK ^"tt tl7 “ 
 
 species. Again in the fossorial hymenoptera the neura° 
 
 because com motto la ° llaracter of , the highest importance, 
 the two sexes of the same SDeoio^ Qjv. t r i i i i 
 
 anterior antenna and by the fifth pa“ of legs “the snL fic 
 
 ffiSt'", principally given by these orfan^ 
 
 the BDMfe? of tfJ meanln « on vie «' : I look at all 
 V, I f V! ot the same genus as having as certainly 
 
 of miv ded fr ° m ac0mm °n progenitor, as have the two sexes 
 
 structare o/ P t e hT S- co Cons «<l«®Btly,.whatever part of the 
 
 nThZ'l'v 8 ’ TZ ? ria “ e > var.!timi 0 s r ’of 0 this°pah S wo e u a it 
 
 it highly probable, be taken advantage of by natural and 
 
14 8 distinct species present 
 
 sexual selection, in order to fit the several places in the 
 economy of nature, and likewise to fit the two sexes of the 
 same species to each other, or to fit the males to strugg e 
 with other males for the possession of the females. 
 
 Finally, then, I conclude that the greater variability of 
 specific characters, or those which distinguish species from 
 species than of generic characters, or those which aie pos¬ 
 sessed by all the species; that the frequent extreme yana- 
 bility of any part which is developed in a species in an 
 extraordinary manner in comparison with the same part in 
 its congeners; and the slight degree of vai lability < 
 part, however extraordinarily it may be developed, if it be 
 common to a whole group of species; that the great vai la¬ 
 bility of secondary sexual characters and then gicat dint 
 ence in closely allied species; that secondary sexual and 
 ordinary specific differences are generally displayed in the 
 same parts of the organization, are all principles closely 
 connected together. All being mainly due to the species 
 of the same group being the descendants of a common 
 progenitor, from whom they have inherited much in 
 common, to parts which have recently and largely varied 
 being more likely still to go on varying than parts whicn 
 have long been inherited and have not varied, to natmal 
 selection having more or less completely, according to tie 
 lapse of time, overmastered the tendency to reversion and 
 to further variability, to sexual selection being less ngi 
 than ordinary selection, and to variations m the same 
 parts having been accumulated by natural and sexual 
 selection, and having been thus adapted for secondaiy 
 sexual, and for ordinary purposes. 
 
 DISTINCT SPECIES PRESENT ANALOGOUS VARIATIONS, SO 
 
 THAT A VARIETY OF ONE SPECIES OFTEN ASSUMES A 
 
 CHARACTER PROPER TO AN ALLIED SPECIES, OR RE¬ 
 VERTS TO SOME OF THE CHARACTERS OF AN EARLY 
 
 PROGENITOR. 
 
 These propositions will be most readily understood by 
 looking; to our domestic races. The most distinct breeds 
 of the pigeon, in countries widely apart, present sub-varie¬ 
 ties with reversed feathers on the head, and with feathers 
 
ANALOGOUS VARIATIONS. 
 
 149 
 
 on the feet, characters not possessed by the aboriginal 
 rock-pigeon; these then are analogous variations in two or 
 more distinct races. The frequent presence of fourteen or 
 even sixteen tail-feathers in the pouter may be con¬ 
 sidered as a variation representing the normal structure of 
 another race, the fantail. I presume that no one will 
 doubt that all such analogous variations are due to the 
 several races of the pigeon having inherited from a common 
 parent the same constitution and tendency to variation,, 
 when acted on by similar unknown influences. In the 
 vegetable kingdom we have a case of analogous variation, 
 in the enlarged stems, or as commonly called roots, of the 
 Swedish turnip and ruta-baga, plants which several bot¬ 
 anists rank as varieties produced by cultivation from a 
 common parent: if this be not so, the case will then be one 
 of analogous variation in two so-called distinct species; and 
 to these a third may be added, namely, the common turnip. 
 According to the ordinary view of each species having been 
 independently created, we should have to attribute this 
 similarity in the enlarged stems of these three plants, not 
 to the vera causa of community of descent, and a conse¬ 
 quent tendency to vary in a like manner, but to three 
 separate yet closely related acts of creation. Many similar 
 cases of analogous variation have been observed by Naudir 
 in the great gourd family, and by various authors in or J 
 cereals. Similar cases occurring with insects under ns 
 ural conditions have lately been discussed with much abii 
 ity by Mr. Walsh, who has grouped them under his law of 
 equable variability. 
 
 With pigeons, however, we have another case, namely, 
 the occasional appearance in all the breeds, of slaty-blue 
 birds with two black bars on the wings, white loins, a bar 
 at the end of the tail, with the outer feathers externallv 
 edged near their basis with white. As all these marks are 
 characteristic of the parent rock-pigeon, I presume that no 
 one will doubt that this is X 'a case of reversion, and not of a 
 new yet analogous variation appearing in the several 
 breeds. We may, I think, confidently come to this con¬ 
 clusion, because, as we have seen, these colored marks are 
 eminently liable to appear in the crossed offspring of two 
 distinct and differently colored breeds; and in this case 
 there is nothing in the external conditions of life to cause 
 
150 
 
 DISTINCT SPECIES PRESENT 
 
 the reappearance of the slaty-bine, with the several marks, 
 beyond the influence of the mere act of crossing on the 
 
 laws of inheritance. ...... , 
 
 No doubt it is a very surprising fact that characters 
 
 should reappear after having been lost for many, probably 
 for hundreds of generations. But when a breed has been 
 crossed only once by some other breed, the offspring occa¬ 
 sionally show for many generations a tendency to revert m 
 character to the foreign breed—some say, for a dozen or even 
 a score of generations. After twelve generations, the pro¬ 
 portion of blood, to use a common expression, from one 
 ancestor, is only one in 2048; and yet, as we.see, it is gen¬ 
 erally believed that a tendency to reversion is retained by 
 this remnant of foreign blood. In a breed which has not 
 been crossed, but in which both parents have lost some 
 character which their progenitor possessed, the tendency, 
 whether strong or weak, to reproduce the lost character 
 might, as was formerly remarked, for all that we can see to 
 the 3 contrarv, be transmitted for almost any number of gen¬ 
 erations. When a character which has been lost m a breed^ 
 reappears after a great number of generations, the most 
 probable hypothesis is, not that one individual suddenly 
 takes after an ancestor removed by some hundred genera¬ 
 tions, but that in each successive generation the character 
 in question has been lying latent, and at last, under 
 unknown favorable conditions, is developed. With the 
 barb-pigeon, for instance, which very rarely produces a 
 blue bird, it is probable that there is a latent tendency in 
 each generation to produce blue plumage. The abstract 
 improbability of such a tendency being transmitted through 
 a vast number of generations, is not greater, than that ot 
 quite useless or rudimentary organs being similarly trans¬ 
 mitted. A mere tendency to produce a rudiment is indeed 
 
 sometimes thus inherited. , 
 
 As all the species of the same genus, are.supposed to be 
 descended from a common progenitor, it might beexpecte ^ 
 that they would occasionally vary in an analogous manner; 
 so that the varieties of two or more species would resemble 
 each other, or that a variety of one species would resemble 
 in certain characters another and distinct species, this 
 other species being, according to our view, only a ^el- 
 marked and permanent variety. But characters exclusively 
 
ANALOGOUS VARIATIONS. 151 
 
 due to analogous variation would probably be of an unim¬ 
 portant nature, for the preservation of all functionally im¬ 
 portant characters will have been determined through 
 natural selection, m accordance with the different habits 
 of the species. It might further be expected that the 
 species of the same genus would occasionally exhibit rever¬ 
 sions to long-lost characters. As, however, we do not 
 know the common ancestor of any natural group, we 
 cannot distinguish between reversionary and analogous 
 characters. If, for instance, we did not know that the 
 parent rock-pigeon was not feather-footed or turn-crowned 
 we could not have told, whether such characters in our 
 domestic breeds were reversions or only analogous varia¬ 
 tions; but we might have inferred that the blue color was 
 a case of reversion from the number of the markings 
 which are correlated with this tint, and which would not 
 probaby have all appeared together from simple variation. 
 More especially we might have inferred this from the blue 
 color and the several marks so often appearing when dif¬ 
 ferently colored breeds are crossed. Hence, although under 
 nature it must generally be left doubtful, what lases are 
 reversions to formerly existing characters, and what are 
 new but analogous variations, yet we ought, on our theory, 
 sometimes to find the varying offspring of a species assum 
 ing characters which are already present in other members 
 of the same group. And this undoubtedly is the case. 
 
 he difficulty in distinguishing variable species is largely 
 due to the varieties mocking, as it were, other species of 
 the same genus. A considerable catalogue, also, could be 
 given of forms intermediate between two other forms 
 which themselves can only doubtfully be ranked as species’; 
 and this shows, unless all these closely allied forms be con¬ 
 sidered as independently created species, that they have in 
 varing assumed some of the characters of the others. But 
 tlie best evidence of analogous variations is afforded by 
 parts or organs which are generally constant in character 
 but which occasionally vary so as to resemble, in some 
 degree, the same part or organ in an allied species. I have 
 collected a long list of such cases; but here, as before, I lie 
 under the great disadvantage of not being able to give 
 wiem. I can only repeat that such cases certainly occur, 
 ana seem to me very remarkable. 
 
152 
 
 DISTINCT SPECIES PRESENT 
 
 I will however, give one curious and complex case, not 
 indeed as affecting any important character, but from 
 occurring in several species of the same genus, partly 
 under domestication and partly under nature. It is a case 
 almost certainly of reversion. The ass sometimesi has 
 very distinct tranverse bars on its legs, like those on 
 the^leas of the zebra. It has been asserted that these are 
 plainest in the foal, and, from inquiries which I have 
 bade I believe this to be true. The stripe on the shoulder is 
 sometimes double, and is very variable m length and outline 
 A white ass, but not an albino, has been descubed without 
 either spinal or shoulder stripe; and these stripes are some¬ 
 times very obscure, or actually quite lost, m dark-colored 
 •isses The koulan of Pallas is said to have been seen with a 
 double shoulder-stripe. Mr. Blyth has seen a specimen 
 of the hemionus with a distinct shouldei-stupe, » 
 
 it properly has none; and I have been informed by Colonel 
 Poole that the foals of this species are generally striped oil the 
 legs and faintly on the shoulder. The quagga, though so 
 plainly barred like a zebra over the body, is without ba.s 
 on the legs; but Dr. Gray has figured one specimen with 
 very distinct zebra-like bars on the hocks. 
 
 With respect to the horse, I have collected cases m 
 England of the spinal stripe in horses of the most distinct 
 breeds and of all colors; transverse bars om the legs are not 
 rare in duns, mouse duns, and in one instance in a chest¬ 
 nut; a faint shoulder-stripe may sometimes be seen m 
 duns, and I have seen a trace in a bay hoise. My -on 
 made a careful examination and sketch for me of a dun 
 Belgian cart-horse with a double stripe on each shoulder 
 and with leg-stripes. I have myself seen a dun Devon¬ 
 shire pony, and a small dun Welsh pony has been carefully 
 described to me, both with three parallel stripes on each 
 
 In the northwest part of India the Kattywar breed of 
 horses is so generally striped, that, as I hear from Colon® 
 Poole, who examined this breed for the Indian Govern¬ 
 ment, a horse without stripes is not considered as purely 
 bred. The spine is always striped, the legs are generally 
 barred, and the shoulder-stripe, which is sometimes double 
 and sometimes treble, is common; the side of the face 
 moreover, is sometimes sb-lned. The stripes are often 
 
ANALOGOUS VARIATIONS. 
 
 153 
 
 plainest in the foal, and sometimes quite disappear in old 
 horses. Colonel Poole has seen both gray and bay Katty- 
 war horses striped when first foaled. I have also reason to 
 suspect, from information given me by Mr. W. W. Ed¬ 
 wards, that with the English race-horse the spinal stripe is 
 much commoner in the foal than in the full-grown animal. 
 I have myself recently bred a foal from a bay mare (off¬ 
 spring of a Turkoman horse and a Flemish mare) by a bay 
 English race-horse. This foal, when a week old, was 
 marked on its hinder quarters and on its forehead with 
 numerous very narrow, dark, zebra-like bars, and its legs 
 were feebly striped. All the stripes soon disappeared com¬ 
 pletely. Without here entering on further details I may 
 state that I have collected cases of leg and shoulder-stripes 
 in horses of very different breeds in various countries from 
 Britain to Eastern China, and from Norway in the north 
 to the Malay Archipelago in the south. In all parts of the 
 world these stripes occur far oftenest in duns and mouse- 
 duns. By the term dun a large range of color is included, 
 from one between brown and black to a close approach to 
 cream color. 
 
 I am aware that Colonel Hamilton Smith, who has writ¬ 
 ten on this subject, believes that the several breeds of the 
 horse are descended from several aboriginal species, one of 
 which, the dun, was striped; and that the above-described 
 appearances are all due to ancient crosses with the dun 
 stock. But this view may be safely rejected, for it is 
 highly improbable that the heavy Belgian cart-horse, 
 Welsh ponies, Norwegian cobs, the lanky Kattywar race, 
 etc., inhabiting the most distant parts of the world, 
 should all have been crossed with one supposed aboriginal 
 stock. 
 
 Now let us turn to the effects of crossing the several 
 species of the horse genus. Kollin asserts that the com¬ 
 mon mule from the ass and horse is particularly apt to 
 have bars on its legs; according to Mr. Gosse, in certain 
 parts of the United States, about nine out of ten mules 
 have striped legs. I once saw a mule with its legs so much 
 striped that any one might have thought that it was a 
 hybrid zebra; and Mr. W. 0. Martin, in his excellent 
 treatise on the horse, has given a figure of a similar mule. 
 In four colored drawings, which I have seen, of hybrids 
 
154 
 
 DISTINCT SPECIES PRESENT 
 
 between the ass and zebra, the legs were much more plainly 
 barred than the rest of the body; and in one of them there 
 was a double shoulder-stripe. In Lord Morton’s famous 
 hybrid, from a chestnut mare and male quagga, the hybrid 
 and even the pure offspring subsequently produced from 
 the same mare by a black Arabian sire, were much more 
 plainly barred across the legs than is even the pure quagga. 
 Lastly, and this is another most remarkable case, a hybrid 
 has been figured by Dr. Gray (and he informs me that he 
 knows of a second case) from the ass and the hemionus; 
 and this hybrid, though the ass only occasionally has stripes 
 on his legs and the hemionus has none and has not even a 
 shoulder-stripe, nevertheless had all four legs barred, and 
 had three short shoulder-stripes, like those on the dun 
 Devonshire and Welsh ponies, and even had some zebra- 
 like stripes on the sides of its face. With respect to this 
 last fact, I was so convinced that not even a stripe of color 
 appears from what is commonly called chance, that I was 
 led solely from the occurrence of the face-stripes on this 
 hybrid from the ass and hemionus to ask Colonel Poole 
 whether such face-stripes ever occurred in the eminently 
 striped Kattywar breed of horses, and was, as we have 
 seen, answered in the affirmative. 
 
 What now are we to say to these several facts? We see 
 several distinct species of the horse genus becoming, by 
 simple variation, striped on the legs like a zebra, or striped 
 on the shoulders like an ass. In the horse we see this 
 tendency strong whenever a dun tint appears—a tint which 
 approaches to that of the general coloring of the other 
 species of the genus. The appearance of the stripes is not 
 accompanied by any change of form, or by any other new 
 character. We see this tendency to become striped most 
 strongly displayed in hybrids from between several of the 
 most distinct species. Now observe the case of the several 
 breeds of pigeons: they are descended from a pigeon (in¬ 
 cluding two or three sub-species or geographical races) of 
 a bluish color, with certain bars and other marks; and 
 when any breed assumes by simple variation a bluish tint, 
 these bars and other marks invariably reappear; but with¬ 
 out any other change of form or character. When the 
 oldest and truest breed of various colors are crossed, we see 
 a strong tendency for the blue tint and bars and marks 
 
ANALOGOUS VARIATIONS. 
 
 155 
 
 to reappear in the mongrels. I have stated that the 
 most probable hypothesis to account for the reappear¬ 
 ance of very ancient characters, is —that there is a 
 tendency in the young of each successive generation 
 to produce the long-lost character, and that this ten¬ 
 dency, from unknown causes, sometimes prevails. And 
 we have just seen that in several species of the horse 
 genus the stripes are either plainer or appear more com¬ 
 monly in the young than in the old. Call the breeds of 
 pigeons, some of which have bred true for centuries, 
 species; and how exactly parallel is the case with that of 
 the species of the horse genus! For myself, I venture con¬ 
 fidently to look back thousands on thousands of genera¬ 
 tions, and I see an animal striped like a zebra, but perhaps 
 otherwise very differently constructed, the common parent 
 of our domestic horse (whether or not it be descended 
 from one or more wild stocks) of the ass, the hemionus, 
 quagga and zebra. 
 
 He who believes that each equine species was independ¬ 
 ently created, will, I presume, assert that each species has 
 been created with a tendency to vary, both under nature 
 and under domestication, in this particular manner, so as 
 often to become striped like the other species of the genus; 
 and that each has been created with a strong tendency, 
 when crossed with species inhabiting distant quarters of 
 the world, to produce hybrids resembling in their stripes, 
 not their own parents, but other species of the genus. To 
 admit this view is, as it seems to me, to reject a real for an 
 unreal, or at least for an unknown cause. It makes the 
 works of God a mere mockery and deception; I would 
 almost as soon believe with the old and ignorant cosmo- 
 gonists, that fossil shells had never lived, but had been 
 created in stone so as to mock the shells living on the sea¬ 
 shore. 
 
 SUMMARY. 
 
 Our ignorance of the laws of variation is profound. 
 Not in one case out of a hundred can we pretend to assign 
 any reason why this or that part has varied. But when¬ 
 ever we have the means of instituting a comparison, the 
 same laws appear to have acted in producing the lesser dif- 
 
156 
 
 SUMMARY. 
 
 ferences between varieties of the same species, and the 
 greater diffences between species of the same genus. Changed 
 conditions generally induce mere fluctuating variability, 
 but sometimes they cause direct and definite effects, and 
 these may become strongly marked in the course of tune, 
 though we have not sufficient evidence on this head. 
 Habit in producing constitutional peculiarities, and use m 
 strengthening, and disuse in weakening and diminishing 
 organs, appear in many cases to have been potent m their 
 effects. Homologous parts tend to vary m the same man¬ 
 ner, and homologous parts tend to cohere. Modifications 
 in hard parts and in external parts sometimes affect softei 
 and internal parts. When one part is largely developed, per¬ 
 haps it tends to draw nourishment from the adjoining paits, 
 and every part of the structure which can be saved without 
 detriment will be saved. Changes of structure at an early 
 age may affect parts subsequently developed; and mam 
 cases of correlated variation, the nature of which we are 
 unable to understand, undoubtedly occur. Mutiple parts 
 are variable in number and in structure, perhaps arising 
 from such parts not having been closely specialized for any 
 particular function, so that their modifications ha\ e not been 
 closely checked by natural selection. . It follows probably 
 from this same cause, that organic beings low m the scale 
 are more variable than those standing higher m the scale, 
 and which have their whole organization more specialized. 
 Rudimentary organs, from being useless, are not regulated by 
 natural selection, and hence ,'je variable. Specific characters 
 —that is, the characters which have come to differ since 
 the several species of the same genus branched off from 
 a common parent—are more variable than generic char¬ 
 acters. or those which have long been inherited, and have 
 not differed within this same period. In these remarks we 
 have referred to special parts or organs being still vari¬ 
 able, because they have recently varied and thus come to 
 
 differ; but we have also seen in the second chapter that the 
 same principle applies to the whole individual; for in a 
 district where many species of a genus are 
 that is, where there has been much former vanation ana 
 differentiation, or where the manufactory of new specific 
 forms has been actively at work—in that district and 
 among these species, we now find, on an average, most 
 
SUMMARY. 
 
 15 ? 
 
 varieties. Secondary sexual characters are highly variable, 
 and such characters differ much in the species of the same 
 group. Variability in the same parts of the organization 
 has generally been taken advantage of in giving secondary 
 sexual differences to the two sexes of the same species, and 
 specific differences to the several species of the same genus. 
 Any part or organ developed to an extraordinary size or in 
 an extraordinary manner, in comparison with the same 
 part or organ in the allied species, must have gone through 
 an extraordinary amount of modification since the genus 
 arose; and thus we can understand why it should often 
 still be variable in a much higher degree than other parts; 
 for variation is a long-continued and slow process, and 
 natural selection will in such cases not as yet have had 
 time to overcome the tendency to further variability and 
 to reversion to a less modified state. But when a species 
 with an extraordinarily developed organ has become the 
 parent of many modified descendants—which on our view 
 must be a very slow process, requiring a long lapse of time 
 —in this case, natural selection has succeeded in giving a 
 fixed character to the organ, in however extraordinary a 
 manner it may have been developed. Species inheriting 
 nearly the same constitution from a common parent, and 
 exposed to similar influences, naturally tend to present 
 analogous variations, or these same species may occasionally 
 revert to some of the characters of their ancient progeni¬ 
 tors. Although new and important modifications may not 
 arise from reversion and analogous variation, such modi¬ 
 fications will add to the beautiful and harmonious diver¬ 
 sity of nature. 
 
 Whatever the cause may be of each slight difference be¬ 
 tween the offspring and their parents—and a cause for 
 each must exist—we have reason to believe that it is the 
 steady accumulation of beneficial differences which has 
 given rise to all the more important modifications of struc¬ 
 ture in relation to the habits of each species. 
 
158 
 
 DIFFICULTIES OF WE THEORY. 
 
 4 
 
 CHAPTER VI. 
 
 DIFFICULTIES OF THE THEORY. 
 
 Difficulties of the theory of descent with modification—Absence or 
 rarity of transitional varieties—Transitions in habits of life— 
 Diversified habits in the same species—Species with habits 
 widely different from those of their allies—Organs of extreme 
 perfection—Modes of transition—Cases of difficulty—Natura non 
 facit saltum—Organs of small importance—Organs not in all 
 cases absolutely perfect—The law of Unity of Type and of the 
 Conditions of * Existence embraced by the theory of Natural 
 Selection. 
 
 Long before the reader has arrived at this part of my 
 work, a crowd of difficulties will have occurred to him. 
 Some of them are so serious that to this day I can hardly 
 reflect on them without being in some degree staggered; 
 but, to the best of my judgment, the greater number are 
 only apparent, and those that are real are not, I think, 
 
 fatal to the theory. ’ 
 
 These difficulties and ejections may be classed under the 
 following heads: First, why, if species have descended from 
 other species by fine gradations, do we not everywhere see 
 innumerable transitional forms? Why k not all nature in 
 confusion, instead of the species being, as we see them, 
 
 well defined? .... _ 
 
 Secondly, is it possible that an animal having, tor 
 
 instance, the structure and habits of a bat, could ha\e been 
 formed by the modification of some other animal with 
 widely different habits and structure? Can we believe that 
 natural selection could produce, on the one hand, an organ 
 of trifling importance, such as the tail of a giraffe, which 
 serves as a fly-flapper, and, on the other hand, an oigan so 
 wonderful as the eye? 
 
 Thirdly, can instincts be acquired and modified through 
 natural selection? What shall we say to the instinct which 
 

 DIFFICULTIES OF THE THEORY. 159 
 
 leads the bee to make cells, and which has practically 
 anticipated the discoveries of profound mathematicians? 
 
 Fourthly, how can we account for species, when crossed, 
 being sterile and producing sterile offspring, whereas, 
 when varieties are crossed, their fertility is unimpaired? 
 
 The two first heads will here be discussed; some miscel¬ 
 laneous objections in the following chapter; Instinct and 
 Hybridism in the two succeeding chapters. 
 
 OK THE ABSEHCE OR RARITY OF TRAHSITIOHAL VARIETIES. 
 
 As natural selection acts solely by the preservation of 
 profitable modifications, each new form will tend in a 
 fully-stocked country to take the place of, and finally to 
 exterminate, its own less improved parent-form and other 
 less-favored forms with which it comes into competition. 
 Thus extinction and natural selection go hand in hand. 
 Hence, if we look at each species as descended from some 
 unknown form, both the parent and all the transitional 
 varieties will generally have been exterminated by the 
 very process of the formation and perfection of the new 
 form. 
 
 But, as by this theory innumerable transitional forms 
 must have existed, why do we not find them imbedded 
 in countless numbers in the crust of the earth? It 
 will be more convenient to discuss this question in the 
 chapter on the Imperfection of the Geological Becord; 
 a . n( ^ here only state that I believe the answer mainly 
 
 lies in the record being incomparably less perfect than is 
 generally supposed. The crust of the earth is a vast 
 museum; but the natural collections have been imperfectly 
 made, and only at long intervals of time. 
 
 But it may be urged that when several closely allied 
 species inhabit the same territory, we surely ought to find 
 at the present time many transitional forms. Let us take 
 a simple case: in traveling from north to south over a con¬ 
 tinent, we generally meet at successive intervals with 
 closely allied or representative species, evidently filling 
 nearly the same place in the natural economy of the land. 
 These representative species often meet and interlock; and 
 as the one becomes rarer and rarer, the other becomes more 
 and more frequent, till the one replaces the other. But 
 
ICO 
 
 ABSENCE OR RARITY 
 
 if we compare these species where they intermingle, they 
 are generally as absolutely distinct from each other in every 
 detail of structure as are specimens taken from the metrop¬ 
 olis inhabited by each. By my theory these allied species 
 are descended from a common parent; and during the 
 process of modification, each has become adapted to the 
 conditions of life of its own region, and has supplanted and 
 exterminated its original parent-form and all the transi¬ 
 tional varieties between its past and present states. Hence 
 we ought not to expect at the present time to meet with 
 numerous transitional varieties in each region, though they 
 must have existed there, and may be imbedded there in a 
 fossil condition. But in the intermediate region, having 
 intermediate conditions of life, why do we not now find 
 closely linking intermediate varieties? This difficulty for 
 a long time quite confounded me. But I think it can be 
 in large part explained. 
 
 In the first place we should be extremely cautious in in¬ 
 ferring, because an area is now continuous, that it has been 
 continuous during a long period. Geology would lead us 
 to believe that most continents have been broken up into 
 islands even during the later tertiary periods; and in such 
 islands distinct species might have been separately formed 
 without the possibility of intermediate varieties existing in 
 the intermediate zones. By changes in the form of the 
 land and of climate, marine areas now continuous must 
 often have existed within recent times in a far less continu¬ 
 ous and uniform condition than at present. But I will pass 
 over this way of escaping from the difficulty; for I believe 
 that many perfectly defined species have been formed on 
 strictly continuous areas; though I do not doubt that the 
 formerly broken condition of areas now continuous, has 
 played an important part in the formation of new species, 
 more especially with freely-crossing and wandering 
 animals. 
 
 In looking at species as they are now distributed over a 
 wide area, we generally find them tolerably numerous over 
 a large territory, then becoming somewhat abruptly rarer 
 and rarer on the confines, and finally disappearing. Hence 
 the neutral territory between two representative species is 
 generally narrow in comparison with the territory proper 
 to each. We see the same fact in ascending mountains. 
 
OF TRANSITION A t, VARIETIES. 
 
 1G1 
 
 and sometimes it is quite remarkable how abruptly, as 
 Alph. de Candolle has observed, a common alpine species 
 disappears. The same fact has been noticed by E. Forbes 
 in sounding the depths of the sea with the dredge. 
 To those who look at climate and the physical conditions 
 of life as the all-important elements of distribution, these 
 facts ought to cause surprise, as climate and height or depth 
 graduate away insensibly. But when we bear in mind that 
 almost every species, even in its metropolis, would increase 
 immensely in numbers, were it not for other competing 
 species; that nearly all either prey on or serve as prey for 
 others; in short, that each organic being is either directly 
 or indirectly related in the most important manner to 
 other organic beings—we see that the range of the inhab¬ 
 itants of any country by no means exclusively depends on 
 insensibly changing physical conditions, but in a large 
 part on the presence of other species, on which it lives, or 
 by which it is destroyed, or with which it comes into com¬ 
 petition; and as these species are already defined objects, 
 not blending one into another by insensible gradations, the 
 range of any one species, depending as it does on the range 
 of others, will tend to be sharply defined. Moreover, each 
 species on the confines of its range, where it exists in les¬ 
 sened numbers, will, during fluctuations in the number of 
 its enemies or of its prey, or in the nature of the seasons, 
 be extremely liable to utter extermination; and thus its 
 geographical range will come to be still more sharply 
 defined. 
 
 As allied or representative species, when inhabiting a 
 continuous area, are generally distributed in such a manner 
 that each has a wide range, with a comparatively narrow 
 neutral territory between them, in which they become 
 rather suddenly rarer and rarer; then, as varieties do not es¬ 
 sentially. differ from species, the same rule will probably 
 apply to both; and if we take a varying species inhabiting a 
 very large area, we shall have to adapt two varieties to two 
 large areas, and a third variety to a narrow intermediate zone. 
 The intermediate variety, consequently, will exist in lesser 
 numbers from inhabiting a narrow and lesser area; and 
 practically, as far as I can make out, this rule holds good 
 with varieties in a state of nature. I have met with strik¬ 
 ing instances of the rule in the case of varieties intermediate 
 
16 * 
 
 ABSENCE OR RARITY 
 
 between well-marked varieties in the genus Balanus. And 
 it would appear from information given me by Mr. Watson, 
 Dr. Asa Gray and Mr. Wollaston, that generally, when 
 varieties intermediate between two other forms occur, they 
 are much rarer numerically than the forms which they con¬ 
 nect. Now, if we may trust these facts and inferences, 
 and conclude that varieties linking two other varieties to¬ 
 gether generally have existed in lesser numbers than the 
 forms which they connect, then we can understand why 
 intermediate varieties should not endure for very long 
 periods! why, as a general rule, they should be extei- 
 minated and disappear, sooner than the forms which they 
 originally linked together. 
 
 For any form existing in lesser numbers would, as already 
 remarked, run a greater chance of being exterminated 
 than one existing in large numbers; and in this particular 
 case the intermediate form would be eminently liable 
 to the inroads of closely allied forms existing on both 
 sides of ito But it is a far more important considera¬ 
 tion, that during the process of further modification, 
 by which two varieties are supposed to be converted 
 and perfected into two distinct species, the two which 
 exist in larger numbers, from inhabiting larger areas, 
 will have a great advantage over the intermediate 
 variety, which exists in smaller numbers in a. narrow and 
 intermediate zone. For forms existing in larger numbers 
 will have a better chance, within any given period, of pre¬ 
 senting further favorable variations for natural selection to 
 seize on, than will the rarer forms which exist in lesser 
 numbers. Hence, the more common forms, in the race for 
 life, will tend to beat and supplant the less common forms, 
 for these will be more slowly modified and improved. It 
 is the same principle which, as I believe, accounts for the 
 common species in each country, as shown in the second 
 chapter, presenting on an average a greater number of well- 
 marked varieties than do the rarer species. I may illus¬ 
 trate what I mean by supposing three varieties of sheep to 
 be kept, one adapted to an extensive mountainous region; 
 a second to a comparatively narrow, hilly tract; and a 
 third to the wide plains at the base; and that the inhabi¬ 
 tants are all trying with equal steadiness and skill to im¬ 
 prove their stocks by selection; the chances in this case 
 
OF TRANSITIONAL VARIETIES. 163 
 
 will be strongly in favor of the great holders on the mount- 
 am . s , ° r ° n tl i le plains, improving their breeds more 
 quickly than the small holders on the intermediate narrow 
 hilly tract; and consequently the improved mountain or 
 plain breed will soon take the place of the less improved 
 lull bleed, and thus the two breeds, which originally ex¬ 
 isted in greater numbers, will come into close contact with 
 each other, without the interposition of the supplanted, in¬ 
 termediate hill variety. 
 
 Po sum up, I believe that species come to be tolerablv 
 well-defined objects, and do not at any one period present 
 an inextricable chaos of varying and intermediate links: 
 first, because new varieties are very slowly formed, for vari¬ 
 ation is a slow process, and natural selection can do noth¬ 
 ing until favorable individual differences or variations 
 occur, and until a place in the natural polity of the coun- 
 tiy can be bettei filled by some modification of some one 
 01 moie of its inhabitants. And such new places will de¬ 
 pend on slow changes of climate, or on the occasional im¬ 
 migration of new inhabitants, and, probablv, in a still more 
 important degree, on some of the old inhabitants becoming 
 slowly modified, with the new forms thus produced and 
 the old ones acting and reacting on each other. So that, 
 m any one region and at any one time, we ought to see 
 only a few species presenting slight modifications of struc¬ 
 ture m some degree permanent; and this assuredlv we do 
 see. J 
 
 Secondly, areas now continuous must often have existed 
 within the recent period.as isolated portions, in which 
 many forms, more especially among the classes which 
 unite for each birth and wander much, may have sepa¬ 
 rately been rendered sufficiently distinct to rank as repre¬ 
 sentative species. In this case, intermediate varieties be¬ 
 tween the se\eial lepresentative species and their common 
 parent, must formerly have existed within each isolated 
 poition of the land, but these links during the process of 
 natural selection will have been supplanted and exterm in- 
 ated so that they will no longer be found in a living state. 
 
 . -thirdly, when two or more varieties have been formed 
 m different, portions of a strictly continuous area, interme¬ 
 diate varieties will, it is probable, at first have been formed 
 in the intermediate zones, but they will generally have had 
 
I( ]4 transitions of organic beings. 
 
 a Short duration. For these intermediate varieties will 
 f rnm reasons already assigned (namely fiom what 
 we know of the actual distribution of closely allied 
 or representative species, and likewise of acknowl¬ 
 edged varieties), exist in the intermediate zones in lesser 
 numbers than the varieties which they tend to connect. 
 From this cause alone the intermediate variety will be 
 li-xble to accidental extermination; and during the piocess 
 of further modification through natural selection, they 
 will almost certainly be beaten and supplanted by the 
 forms which tliev connect; for these, from existing in 
 greater numbers/will, in the aggregate, present moie 
 varieties, and thus be further improved through natuial 
 
 selection and gain further advantages. 
 
 Lastly looking not to any one time, but at all time, n 
 mv theory be true, numberless intermediate varieties, lm - 
 i n I closely together all the species of the same group, must 
 asfuredly have existed; but the very process of natural 
 selection constantly tends, as has been so often remarked, 
 to exterminate the parent-forms and the intermediate links. 
 Consequently evidence of their former existence could be 
 found among fossil remains, which are preserved as we 
 shah attempt to show in a future chapter, in an extremely 
 imperfect and intermittent record. 
 
 ON THE ORIGIN AND TRANSITION OF ORGANIC BEINGS 
 WITH PECULIAR HABITS AND STRUCTURE. 
 
 It'has been asked by the opponents of such v 'ews as I 
 hold how, for instance, could a land carnivorous anim 
 have been converted into one with aquatic habits; for 
 how could the animal in its transitional state have sub¬ 
 sisted? It would be easy to show that there now exis 
 carnivorous animals presenting close intermediate grades 
 from strictly terrestrial to aquatic habits; and as each 
 exists by a struggle for life, it is clear that each must be 
 
 well adapted to its place in nature Look at f w and 
 vision of North America, which has webbed ^eet, and 
 which resembles an otter in its fur, short legs, and for 
 of tail. During the summer this animal dives for a 
 nrevs on fish, but during the long winter it leaves the 
 frozen waters, and preys, like other pole-cats, on mice and 
 
TRANSITIONS OF ORGANIC BEINGS. 
 
 165 
 
 land animals. If a different case had been taken, and it 
 had been asked how an insectivorous quadruped could pos¬ 
 sibly have been converted into a flying bat, the question 
 would have been far more difficult to answer. Yet I think 
 such difficulties have little weight. 
 
 Here, as on other occasions, 1 lie under a heavy disad¬ 
 vantage, for, out of the many striking cases which I have 
 collected, I can give only one or two instances of transitional 
 habits and structures in allied species; and of diversified 
 habits, either constant or occasional, in the same species. 
 And it seems to me that nothing less than a long list of 
 such cases is sufficient to lessen the difficulty in any par¬ 
 ticular case like that of the bat. 
 
 Look at the family of squirrels; here we have the finest 
 gradation from animals with their tails only slightly flat¬ 
 tened, and from others, as Sir J. Richardson has remarked, 
 with the posterior part of their bodies rather wide and with 
 the skin on their flanks rather full, to the so-called flying 
 squirrels; and flying squirrels have their limbs and even the 
 base of the tail united by a broad expanse of skin, which 
 serves as a parachute and allows them to glide through the 
 air to an astonishing distance from tree to tree. We can¬ 
 not doubt that each structure is of use to each kind of 
 squirrel in its own country, by enabling it to escape birds 
 or beasts of prey, to collect food more quicklv, or, 
 as there is reason to believe, to lessen the danger from 
 occasional falls. But it does not follow from this fact that 
 the structure of each squirrel is the best that it is possible 
 to conceive under all possible conditions. Let the climate 
 and vegetation change, let other competing rodents or new 
 beasts of prey immigrate, or old ones become modified, and 
 all analogy would lead us to believe that some, at least, of 
 the squirrels would decrease in numbers or become exter¬ 
 minated, unless they also become modified and improved 
 in structure in a corresponding manner. Therefore, I can 
 see no difficulty, more especially under changing conditions 
 of life, in the continued preservation of individuals with 
 fuller and fuller flank-membranes, each modification being 
 useful, each being propagated, until, by the accumulated 
 effects of this process of natural selection, a perfect so- 
 called flying squirrel was produced. 
 
 Now look at the Galeopithecus or so-called flying lemur. 
 
TRANSITIONS OF ORGANIC BEINGS. 
 
 106 
 
 which, was formerly ranked among hats, hut is now believed 
 to belong to the Insectivora. An extremely wide flank- 
 membrane stretches from the corners of the jaw to the tail, 
 and includes the limbs with the elongated fingers. This 
 flank-membrane is furnished with an extensor muscle. 
 Although no graduated links of structure, fitted for 
 gliding through the air, now connect the. Galeopi- 
 thecus with the other Insectivora, yet there is no dif¬ 
 ficulty in supposing that such links formerly existed, 
 and that each was developed in the same manner 
 as with the less perfectly gliding squirrels; each grade 
 of structure having been useful to its possessor. Nor 
 can I see any insuperable difficulty in further believ¬ 
 ing that the membrane connected fingers and forearm of 
 the Galeopithecus might have been greatly lengthened by 
 natural selection; and this, as far as the organs of .flight 
 are concerned, would have converted the animal into a 
 bat. In certain bats in which the wing-membrane extends 
 from the top of the shoulder to the tail and includes the 
 hind-legs, we perhaps see traces of an apparatus originally 
 fitted for gliding through the air rather than for flight. 
 
 If about a dozen genera of birds were to become extinct, 
 who would have ventured to surmise that birds might have 
 existed which used their wings solely as flappers, like the 
 logger-headed duck (Micropterus of Eyton); as fins in the 
 water and as front-legs on the hand, like the penguin; as 
 sails, like the ostrich; and functionally for no purpose, 
 like the apteryx? Yet the structure of each of these 
 birds is good for it, under the conditions of life to which 
 it is exposed, for each has to live by a struggle: but it is 
 not necessarially the best possible under all possible con¬ 
 ditions. It must not be inferred from these remarks that 
 any of the grades of wing-structure here alluded to, which 
 perhaps may all be the result of disuse, indicate the steps 
 by which birds actually acquired their perfect power of 
 flight; but they serve to show what diversified means of 
 transition are at least possible. 
 
 Seeing that a few members of such water-breathing 
 classes as the Crustacea and Mollusca are adapted to live 
 on the land; and seeing that we have flying birds and 
 mammals, flying insects of the most diversified types, and 
 formerly had flying reptiles, it is conceivable that flying- 
 
TRANSITIONS OF ORGANIC BEINGS, 16 ? 
 
 ^ which now glide far through the air, slightly rising 
 and turning by the aid of their fluttering fins, might have 
 been modified into perfectly winged animals. If this had 
 been effected, who would have ever imagined that in an 
 early transitional state they had been the inhabitants of 
 a' u^P en ocean, &nd had used their incipient organs of 
 flight exclusively, so far as we know, to escape being de¬ 
 voured by other fish? 
 
 ^hen we see any structure highly perfected for any par¬ 
 ticular habit, as the wings of a bird for flight, we should 
 beai in mind that animals displaying early transitional 
 giades of the structure will seldom have survived to the 
 present day, for they will have been supplanted by their 
 successors, which were gradually rendered more perfect 
 through natural selection. Furthermore, we may con¬ 
 clude that transitional states between structures fitted for 
 veiy diffeient habits of life will rarely have been developed 
 at an early period in great numbers and under many sub¬ 
 ordinate forms. 1 hus, to return to our imaginary illus¬ 
 tration of the flying-fish, it does not seem probable that 
 nshes capable of true flight would have been developed 
 under many subordinate forms, for taking prey of many 
 kinds m many ways, on the land and in the water, until 
 their organs of flight, had come to a high stage of perfec¬ 
 tion, so as to have given them a decided advantage over 
 other animals in the battle for life. Hence the chance of 
 discovering species with transitional grades of structure in 
 a fossil condition will always be less, from their having 
 existed in lesser numbers, than in the case of species with 
 iully developed structures. 
 
 I will now give two or three instances, both of diversified 
 and. of changed habits, in the individuals of the same 
 species. In either case it would be easy for natural selec¬ 
 tion to adapt the structure of the animal to its changed 
 habits, or exclusively to. one of its several habits. It is, 
 however, difficult to decide and immaterial for us, whether 
 habits generally change first and structure afterward; or 
 whether slight modifications of structure lead to changed 
 habits; both probably often occurring almost simultane¬ 
 ously. Of cases of changed habits it will suffice merely to 
 allude to that of the many British insects which now feed 
 on exotic plants, or exclusively on artificial substances. 
 
168 
 
 TRANSITIONS OF ORGANIC BEINGS. 
 
 Of diversified habits innumerable instances could be given: 
 I have often watched a tyrant flycatcher (Saurophagus sul- 
 phuratus) in South America, hovering over one spot and 
 then proceeding to another, like a kestrel, and at other 
 times standing stationary on the margin of water, and then 
 dashing into it like a kingfisher at a fish. In our own 
 country the larger titmouse (Parus major) may be seen 
 climbing branches, almost like a creeper; it sometimes, 
 like a shrike, kills small birds by blows on the head; and I 
 have many times seen and heard it hammering the seeds of 
 the yew on a branch, and thus breaking them like a nut¬ 
 hatch. In North America the black bear was seen by 
 Hearne swimming for hours with widely open mouth, thus 
 catching, almost like a whale, insects in the water. 
 
 As we sometimes see individuals following habits differ¬ 
 ent from those proper to their species and to the other 
 species of the same genus, we might expect that such in¬ 
 dividuals would occasionally give rise to new species, 
 having anomalous habits, and with their structure 
 either slightly or considerably modified from that of their 
 type. And such instances occur in nature. Can a more 
 striking instance of adaptation be given than that of 
 a woodpecker for climbing trees and seizing insects in the 
 chinks of the bark? Yet in North America there are 
 woodpeckers which feed largely on fruit, and others 
 with elongated wings which chase insects on the wing. 
 On the plains of La Plata, where hardly a tree grows, 
 there is a woodpecker (Colaptes campestris) which has two 
 toes before and two behind, a long-pointed tongue, pointed 
 tail-feathers, sufficiently stiff to support the bird in a verti¬ 
 cal position on a post, but not so stiff as in the typical wood¬ 
 peckers, and a straight, strong beak. The beak, however, 
 is not so straight or so strong as in the typical woodpeckers 
 but it is strong enough to bore into wood. Hence this 
 Colaptes, in all the essential parts of its structure, is a wood¬ 
 pecker. Even in such trifling characters as the coloring, 
 the harsh tone of the voice, and undulatory flight, its close 
 blood-relationship to our common woodpecker is plainly 
 declared; yet, as I can assert, not only from my own ob¬ 
 servations, but from those of the accurate Azara, in certain 
 large districts it does not climb trees, and it makes its 
 nest in holes in banks! In certain other districts, however, 
 
transitions of organic BEING is. 
 
 169 
 
 this same woodpecker, as Mr. Hudson states, frequents 
 trees and bores holes in the trunk for its nest. I 
 mention as another illustration of the varied habits of 
 genus, that a Mexican Colaptes has been described by De 
 
 S tor: S of re acorns nnS 68 ^ hard W °° d in 0rdei ' to la /“P a 
 
 . Petrels . a [e the most aerial and oceanic of birds but 
 m the quiet sounds of Tierra del Fuego, the Puffinuria 
 beiardi, in its general habits, in its astonishing power of 
 diving m i s manner of swimming and of flying when 
 made to take flight, would be mistaken b/any one 
 
 „ t a , n J. r ,, a Srebe; nevertheless it is essentially a 
 petiel, but with many parts of its organization pro- 
 
 wW d 7 ,? lodlfled ln , relation to its new habits of life- 
 whereas the woodpecker of La Plata has had its structure 
 on y slightly modified. In the case of the water-ouzel 
 the acutest observer, by examining its dead body, would 
 ever have suspected its sub-aquatic habits; yet this bird 
 which is allied to the thrush family, subsists by divine- 
 
 fee ^ S lVZ g lZl er Wa f te + n and gasping stones with°its 
 teet. All the members of the great order of Hvmenonter 
 
 oils insects are terrestrial, excepting the genuTPronto 
 rupes which Sir John Lubbock ifas discovered to be' 
 acquatic in its habits; it often enters the water and dives 
 about by the use not of its legs but of its wings, and re¬ 
 mains as long as four hours beneath the surface- vet it 
 
 SSiZSlt 110 " in 
 
 as met with an animal having habits and structure not in 
 
 fETnfT'Y W !, at Can be P lainer than that the webbed 
 eet of ducks and geese are formed for swimming? Yet 
 
 nesr 6 fh® l ' P i aild g ®? Se with webbed feet which rarely go 
 near the water; and no one, except Audubon, has sefn 
 
 on tho gate r blrd % W il lch has a11 lts four toes webbed, alight 
 on the surface of the ocean. On the other hand grebes 
 
 onh W S “a® ® mmen % aquatic, although their toes are 
 
 thlt Z ? ed r 7 membrane -. What seems plainer than 
 that the long toes, not furnished with membrane of the 
 
 ing plants 8 ? f f ? r walk ' n g over swamps and float¬ 
 
 ing plants.? The water-lieu and landrail are members of 
 
170 
 
 ORGANS OF EXTREME PERFECTION. 
 
 this order, yet the first is nearly as aquatic, as the coot, and 
 the second is nearly as terrestrial as the quail or partridge. 
 In such cases, and many others could be given, habits have 
 changed without a corresponding change of structure. The 
 webbed feet of the upland goose may be said to have be¬ 
 come almost rudimentary in function, though not in struc¬ 
 ture. In the frigate-bird, the deeply scooped membrane 
 between the toes shows that structure has begun to change. 
 
 He who believes in separate and innumerable acts of 
 creation may say, that in these cases it has pleased the 
 Creator to cause a being of one type to take the place of one 
 belonging to another type; but this seems to me only re¬ 
 stating the fact in dignified language. He who believes in 
 the struggle for existence and in the principle of natural 
 selection, will acknowledge that every organic being is con¬ 
 stantly endeavoring to increase in numbers; and that if 
 any one being varies ever so little, either in habits or struc¬ 
 ture, and thus gains an advantage over some other inhab¬ 
 itant of the same country, it will seize on the place of that 
 inhabitant, however different that may be from its own 
 place. Hence it will cause him no surprise that there should 
 be geese and frigate-birds with webbed feet, living on the 
 dry land and rarely alighting on the water, that there 
 should be long-toed corncrakes, living in meadows instead 
 of in swamps; that there should be woodpeckers where 
 hardly a tree grows; that there should be diving thrushes 
 and diving Hymenoptera, and petrels with the habits of 
 auks. 
 
 ORGAN'S OF EXTREME PERFECTION AND COMPLICATION. 
 
 To suppose that the eye with all its inimitable contri¬ 
 vances for adjusting the focus to different distances, for 
 admitting different amounts of light, and for the correction 
 of spherical and chromatic aberration, could have been 
 formed by natural selection, seems, I freely confess, 
 absurd in the highest degree. When it was first said that 
 the sun stood still and the world turned round, the com¬ 
 mon sense of mankind declared the doctrine false; but the 
 old saying of Vox popali, vox Dei, as every philosopher 
 knows, can not be trusted in science. Reason tells me, 
 that if numerous gradations from a simple and imperfect 
 
 
ORGANS OF EXTREME PERFECTION. 
 
 171 
 
 eye to one complex and perfect can be shown to exist, each 
 grade being useful to its possessor, as is certainly the case; 
 if further, the eye ever varies and the variations be in¬ 
 herited, as is likewise certainly the case; and if such varia¬ 
 tions should be useful to any animal under changing con¬ 
 ditions of life, then the difficulty of believing that a per¬ 
 fect and complex eye could be formed by natural selection, 
 though insuperable by our imagination, should not be con¬ 
 sidered as subversive of the theory. How a nerve comes to 
 be sensitive to light, hardly concerns us more than how life 
 itself originated; but I may remark that, as some of the low¬ 
 est organisms in which nerves can not be detected, are 
 capable of perceiving light, it does not seem impossible that 
 certain sensitive elements in their sarcode should become 
 aggregated and developed into nerves, endowed with this 
 special sensibility. 
 
 In searching for the gradations through which an organ in 
 any species has been perfected, we ought to look exclusively 
 to its lineal progenitors; but this is scarcely ever possible, 
 and we are forced to look to other species and genera of the 
 same group, that is to the collateral descendants from the 
 same parent-form, in order to see what gradations 
 aie possible, and for the chance of some gradations ha vino" 
 been transmitted in an unaltered or little altered condition. 
 But the state of the same organ in distinct classes may in¬ 
 cidentally throw light on the steps by which it has been 
 perfected. 
 
 I he simplest organ which can be called an eye consists 
 of an optic nerve, surrounded by pigment-cells and covered 
 by translucent skin, but without any lens or other refract¬ 
 ive body. We may, however, according to M. Jourdain, 
 descend even a step lower and find aggregates of pigment- 
 cells, apparently serving as organs of vision, without any 
 nerves, and resting merely on sarcodic tissue. Eyes of the 
 above simple nature are not capable of distinct vision, 
 and serve only to distinguish light from darkness. In 
 certain star-fishes, small depressions in the layer of pig- 
 ment which surrounds the nerve are filled, as described by 
 the author just quoted, with transparent gelatinous matter, 
 projecting with a convex surface, like the cornea in the 
 higher animals. He suggests that this serves not to form 
 an image, but only to concentrate the luminous rays and 
 
172 ORGANS OF EXTREME PERFECTION. 
 
 render their perception more easy. In this concentration 
 of the rays we gain the first and by far the most important 
 step toward the formation of a true, picture-forming eye; 
 for we have only to place the naked extremity of the optic; 
 nerve, which in some of the lower animals lies deeply 
 buried in the body, and in some near the surface, at the 
 right distance from the concentrating apparatus, and an 
 image will be formed on it. 
 
 In the great class of the Articulata, we may start from 
 an optic nerve simply coated with pigment, the latter some¬ 
 times forming a sort of pupil, but destitute of lens or 
 other optical contrivance. With insects it is now known 
 that the numerous facets on the cornea of their great com¬ 
 pound eyes form true lenses, and that the cones include 
 curiously modified nervous filaments. But these organs in 
 the Articulata are so much diversified that Muller formerly 
 made three main classes with seven subdivisions, besides a 
 fourth main class of aggregated simple eyes. 
 
 When we reflect on these facts, here given much too 
 briefly, with respect to the wide, diversified, and graduated 
 range of structure in the eyes of the lower animals; and 
 when we bear in mind how small the number of all living 
 forms must be in comparison with those which have 
 become extinct, the difficulty ceases to be very great in 
 believing that natural selection may have converted the 
 simple apparatus of an optic nerve, coated with pigment 
 and invested by transparent membrane, into an optical 
 instrument as perfect as is possessed by any member of the 
 Articulata class. 
 
 He who will go thus far, ought not to hesitate to go 
 one step further, if he finds on finishing this volume 
 that large bodies of facts, otherwise inexplicable, can be 
 explained by the theory of modification through natural 
 selection; he ought to admit that a structure even as 
 perfect as an eagle's eye might thus be formed, although 
 in this case he does not know the transitional states. It 
 has been objected that in order to modify the eye 
 and still preserve it as a perfect instrument, many 
 changes would have to be effected simultaneously, which, 
 it is assumed, could not be done through natural 
 selection; but as I have attempted to show in my 
 work on the variation of domestic animals, it is not 
 
ORGANS OF EXTREME PERFEOTIOX. \ 73 
 
 necessary to suppose that the modifications were all 
 simultaneous, if they were extremely slight and gradual. 
 Different kinds of modification would, also, serve for the 
 same general purpose: as Mr. Wallace has remarked “If 
 a len has too short or too long a focus, it may be amended 
 eithei by an alteration of curvature, or an alteration of 
 density; if the curvature be irregular, and the rays do not 
 converge to a point, then any increased regularity of curva- 
 ture will be an improvement. So the contraction of the 
 111s and the muscular movements of the eye are neither of 
 
 to vision, but only improvements which 
 might have been added and perfected at any stage of the 
 construction of the instrument.” Within the highest 
 division of the animal kingdom, namely, the Vertebrata, 
 
 fr i )m r?S eye f s i m P le > that H consists, as in 
 the lancelet, of a little sack of transparent skin, furnished 
 
 with a nerve and lined with pigment, but destitute of any 
 other apparatus. In fishes and reptiles, as Owen has re- 
 marked, I he range of gradation of dioptric structures 
 is very great It is a significant fact that even in man 
 according to the high authority of Virchow, the beautiful 
 crystalline lens is formed m the embryo by an accumula¬ 
 tion of epidermic cells, lying in a sack-like fold of the skin- 
 and the vitreous body is formed from embryonic sub¬ 
 cutaneous tissue. To arrive, however, at a just conclusion 
 regarding the formation of the eye, with all its marvellous 
 absolute] y perfect characters, it is indispensable 
 that the reason should conquer the imagination; but I 
 have felt the difficulty far too keenly to be surprised at 
 others hesitating to extend the principle of natural selec¬ 
 tion to so startling a length. 
 
 It is scarcely possible to avoid comparing the eye with 
 a telescope We know that this instrument has been per- 
 fected by the long-continued efforts of the highest human 
 intellects, and we naturally infer that the eye has been 
 iormed by a somewhat analogous process. But may not 
 this inference be presumptuous? Have we any right to 
 assume that the Creator works by intellectual powers like 
 those of man. If we must compare the eye to an optical 
 instrument, we ought m imagination to take a thick layer 
 ot transparent tissue, with spaces filled with fluid and 
 with a nerve sensitive to light beneath, and then suppose 
 
MODES OF TRANSITION . 
 
 174 
 
 every part of this layer to be continually changing slowly 
 in density, so as to separate into layers of diffeient densi» 
 ties and thicknesses, placed at different distances from each 
 other, and with the surfaces of each layer slowly changing 
 in form. Further we must suppose that there is a power, 
 represented by natural selection or the suivival of the 
 fittest, always intently watching each slight alteration in 
 the transparent layers; and carefully preserving each 
 which, under varied circumstances, in any way or degree, 
 tends to produce a distincter image. We must suppose 
 each new state of the instrument to be multiplied by the 
 million; each to be preserved until a better one is pro¬ 
 duced, and then the old ones to be all destroyed. In 
 living bodies, variation will cause the slight alteration, 
 generation will multiply them almost infinitely, and natural 
 selection will pick out with unerring skill each improve¬ 
 ment. Let this process go on for millions of years;. and 
 during each year on millions of individuals of many kinds; 
 and mav we not believe that a living optical instrument 
 might thus be formed as superior to one of glass, as the 
 works of the Creator are to those of man? 
 
 MODES OF TRANSITION. 
 
 If it could be demonstrated that any complex organ ex¬ 
 isted, which could not possibly have been foimed by nu¬ 
 merous, successive, slight modifications, my tlieoiy would 
 absolutely break down. But I can find out no such case. 
 No doubt many organs exist of which we do not know the 
 transitional grades, more especially if we look to much- 
 isolated species, around which, according to the theory, 
 there has been much extinction. Or again, if we take an 
 organ common to all the members of a class, for in this 
 latter case the organ must have been originally formed at 
 a remote period, since which all the many members of the 
 class have been developed; and in order to discover the 
 early transitional grades through which the organ has 
 passed, we should have to look to very ancient ancestral 
 
 forms, long since become extinct. 
 
 We should be extremely cautious in concluding that an 
 organ could not have been formed by transitional grada¬ 
 tions of some kind. Numerous cases could be given 
 
MODE'S OF TRANSITION. 
 
 175 
 
 among the lower animals of the same organ performing at 
 the same time wholly distinct functions; thus in the larva 
 of the ca agon-fly and in the fish Cobites the alimentary 
 canal respires, digests and excretes. In the Hydra, the 
 animal may be turned inside out, and the exterior surface 
 will then digest and the stomach respire. In such cases 
 natural selection might specialize, if any advantage were 
 thus gained, the whole or part of an organ, which had 
 previously performed, two . functions, for one function 
 alone, and thus by insensible steps greatly change its 
 nature, IVIany plants are known which regularly produce 
 at the same time differently constructed flowers; and if 
 such plants were to produce one kind alone, a great change 
 would, be effected with comparative suddenness in the 
 character of the species. It is, however, probable that the 
 two sorts of flowers borne by the same plant were originally 
 differentiated by finely graduated steps, which may still 
 be followed in some few cases. 
 
 Again, two distinct organs, or the same organ under two 
 very different forms, may simultaneously perform in the 
 same individual the same function, and this is an extremely 
 important .means of transition: to give one instance—there 
 are fish with gills or branchia? that breathe the air dis¬ 
 solved in the water, at the same time that they breathe 
 free air in their swim-bladders, this latter organ being 
 divided by highly vascular partitions and having a ductus 
 pneumaticus for the supply of air. To give another in¬ 
 stance from the vegetable kingdom: plants climb by three 
 distinct means,, by spirally twining, by clasping a support 
 with their sensitive tendrils, and by the emission of aerial 
 rootlets; these three means are usually found in distinct 
 groups, but some few species exhibit two of the means, or 
 even all three, combined in the same individual. In all 
 such cases one of the two organs might readily be modified 
 and perfected so as to perform all the work, being aided 
 during the progress of modification by the other organ; 
 and then this other organ might be modified for some 
 other and quite distinct purpose, or be wholly obliterated. 
 
 The illustration of the swim-bladder in fishes is a 
 good one, because it shows us clearly the highly 
 important fact that an organ originally constructed for 
 one purpose, namely, flotation, may be converted into 
 
176 ' MODES OF TRANSITION. 
 
 one for a widely different purpose, namely, respiration. 
 The swim-bladder has, also, been worked in as an accessory 
 to the auditory organs of certain fishes. All physiologists 
 admit that the swim-bladder is homologous, or “ ideally 
 similar ” in position and structure with the longs of the 
 higher vertebrate animals: hence there is no reason to 
 doubt that the swim-bladder has actually been converted 
 into lungs, or an organ used exclusively for respiration. 
 
 According to this view it may be inferred that all verte¬ 
 brate animals with true lungs are descended by ordinary 
 generation from an ancient and unknown prototype, whirl 
 was furnished with a floating apparatus or swim bladder. 
 We can thus, as I infer from Owen’s interesting descrip¬ 
 tion of these parts, understand the strange fact that every 
 particle of food and drink which we swallow has to pass 
 over the orifice of the trachea, with some risk of falling 
 into the lings, notwithstanding the beautiful contrivance 
 by which tho glottis is closed. In the higher Vertebrata 
 the branchke have wholly disappeared—but in the embryo 
 the slits on the sides of the neck and the loop-like course 
 of the arteries still mark their former position. But it is 
 conceivable that the now utterly lost branchiae might have 
 been gradually worked in by natural selection for some dis¬ 
 tinct purpose: for instance, Landois has shown that the 
 wings of insects are developed from the trachea; it is there¬ 
 fore" highly probable that in this great class organs which 
 once served for respiration have been actually converted 
 into organs for flight. 
 
 In considering transitions of organs, it is so important to 
 bear in mind the probability of conversion from one func¬ 
 tion to another, that I will give another instance. Pedun¬ 
 culated cirripedes have two minute folds of skin, called by 
 me the ovigerous frena, which serve, through the means of 
 a sticky secretion, to retain the eggs until they are hatched 
 within the sack. These cirripedes have no branchiae, the 
 whole surface of the body and of the sack, together with 
 the small frena, serving for respiration. The Balanidae or 
 sessile cirripedes, on the other hand, have no ovigerous 
 frena, the eggs lying loose at the bottom of the sack, 
 within the well-inclosed shell; but they have, in the same 
 relative position with the frena, large, much-folded mem¬ 
 branes, which freely communicate with the circulatory 
 
MODES OF TRANSITION,\ 
 
 177 
 
 lacunae of the sack and body, and which have been consid¬ 
 ered by all naturalists to act as branchiae. Now I think no 
 one will dispute that the oviperous frena in the one family 
 are strictly homologous with the branchiae of the other 
 family; indeed, they graduate into each other. Therefore 
 it need not be doubted that the two little folds of skin, 
 which originally served as ovigerous frena, but which, like¬ 
 wise, very slightly aided in the act of respiration, have 
 been gradually converted by natural selection into branchiae, 
 simply through an increase in their size and the obliteration 
 of their adhesive glands. If all pedunculated cirripedes 
 had become extinct, and they have suffered far more extinc¬ 
 tion than have sessile cirripedes, who would ever have im¬ 
 agined that the branchiae in this latter family had origin¬ 
 ally existed as organs for preventing the ova from being 
 washed out of the sack? 
 
 There is another possible mode of transition, namely, 
 through the acceleration or retardation of the period of re¬ 
 production. This has lately been insisted on by Professor 
 Cope and others in the United States. It is now known 
 that some animals are capable of reproduction at a very 
 early age, before they have acquired their perfect charac¬ 
 ters; and if this power became thoroughly well developed 
 in a species, it seems probable that the adult stage of devel¬ 
 opment would sooner or later be lost; and in this case, 
 especially if the larva differed much from the mature form, 
 the character of the species would be greatly changed and 
 degraded. Again, not a few animals, after arriving at 
 maturity, go on changing in character during nearly their 
 whole lives. With mammals, for instance, the form of the 
 skull is often much altered with age, of which Ur. Mu.rie 
 has given some striking instances with seals. Every one 
 knows how the horns of stags become more and more 
 branched, and the plumes of some birds become more finely 
 developed, as they grow older. Professor Cope states that 
 the teeth of certain lizards change much in shape with ad¬ 
 vancing years. With crustaceans not only many trivial, 
 but some important parts assume a new character, as re¬ 
 corded by Fritz Muller, after maturity. In all such cases 
 and many could be given—if the age for reproduction 
 were retarded, the character of the species, at least in its 
 adult state, would be modified; nor is it improbable that 
 
178 DIFFICULTIES OF THE ’THEORY 
 
 the previous and earlier stages of development would in 
 some cases be hurried through and finally lost. Whether 
 species have often or ever been modified through this com¬ 
 paratively sudden mode of transition, I can form no 
 opinion; but if this has occurred, it is probable that the 
 differences between the young and the mature, and be¬ 
 tween the mature and the old, were primordially acquired 
 by graduated steps. 
 
 SPECIAL DIFFICULTIES OF THE THEORY OF NATURAL 
 
 SELECTION. 
 
 Although we must be extremely cautious in concluding 
 that any organ could not have been produced by successive, 
 small, transitional gradations, yet undoubtedly serious 
 cases of difficulty occur. 
 
 One of the most series is that of neuter insects, which 
 are often differently constructed from either the males or 
 fertile females; but this case will be treated of in the next 
 chapter. The electric organs of fishes offer another case 
 of special difficulty, for it is impossible to conceive by what 
 steps these wondrous organs have been produced. But 
 this is not surprising, for we do not even know of what 
 use they are. In the gymnotus and torpedo they no doubt 
 serve as powerful means of defense, and perhaps for secur¬ 
 ing prey; yet in the ray, as observed by Matteiicc^ an 
 analogous organ in the tail manifests but little electricity, 
 even when the animal is greatly irritated; so little that it 
 can hardly be of any use for the above purposes. More¬ 
 over, in the ray, besides the organ just referred to, there 
 is, as Dr. R. McDonnell has shown, another organ near 
 the head, not known to be electrical, but which appears to 
 be the real homologue of the electric battery in the tor¬ 
 pedo. It is generally admitted that there exists between 
 these organs and ordinary muscle a close analogy, in inti¬ 
 mate structure, in the distribution of the nerves, and in 
 the manner in which they are acted on by various reagents. 
 It should, also, be especially observed that muscular con¬ 
 traction is accompanied by an electrical discharge; and, as 
 Dr. Radcliffe ’insists! 1 of the 
 torpedo during rest, there would seem to be a charge in 
 every respect like that which is met with in muscle and 
 
OF NATURAL SELECTION ,. 
 
 179 
 
 nerve during the rest, and the discharge of the torpedo, 
 instead of being peculiar, may be only another form of the 
 discharge which attends upon the action of muscle and 
 motor nerve.” Beyond this we cannot at present go in the 
 wav of explanation; but as we know so little about the uses 
 of these organs, and as we know nothing about the habits 
 and structure of the progenitors of the existing electric 
 fishes, it would be extremely bold to maintain that no 
 serviceable transitions are possible by which these organs 
 might have been gradually developed. 
 
 These organs appear at first to offer another and far 
 more serious difficulty; for they occur in about a dozen 
 kinds of fish, of which several are widely remote in their 
 affinities. When the same organ is found in several mem¬ 
 bers of the same class, especially if in members having 
 very different habits of life, we may generally attribute its 
 presence to inheritance from a common ancestor; and its 
 absence in some of the members to loss through disuse or 
 natural selection. So that, if the electric organs had been 
 inherited from some one ancient progenitor, we might have 
 expected that all electric fishes would have been specially 
 related to each other; but this is far from the case. Nor 
 does geology at all lead to the belief that most fishes for¬ 
 merly possessed electric organs, which their modified 
 descendants have now lost. But when we look at the sub¬ 
 ject more closely, we find in the several fishes provided with 
 electric organs, that these are situated in different parts of 
 the body, that they differ in construction, as in the 
 arrangement of the plates, and, according to Pacini, in the 
 process or means by which the electricity is excited—and 
 lastly, in being supplied with nerves proceeding from dif¬ 
 ferent sources, and this is perhaps the most important of 
 all the differences. Hence in the several fishes furnished 
 with electric organs, these cannot be considered as hom¬ 
 ologous, but only as analogous in function. Consequently 
 there is no reason to suppose that they have been inherited 
 from a common progenitor; for had this been the case they 
 would have, closely resembled each other in all respects. 
 Thus the difficulty of an organ, apparently the same, aris¬ 
 ing in several remotely allied species, disappears, leaving 
 «> y still great difficulty: namely, by what 
 
 graduated steps these organs have been developed in each 
 separate group of fishes. 
 
180 
 
 DIFFICULTIES OF TIIE THEORY 
 
 The luminous organs which occur in a few insects, 
 belonging to widely different families, and which are sit¬ 
 uated in different parts of the body, offer, under our pres¬ 
 ent state of ignorance, a difficulty almost exactly parallel 
 with that of the electric organs. Other similar cases could 
 be given; for instance in plants, the very curious contriv¬ 
 ance of a mass of pollen-grains, borne on a foot-stalk with 
 an adhesive gland* is apparently the same in Orchis and 
 Asclepias, genera almost as remote as is possible among 
 flowering plants; but here again the parts are not 
 homologous. In all cases of beings, far removed from 
 each other in the scale of organization, which are fur¬ 
 nished with similar and peculiar organs, it will be found 
 that although the general appearance and function of the 
 organs may be the same, yet fundamental differences 
 between them can always be detected. For instance, the 
 eyes of Cephalopods or cuttle-fish and of vertebrate ani¬ 
 mals appear wonderfully alike; and in such widely sun¬ 
 dered groups no part of this resemblance can be due 
 to inheritance from a common progenitor. Mr. Mivart 
 has advanced this case as one of special difficulty, but I 
 am unable to see the force of his argument. An organ 
 for vision must be formed of transparent tissue, and must 
 include some sort of lens for throwing an image at the 
 back of a darkened chamber. Beyond this superficial re¬ 
 semblance, there is hardly any real similarity between the 
 eyes of cuttle-fish and vertebrates, as may be seen by con¬ 
 sulting IienseAs admirable memoir on these organs in the 
 Cephalopoda. It is impossible for me here to enter on 
 details, but I may specify a few of the points of difference. 
 The crystalline lens in the higher cuttle-fish consists of 
 two parts, placed one behind the other like two lenses, 
 both having a very different structure and disposition to 
 what occurs in the vertebrata. The retina is wholly dif¬ 
 ferent, with an actual inversion of the elemental parts, 
 and with a large nervous ganglion included within the 
 membranes of the eye. The relations of the muscles 
 are as different as it is possible to conceive, and so in 
 in other points. Hence it is not a little difficult to decide 
 how far even the same terms ought to be employed in 
 describing the eyes of the Cephalopoda and Vertebrata. 
 It is, of course, open to any one to deny that the eye in 
 
OF NATURAL SELECTION. 
 
 181 
 
 either case could have been developed through the natural 
 selection of successive slight variations; but if this be ad¬ 
 mitted in the one case it is clearly possible in the other; 
 and fundamental differences of structure in the visual 
 organs of two groups might have been anticipated, in ac¬ 
 cordance with this view of their manner of formation. 
 As two men have sometimes independently hit on the 
 same invention, so in the several foregoing cases it appears 
 that natural selection, working for the good of each being, 
 and taking advantage of all favorable variations, has pro¬ 
 duced similar organs, as far as function is concerned, in 
 distinct organic beings, which owe none of their structure 
 in common to inheritance from a common progenitor. 
 
 Fritz Muller, in order to test the conclusions arrived at 
 in this volume, has followed out with much care a nearly 
 similar line of argument. Several families of crustaceans 
 include a few species, possessing an air-breathing appara¬ 
 tus and fitted to live out of the water. In two of these 
 families, which were more especially examined by Muller, 
 and which are nearly related to each other, the species 
 agree most closely in all important characters: namely in 
 their sense organs, circulating systems, in the position of 
 the tufts of hair within their complex stomachs, and lastly in 
 the whole structure of the water-breathing branchiae, even to 
 the microscopical hooks by which they are cleansed. Hence 
 it might have been expected that in the few species belong¬ 
 ing to both families which live on the land, the equally 
 important air-breathing apparatus would have been the 
 same; for why should this one apparatus, given for the 
 same purpose, have been made to differ, while all the other 
 important organs were closely similar, or rather, identical. 
 
 Fritz Muller argues that this close similarity in so 
 many points of structure must, in accordance with the 
 views advanced by me, be accounted for by inheritance 
 from a common progenitor. But as the vast majority of 
 the species in the above two families, as well as most 
 other crustaceans, are aquatic in their habits, it is improb¬ 
 able in the highest degree that their common progenitor 
 should have been adapted for breathing air. Muller 
 was thus led carefully to examine the apparatus in the air- 
 breathing species; and he found it to differ in each in 
 several important points, as in the position of the orifices. 
 
182 
 
 DIFFICULTIES OF TIIE THEORY 
 
 in the manner in which they are opened and closed, and in 
 some accessory details. Now such differences are intelligi¬ 
 ble, and might even have been expected, on the supposition 
 that species belonging to distinct families had slowly be¬ 
 come adapted to live more and more out of water, and to 
 breathe the air. For these species, from belonging to dis¬ 
 tinct families, 'would have differed to a certain extent, and 
 in accordance with the principle that the nature of each 
 variation depends on two factors, viz., the nature of the 
 organism and that of the surrounding conditions, their 
 variability assuredly would not have been exactly the same. 
 Consequently natural selection would have had different 
 materials or variations to work on, in order to arrive at the 
 same functional result; and the structures thus acquired 
 would almost necessarily have differed. On the hypothesis 
 of separate acts of creation the whole case remains unintel¬ 
 ligible. This line of argument seems to have had great 
 weight in leading Fritz Muller to accept the views main¬ 
 tained by me in this volume. 
 
 Another distinguished zoologist, the late Professor Cla- 
 parede, has argued in the same manner, and has arrived at 
 the same result. He shows that there are parasitic mites 
 (Acarida^), belonging to distinct sub-families and families, 
 which are furnishes with hair-claspers. These organs must 
 have been independently developed, as they could not have 
 been inherited from a common progenitor; and in the 
 several groups they are formed by the modification of the 
 fore legs, of the hind legs, of the maxillae or lips, and 
 of appendages on the under side of the hind part of the 
 body. 
 
 In the foregoing cases, we see the same end gained and 
 the same function performed, in beings not at all or only 
 remotely allied, by organs in appearance, though not in 
 development, closely similar. On the other hand, it is a 
 common rule throughout nature that the same end should 
 be gained, even sometimes in the case of closely related be¬ 
 ings, by the most diversified means. How differently con¬ 
 structed is the feathered wing of a bird and the membrane- 
 covered wing of a bat; and still more so the four wings of a 
 butterfly, the two wings of a fly, and the two wings with 
 the eiytra of a beetle. Bivalve shells are made to open and 
 
OF NATURAL SELECTION . 
 
 183 
 
 shut, out on what a number of patterns is the hinge con¬ 
 structed, from the long row of neatly interlocking teeth 
 in a Nucula to the simple ligament of a Mussel! Seeds 
 are disseminated by their minuteness, by their capsule 
 being converted into a light balloon-like envelope, by 
 being embedded in pulp or flesh, formed of the most 
 diverse parts, and rendered nutritious, as well as conspicu¬ 
 ously colored, go as to attract and be devoured by birds,' 
 by having hooks and grapnels of many kinds and serrated 
 awns, so as to adhere to the fur of quadrupeds, and by 
 being furnished with wings and plumes, as different in 
 shape as they are elegant in structure, so as to be wafted 
 by every breeze. I will give one other instance: for this 
 subject of the same end being gained by the most diversi¬ 
 fied means well deserves attention. Some authors main¬ 
 tain that organic beings have been formed in many ways 
 for the sake of mere variety, almost like toys in a shop, 
 but. such a view of nature is incredible. With plants 
 having separated sexes, and with those in which, though 
 hermaphrodites, the pollen does not spontaneously fall on 
 the stigma, some aid is necessary for^ their fertilization. 
 With several kinds this is effected by the pollen-grains, 
 which are light and incoherent, being blown by the wind 
 through mere chance on to the stigma; and this is the sim¬ 
 plest plan which can well be conceived. An almost equally 
 simple, though very different plan occurs in many plants in 
 which a symmetrical flower secretes a few drops of nectar, 
 and is consequently visited by insects; and these carry the 
 pollen from the anthers to the stigma. 
 
 From this simple stage we may pass through an inex¬ 
 haustible number of contrivances, all for the same pur¬ 
 pose and effected in essentially the same manner, but en¬ 
 tailing changes. in every part of the flower. The nectar 
 may be stored in variously shaped receptacles, with the 
 stamens and pistils modified in many ways, sometimes 
 forming trap-like contrivances, and sometimes capable of 
 neatly adapted movements through irritability or elasticity. 
 From such structures we may advance till we come to 
 such a case of extraordinary adaptation as that lately de¬ 
 scribed by Dr. Criiger in the Coryanthes. This orchid has 
 part of its labellum or lower lip hollowed out into a great 
 bucket, into which drops of almost pure water continually 
 
184 
 
 DIFFICULTIES OF THE TIIEORT 
 
 fall from two secreting horns which stand above it; and 
 when the bucket is half-full, the water overflows by a spout 
 on one side. The basal part of the labellum stands over 
 the bucket, and is itself hollowed out into a sort of cham¬ 
 ber with two lateral entrances; within this chamber there 
 are curious fleshy ridges. The most ingenious man, if he 
 had not witnessed what takes place, could never have 
 imagined what purpose all these parts serve. But Dr. 
 Criiger saw crowds of large humble-bees visiting the gigan¬ 
 tic flowers of this orchid, not in order to suck nectar, but 
 to gnaw off the ridges within the chamber above the bucket; 
 in doing this they frequently pushed each other into the 
 bucket, and their wings being thus wetted they could not 
 fly awav, but were compelled to crawl out through the 
 passage formed by the spout or overflow. Dr. Criiger saw 
 a “ continual procession ” of bees thus crawling out of their 
 involuntary bath. The passage is narrow, and is roofed over 
 by the column, so that a bee, in forcing its way out, first 
 rubs its back against the viscid stigma and then against the 
 viscid glands of the pollen-masses. The pollen-masses are 
 thus glued to the back of the bee which first happens to 
 crawl out through the passage of a lately expanded flower, 
 and are thus carried away. Dr. Criiger sent me a flower in 
 spirits of wine, with a bee which he had killed before it 
 had quite crawled out, with a pollen-mass still fastened to 
 its back. When the bee, thus provided, flies to another 
 flower, or to the same flower a second time, and is pushed 
 by its comrades into the bucket and then crawls out by the 
 passage, the pollen-mass necessarily comes first into con¬ 
 tact with the viscid stigma, and adheres to it, and the 
 flower is fertilized. Now at last we see the full use of every 
 part of the flower, of the water-secreting horns of the 
 bucket half-full of water, which prevents the bees from flying 
 away, and forces them to crawl out through the spout, and 
 rub against the properly placed viscid pollen-masses and 
 the viscid stigma. 
 
 The construction of the flower in another closely allied 
 orchid, namely, the Catasetum, is widely different, though 
 serving the same end; and is equally curious. Bees visit 
 these flowers, like those of the Coryanthes, in order to gnaw 
 the labellum; in doing this they inevitably touch a. long, 
 tapering, sensitive projection, or, as I have called it, the 
 
OF NATURAL SELECTION. 
 
 185 
 
 antenna. This antenna, when touched, transmits a sensa¬ 
 tion or vibration to a certain membrane which is instantly 
 ruptured; this sets free a spring by which the pollen-mass 
 is shot forth, like an arrow, in the right direction, and 
 adheres by its viscid extremity to the back of the bee. The 
 pollen-mass of the male plant (for the sexes are separate in 
 this orchid) is thus carried to the flower of the female 
 plant, where it is brought into contact with the stigma, 
 which is viscid enough to break certain elastic threads, 
 and retain the pollen,thus effecting fertilization. 
 
 How, it may be asked, in the foregoing and in innumer¬ 
 able other instances, can we understand the graduated 
 scale of complexity and the multifarious means for gaining 
 the same end. The answer no doubt is, as already re¬ 
 marked, that when two forms vary, which already differ 
 from each other in some slight degree, the variability will 
 not be of the same exact nature, and consequently the 
 results obtained through natural selection for the same 
 general purpose will not be the same. We should also bear 
 in mind that every highly developed organism has passed 
 through many changes; and that each modified structure 
 tends to be inherited, so that each modification will not 
 readily be quite lost, but may be again and again further 
 altered. Hence, the structure of each part of each species, 
 for whatever purpose it may serve, is the sum of many 
 inherited changes, through which the species has passed 
 during its successive adaptations to changed habits and 
 conditions of life. 
 
 Finally then, although in many cases it is most difficult 
 even to conjecture by what transitions organs have ariived 
 at their present state; yet, considering how small the pro¬ 
 portion of living and known forms is to the extinct and 
 unknown, I have been astonished how rarely an organ can 
 be named, toward which no transitional grade is known to 
 lead. It certainly is true, that new organs appearing as if 
 created for some special purpose rarely or never appear in 
 any being; as indeed is shown by that old, but somewhat 
 exaggerated, canon in natural history of “ Natura non facit 
 saltum.” We meet with this admission in the writings of 
 almost every experienced naturalist; or as Milne Edwards 
 has well expressed it, “Nature is prodigal in variety, but 
 niggard in innovation.” Why, on the theory of Creation, 
 
186 
 
 ORGANS OF LITTLE IMPORTANCE 
 
 should there be so much variety and so little real novelty? 
 Why should all the parts and organs of many independent 
 beings, each supposed to have been separately created for 
 its own proper place in nature, be so commonly linked to¬ 
 gether by graduated steps? Why should not Nature take 
 a sudden leap from structure to structure? On the theory 
 of natural selection, we can clearly understand why she 
 should not; for natural selection acts only by taking ad¬ 
 vantage of slight successive variations; she can never take 
 a great and sudden leap, but must advance by short and 
 sure, though slow steps. 
 
 ORGAN'S OF LITTLE APPARENT IMPORTANCE, AS AFFECTED 
 
 BY NATURAL SELECTION. 
 
 As natural selection acts by life and death, by the sur¬ 
 vival of the fittest, and by the destruction of the less well- 
 fitted individuals, I have sometimes felt great difficulty in 
 understanding the origin or formation of parts of little 
 importance; almost as great, though of a very different 
 kind, as in the case of the most perfect and complex 
 organs. 
 
 In the first place, we are much too ignorant in regard 
 to the whole economy of any one organic being to say 
 what slight modifications would be of importance or not. 
 In a former chapter I have given instances of very trifling 
 characters, such as the down on fruit and the color of its 
 flesh, the color of the skin and hair of quadrupeds, which, 
 from being correlated with constitutional differences, or 
 from determining the attacks of insects, might assuredly 
 be acted on by natural selection. The tail of the giraffe 
 looks like an artificially constructed fly-flapper; and it 
 seems at first incredible that this could have been adapted 
 for its present purpose by successive slight modifications, 
 each better and better fitted, for so trifling an object as to 
 drive away flies; yet we should pause before being too 
 positive even in this case, for we know that the distribu¬ 
 tion and existence of cattle and other animals in South 
 America absolutely depend on their power of resisting the 
 attacks of insects: so that individuals which could by any 
 means defend themselves from these small enemies, would 
 be able to range into pew pastures and thus gain a great 
 
AFFECTED BY NATURAL SELECTION. 1S7 
 
 advantage. It is not that the larger quadrupeds are 
 actually destroyed (except in some rare cases) by flies, but 
 they are incessantly harassed and their strength reduced, 
 so that they are more subject to disease, or not so well 
 enabled in a coming dearth to search for food, or to escape 
 from beasts of prey. 
 
 Organs now of trifling importance have probably in 
 some cases been of high importance to an early progenitor, 
 and, after having been slowly perfected at a former period, 
 have been transmitted to existing species in nearly the 
 same state, although now of very slight use; but anv 
 actually injurious deviations in their structure would of 
 course have been checked by natural selection. Seeing 
 how important an organ of locomotion the tail is in most 
 aquatic animals, its general presence and use for many 
 purposes in so many land animals, which in their lungs or 
 modified swim-bladders betray their aquatic origin, may 
 perhaps be thus accounted for. A well-developed tail 
 having been formed in an aquatic animal, it might subse¬ 
 quently come to be worked in for all sorts of purposes, as a 
 fly-flapper, an organ of prehension, or as an aid in turn- 
 ing, as in the case .of the dog, though the aid in this latter 
 respect must be slight, for the hare, with hardly any tail, 
 can double still more quickly. 
 
 In the second place, we may easily err in attributing 
 importance to characters, and in believing that they have 
 been developed through natural selection. We must by 
 no means overlook the effects of the definite action of 
 changed conditions of life, of so-called spontaneous varia¬ 
 tions, which seem to depend in a quite subordinate 
 degree on the nature of the conditions, of the tendency 
 to reversion to long-lost characters, of the complex 
 laws of growth, such as of correlation, comprehension, 
 of the pressure of one part on another, etc., and finally of 
 sexual selection, by which characters of use to one sex are 
 often gained and then transmitted more or less perfectly to 
 the other sex, though of no use to the sex. But structures 
 thus indirectly gained, although at first of no advantage to 
 a species, may subsequently have been taken advantage of 
 by its modified descendants, under new conditions of life 
 and newly acquired habits. 
 
 If green woodpeckers alone had existed, and we did not 
 
188 
 
 ORGANS OF LITTLE IMPORTANCE 
 
 know that there were many black and pied kinds, I dare 
 say that we should have thought that the green color was a 
 beautiful adaptation to conceal this tree-frequenting bird 
 from its enemies; and consequently that it was a character 
 of importance, and had been acquired through natural 
 selection; as it is, the color is probably in chief part due to 
 sexual selection. A trailing palm in the Malay Archipel¬ 
 ago climbs the loftiest trees by the aid of exquisitely con¬ 
 structed hooks clustered around, the ends of the branches, 
 and this contrivance, no doubt, is of the highest service to 
 the plant; but as we see nearly similar hooks on many 
 trees which are not climbers, and which, as there is reason 
 to believe from the distribution of the thorn-bearing species 
 in Africa and South America, serve as a defense against 
 browsing quadrupeds, so the spikes, on the palm may at 
 first have been developed for this object, and subsequently 
 have been improved and taken advantage of by the .plant, 
 as it underwent further modification and became a climber. 
 The naked skin on the head of a vulture is generally con¬ 
 sidered as a direct adaptation for wallowing in putridity; 
 and so it may be, or it may possibly be due to the direct 
 action of putrid matter; but we should be very cautious in 
 drawing any such inference, when we 'see that the skin on 
 the head of the clean-feeding male turkey is likewise 
 naked. The sutures in the skulls of ycung mammals 
 have been advanced as a beautiful adaptation for aiding 
 parturition, and no doubt they facilitate, or may be indis 
 pen sable for this act: but as sutures occur in the skulls of 
 young birds and reptiles, which have only to escape from a 
 broken egg, we may infer that this structure has arisen 
 from the laws of growth, and has been taken advantage of 
 in the parturition of the higher animals. 
 
 We are profoundly ignorant of the cause of. each slight 
 variation or individual difference; and we are immediately 
 made conscious of this by reflecting on the differences 
 between the breeds of our domesticated animals in differ¬ 
 ent countries, more especially in the less civilized coun¬ 
 tries, where there has been but little methodical selection. 
 Animals kept by savages in different countries often have 
 to struggle for their own subsistence, and are exposed to a 
 certain extent to natural selection, and individuals with 
 slightly different constitutions would succeed best under 
 
AFFECTED BY NATURAL SELECTION. 139 
 
 climates. With cattle susceptibility to the attacks 
 of flies is correlated with color, as is the liability to be pois¬ 
 oned by certain plants; so that even color would be thus 
 subjected to the action of natural selection. Some observ¬ 
 ers are convinced that a damp climate affects the growth 
 of the hair, and. that with the hair the horns are corre¬ 
 lated. Mountain breeds always differ from lowland 
 breeds; and. a mountainous country would probablv 
 affect the hind limbs from exercising them more, and 
 possibly even the form of the pelvis; and then by the 
 law of homologous variation, the front limbs and the head 
 would probably be affected. The shape, also, of the pelvis 
 might affect by pressure the shape of certain parts of the 
 young in the womb. The laborious breathing necessary in 
 high regions tends, as we have good reason to believe, to 
 increase the size of the chest; and again correlation would 
 come into play. The effects of lessened exercise, together 
 with abundant food, on the whole organization is probably 
 still more important; and this, as H. von Nathusius has 
 lately shown in his excellent Treatise, is apparently one 
 chief cause of the great modification which the breeds of 
 swine have undergone. But we are far too ignorant to 
 speculate on the relative importance of the several known 
 and unknown causes of variation; and I have made these 
 remarks only to show that, if we are unable to account for 
 the characteristic differences of our several domestic breeds, 
 which nevertheless are generally admitted to have arisen 
 through ordinary generation from one or a few parent- 
 stocks, we ought not to lay too much stress on our ignor¬ 
 ance of the precise cause of the slight analogous differences 
 between true species. 
 
 UTILITARIAN DOCTRINE, HOW FAR TRUE: BEAUTY, HOW 
 
 ACQUIRED. 
 
 The foregoing remarks lead me to say a few words on 
 the protest lately made by some naturalists against the 
 utilitarian doctrine that every detail of structure has been 
 produced for the good of its possessor. They believe that 
 many structures have been created for the sake of beauty, 
 to delight man or the Creator (but this latter point is be¬ 
 yond the scope of scientific discussion), or for the sake of 
 
190 UTILITARIAN DOCTRINE, HOW FAR TRUE: 
 
 mere variety, a view already discussed. Such doctrines, it 
 true, would be absolutely fatal to my theory. I fully 
 admit that many structures are now of no direct use to 
 their possessors, and may never have been of any use to 
 their progenitors; but this does not prove that they were 
 formed solely for beauty or variety. IN o doubt the definite 
 action of changed conditions, and the various causes of 
 modifications, lately specified, have all produced an effect, 
 probably a great effect, independently of any advantage 
 thus gained. But a still more important consideration is 
 that the chief part of the organization of every living 
 creature is due to inheritance; and consequently, though 
 each being assuredly is well fitted for its place in nature, 
 many structures have now no very close and direct rela¬ 
 tion to present habits of life. Thus, we can hardly believe 
 that the webbed feet of the upland goose, or of the frigate- 
 bird, are of special use to these birds; we can not believe 
 that the similar bones in the arm of the monkey, in the 
 fore leg of the horse, in the wing of the bat, and in the 
 flipper of the seal, are of special use to these animals. We 
 may safely attribute these structures to inheritance. But 
 webbed feet no doubt were as useful to the progenitor of 
 the upland goose and of the frigate-bird, as they now are 
 to the most aquatic of living birds. So we may believe 
 that the progenitor of the seal did not possess a flipper, 
 but a foot with five toes fitted for walking or grasping; and 
 we mav further venture to believe that the several bones 
 in the limbs of the monkey, horse and bat, were originally 
 developed, on the principle of utility, probably through 
 the reduction of more numerous bones in the fin of some 
 ancient fish-like progenitor of the whole class. It is 
 scarcely possible to decide how much allowance. ought, to 
 be made for such causes of change, as the definite, action 
 of external conditions, so-called spontaneous variations, 
 and the complex laws of growth; but with these important 
 exceptions, we may conclude that the structure of every 
 living creature either now is, or was formerly, of some 
 direct or iudirect use to its possessor. 
 
 With respect to the belief that organic beings have, been 
 created beautiful for the delight of man—a belief which it 
 lias been pronounced is subversive of my whole theory — 
 I may first remark that the sense of beauty obviously de- 
 
BE A XJTY\ HOW ACQ VIRED . 191 
 
 pends on the nature of the mind, irrespective of any real 
 quality in the admired object; and that the idea of what 
 is beautiful, is not innate or unalterable. We see this, for 
 instance, in the men of different races admiring an en¬ 
 tirely different standard of beauty in their women. If beau¬ 
 tiful objects had been created solely for man’s gratification, 
 it ought to be shown that before man appeared there was 
 less beauty on the face of the earth than since he came on 
 the stage. Were the beautiful volute and cone shells of 
 the Eocene epoch, and the gracefully sculptured ammonites 
 of the Secondary period, created that man might ages 
 afterward admire them in his cabinet? Few objects are 
 more beautiful than the minute siliceous cases of the 
 diatomaceae : were these created that they might be ex¬ 
 amined and admired under the higher "powers of the 
 microscope? The beauty in this latter case, and in many 
 others, is apparently wholly due to symmetry of growth. 
 Flowers rank among the most beautiful productions of 
 nature; but they have been rendered conspicuous in con¬ 
 trast with the green leaves, and in consequence at the 
 same time beautiful, so that they may be easily observed 
 by insects. I have come to this conclusion from finding it 
 an invariable rule that when a flower is fertilized by the 
 wind it never has a gaily-colored corolla. Several plants 
 habitually produce two kinds of flowers; one kind open and 
 colored so as to attract insects; the other closed, not- 
 colored, destitute of nectar, and never visited by insects. 
 Hence, we may conclude that, if insects had not been de¬ 
 veloped on the face of the earth, our plants would not have 
 been decked with beautiful flowers, but would have pro¬ 
 duced only such poor flowers as we see on our fir, oak, nut 
 and ash trees, on grasses, spinach, docks and nettles, 
 which are all fertilized through the agency of the wind. 
 A similar line of argument holds good with fruits; that a 
 ripe strawberry or cherry is as pleasing to the eye as to the 
 palate that the gaily-colored fruit of the spindle-wood 
 tree and the scarlet berries of the holly are beautifu. objects 
 —will be admitted by every one. But this beauty serves 
 merely as a guide to birds and beasts, in order that the 
 fruit may. be devoured and the matured seeds dissem¬ 
 inated. I infer tnat this is the case from having as vet 
 found no exception to the rule that seeds are always thus 
 
192 UTILITARIAN DOCTRINE , ROW FAR TRUE: 
 
 disseminated when imbedded within a fruit of any kind 
 (that is within a fleshy or pulpy envelope), if it be colored 
 of any brilliant tint, or rendered conspicuous by being 
 white or black. 
 
 On the other hand, I willingly admit that a great 
 number of male animals, as all our most gorgeous birds, 
 some fishes, reptiles, and mammals, and a host of 
 magnificently colored butterflies, have been rendered 
 beautiful for beauty's sake. But this has been effected 
 through sexual selection, that is, by the more beautiful 
 males having been continually preferred by the females, 
 and not for the delight of man. So it is with the music of 
 birds. We may infer from all this that a nearly similar 
 taste for beautiful colors and for musical sounds runs 
 through a large part of the animal kingdom. When the 
 female is as beautifully colored as the male, which is not 
 rarely the case with birds and butterflies, the cause ap¬ 
 parently lies in the colors acquired through sexual selec¬ 
 tion having been transmitted to both sexes, instead of to 
 the males alone. How the sense of beauty in its simplest 
 form—that is, the reception of a peculiar kind of pleasure 
 from certain colors, forms and sounds—nvas first developed 
 in the mind of man and of the lower animals, is a very ob¬ 
 scure subject. The same sort of difficulty is presented if 
 we inquire how it is that certain flavors and odors give 
 pleasure, and others displeasure. Habit in all these cases 
 appears to have come to a certain extent into play; but 
 there must be some fundamental cause in the constitution 
 of the nervous system in each species. 
 
 Natural selection cannot possibly produce any modifica¬ 
 tion in a species exclusively for the good of another 
 species, though throughout nature one species inces¬ 
 santly takes advantage of and profits by the structures of 
 others. But natural selection can and does often produce 
 structures for the direct injury of other animals, as we 
 see in the fang of the adder, and in the ovipositor of the 
 ichneumon, by which its eggs are deposited in the living 
 bodies of other insects. If it could be proved that any 
 part of the structure of any one species had been formed 
 for the exclusive good of another species, it would anni¬ 
 hilate my theory, for such could not have been produced 
 
BEA UTY, HO W ACQ UIRED. I93 
 
 through natural selection. Although many statements 
 may be found in works on natural history to this effect, I 
 cannot find even one which seems to me of any weight. It 
 is admitted that the rattlesnake has a poison fang for its 
 own defence and for the destruction of its prey; but some 
 authois suppose that at the same time it is furnished with 
 a rattle for its own injury, namely, to warn its prey. I 
 would almost as soon believe that the cat curls the end of 
 its tail when preparing to spring, in order to warn the 
 doomed mouse. It is a much more probable view that the 
 rattlesnake uses its rattle, the cobra expands its frill and 
 the puff-adder swells while hissing so loudly and harshly, 
 in order to alarm the many birds and beasts which are 
 known to attack even the most venomous species. Snakes 
 act on the same principle which makes the hen ruffle her 
 feathers and expand her wings when a dog approaches her 
 chickens. But I have not space here to enlarge on the 
 many ways by which animals endeavor to frighten away 
 their enemies. 
 
 atural selection will never produce in a being any 
 structure more injurious than beneficial to that being, for 
 natural selection acts solely by and for the good of each. 
 No organ will be formed, as Paley has remarked, for the 
 purpose of causing pain or for doing an injury to its pos¬ 
 sessor. If a fair balance be struck between the good and 
 evil caused by each part, each will be found on the whole 
 advantageous. . After the lapse of time, under changing 
 conditions of life, if any part comes to be injurious, it will 
 be modified;, or if it be not so, the being will become ex¬ 
 tinct as myriads have become extinct. 
 
 Natural selection tends only to make each organic being 
 is perfect as, or slightly more perfect than the other in¬ 
 habitants of the same country with which it comes into com¬ 
 petition. . And we see that this is the standard of perfec¬ 
 tion attained under nature. The endemic productions of 
 New Zealand, for instance, are perfect, one compared with 
 another; but they are now rapidly yielding before the ad¬ 
 vancing legions of plants and animals introduced from 
 Europe. Natural selection will not produce absolute per¬ 
 fection,. nor do we always meet, as far as we can judge, 
 with this high standard under nature. The correction for 
 the aberration of light is said by Muller not to be perfect 
 
194 UTILITARIAN DOCTRINE , BOW EAR TRUE: 
 
 even in that most perfect organ, the human eye. Helm¬ 
 holtz, whose judgment no one will dispute, after describ¬ 
 ing in the strongest terms the wonderful powers of the 
 human eye, adds these remarkable words: * That whicn 
 we have discovered in the way of inexactness and imper¬ 
 fection in the optical machine and in the linage on the 
 retina, is as nothing in comparison with the incongruities 
 which we have just come across m the domain of the sen¬ 
 sations. One might say that nature has taken delight 1 
 accumulating contradictions m order to remove all founda¬ 
 tion from the theory of a pre-existing harmony between 
 the external and internal worlds.” If our reason leads us 
 to admire with enthusiasm a multitude of inimitable con¬ 
 trivances in nature, this same reason tells us, though we 
 may easily err on both sides, that some other contrivances 
 are less perfect. Can we consider the sting of the bee as 
 perfect, which, when used against many kinds of enemies, 
 can not be withdrawn, owing to the backward serratuies, 
 and thus inevitably causes the death of the insect by teai- 
 
 ing out its viscera? . . , , • 0 
 
 If we look at the sting of the bee, as having existed m a 
 
 remote progenitor, as a boring and serrated instrument, 
 like that in so many members of the same great order, and 
 that it has since been modified but _ not perfected for 
 its present purpose, with the poison originally adapted for 
 some other object, such as to produce galls, since inten¬ 
 sified, we can perhaps understand how it is that the use of 
 the sting should so often cause the insects own death: for 
 if on the whole the power of stinging be useful to the social 
 community, it will fulfil all the requirements of natural 
 selection, though it may cause the death of some few mem¬ 
 bers. If we admire the truly wonderful power of scent by 
 which the males of many insects find their females, can we 
 admire the production for this single purpose of thousands 
 of drones, which are utterly useless to the community ioj 
 any other purpose, and which are ultimately slaughtered by 
 their industrious and sterile sisters? ^ It may be difficult 
 but we ought to admire the savage instinctive hatred o^ t le 
 queen-bee, which urges her to destroy the young queens, her 
 daughters, as soon as they are born, or to perish herself m 
 the combat; for undoubtedly this is for the good of the 
 community; and maternal love or maternal hatred, though 
 
BE A UTT ,, HO W ACQ UIRED. 
 
 195 
 
 the latter fortunately is most rare, is all the same to the 
 inexorable principles of .natural selection. If we admire 
 the several ingenious contrivances by which orchids and 
 many other plants are fertilized through insect agency, can 
 we consider as equally perfect the elaboration of dense 
 clouds of pollen by our fir-trees, so that a few granules 
 may be wafted by chance on to the ovules? 
 
 summary: the law of unity of type and of the con¬ 
 ditions OF EXISTENCE EMBRACED BY THE THEORY OF 
 NATURAL SELECTION. 
 
 We have in this chapter discussed some of the difficulties 
 and objections which may be urged against the theory. 
 Many of them are serious; but I think that in the discussion 
 light has been thrown on several facts, which on the belief 
 of independent acts of creation are utterly obsure. We 
 have seen that species at any one period are not indefinitely 
 variable, and are not linked together by a multitude of 
 intermediate gradations, partly because the process of 
 natural selection is always very slow, and at any one time 
 acts only on a few forms; and partly because the very pro¬ 
 cess of natural selection implies the continual supplanting 
 and extinction of preceding and intermediate gradations. 
 Closely allied species, now living on a continuous area, 
 must often have been formed when the area was not con¬ 
 tinuous, and when the conditions of life did not insensibty 
 graduate away from one part to another. When two vari¬ 
 eties are formed in two districts of a continuous area, an 
 intermediate variety will often be formed, fitted for an 
 intermediate zone; but from reasons assigned, the inter¬ 
 mediate variety will usually exist in lesser numbers than 
 the two forms which it connects; consequently the two 
 latter, during the course of further modification, from ex¬ 
 isting in greater numbers, will have a great advantage over 
 the less numerous intermediate variety, and will thus gen¬ 
 erally succeed in supplanting and exterminating it. 
 
 We have seen in this chapter how cautious we should be 
 in concluding that the most different habits of life could 
 not graduate into each other; that a bat, for instance, 
 could not have been formed by natural selection from an 
 animal which at first only glided through the air. 
 
196 
 
 SUMMARY, 
 
 We have seen that a species under new conditions of life 
 may change its habits; or it may have diversified habits, 
 with some very unlike those of its nearest congeners. 
 Hence we can understand, bearing in mind that each or¬ 
 ganic being is trying to live wherever it can live, how it 
 has arisen that there are upland geese with webbed feet, 
 ground woodpeckers, diving thrushes, and petrels with the 
 habits of auks. 
 
 Although the belief that an organ so perfect as the eye 
 could have been formed by natural selection, is enough to 
 stagger anyone; yet in the case of any organ, if we know 
 of a long series of gradations in complexity, each good for 
 its possessor, then under changing conditions of life, there 
 is no logical impossibility in the acquirement of any con¬ 
 ceivable degree of perfection through natural selection. 
 In the cases in which we know of no intermediate or transi¬ 
 tional states, we should be extremely cautious in concluding 
 that none can have existed, for the metamorphoses of many 
 organs show what wonderful changes in function are at 
 least possible. For instance, a swim-bladder has appar¬ 
 ently been converted into an air-breathing lung. The 
 same organ having performed simultaneously very different 
 functions, and then having been in part or in whole special¬ 
 ized for one function; and two distinct organs having per¬ 
 formed at the same time the same function, the one having 
 been perfected while aided by the other, must often have 
 largely facilitated transitions. 
 
 We have seen that in two beings widely remote from each 
 other in the natural scale, organs serving for the same pur¬ 
 pose and in external appearance closely similar may have 
 been separately and independently formed; but when such 
 organs are closely examined, essential differences in their 
 structure can almost always be detected; and this naturally 
 follows from the principle of natural selection. On the 
 other hand, the common rule throughout nature is infinite 
 diversity of structure for gaining the same end; and this 
 again naturally follows from the same great principle. 
 
 In many cases we are far too ignorant to be enabled to 
 assert that a part or organ is so unimportant for the wel¬ 
 fare of a species, that modifications in its structure could 
 not have been slowly accumulated by means of natural 
 selection, In many other cases, modifications are probably 
 
SUMMARY. 
 
 197 
 
 the direct result of the laws of variation or of growth, in¬ 
 dependently of any good having been thus gained. But 
 even such structures have often, as we may feel assured 
 been subsequently taken advantage of, and still further 
 modified, for the good of species under new conditions of 
 life. We may, also, believe that a part formerly of high 
 importance has frequently been retained (as the tail of an 
 aquatic animal by its terrestrial descendants), though it 
 has become of such small importance that it could not, in 
 its present state, have been acquired by means of natural 
 selection. 
 
 Natural, selection can produce nothing in one species for 
 the exclusive good or injury of another; though it may well 
 pioduce parts, organs, and excretions highly useful or even 
 indispensable, or again highly injurious to another species, 
 but in all cases at the same time useful to the jiossessor. 
 In each well-stocked country natural selection acts through 
 the competition of the inhabitants and consequently leads 
 to success in the battle for life, only in accordance with the 
 standard of that particular country. Hence the inhabi¬ 
 tants of one country, generally the smaller one, often yield 
 to the inhabitants of another and generally the larger 
 country. For in the larger country there will have existed 
 more individuals and more diversified forms, and the com¬ 
 petition will. have been severer, and thus the standard of 
 perfection will have been rendered higher. Natural selec¬ 
 tion will not necessarily lead to absolute perfection; nor 
 as far as we can judge by our limited faculties, can absolute 
 perfection be everywhere predicated. 
 
 On the theory of natural selection we can clearly under- 
 stand thefuH meaning of that old canon in natural historv, 
 
 Natura non.facit saltum.” This canon, if we look to the 
 present inhabitants alone of the world, is not strictly cor¬ 
 rect; but if we include all those of past times, whether 
 known or unknown, it must on this theory be strictly true. 
 
 It is generally acknowledged that all organic beings have 
 been formed on two great laws—Unity of Type, and the 
 Conditions of Existence. By unity of type is meant that 
 fundamental agreement in structure which we see in 
 organic beings of the same class, and which is quite inde¬ 
 pendent of their habits of life. On my theory, unity of 
 type is explained by unity of descent. The expression of 
 
193 
 
 SUMMARY . 
 
 conditions of existence, so often insisted on by the illus¬ 
 trious Cuvier, is fully embraced by the principle of natural 
 selection. For natural selection acts by either now adapt¬ 
 ing the varying parts of each being to its organic and in¬ 
 organic conditions of life; or by having adapted them 
 during past periods of time: the adaptations being aided in 
 many cases by the increased use or disuse of parts, being 
 affected by the direct action of the external conditions of 
 life, and subjected in all cases to the several laws of growth 
 and variation. Hence, in fact, the law of the Conditions 
 of Existence is the higher law; as it includes, through the 
 inheritance of former variations and adaptations, that of 
 Unity of Type. 
 
f 
 
 MISCELLANEOUS OBJECTIONS . 
 
 199 
 
 CHAPTER VII. 
 
 MISCELLANEOUS OBJECTIONS TO THE THEORY OF NATURAL 
 
 SELECTION. 
 
 Longevity — Modifications not necessarily simultaneous — Modifica¬ 
 tions apparently of no direct service — Progressive develop¬ 
 ment Characters of small functional importance, the most con¬ 
 stant—.Supposed incompetence of natural selection to account for 
 the incipient stages of useful structures—Causes which interfere 
 with the acquisition through natural selection of useful struct¬ 
 ures—Gradations of structure with changed functions—Widely 
 different organs in members of the same class, developed from 
 one and the same source—Reasons for disbelieving in great and 
 abrupt modifications. 
 
 I will devote this chapter to the consideration of 
 various miscellaneous objections which have been advanced 
 against my views, as some of the previous discussions may 
 thus be made clearer; but it would be useless to discuss all 
 of them, as many have been made by writers who have not 
 taken the trouble to understand the" subject. Thus a dis- 
 guished German naturalist has asserted that the weakest 
 part of my theory is, that I consider all organic beings as 
 imperfect: what I have really said is, that all are not as 
 perfect as they might have been in relation to their condi¬ 
 tions; and this is shown to be the case by so many native 
 forms in many quarters of the world having yielded their 
 places to intruding foreigners. Nor can organic beings, 
 even if they were at any one time perfectly adapted to 
 their conditions of life, have remained so, when their con¬ 
 ditions changed, unless they themselves likewise changed; 
 and no one will dispute that the physical conditions of 
 each country, as well as the number and kinds of its inhab¬ 
 itants, have undergone many mutations. 
 
 A critic has lately insisted, with some parade of mathe¬ 
 matical accuracy, that longevity is a great advantage to all 
 species, so that he who believes in natural selection ‘‘must 
 
200 MISCELLANEOUS OBJECTIONS TO TEE 
 
 arrange his genealogical tree in such a manner that all 
 the descendants have longer lives than their progenitors! 
 Cannot our critics conceive that a biennial plant or one of 
 the lower animals might range into a cold climate and 
 perish there every winter; and yet, owing to advantages 
 gained through natural selection, survive from year to 
 year by means of its seeds or ova? Mr. E. Ray Lankester 
 has recently discussed this subject, and he concludes, as 
 far as its extreme complexity allows him to form a judg¬ 
 ment, that longevity is generally related to the standard of 
 each species in the scale of organization, as well as to the 
 amount of expenditure in reproduction and in geneial 
 activity. And these conditions have, it is probable, been 
 largely determined through natural selection. 
 
 It has been argued that, as none of the animals and 
 plants of Egypt, of which we know anything, have changed 
 during the last three or four thousand years, so probably 
 have none in any part of the world. But, as Mr. G. H. 
 Lewes has remarked, this line of argument proves too 
 much, for the ancient domestic races figured on the 
 Egyptian monuments, or embalmed, are closely similar or 
 even identical with those now living; yet all naturalists 
 admit that such races have been produced through the 
 modification of their original types. The many animals 
 which have remained unchanged since the commencement 
 of the glacial period, would have been an incomparably 
 stronger case, for these have been exposed to great changes 
 of climate and have migrated over great distances; whereas, 
 in Egypt, during the last several thousand years, the con¬ 
 ditions of life, as far as we know, have remained absolutely 
 uniform. The fact of little or no modification having 
 been effected since the glacial period, would have been of 
 some avail against those who believe in an innate and 
 necessary law of development, but is powerless against the 
 doctrine of natural selection or the survival of the fittest, 
 which implies that when variations or individual differences 
 of a beneficial nature happen to arise, these will be pre¬ 
 served; but this will be effected only under certain favor¬ 
 able circumstances. . 
 
 The celebrated palaeontologist, Bronn, at the close of his 
 German translation of this work, asks how, on the prin¬ 
 ciple of natural selection, can a variety live side by side 
 
THEORY OE NATURAL SELECTION. 201 
 
 wUh the pareut; species? If both have become fitted for 
 ?ive different habits of life or conditions, they might 
 live >gether;_ and if we lay on one side polymorohic 
 
 nature’ an/all nm 6 V t ariabilit 3' seems to be of a peculiar 
 aIbinisn f d fo f) i ' e tem P orar y variations, such as size, 
 aioimsm, etc., the more permanent varieties are generally 
 
 uch ks aS Wh aS ls T diS , C0Ve ^ inbabitin g distinction ! 
 
 Moreover fn the 1“' l0 / ***, *? or moist districts! 
 oicover, in the case of animals which wander much 
 
 about and cross freely, their varieties seem to be generally 
 confined to distinct regions. fceneiaiiy 
 
 Broun also insists _ that distinct species never differ 
 om each other in single characters, but in many parts- 
 and he asks, how it always comes that many pai t/of the’ 
 
 S n T • S , b ° U d bave been modified at the same time 
 thlough variation and natural selection? But there is no 
 
 necessity for supposing that all the parts of any being 
 have been simultaneously modified. The most striking 
 modifications, excellently adapted for some purpose might 5 
 
 a ioZ ifXhf 7T: ked ’ be ac< 3 uired by P sueSve 4, : 
 
 ations, if slight, first m one part and then in another- and 
 
 pear to us“as i? tb™ FH*? M - to « etbel '’ tbe J would ap 
 Tut hit f i. they had been simultaneously developed. 
 The best answer, however, to the above objection is afforded 
 by those domestic races which have been modified chiefly 
 tlnough man s power of selection, for some special purpose^ 
 
 mastiff ‘tV- C e 1“ 1 d !' ay - h01se > at «ie |reyhouncf and 
 mastiff Their whole frames, and even their mental char¬ 
 acteristics, have been modified; but if we could trace each 
 step in the history of their transformation—and the latter 
 steps can be traced—we should not see great and simulta- 
 
 mo°d U ifiS an ^ bUt fil I t 0I l e P art and then another slightly 
 modified and improved. Even when selection has been 
 
 plied by man to some one character alone—of which our 
 
 be found 1 th^lth** ‘wu- 8 * instan °es—it will invariably 
 
 flower f d n,ff L li h0Ugh i “t one P art > whetl mr it be the 
 nower, fruit, or leaves, has been greatly changed almost 
 
 hi ^ -w 6r i parts i llave been sightly modified. ^ This may 
 be attributed partly to the principle of correlated growth 
 and partly to so-called spontaneous variation. S ’ 
 
 A much more serious objection has been urged by Broun 
 and recently by Broca, namely, that maSy characters 
 
202 MISCELLANEOUS OBJECTIONS TO THE 
 
 appear to be of no service whatever to their possessors, and 
 therefore cannot have been influenced through natural 
 selection. Bronn adduces the length of the ears and taiio 
 in the different species of hares and mice—the complex 
 folds of enamel in the teeth of many animals, and a multi¬ 
 tude of analogous cases. With respect to plants, this sub¬ 
 ject has been discussed by Nageli m an admirable essay. 
 He admits that natural selection has effected much, but he 
 insists that the families of plants differ chiefly from each 
 other in morphological characters, which appear to be quite 
 unimportant for the welfare of the species. He conse¬ 
 quently believes in an innate tendency toward pi ogiessive 
 and more perfect development. He specifies the arrange¬ 
 ment of the cells in the tissues, and of the leaves on the 
 axis, as cases in which natural selection could not have 
 acted. To these may be added the numerical divisions m 
 the parts of the flower, the position of the ovules, the 
 shape of the seed, when not of any use for dissemina- 
 
 10 There’is much force in the above objection. Neverthe¬ 
 less we ought, in the first place, to be extremely cautious 
 in pretending to decide what structures now are, or have 
 formerly been, of use to each species. In the second place, 
 it should always be borne in mind that when one part is 
 modified, so will be other parts, through certain dimly seen 
 causes, such as an increased or diminished flow of nutri¬ 
 ment to a part, mutual pressure, an early developed part 
 affecting one subsequently developed, and so forth as yell 
 as through other causes which lead to the many mysterious 
 cases of correlation, which we do not m the least undei- 
 stand. These agencies may be all grouped together, 
 for the sake of brevity, under. the expression of 
 the laws of growth. In the third place, we have 
 to allow for the direct and definite action of 
 
 changed conditions of life, and for so-called spontaneous 
 variations, in which the nature of the conditions appar¬ 
 ently plays a quite subordinate part. Bud-variations, such 
 as the appearance of a moss-rose on a common rose, 01 o 
 a nectarine on a peach-tree, offer good instances of spon¬ 
 taneous variations; but even in these cases, if we bear m 
 mind the power of a minute drop of poison in producing 
 complex galls, we ought not to feel too sure that the above 
 
THEORT OF NATURAL SELE0T10N. 203 
 
 \ai iations aie not the effect of some local change in the 
 nature of the sap, due to some change in the conditions. 
 I.here must be some efficient cause for each slight indi¬ 
 vidual difference, as well as for more strongly marked 
 variations which occasionally arise; and if the unknown 
 cause were to act persistently, it is almost certain that all 
 the individuals of the species would be similarly modified. 
 
 In the earlier editions of this work I underrated, as it 
 
 n °'^--G eer ^ S frequency and importance of 
 
 modifications due to spontaneous variability. But it is im¬ 
 possible to attribute to this cause the innumerable struct- 
 ures.which are so well adapted to the habits of life of each 
 species. I can no more believe in this than that the well- 
 adapted form of a race-horse or greyhound, which before 
 the principle of selection by man was well understood, ex¬ 
 cited so much surprise in the minds of the older natural¬ 
 ists, can thus be explained. 
 
 It may be worth while to illustrate some of the foregoing 
 remarks. With respect to the assumed inutility of various 
 parts and organs, it is hardly necessary to observe that 
 even m.the higher and best-known animals many struct- 
 ures exist, which are so highly developed that * no one 
 doubts that they are of importance, yet their use has not 
 been, or has only recently been, ascertained. As Bronn 
 gives, the length of the ears and tail in the several species 
 o mice as instances, though trifling ones, of differences in 
 s tincture which can be of no special use, I may mention 
 that, according to Dr. Schobl, the external ears of the 
 common mouse are supplied in an extraordinary manner 
 with nerves, so that they no doubt serve as tactile organs- 
 hence the length of the ears can hardly be quite unimpor- 
 tant. We shall, also, presently see that the tail is a highly 
 useful prehensile organ to some of the species; and its°use 
 would be much influenced by its length. 
 
 With respect to plants, to which on account of Nao'elks 
 essay I shall confine myself in the following remarks, it 
 will be admitted that the flowers of the orchids present a 
 multitude of curious structures, which a few years ago 
 would have been considered as mere morphological differ¬ 
 ences without any special function; but they are now 
 known to be of the highest importance for the fertilization 
 of the species through the aid of insects, and have prob- 
 
204 MISCELLANEOUS OBJECTIONS TO THE 
 
 ably been gained through natural selection. No one until 
 lately would have imagined that in dimorphic and tri- 
 morphic plants the different lengths of the stamens and 
 pistils, and their arrangement, could have been of any 
 service, but now we know this to be the case. 
 
 In certain whole groups of plants the ovules stand erect, 
 and in others they are suspended; and within the same 
 ovarium of some few plants, one ovule holds the former 
 and a second ovule the latter position. These positions 
 seem at first purely morphological, or of no physiological 
 signification; but Dr. Hooker informs me that within the 
 same ovarium, the upper ovules alone in some cases, and 
 in others the lower ones alone are fertilized; and he sug¬ 
 gests that this probably depends on the direction in which 
 the pollen-tubes enter the ovarium. If so, the position of 
 the ovules, even when one is erect and the other suspended 
 within the same ovarium, would follow the selection of any 
 slight deviations in position which favored their fertiliza¬ 
 tion, and the production of seed. 
 
 Several plants belonging to distinct orders habitually 
 produce flowers of two kinds—the one open, of the ordi¬ 
 nary structure, the other closed and imperfect. These two 
 kinds of flowers sometimes differ wonderfully in structure, 
 yet may be seen to graduate into each other on the same 
 plant. The ordinary and open flowers can be intercrossed; 
 and the benefits which certainly are derived from this pro¬ 
 cess are thus secured. The closed and imperfect flowers 
 are, however, manifestly of high importance, as. they yield 
 with the utmost safety a large stock of seed, with the ex¬ 
 penditure of wonderfully little pollen. The two kinds of 
 flowers often differ much, as just stated, in structure.. The 
 petals in the imperfect flowers almost always consist of 
 mere rudiments, and the pollen-grains are reduced in 
 diameter. In Ononis columnse five of the alternate sta¬ 
 mens are rudimentary; and in some species of Viola three 
 stamens are in this state, two retaining their proper func¬ 
 tion, but being of very small size. In six out of thirty of 
 the closed flowers in an Indian violet (name unknown, for 
 the plants have never produced with me perfect flowers), 
 the sepals are reduced from the normal number of five to 
 three. In one section of the Malpighiaceae the closed 
 flowers, according to A. de Jussieu, are still further modi- 
 
THEORY OF NATURAL SELECTION ^05 
 
 fled, for the five stamens which stand opposite to the sepals 
 me all aborted, a sixth stamen standing opposite to a petal 
 being alone developed; and this stamen fnot present in 
 th® ordinaly flowers of this species; the style is aborted- 
 and the ovana are reduced from three to two. Now al¬ 
 though natural selection may well have had the power to 
 prevent some of the flowers from expanding, and to reduce 
 tie amount of pollen, when rendered by the closure of the 
 floweis superfluous, yet hardly any of the above special 
 
 „ can have been thus determined, but must 
 have followed from the laws of growth, including thefunc- 
 
 t on of ?be tlV n y ° f P u rt i S ’ d V nng the P ro gress of the reduc¬ 
 tion of the pollen and the closure of the flowers. 
 
 f T,_,* s so " ecessar y to appreciate the important effects of 
 the laws of growth, that I will give some additional cases 
 of another kind, namely of differences in the same part or 
 
 plain?' d Tn ti dl * ereno , es \ n relative position on the same 
 plant. In the Spanish chestnut, and in certain fir-trees, 
 
 SeW$ eS - 0f d ' vergenc f of the leaves differ, according to 
 Schacht, m the nearly horizontal and in the upnght 
 branches. In the common rue and some other plants, one 
 flowei, usually the central or terminal one, opens first, and 
 
 P? ta s ’ and five divisions to the ovarium; 
 In tl? \ e 5 flo 'rers on the plant are tetramerous. 
 
 in the Biitigh Adoxa the uppermost flower generally has 
 two calyx-lobes with the other organs tetramerous, while 
 « e surroundmg flowers generally have three calyx-lobes 
 
 m l TT^m, i f ° r f n !, P entamer ous. In many Composite 
 and Umbelliferaj (and in some other plants) the circum- 
 
 eiential flowers have their corollas much more developed 
 
 with th ° Se h°V he C ? n ? er; and this seems often connected 
 abor tiou of the reproductive organs. It is a more 
 
 ‘ Previously referred to, that the achenes 
 
 ,i • , tle circumference and center sometimes differ 
 greatly in form, color and other characters. In Cartha- 
 mus and some other Composite the central achenes alone 
 are furnished with a pappus; and in Hvoseris the same 
 ITmhJrf dS a °benes of three different forms. In certain 
 
 ortW i ferai t le e i Xt ,f 10r seeds > according to Tausch, are 
 rthospermous, and tho central one ccelospermous, and this 
 
 is a character which was considered by De Candolle to be in 
 othei species of the highest systematic importance. Pro- 
 
206 
 
 miscellaneous objections to the 
 
 fessor Braun mentions a Fumariaceous genus, in which the 
 
 flowers in the lower part of the spike bear oval ribbed 
 
 one-seeded nutlets; and in the upper part of the S P‘“> 
 
 lanceolate, two-valved and two-seeded sihques 
 
 several eases, with the exception o , . , i flowers 
 
 „ nprj rav florets which are of service m making tiie noweis 
 
 conspicuous to’insects, natural seiection cannot as fa^as 
 
 we can iudge, have come into play, or only m a quite suo 
 onlinate manner. All these modifications follow from the 
 relative position and inter-action of the parts; and it can 
 hardly be doubted that if all the flowers and leaves on the 
 same "plant had been subjected to the same external and 
 internal 'condition, as are hie flowers and e-es in cer am 
 positions, all would have been modified in the 
 
 "numerous other cases we find modifications of struct¬ 
 ure, which are considered by botanists to be generally of a 
 highly important nature, affecting only some of the flowers 
 orf the same plant, or occurring on distinct plants, which 
 otow close together under the same conditions. As these 
 variation?seem of no special use to the plants they canno 
 have been influenced by natural selection Of thea ca 
 we are quite ignorant; we cannot even attnbute them, as 
 in the last clasf of cases, to any proximate agency, such as 
 relative position. I will give only a few instances It is 
 so common to observe on the same plant flowers ndiflm 
 pntlv tetramerous, nentamerous, etc., that I need not g 
 
 Numerical variation. are ““HSS 
 rare when the parts are few, I may mention that, accoia 
 ing to De Candolle, the flowers of Papaver bracteatum- 
 offer either two sepals with four petals (which is 
 common type with poppies), or three sepals with s x 
 netals. The manner in which the petals are folded 1 
 bud is in most groups a very constant morphological c - 
 acter* but Professor Asa Gray states that with some specie 
 of Mimulus, the sestivation is almost as frequently that; of 
 the Rhinanthidese as of the Antirrhimdeae, to which.latte 
 tribe the genus belongs. Aug. St. Hilaire gi\es t _ 
 lowing case® : the genus Zanthoxylon belongs to a division 
 of the Rutace* with a single ovary, but m some spe 
 flowers may be found on (the same plant, and even in t 
 same panicle, with either one or two ovaries. In 
 
THEOR Y OF NA TURAL SELEOTIO.N. 207 
 
 Ilelianthemum the capsule has been described as unilocu¬ 
 lar or tri-locular; and in H. mutabile, “Une lame plus on 
 moms large, s etend entre le pericarpe et le placenta/' In 
 the flowers of Saponaria officinalis Dr. Masters has 
 observed instances of both marginal and free central plac- 
 entation. Lastly, St. Hilaire found toward the southern 
 extreme of the range of Gomphia oleseformis two forms 
 which he did not at first doubt were distinct species, but 
 he subsequently saw them growing on the same bush: and 
 he then adds, “ Voila done dans un meme individu des 
 loges et un style qui se rattachent tantot a un axe verticale 
 et tantot a un gynobase/' 
 
 We thus see that with plants many morphological 
 changes may be attributed to the laws of growth and the 
 mtei-action of parts, independently of natural selection. 
 But with respect to Nageli's doctrine of an innate tend¬ 
 ency tovvard perfection or progressive development, can it 
 
 f-u wi m i e case ^ iese strongly pronounced variations, 
 that the plants have been caught in the act of progressing 
 toward a higher state of development? On the contrary* 
 j-S 10 ? ^ m ? er -from the mere fact of the parts in question 
 drftering °r varying greatly on the same plant, that such 
 modifications were of extremely small importance to the 
 plants themselves, of whatever importance they may gener¬ 
 ally be to us for our classifications. The acquisition of a 
 useless part can hardly be said to raise an organism in the 
 natuial scale; and in the case of the imperfect, closed 
 flowers above described, if any new principle has to be 
 invoked, it must be one of retrogression rather than of 
 pi ogi ession; and so it must be with many parasitic and 
 degraded animals.. We are ignorant of the'exciting cause 
 of the above specified modifications; but if the unknown 
 cause were to act almost uniformly for a length of time 
 )' e niay infer that the.result would be almost uniform; and 
 
 ln i. ] i s -, c ?' se , a ^ ^ ie individuals of the species would be 
 modified in the same manner. 
 
 From the fact of the above characters being unimpor- 
 tant for the welfare of the species, any slight variations 
 which occurred m them would not have been accumulated 
 and augmented through natural selection. A structure 
 which has been developed through long-continued selec- 
 1011 , when it ceases to be of service to a species, generally 
 
208 MISCELLANEOUS OBJECTIONS TO TEE! 
 
 becomes variable, as we see with rudimentary organs; for 
 it will no longer be regulated by this same power of selec¬ 
 tion. But when, from the nature of the organism and of 
 the conditions, modifications have been induced which are 
 unimportant for the welfare of the species, they may be, 
 and apparently often have been, transmitted in nearly the 
 same state to numerous, otherwise modified, descendants. 
 It cannot have been of much importance to thegieatei 
 number of mammals, birds, or reptiles, whether they were 
 clothed with hair, feathers or scales; yet hair has been trans¬ 
 mitted to almost all mammals, feathers to all birds, and 
 •scales to all true reptiles. A structure, whatever it may 
 be, which is common to many allied forms, is ranked by 
 us'as of high systematic importance, and consequently is 
 often assumed to be of high vital importance to the 
 species. Thus, as I am inclined to believe, morphological 
 differences, which we consider as important—such as the 
 arrangement of the leaves, the divisions of the flowei 01 of 
 the ovarium, the position of the ovules, etc., first appeared 
 in many cases as fluctuating variations, which sooner. 01 
 later became constant through .the nature of the organism 
 and of the surrounding conditions, as well as through the 
 intercrossing of distinct individuals, but not through 
 natural selection; for as these morphological characters do 
 not affect the welfare of the species, any slight deviations in 
 them could not have been governed or accumulated through 
 this latter agency. It is a strange result which we thus 
 arrive at,namely, that characters of slight vital importance to 
 the species, are the most important to the systematist, but, 
 as we shall hereafter see when we treat of the genetic 
 principle of classification, this is by no means so paradoxi¬ 
 cal as it may at first appear. 
 
 Although we have no good evidence of the existence 
 in organic beings of an innate, tendency toward progressive 
 development, yet this necessarily follows, as I have attempt¬ 
 ed to show in the fourth chapter, through the continued 
 action of natural selection. For the best definition which 
 has ever been given of a high standard of organization, is 
 the degree to which the parts have been specialized or dif¬ 
 ferentiated; and natural selection tends toward, this end, 
 inasmuch as the parts are thus enabled to perform theii 
 functions more efficiently. 
 
209 
 
 THEORY OF NATURAL SELECTION. 
 
 A distinguished zoologist, Mr. St. George Mivart, has 
 recently collected all the objections which have ever been 
 advanced by myself and others against the theory of natural 
 selection, as propounded by Mr. Wallace and myself, and 
 has illustrated them with admirable art and force. When 
 thus marshaled, they make a formidable array; and as it 
 forms no part of Mr. MivarGs plan to give the various 
 facts and considerations opposed to his conclusions, no 
 slight effort of reason and memory is left to the reader, 
 who may wish to weigh the evidence on both sides. When 
 discussing special cases, Mr. Mivart passes over the effects 
 of the increased use and disuse of parts, which I have 
 always maintained to be highly important, and have treated 
 in my “ Variation under Domestication ” at greater length 
 than, as I believe, any other writer. He likewise often 
 assumes that I attribute nothing to variation, independently 
 of natural selection, whereas in the work just referred to 
 I have collected a greater number of well-established cases 
 than can be found in any other work known to me, 
 M y judgment may not be trustworthy, but after reading 
 with care Mr. Mivart’s book, and comparing each section 
 with what I have said on the same head, I never before 
 felt so strongly convinced of the general truth of the con¬ 
 clusions here arrived at, subject, of course, in so intricate 
 a subject, to much partial error. 
 
 . All Mr. MivarGs objections will be, or have been, con¬ 
 sidered in the present volume. The one new point which 
 appears to have struck many readers is, “ That natural 
 selection is incompetent to account for the incipient stages 
 of useful structures.” This subject is intimately connected 
 with that of the gradation of the characters, often 
 accompanied by a change of function, for instance, the 
 conversion of a swim-bladder into lungs, points which 
 were discussed in the last chapter under two headings. 
 Nevertheless, I will here consider in some detail several of 
 the cases advanced by Mr. Mivart, selecting those which 
 are the most illustrative, as want of space p rotr ents me 
 from considering all. 
 
 The giraffe, by its lofty stature, much elongated neck, 
 fore legs, head and tongue, has its whole frame beautifully 
 adapted for browsing on the higher branches of trees. It 
 can thus obtain food beyond the reach of the other Ungulate 
 
2J0 MISCELLANEOUS OBJECTIONS TO THE 
 
 or hoofed animals inhabiting the same country; and this 
 must be a great advantage to it during dearths. The Mata 
 cattle in South America show us how small a difference in 
 structure may make, during such periods, a gi eat differ¬ 
 ence in preserving an animal*s life. .These cattle can bi o\v se 
 as well as others on grass, but from the projection of. the 
 lower jaw they cannot, during the often recuri cut di oughts, 
 browse on the twigs of trees, reeds, etc., to which food t le 
 common cattle and horses are then driven; so that at 
 these times the Matas perish, if not fed by their 
 owners. Before coming to Mr. Mivart’s objections, 
 
 it may be well to explain once again how natural 
 selection will act in all ordinary cases. Man has 
 modified some of his animals, without necessanly having 
 attended to special points of structure, by simply pre- 
 serving and breeding from the fleetest individuals, as with 
 the race-horse and greyhound, or as with the game-cock, 
 by breeding from the victorious birds. So undermature with 
 the nascent giraffe, the individuals which were the highest 
 browsers and were able during dearths to reach even an 
 inch or two above the others, will often have been pre¬ 
 served; for they will have roamed over the whole country 
 in search of food. That the individuals of the same species 
 often differ slightly in the relative lengths of all their parts 
 may be seen in many works of natural history, in which 
 careful measurements are given. These slight proportional 
 differences, due to the laws of growth and variation, are 
 not of the slightest use or importance to most species. But 
 it will have been otherwise with the nascent giraffe, con¬ 
 sidering its probable habits of life; for those individuals 
 which bad some one part or several parts of their bodies 
 rather more elongated than usual, would generally have 
 survived. These will have intercrossed and left offspring, 
 either inheriting the same bodily peculiarities, or with a 
 tendency to vary again in the same manner ; while the 
 individuals less favored in the same respects will have 
 
 been the most liable to perish. 
 
 We here see that there is no need to separate single pairs, 
 as man does, when he methodically improves a breed: natu¬ 
 ral selection will preserve and thus separate all the supenor 
 individuals, allowing them freely to intercross, and will 
 destroy all the inferior individuals. By this process long- 
 
| THEORY OF HA TUT A L SELECTIO H. 211 
 
 continue*!, which exactly corresponds with what I have 
 called unconscious selection by man, combined, no doubt, 
 m a most important manner with the inherited effects of 
 the increased use of parts, it seems to me almost certain 
 that an ordinary hoofed quadruped might be converted 
 into a giraffe. 
 
 To this conclusion Mr. Mivart brings forward two ob¬ 
 jections, One is that the increased size of the body would 
 obviously require an increased supply of food, and he con¬ 
 siders it as “ very problematical whether the disadvantages 
 thence arising would not, in times of scarcity, more than 
 counterbalance the advantages.” But as the giraffe does 
 actually exist in large numbers in Africa, and as some of the 
 largest antelopes in the world, taller than an ox, abound 
 theie, why should we doubt that, as far as size is concerned, 
 intermediate gradations could formerly have existed there, 
 subjected as now to severe dearths. Assuredly the being 
 able to leach, at each stage of increased size, to a supply 
 of food, left untouched by the other hoofed quadrupeds of 
 the country, would have been of some advantage to the 
 nascent giraffe. Nor must we overlook the fact, that in¬ 
 creased bulk would act as a protection against almost all 
 beasts of prey excepting the lion; and against this animal, 
 its tall neck——and the taller the better—would, as Mr. 
 Chauncey AY right has remarked, serve as a watch-tower. 
 It is from this cause, as Sir S. Baker remarks, that no 
 animal is more difficult to stalk than the giraffe. This 
 animal also uses its long neck as a means of offence or de¬ 
 fence, by violently swinging its head armed with stump- 
 lke hoi ns. I he preservation of each species can rarely be 
 determined by any one advantage, but by the union of'all 
 great and small. 
 
 Mi. Mivart then asks (and this is his second objection), 
 i natuial selection be so potent, and if high browsing be 
 so great an advantage, why has not any other hoofed quad¬ 
 ruped acquired a long neck and lofty stature, besides the 
 giraffe, and,, in a lesser degree, the camel, guanaco and 
 inacrauchenia? Or, again, why has not any member of 
 the group acquired a long proboscis? With respect to 
 bouth Africa, which was formerly inhabited by numerous 
 herds of the giraffe, the answer is not difficult, and can 
 best be given by an illustration. In every meadow in 
 
212 
 
 MISCELLANEOUS OBJECTIONS TO THE 
 
 England, in which trees grow, we see the lower branches 
 trimmed or planed to an exact level by the browsing of the 
 horses or cattle; and what advantage would it be, for in¬ 
 stance, to sheep, if kept there, to acquire slightly longer 
 necks? In every district some one kind of animal will 
 almost certainly t>e able to browse higher than the others; 
 and it is almost equally certain that this one kind alone 
 could have its neck elongated for this purpose, through 
 natural selection and the eifects of increased use. In 
 South Africa the competition for browsing on the higher 
 branches of the acacias and other trees must be between 
 giraffe and giraffe, and not with the other ungulate 
 animals. 
 
 Why, in other quarters of the world, various animals 
 belonging to this same order have not acquired either an 
 elongated neck or a proboscis, cannot be distinctly 
 answered; but it is as unreasonable to expect a distinct 
 answer to such a question as why some event in the history 
 of mankind did not occur in one country while it did in 
 another. We are ignorant with respect to the conditions 
 which determine the numbers and range of each species, 
 and we cannot even conjecture what changes of structure 
 would be favorable to its increase in some new country. 
 We can, however, see in a general manner that various 
 causes might have interfered with the development of a 
 long neck or proboscis. To reach the foliage at a consid¬ 
 erable height (without climbing, for which hoofed animals 
 are singularly ill-constructed) implies greatly increased 
 bulk of body; and we know that some areas support singu¬ 
 larly few large quadrupeds, for instance South America, 
 though it is so luxuriant, while South Africa abounds 
 with them to an unparalleled degree. Why this should be 
 so we do not know; nor why the later tertiary periods 
 should have been much more favorable for their existence 
 than the present time. Whatever the causes may have 
 been, we can see that certain districts and times would have 
 been much more favorable than others for the development 
 of so large a quadruped as the giraffe. 
 
 In order that an animal should acquire some structure 
 specially and largely developed, it is almost indispensable 
 that several other parts should be modified and coadapted. 
 Although every part of the Dody varies slightly, it does not 
 
TIIEOR Y OF NA TURA L SELECTION. 213 
 
 follow that the necessary parts should always vary in the 
 right direction and to the right degree. With the differ¬ 
 ent species of our domesticated animals we know that the 
 parts vary in a different manner and degree, and that some 
 species are much more variable than others. Even if the 
 fitting variations did arise, it does not follow that natural 
 selection would be able to act on them and produce a 
 structure which apparently would be beneficial to the spe¬ 
 cies. Foi instance, if the number of individuals existing 
 m a country is determined chiefly through destruction by 
 beasts of prey—by external or internal parasites, etc.—as 
 seems often to be the case, then natural selection will be 
 able to do little, or will be greatly retarded, in modifying 
 any paiticular structure for obtaining food. Lastlv, nat- 
 111 al selection is a slow process, and the same favorable 
 conditions must long endure in order that any marked 
 effect should thus be produced. Except by assigning such 
 general and vague reasons, we cannot explain why, in 
 many quarters of the world, hoofed quadrupeds have not 
 acquired much elongated necks or other means for brows¬ 
 ing on the higher branches of trees. 
 
 Objections of the same nature as the foregoing have been 
 advanced by many writers. In each case various causes, 
 besides the general ones just indicated, have probably in¬ 
 terfered with the acquisition through natural selection of 
 structures, which it is thought would be beneficial to cer¬ 
 tain species. One writer asks, why has not the ostrich 
 acquired the power of flight? But a moments reflection 
 will show what an enormous supplv of food would be nec¬ 
 essary to give to this bird of the desert force to movo its 
 huge body through the air. Oceanic islands are inhabited by 
 bats and seals, but by no terrestrial mammals; yet as some 
 of these bats are peculiar species, they must have long in¬ 
 habited their present homes. Therefore Sir C. Lyell asks, 
 and assigns certain reasons in answer, why have not seals 
 and bats given birth on such islands to forms fitted to live 
 on the land ? But seals would necessarily be first converted 
 into terrestrial carnivorous animals of considerable size, 
 and bats into terrestrial insectivorous animals; for the 
 former there would be no prey; for the bats ground-insects 
 would serve as food, but these would already be largely preyed 
 on by the reptiles or birds, which first colonize and abound 
 
214 MISCELLANEOUS OBJECTIONS TO TEE 
 
 on most oceanic islands. Gradations of structure, with each 
 stage beneficial to a changing species, will be favored only 
 under certain peculiar conditions. A strictly terrestiial 
 animal, by occasionally hunting for food in shallow water, 
 then in streams or lakes, might at last be converted into 
 an animal so thoroughly accjuatic as to brave the open 
 ocean. But seals would not find on oceanic islands the 
 conditions favorable to their gradual reconversion into a 
 terrestrial form. Bats, as formerly shown, probably ac¬ 
 quired their wings by at first gliding through the air from 
 tree to tree, like the so-called flying squirrels, for the sake 
 of escaping from their enemies, or for avoiding falls; but 
 when the power of true flight had once been acquired, it 
 would never be reconverted back, at least for the above 
 purposes, into the less efficient power of gliding through 
 the air. Bats, might, indeed, like many birds, have had 
 their wings greatly reduced in size, or completely lost, 
 through disuse; but in this case it would be necessary that 
 they should first have acquired the power of running 
 quickly on the ground, by the aid of their hind legs alone, 
 so as to compete with birds or other ground animals;^ and 
 for such a change a bat seems singularly ill-fitted, GLhese 
 conjectural remarks have been made merely to show that 
 a transition of structure, with each step beneficial, is a 
 highly complex affair; and that there is nothing strange 
 in a transition not having occurred in any particular case. 
 
 Lastly, more than one writer has asked why have some 
 animals had their mental powers more highly developed 
 than others, as such development would be advantageous 
 to all? Why have not apes acquired the intellectual 
 powers of man? Various causes could be assigned; but as 
 they are conjectural, and their relative probability can not 
 be weighed, it would be useless to give them. A definite 
 answer to the latter question ought not to be expected, 
 seeing that no one can solve the simpler problem, why, of 
 two races of savages, one has risen higher in the scale of 
 civilization than the other; and this apparently implies in¬ 
 creased brain power. 
 
 We will return to Mr. MivarGs other objections. Insects 
 often resemble for the sake of protection various objects, 
 such as green or decayed leaves, dead twigs, bits of lichen, 
 flowers, spines, excrement of birds, and living insects; but 
 
THEORY OF NATURAL SELECTION. 215 
 
 to this latter point I shall hereafter recur. The resem¬ 
 blance is often wonderfully close, and is not confined to 
 color, but extends to form, and even to the manner in 
 which the insects hold themselves. The caterpillars which 
 project motionless like dead twigs from the bushes on 
 which they feed, offer an excellent instance of a resem¬ 
 blance of this kind. The cases of the imitation of such 
 objects as the excrement of birds, are rare and exceptional. 
 On this head, Mr. Mivart remarks, “As, according to Mr. 
 Darwin's theory, there is a constant tendency to indefinite 
 variation, and as the minute incipient variations will be in 
 all directions, they must tend to neutralize each other, and 
 at first to form such unstable modifications that it is diffi¬ 
 cult, if not impossible, to see how such indefinite oscilla¬ 
 tions of infinitesimal beginnings can ever build up a suffi¬ 
 ciently appreciable resemblance to a leaf, bamboo, or other 
 object, for natural selection to seize upon and perpetuate.” 
 
 But in all the forgoing cases the insects in their original 
 state no doubt presented some rude and accidental resem¬ 
 blance to an object commonly found in the stations fre¬ 
 quented by them. Nor is this at all improbable, consider¬ 
 ing the almost infinite number of surrounding objects and 
 the diversity in form and color of the hosts of insects 
 which exist. As some rude resemblance is necessary for 
 the first start, we can understand how it is that the larger 
 and higher animals do not (with the exception, as far as I 
 know, of one fish) resemble for the sake of protection 
 special objects, but only the surface which commonly sur¬ 
 rounds them, and this chiefly in color. Assuming that an 
 insect originally happened to resemble in some degree a 
 dead twig or a decayed leaf, and that it varied slightly in 
 many ways, then all the variations which rendered the in¬ 
 sect at all more like any such object, and thus favored its 
 escape, would be preserved, while other variations would 
 be neglected and ultimately lost; or, if they rendered the 
 insect at all less like the imitated object, they would be 
 eliminated. There would indeed be force in Mr. Mivarffs 
 objection, if we were to attempt to account for the above 
 resemblances, independently of natural selection, through 
 mere fluctuating variability; but as the case stands there is 
 none. 
 
 Nor can I see any force in Mr. Mivart’s difficulty with 
 
21(3 MISCELLANEOUS OBJECTIONS TO TEE 
 
 respect to “ the last touches of perfection in the mimicry,* 
 as in the case given by Mr. Wallace, of a walking-stick in¬ 
 sect (Ceroxyluslaceratus), which resembles “a stick grown 
 over oy a creeping moss or jungermannia.” So close was 
 this resemblance, that a native Dyak maintained that the 
 foliaceous excrescences were really moss. Insects are preyed 
 on by birds and other enemies whose sight is probably 
 sharper than ours, and every grade in resemblance which 
 aided an insect to escape notice or detection, would tend 
 toward its preservation; and the more perfect the resem¬ 
 blance so much the better for the insect. Considering the 
 nature of the differences between the species in the group 
 which includes the above Ceroxylus, there is nothing im¬ 
 probable in this insect having varied in the irregularities 
 on its surface, and in these having become more or less 
 green-colored; for in every group the characters which 
 differ in the several species are the most apt to vary, while 
 the generic characters, or those common to all the species, 
 are the most constant. 
 
 The Greenland whale is one of the most wonderful am 
 mals in the world, and the baleen, or whalebone, one of 
 its greatest peculiarities. The baleen consists of a row, on 
 each side of the upper jaw, of about 300 plates or laminae, 
 which stand close together transversely to the longer axis 
 of the mouth. Within the main row there are some subsid- 
 iary rows. The extremities and inner margins of all the 
 plates are frayed into stiff bristles, which clothe the whole 
 gigantic palate, and serve to strain or sift the water, and 
 thus to secure the minute prey on which these great ani¬ 
 mals subsist. The middle and longest lamina in the Green¬ 
 land whale is ten, twelve, or even fifteen feet in length; 
 but in the different species of Cetaceans there are grada¬ 
 tions in length; the middle lamina being in one species, 
 according to Scoresby, four feet, in another three, in 
 another eighteen inches, and in the Balsenoptera rostrata 
 only about nine inches in length. The quality of the 
 whalebone also differs in the different species. 
 
 With respect to the baleen, Mr. Mivart remarks that if 
 it “ had once attained such a size and development as to be 
 at all useful, then its preservation and augmentation within 
 serviceable limits would be promoted by natural selection 
 
THEORY OF NATURAL SELECTION 
 
 217 
 
 alone. But how to obtain the beginning of such useful 
 development?” In answer, it may be asked, why should 
 not the early progenitors of the whales with baieen have 
 possessed a mouth constructed something like the lamel- 
 lated beak of a duck? Ducks, like whales, subsist by sift¬ 
 ing the mud and water; and the family has sometimes 
 been called Criblatores , or sifters. I hope that I may not 
 be misconstrued into saying that the progenitors of whales 
 did actually possess mouths lamellated like the beak of a 
 duck. I wish only to show that this is not incredible, and 
 that the immense plates of baleen in the Greenland whale 
 might have been developed from such lamellae by finely 
 graduated steps, each of service to its possessor. 
 
 The beak of a shoveller-duck (Spatula clypeata) is a 
 more beautiful and complex structure than the mouth of a 
 whale. The upper mandible is furnished on each side (in 
 the specimen examined by me) with a row or comb formed 
 of 188 thin, elastic lamellae, obliquely bevelled so as to be 
 pointed, and placed transversely to the longer axis of the 
 mouth. They arise from the palate, and are attached by 
 flexible membrane to the sides of the mandible. Those 
 standing toward the middle are the longest, being about 
 one-third of an inch in length, and they project fourteen 
 one-hundreths of an inch beneath the edge. At their 
 bases there is a short subsidiary row of obliquely transverse 
 lamellae. In these several respects they resemble the plates 
 of baleen in the mouth of a whale. But toward the ex¬ 
 tremity of the beak they differ much, as they project in¬ 
 ward, instead of straight downward. The entire head of 
 the shoveller, though incomparably less bulky, is about one- 
 eighteenth of the length of the head of a moderately large 
 Balaenoptera rostrata, in which species the baleen is only 
 nine inches long; so that if we were to make the head of 
 the shoveller as long as that of the Balaenoptera, the lam¬ 
 ellae would be six inches in length, that is, two-thirds of 
 the length of the baleen in this species of whale. The 
 Lower mandible of the shoveller-duck is furnished with 
 lamellae of equal length with these above, but finer; and in 
 being thus furnished it differs conspicuously from the 
 lower jaw of a whale, which is destitute of baleen. On 
 the other hand, the extremities of these lower lamellae are 
 frayed into fine bristly points, so that they thus curiously 
 
318 
 
 MISCELLANEOUS OBJECTIONS TO THE 
 
 resemble the plates of baleen. In the genus Prion, a 
 member of the distinct family of the Petrels, the upper 
 mandible alone is furnished with lamellae, which are well 
 developed and project beneath the margin; so that the 
 beak of this bird resembles in this respect the mouth of a 
 whale. 
 
 From the highly developed structure of the shoveller s 
 beak we may proceed (as I have learned from information 
 and specimens sent to me by Mr. Salvin), without any great 
 break, as far as fitness for sifting is concerned, through 
 the beak of the Merganetta armata, and in some respects 
 through that of the Aix sponsa, to the beak of the common 
 duck. In this latter species the lamellae are much coarsei 
 than in the shoveller, and are firmly attached to the sides 
 of the mandible; they are only about fifty in number 01 
 each side, and do not project at all beneath the margin. 
 They are square-topped, and are edged with translucent, 
 hardish tissue, as if for crushing food. The edges of the 
 lower mandible are crossed by numerous fine ridges, which 
 project very little. Although the beak is thus very interim 
 as a sifter to that of a shoveller, yet this bird, as every one 
 knows, constantly uses it for this purpose. There are 
 other species, as I hear from Mr. Salvin, in which the 
 lamellae are considerably less developed than in the commoc 
 duck; but I do not know whether they use their beaks for 
 sifting the water. 
 
 Turning to another group of the same family. In the 
 Egyptian goose (Chenalopex) the beak closely resembles, 
 that of the common duck; but the lamellas are not so 
 numerous, nor so distinct from each other, nor. do they 
 project so much inward; yet this goose, as I am informed 
 by Mr. E. Bartlett, “ uses its bill like a duck by throwing 
 the water out at the corners.” Its chief food, however, is 
 grass, which it crops like the common goose. In this latter 
 bird the lamellae of the upper mandible are much coarser 
 than in the common duck, almost confluent,.about twenty- 
 seven in number on each side, and terminating upward in 
 teeth-like knobs. The palate is also covered with hard 
 rounded knobs. The edges of the lower mandible are 
 serrated with teeth much more prominent, coarser and 
 sharper than in the duck. The common goose does not sift 
 the water, but uses its-beak exclusively for tearing or cut- 
 
TBEOR Y OF NA TURAL SELECTION. 210 
 
 ting herbage, for which purpose it is so well fitted that it 
 can crop grass closer than almost any other animal. There 
 are other species of geese, as I hear from Mr. Bartlett, in 
 which the lamellae are less developed than in the common 
 goose. 
 
 We thus see that a member of the duck family, with a 
 beak constructed like that of a common goose and adapted 
 solely for grazing, or even a member with a beak having 
 less well-developed lamellae, might be converted by small 
 changes into a species like the Egyptian goose—this into 
 one like the common duck—and, lastly, into one like the 
 shoveller, provided with a beak almost exclusively adapted 
 for sifting the water; for this bird could hardly use any 
 part of its beak, except the hooked tip, for seizing or tear¬ 
 ing solid food. The beak of a goose, as I may add, might 
 also be converted by small changes into one provided with 
 prominent, recurved teeth, like those of the Merganser (a 
 member of the same family), serving for the widely differ¬ 
 ent purpose of securing live fish. 
 
 Returning to the whales. The Hyperoodon bidens is 
 destitute of true teeth in an efficient condition, but its 
 palate is roughened, according to Lacepede, with small 
 unequal, hard points of horn. There is. therefore, noth¬ 
 ing improbable in supposing that some early Cetacean form 
 was provided with similar points of horn on the palate, 
 but rather more regularly placed, and which, like the 
 knobs on the beak of the goose, aided it in seizing or tear¬ 
 ing its food. If so, it will hardly be denied that the points 
 might have been converted through variation and natural 
 selection into lamellas as well-developed as those of the 
 Egyptian goose, in which case they would have been used 
 both for seizing objects and for sifting the water; then 
 into lamellce like those of the domestic duck; and so on¬ 
 ward, until they became as well constructed as those cf the 
 shoveller, in which case they would have served exclusively 
 as a sifting apparatus. Erom this stage, in which the 
 lamellas would be two-thirds of the length of the plates of 
 baleen in the. Balasnoptera rostrata, gradations, which may 
 be observed in still-existing Cetaceans, lead us onward to 
 tne enormous plates oi baleen in the Greenland whale. 
 Noi is there, the least reason to doubt that each step in 
 this scale might have been as serviceable to certain ancient 
 
220 
 
 MISCELLANEOUS OBJECTIONS TO THE 
 
 Cetaceans, with the functions of the parts slowly changing 
 during the progress of development, as are the gradations 
 in the beaks of the different existing members of the duck- 
 family. We should bear in mind that each species of duck 
 is subjected to a severe struggle for existence, and that the 
 structure of every part of its frame must be well adapted 
 to its conditions of life. 
 
 The Pleuronectidae, or Flat-fish, are remarkable for 
 their asymmetrical bodies. They rest on one side—in the 
 greater number of species on the left, but in some on the 
 right side; and occasionally reversed adult specimens 
 occur. The lower, or resting-surface, resembles at first 
 sight the ventral surface of an ordinary fish; it is of a white 
 color, less developed in many ways than the upper side, 
 with the lateral fins often of smaller size. But the eyes 
 offer the most remarkable peculiarity; for they are both 
 placed on the upper side of the head. During early youth, 
 however, they stand opposite to each other, and the whole 
 body is then symmetrical, with both sides equally colored. 
 Soon the eye proper to the lower side begins to glide 
 slowly round the head to the upper side; but does not pass 
 right through the skull, as was formerly thought to be 
 the case. It is obvious that unless the lower eye did thus 
 travel round, it could not be used by the fish while lying 
 in its habitual position on one side. The lower eye would, 
 also, have been liable to be abraded by the sandy bottom. 
 That the Pleuronectidae are admirably adapted by theii 
 flattened and asymmetrical structure for their habits of 
 life, is manifest from several species, such as soles, flound¬ 
 ers, etc., being extremely common. The chief advantages 
 thus gained seem to be protection from their enemies, and 
 facility for feeding on the ground. The different mem 
 bers, however, of the family present, as Schiodte remarks, 
 “a long series of forms exhibiting a gradual transition 
 from Hippoglossus pinguis, which does not in any consid¬ 
 erable degree alter the shape in which it leaves the ovum, 
 to the soles, which are entirely thrown to one side.” 
 
 Mr. Mivart has taken up this case, and remarks that a 
 sudden spontaneous transformation in the position of the 
 eyes is hardly conceivable, in which I quite agree with him. 
 He then adds: “ If the transit was gradual, then how such 
 transit of one eye a minute fraction of the journey toward 
 
THEORY OF NATURAL SELECTION. 
 
 221 
 
 the other side of the head could benefit the individual is, 
 indeed, far from clear. It seems, even, that such an in¬ 
 cipient transformation must rather have been injurious.” 
 But ho might have found an answer to this objection in 
 the excellent observations published in 1867 by Malm. 
 The Pleuronectidse, while very young and still symmetri¬ 
 cal, with their eyes standing on opposite sides of the head, 
 cannot long retain a vertical position, owing to the exces¬ 
 sive depth of their bodies, the small size of their lateral 
 fins, and to their being destitute of a swim-bladder. 
 Hence, soon growing tired, they fall to the bottom on one 
 side. While thus at rest they often twist, as Malm ob¬ 
 served, the lower eye upward, to see above them; and they 
 do this so vigorously that the eye is pressed hard against 
 the upper part of the orbit. The forehead between the 
 eyes consequently becomes, as could be plainly seen, tem¬ 
 porarily contracted in breadth. On one occasion Malm 
 saw a young fish raise and depress the lower eye through 
 an angular distance of about seventy degrees. 
 
 We should remember that the skull at this early age is 
 cartilaginous and flexible, so that it readily yields to mus¬ 
 cular action. It is also known with the higher animals, 
 even after early youth, that the skull yields and is altered 
 in shape, if the skin or muscles be permanently contracted 
 through disease or some accident. With long-eared rab¬ 
 bits, if one ear flops forward and downward, its weight 
 drags forward all the bones of the skull on the same side, 
 of which I have given a figure. Malm states that the 
 newly-hatched young of perches, salmon, and several other 
 symmetrical fishes, have the habit of occasionally resting 
 on one side at the bottom; and he has observed that they 
 often then strain their lower eyes so as to look upward; 
 and their skulls are thus rendered rather crooked. These 
 fishes, however, are soon able to hold themselves in a ver¬ 
 tical position, and no permanent effect is thus produced. 
 With the Pleuronectidae, on the other hand, the older they 
 grow the more habitually they rest on one side, owing to 
 the increasing flatness of* their bodies, and a permanent 
 effect is thus produced on the form of the head, and on the 
 position of the eyes. Judging from analogy, the tendency 
 to distortion would no doubt be increased through the 
 principle of inheritance. Schiodte believes, in opposition 
 
222 
 
 MISCELLANEOUS OBJECTIONS TO THE 
 
 to some other naturalists, that the Pleuronectidae are not 
 quite symmetrical even in the embryo; and if this be so, 
 we could understand how it is that certain species, while 
 young, habitually fall over and rest on the left side, and 
 other species on the right side. Malm adds, in confirma¬ 
 tion of the above view, that the adult Trachypterus arcti- 
 cus, which is not a member of the Pleuronectidae, rests on 
 its left side at the bottom, and swims diagonally through 
 the water; and in this fish, the two sides of the head are 
 said to be somewhat dissimilar. Our great authority on 
 Fishes, Dr. Gunther, concludes his abstract of Malm’s 
 paper, by remarking that “the author gives a very simple 
 explanation of the abnormal condition of the Pleu- 
 ronectoids.” 
 
 We thus see that the first stages of the transit of the 
 eye from one side of the head to the other, which Mr. 
 Mivart considers would be injurious, may be attributed 
 to the habit, no doubt beneficial to the individual and 
 to the species, of endeavoring to look upward with both 
 eyes, while resting on one side at the bottom. We may 
 also attribute to the inherited effects of use the fact of the 
 mouth in several kinds of flat-fish being bent toward the 
 lower surface, with the jaw bones stronger and more effect¬ 
 ive on this, the eyeless side of the head, than on the other, 
 for the sake, as Dr. Traquair supposes, of feeding with ease 
 on the ground. Disuse, on the other hand, will account 
 for the less developed condition of the whole inferior half 
 of the body, including the lateral fins; though Yarrel 
 thinks that the reduced size of these fins is advantageous 
 to the fish, as “ there is so much less room for their action, 
 than with the larger fins above.” Perhaps the lesser 
 number of teeth in the proportion of four to seven in the 
 upper halves of the two jaws of the plaice, to twenty-five 
 to thirty in the lower halves, may likewise be accounted 
 for by disuse. From the colorless state of the ventral sur¬ 
 face of most fishes and of many other animals, we may 
 reasonably suppose that the absence of color in flat-fish on 
 the side, whether it be the right or left, which is under¬ 
 most, is due to the exclusion of light. But it cannot be 
 supposed that the peculiar speckled appearance of the 
 upper side of the sole, so like the sandy bed of the sea, or 
 the power in some species, as recently shown by Pouchet, 
 
THEORY OF NATURAL SELECTION. 
 
 223 
 
 of changing their color in accordance with the surround¬ 
 ing surface, or the presence of bony tubercles on the upper 
 side of the turbot, are due to the action of the light. 
 Here natural selection has probably come into play, as well 
 as in adapting the general shape of the body of these 
 fishes, and many other peculiarities, to their habits of life. 
 We should keep in mind, as I have before insisted, that 
 the inherited effects of the increased use of parts, and per¬ 
 haps of their disuse, will be strengthened by natural selec¬ 
 tion. For all spontaneous variations in the right direc¬ 
 tion will thus be preserved; as will those individuals which 
 inherit in the highest degree the effects of the increased 
 and beneficial use of any part. How much to attribute in 
 each particular case to the effects of use, and how much to 
 natural selection, it seems impossible to decide. 
 
 I may give another instance of a structure which appar¬ 
 ently owes its origin exclusively to use or habit. The 
 extremity of the tail in some American monkej's has been 
 converted into a wonderfully perfect prehensile organ, and 
 serves as a fifth hand. A reviewer, who agrees with Mr. 
 Mivart in every detail, remarks on this structure: “It is 
 impossible to believe that in any number of ages the first 
 slight incipient tendency to grasp could preserve the lives 
 of the individuals possessing it, or favor their chance of 
 having and of rearing offspring.” But there is no neces¬ 
 sity for any such belief. Habit, and this almost implies 
 that some benefit great or small is thus derived, would in 
 all probability suffice for the work. Brehm saw the young 
 of an African monkey (Cercopithecus) clinging to the 
 under surface of their mother by their hands, and at the 
 same time they hooked their little tails round that of their 
 mother. Professor Henslow kept in confinement some 
 harvest mice (Mus messorius) which do not pos¬ 
 sess a structurally prehensive tail; but he frequently 
 observed that they curled their tails round the 
 branches of a bush placed in the cage, and thus aided 
 themselves in climbing. I have received an analo¬ 
 gous account from Dr. Gunther, who has seen a 
 mouse thus suspend itself. If the harvest mouse had 
 been more strictly arboreal, it would perhaps have 
 had its tail rendered structurally prehensile, as is 
 the case with some members of the same order. Why 
 
 
MISCELLANEOUS OBJECTIONS TO THE 
 
 224 
 
 Cercopithecus, considering its habits while young, has not 
 become thus provided, it would be difficult to say. It is, 
 however, possible that the long tail of this monkey may be 
 of more service to it as a balancing organ in making its 
 prodigious leaps, than as a prehensile organ. 
 
 The mammary glands are common to the whole class of 
 mammals, and are indispensable for their existence; they 
 must, therefore, have been developed at an extremely 
 remote period, and we can know nothing positively about 
 their manner of development. Mr. Mivart asks: “Is it 
 conceivable that the young of any animal was ever saved 
 from destruction by accidentally sucking a drop of scarcely 
 nutritious fluid from an accidentally hypertrophied cuta¬ 
 neous gland of its mother? And even if one was so, what 
 chance was there of the perpetuation of such a variation V* 
 But the case is not here put fairly. It is admitted by most 
 evolutionists that mammals are descended from a marsu¬ 
 pial form; and if so, the mammary glands will have been 
 at first developed within the marsupial sack. In the case 
 of the fish (Hippocampus) the eggs are hatched, and the 
 young are reared for a time, within a sack of this nature; 
 and an American naturalist, Mr. Lockwood, believes from 
 what he has seen of the development of the young, that 
 they are nourished by a secretion from the cutaneous 
 glands of the sack. Now, with the early progenitors of 
 mammals, almost before they deserved to be thus desig¬ 
 nated, is it not at least possible that the young might have 
 been similiarly nourished? And in this case, the individu¬ 
 als which secreted a fluid, in some degree or manner the 
 most nutritious, so as to partake of the nature of milk, 
 would in the long run have reared a larger number of well- 
 nourished offspring, than would the individuals which 
 secreted a poorer fluid; and thus the cutaneous glands, 
 which are the homologues of the mammary glands, would 
 have been improved or rendered more effective. It accords 
 with the widely extended principle of specialization, that 
 the glands over a certain space of the sack should have 
 become more highly developed than the remainder; and 
 they would then have formed a breast, but at first without 
 a nipple, as we see in the Ornithorhyncus, at the base of 
 the mammalian series. Through what agency the glands 
 

 THEORY OF NATURAL SELEGTION. 225 
 
 over a certain space became more highly specialized than 
 the others, I will not pretend to decide, whether in part 
 through compensation of growth, the effects of use, or of 
 natural selection. 
 
 The development of the mammary glands would have 
 been of no service, and could not have been affected 
 through natural selection, unless the young at the same 
 time were able to partake of the secretion. There is no 
 greater difficulty in understanding how young mammals 
 have mstinctiveiy learned to suck the breast, than in under* 
 standing how unhatched chickens have learned to break the 
 egg-shell by tapping against it with their specially adapted 
 beaks; or how a few hours after leaving the shell thev have 
 learned to pick up grains of food. In such cases the most 
 probable solution seems to be, that the habit was at first 
 acquired by practice at a more advanced age, and after¬ 
 ward transmitted to the offspring at an earlier age. But the 
 young kangaroo is said not to suck, only to cling to the 
 nipple of its mother, who has the power of injecting milk 
 into the mouth of her helpless, half-formed offspring. On 
 this head Mr. Mivart remarks: “Did no special provision 
 exist, the young one must infallibly be choked by the in¬ 
 trusion of the milk into the wind-pipe. But there is a 
 special provision. . The larynx is so elongated that it rises 
 
 U P u i j P os ^ er ^ or en d of the nasal passage, and is thus 
 enabled to give free entrance to the air for the lungs, while 
 the milk passes harmlessly on each side of this elongated 
 larynx, and so safely attains the gullet behind it.” Mr. 
 Mivart then asks how did natural selection remove in the 
 adult kangaroo (and in most other mammals, on the assump¬ 
 tion that they are descended from a marsupial form), “this 
 at least perfectly innocent and harmless structure?” It 
 may be suggested in answer that the voice, which is cer¬ 
 tainly of high importance to many animals, could hardly 
 have been used with full force as long as the larynx en¬ 
 tered the nasal passage; and Professor Flower has suggested 
 to me that this structure would have greatly interfered with 
 an animal swallowing solid food. 
 
 We will now turn for a short space to the lower divisions 
 of the animal kingdom. The Echinodermata (star-fishes, 
 sea-urchins, etc.) are furnished with remarkable organs, 
 called pedicellarias, which consist, when well developed, of 
 
226 MISCELLANEOUS OBJECTIONS TO THE 
 
 a tridactvle forceps— that is, of one formed of three ser- 
 rated arms, neatly fitting together and placed oni the 
 summit of a flexible stem, moved by muscles, these tor- 
 ceps can seize firmly hold of any object; and Alexander 
 Agassiz has seen an Echinus or sea-urchin rapidly passing 
 particles of excrement from forceps to forceps down certain 
 lines of its body, in order that its shell should not be 
 fouled. But there is no doubt that besides removing dirt 
 of all kinds, they subserve other functions; and one ot 
 these apparently is defence. 
 
 With respect to these organs, Mr. Mivart, as on so many 
 previous occasions, asks: “ What would be the utility of 
 the first rudimentary beginnings of such structures, ana 
 how could such insipient buddings have ever preserved the 
 life of a single Echinus?” He adds, “not even the sudden 
 development of the snapping action could have been bene¬ 
 ficial without the freely movable stalk, nor could the 
 latter have been efficient without the snapping jaws yet 
 no minute, merely indefinite variations could simultane¬ 
 ously evolve these complex co-ordinations of structure; to 
 deny this seems to do no less than to affirm a startling 
 paradox.” Paradoxical as this may appear to Mr. Mivait, 
 tridactyle forcepses, immovably fixed at the base, but capa¬ 
 ble of a snapping action, certainly exist on some star-fishes; 
 and this is intelligible if they serve, at least m part, as a 
 means of defence. Mr. Agassiz, to whose great kindness 
 lam indebted for much information on the subject, in¬ 
 forms me that there are other star-fishes, m which one oi 
 the three arms of the forceps is reduced, to a support lor 
 the other two; and again, other genera m which the thud 
 arm is completely lost. In Ecliinoneus the shell is de¬ 
 scribed by M. Perrier as bearing two kinds ot pediceilai iae, 
 one resembling those of Echinus, and the other those oi 
 Spatangus; and such cases are always interesting as attord- 
 ing the means of apparently sudden transitions, through 
 the abortion of one of the two states of an oigan. 
 
 With respect to the steps by which these curious organs 
 have been evolved, Mr. Agassiz infers from Ins own re¬ 
 searches and those of Mr. Muller, that both m star-fishes 
 and sea-urchins the pedicellariae must undoubtedly be 
 looked at as modified spines. This may be inferred fi°ni 
 their manner of development in the individual, as well as 
 
THEORY OF NATURAL SELECTION. 
 
 227 
 
 from a long and perfect series of gradations in different 
 species and genera, from simple granules to ordinary 
 spines, to perfect tridactyle pedicellariae. The gradation 
 extends even to the manner in which ordinary spines and 
 The pedicellariae, with their supporting calcareous rods, are 
 articulated to the shell. In certain genera of star-fishes, 
 “ the very combinations needed to show that the pedicel¬ 
 lariae are only modified branching spines ” may be found. 
 Thus we have fixed spines, with three equi-distant, serrated, 
 movable branches, articulated to near their bases; and 
 higher up, on the same spine, three other movable 
 branches. Now when the latter arise from the summit of 
 a spine they form, in fact, a rude tridactyle pedicellariae, 
 and such may be seen on the same spine together with the 
 three lower branches. In this case the identity in nature 
 between the arms of the pedicellariae and the movable 
 branches of a spine, is unmistakable. It is generally 
 admitted that the ordinary spines serve as a protection; 
 and if so, there can be no reason to doubt that those fur¬ 
 nished with serrated and movable branches likewise serve 
 for the same purpose; and they would thus serve still more 
 effectively as soon as by meeting together they acted as a 
 prehensile or snapping apparatus. Thus every gradation, 
 from an ordinary fixed spine to a fixed pedicellariae, would 
 be of service. 
 
 In certain genera of star-fishes these organs, instead of 
 being fixed or borne on an immovable support, are placed on 
 the summit of a flexible and muscular, though short, stem; 
 and in this case they probably subserve some additional 
 function besides defence. In the sea-urchins the steps can 
 be followed by which a fixed spine becomes articulated to 
 the shell, and is thus rendered movable. I wish I had 
 space here to give a fuller abstract of Mr. Agassiz’s inter¬ 
 esting observations on the development of the pedicellariae. 
 All possible gradations, as he adds, may likewise be found 
 between the pedicellariae of the star-fishes and the hooks 
 of the Ophiurians, another group of the Echinodermata; 
 and again between the pedicellariae of sea-urchins and the 
 anchors of the Holothuriae, also belonging to the same 
 great class. 
 
 Certain compound animals, or zoophytes, as they have 
 
228 
 
 MISCELLANEOUS OBJECTIONS TO TEE 
 
 been termed, namely the Polyzoa, are provided with curious 
 organs called avicularia. These differ much in structure 
 in the different species. In their most perfect condition 
 they curiously resemble the head and beak of a vulture in 
 miniature, seated on a neck and capable of movement, as 
 is likewise the lower jaw or mandible. In one species ob¬ 
 served by me, all the avicularia on the same branch often 
 moved simultaneously backward and forward, with the 
 lower jaw widely open, through an angle of about 90 
 degrees, in the course of five seconds; and their movement 
 caused the whole polyzoary to tremble. When the jaws 
 are touched with a needle they seize it so firmly that the 
 branch can thus be shaken. 
 
 Mr. Mivart adduces this case, chiefly on account of the 
 supposed difficulty of organs, namely the avicularia of 
 the Polyzoa and the pedicellariae of the Echinodermata, 
 which he considers as “ essentially similar,” having been 
 developed through natural selection in widely distinct 
 divisions of the animal kingdom. But, as far as struct¬ 
 ure is concerned, 1 can see no similarity between tridac- 
 tyle pedicellariae and avicularia. The latter resembles 
 somewhat more closely the chelae or pincers of Crusta¬ 
 ceans; and Mr. Mivart might have adduced with equal 
 appropriateness this resemblance as a special difficulty, or 
 even their resemblance to the head and beak of a bird. 
 The avicularia are believed by Mr. Busk, Dr. Smitt and 
 Dr. Nitsche—naturalists who have carefully studied this 
 g r0U p—to be homologous with the zooids and their cells 
 which compose the zoophyte, the moveable lip or lid of the 
 cell corresponding with the lower and movable mandible of 
 the avicularium. Mr. Busk, however, does not know of 
 any gradations now existing between a zooid and an avicu- 
 larium. It is therefore impossible to conjecture by what 
 serviceable gradations the one could have been converted 
 into the other, but it by no means follows from this that 
 such gradations have not existed. 
 
 As the chelae of Crustaceans resemble in some degree the 
 avicularia of Polyzoa, both serving as pincers, it may be 
 worth while to show that with the former a long series of 
 serviceable gradations still exists. In the first and simplest 
 stage, the terminal segment of a limb shuts down either on 
 the sauare summit of the broad penultimate segment, or 
 
THEORY OF NATURAL SELECTION, 229 
 
 against one whole side, and is thus enabled to catch hold 
 of an object, but the limb still serves as an organ of loco¬ 
 motion. We next find one corner of the broad penulti¬ 
 mate segment slightly prominent, sometimes furnished 
 with irregular teeth, and against these the terminal seg¬ 
 ment shuts down. By an increase in the size of this pro¬ 
 jection, with its shape, as well as that of the terminal 
 segment, slightly modified and improved, the pincers are 
 rendered more and more perfect, until we have at last an 
 instrument as efficient as the chelae of a lobster. And all 
 these gradations can be actually traced. 
 
 Besides the avicularia, the polyzoa possess curious organs 
 called vibracula. These generally consist of long bristles, 
 capable of movement and easily excited. In one species 
 examined by me the vibracula were slightly curved and 
 serrated along the outer margin, and all of them on the 
 same polyzoary often moved simultaneously; so that, acting 
 like long oars, they swept a branch rapidly across the object- 
 glass of my microscope. When a branch was placed on its 
 face, the vibracula became entangled, and they made vio¬ 
 lent efforts to free themselves. They are supposed to serve 
 as a defence, and may be seen, as Mr. Busk remarks, (i to 
 sweep slowly and carefully over the surface of the poly¬ 
 zoary, removing what might be noxious to the delicate 
 inhabitants of the cells when their tentacula are pro¬ 
 truded. The avicularia, like the vibracula, probably 
 seive for defence, but they also catch and kill small living 
 animals, which, it is believed, are afterward swept by the 
 currents within reach of the tentacula of the zooids. Some 
 species are provided with avicularia and vibracula, some 
 with avicularia alone and a few with vibracula alone. 
 
 It is not easy to imagine two objects more widely dif¬ 
 ferent in appearance than a bristle or vibraculum, and an 
 avicularium like the head of a bird; vet they are almost 
 certainly homologous and have been developed from the 
 same common source, namely a zooid with its cell. Hence, 
 we can understand how it is that these organs graduate in 
 some cases, as I am informed by Mr. Busk, into each 
 other. . Thus, with the avicularia of several species of 
 Lepralia, the movable mandible is so much produced and 
 is so like a bristle that the presence of the upper or fixed 
 beak alone serves to determine its avicularian nature. The 
 
230 
 
 MISCELLANEOUS OBJECTIONS TO TEE 
 
 vibracula may have been directly developed from the lips 
 of the cells, without having passed through the avicularian 
 stage; but it seems more probable that they have passed 
 through this stage, as during the early stages of the trans¬ 
 formation, the other parts of the cell, with the included 
 zooid, could hardly have disappeared at once. In many 
 cases the vibracula have a grooved support at the base, 
 which seems to represent the fixed beak; though this sup¬ 
 port in some species is quite absent. This view of the de¬ 
 velopment of the vibracula, if trustworthy, is interesting; 
 for supposing that all the species provided with avicularia 
 had become extinct, no one with the most vivid imagina¬ 
 tion would ever have thought that the vibracula had orig¬ 
 inally existed as part of an organ, resembling a bird's head, 
 or an irregular box or hood. It is interesting to see two 
 such widely different organs developed from a common 
 origin; and as the movable lip of the cell serves as a protec¬ 
 tion to the zooid, there is no difficulty in believing that all 
 the gradations, by which the lip became converted first into 
 the lower mandible of an avicularium, and then into an 
 elongated bristle, likewise served as a protection in different 
 ways and under different circumstances. 
 
 In the vegetable kingdom Mr. Mivart only alludes to two 
 cases, namely the structure of the flowers of orchids, and 
 the movements of climbing plants. With respect to the 
 former, he says: “ The explanation of their origin is deemed 
 thoroughly unsatisfactory—utterly insufficient to explain 
 the incipient, infinitesimal beginnings of structures which 
 are of utility only when they are considerably developed." 
 As I have fully treated this subject in another work, I will 
 here give only a few details on one alone of the most strik¬ 
 ing peculiarities of the flowers of orchids, namely, their pol- 
 linia. A pollinium, when highly developed, consists of a 
 mass of pollen-grains, affixed to an elastic foot-stalk or 
 caudicle, and this to a little mass of extremely viscid 
 matter. The pollinia are by this means transported by in¬ 
 sects from one flower to the stigma of another. In some 
 orchids there is no caudicle to the pollen-masses, and the 
 grains are merely tied together by fine threads; but as these 
 are not confined to orchids, they need not here be consid¬ 
 ered; yet I may mention that at the base of the orchid*- 
 
THEORY OF NATURAL SELECTION. 
 
 231 
 
 ceous series, in Cypripedium, we can see how the threads 
 were probably first developed. In other orchids the 
 threads cohere at one end of the pollen-masses; and this 
 forms the first or nascent trace of a caudicle. That this is 
 the origin of the caudicle, even when of considerable 
 length and highly developed, we have good evidence in the 
 aborted pollen-grains which can sometimes be detected em= 
 bedded within the central and solid parts. 
 
 With respect to the second chief peculiarity, namely, the 
 little mass of viscid matter attached to the end of the cau¬ 
 dicle, a long series of gradations can be specified, each of 
 plain service to the plant. In most flowers belonging to 
 other orders the stigma secretes a little viscid matter. Now, 
 in certain orchids similar viscid matter is secreted, but in 
 much larger quantities by one alone of the three stigmas; 
 and this stigma, perhaps in consequence of the copious 
 secretion, is rendered sterile. When an insect visits a 
 flower of this kind, it rubs off some of the viscid matter, 
 and thus at the same time drags away some of the 
 pollen-grains. From this simple condition, which differs 
 but little from that of a multitude of common 
 flowers, there are endless gradations—to species in which 
 the pollen-mass terminates in a very short, free cau¬ 
 dicle—to others in which the caudicle becomes firmly at¬ 
 tached to the viscid matter, with the sterile stigma itself 
 much modified. In this latter case we have a pollinium 
 in its most highly developed and perfect condition. He 
 who will carefully examine the flowers of orchids for 
 himself will not deny the existence of the above series of 
 gradations—from a mass of pollen-grains merely tied 
 together by threads, with the stigma differing but little 
 from that of the ordinary flowers, to a highly complex 
 pollinium, admirably adapted for transportal by insects; 
 nor will he deny that all the gradations in the several 
 species are admirably adapted in relation to the general 
 structure of each flower for its fertilization by different 
 insects. In this, and in almost every other case, the in¬ 
 quiry may be pushed further backward; and it may be 
 asked how did the stigma of an ordinary flower become 
 viscid, but as we do not know the full history of any one 
 group of beings, it is as useless to ask, as it is hopeless to 
 attempt answering* such auestions.> 
 
232 MISCELLANEOUS OBJECTIONS TO THE 
 
 We will now turn to climbing plants. These can be ar¬ 
 ranged in a long series, from those which simply twine 
 round a support, to those which I have called leaf-climbers, 
 and to those provided with tendrils. In these two latter 
 classes the stems have generally, but not always, lost the 
 power of twining, though they retain the power of revolv¬ 
 ing, which the tendrils likewise possess. The gradations 
 from leaf-climbers to tendril bearers are wonderfully close, 
 and certain plants may be differently placed in either 
 class. But in ascending the series from simple twiners to 
 leaf-climbers, an important quality is added, namely sen¬ 
 sitiveness to a touch, by which means the foot-stalks of the 
 leaves or flowers, or these modified and converted into ten¬ 
 drils, are excited to bend round and clasp the touching 
 object. He who will read my memoir on these plants will, 
 I think, admit that all the many gradations in function 
 and structure between simple twiners and tendril-bearers 
 are in each case beneficial in a high degree to the species. 
 Tor instance, it is clearly a great advantage to a twining 
 plant to become a leaf-climber; and it is probable that 
 every twiner which possessed leaves with long foot-stalks 
 would have been developed into a leaf-climber, if the foot¬ 
 stalks had possessed in any slight degree the requisite sen¬ 
 sitiveness to a touch. 
 
 As twining is the simplest means of ascending a support, 
 and forms the basis of our series, it may naturally be asked 
 how did plants acquire this power in an incipient degree, 
 afterward to be improved and increased through natural 
 selection.. The power of twining depends, firstly, on the 
 stems while young being extremely flexible (but"this is a 
 character common to many plants which are not climbers) ; 
 and, secondly, on their continually bending to all points of 
 the compass, one after the other in succession, in the same 
 order. By this movement the stems are inclined to all 
 sides, and are made to move round and round. As soon 
 as the lower part of a stem strikes against any object and 
 is stopped, the upper part still goes on bending and revolv¬ 
 ing, and thus necessarily twines round and up the support. 
 The revolving movement ceases after the early growth of 
 each shoot. As in many widely separated families of 
 plants, single species and single genera possess the power 
 of revolving, and have thug become twiners, they must have 
 
THEORY OF NATURAL SELECTION 
 
 233 
 
 independently acquired it, and cannot have inherited it from 
 a common proge^ntor. Hence, I was led to predict tha 
 , n i e S ^! lt 1 ten / en ?y to a movement of this* kind would 
 
 JJT^ 0 b /i fr< ? 1 ? uncom nion with plants which did 
 t climb, and that this had afforded the basis for natural 
 
 diction n /knp° rk f° n T d im P. rove - When I made this pre- 
 J.ction, I knew of only one imperfect case, namelv of the 
 
 young flower-peduncles of a Maurandia which revolted 
 
 lrr f? ula rfy, like the stems of twining pknts 
 
 "?. akln g any use of this habit. Soon afterward 
 
 fnfof a Dimmer' 6 ? ^ S 1 ? -terns of an llfsma 
 sena-nted in P lants which do not climb and are widely 
 irret?]^^ ^ s y sfc em—revolved plainly, though 
 
 thaTfPii 7 ’ and he ., s ^ ates that hQ has reason to suspect 
 that this occurs with some other plants. These slight 
 
 movements appear to be of no service to the plants in ques 
 
 t on; anyhow, they are not of the least use in the wav of 
 
 c lmbmg, which is the point that concerns us. Neverthe 
 
 flelibV C aod Se *f 4 ^ lf + t 1 hestemsof these plants had been 
 flexible and if under the conditions to which they are ex 
 
 posea it had profited them to ascend to a height idien the 
 
 r r 0l l inS m >ght havVbeen 
 mcieasea and utilized through natural selection, until thev 
 
 h Wnh°reL C eT e tnil Ult0 we . 11 ; develo P ed twining species 7 
 i respect to the sensitiveness of the foot-stalks 
 
 of the leaves and flowers, and of tendrils, nearlv the 
 
 same remarks are applicable as in the case of the revolv- 
 
 g movements of twining plants. As a vast number of 
 
 whh this'MndTf sp W v 6ly dist i not g rou P s , are endowed 
 witn tins kind of sensitiveness, it ought to be found in 
 
 com? 0 c e flmbeTs dltl Th' mplants which have not be¬ 
 come cumbers. This is the case: I observed tint tha 
 
 young flower-peduncles of the above Maurandia curbed 
 
 themselves a little toward the side which Tas touched 
 
 Md tblf 0 r nt l f, eyeral s Pecies of Oxalis that the leaves 
 
 hot sun wlmn H 3 kS moved ’ 1 especially after exposure to a 
 TT s , n > when they were gently and repeatedly touched or 
 
 when the plant was shaken, f repeated these obsefvati’ons 
 
 some fif tn her ®? ecies of 0xalis with the same result- in 
 in f thl h ! m th ? move “ ent was distinct, but was best 
 I??" the y° n . n S leayes i ™ others it was extremely slight 
 It is a more important fact that according to the high 
 
234 MISCELLANEOUS OBJECTIONS TO THE 
 
 authority of Hofmeister, the young shoots and leaves of 
 all plants move after being shaken; and with climbing 
 plants it is, as we know, only during the early stages of 
 growth that the foot-stalks and tendrils are sensitive. 
 
 it is scarcely possible that the above slight movements, 
 due to a touch or shake, in the young and growing organs 
 of plants, can be of any functional importance to them. 
 But plants possess, in obedience to various stimuli, poweis 
 of movement, which are of manifest importance to them, 
 for instance, toward and more rarely from the hgh 
 in opposition to, and more rarely m tne direction ot, the 
 attraction of gravity. When the nerves and muscles of an 
 animal are excited by galvanism or by the absorption of 
 strychnine, the consequent movements may be called an 
 incidental^result, for the nerves and muscles have not been 
 rendered specially sensitive to these stimuli, oo aw 1 
 plants it i ppears that, from having the power of movement 
 in obedience to certain stimuli, they are excited man in¬ 
 cidental manner by a touch, or by being shaken, lienee 
 there is no great difficulty in admitting that in the case ot 
 leaf-climbers and tendril-bearers, it is this tendency which 
 has been taken advantage of and increased through natuial 
 selection. It is, however, probable, from reasons which 1 
 have assigned in my memoir, that this will have occurred 
 only with plants which had already, acquired the power 
 of revolving, and had thus become twiners. 
 
 I have already endeavored to explain how plants became 
 twiners, namely, by the increase of a tendency to slight 
 and irregular revolving movements, which were at first of 
 no use to them; this movement, as well as that due to a 
 touch or shake, being the incidental result of the power ot 
 moving, gained for other and beneficial purposes. W nether, 
 during 0 the gradual development of climbing plants, nat¬ 
 ural selection has been aided by the inherited effects of 
 use, I will not pretend to decide; but we know that certain 
 periodical movements, for instance the so-called sleep of 
 plants, are governed by habit. 
 
 I have now considered enough, perhaps more than 
 enough, of the cases, selected with care by a skillful natu¬ 
 ralist, to prove that natural selection is incompetent to ac¬ 
 count for the incipient stages of useful structures; and 
 
235 
 
 THEOR T OF NA TURAL SELEGT10 W. 
 
 have shown, as 1 hope, that there is no great difficulty on 
 tins bead. A good opportunity has thus been afforded for 
 a on gradations of structure, often associ¬ 
 ated with strange functions—an important subject, which 
 tre . ated T at sufficient length in the former editions 
 o, i,his work. I will now briefly recapitulate the foregoing 
 ^ases. 
 
 With the giraffe, the continued preservation of the indi¬ 
 viduals of some extinct high-reaching ruminant, which had 
 the longest necks, legs, etc., and could browse a little 
 above the average height, and the continued destruction of 
 those which could not browse so high, would have sufficed 
 ioi the production of this remarkable quadruped: but the 
 prolonged use of all the parts, together with inheritance, 
 will have aided in an important manner in their jo-ordina- 
 tion. With the many insects which imitate vt rious ob¬ 
 jects there is no improbability in the belief that an acci¬ 
 dental resemblance to some common object was in each case 
 the foundation for the work of natural selection, since per¬ 
 fected through the occasional preservation of slight variations 
 which made the resemblance at all closer; and this will have 
 been carried on as long as the insect continued to vary, 
 and as long as a more and more perfect resemblance led to 
 \ts escape from sharp-sighted enemies. In certain species 
 of whales there is a tendency to the formation of irregular 
 httle points of horn on the palate; and it seems to be quite 
 within the scope of natural selection to preserve all favor¬ 
 able variations, until the points were converted, first into 
 lamellated knobs or teeth, like those on the beak of a 
 goose—then into short lamellae, like those of the domestic 
 clucks—and then into lamellae, as perfect as those of the 
 shoveller-duck—and finally into the gigantic plates of 
 baleen, as m the mouth of the Greenland whale. In the 
 iamily of the ducks, the lamellae are first used as teeth 
 en partly as teeth and partly as a sifting apparatus, and 
 at last almost exclusively for this latter purpose. 
 
 With such structures as the above lamellae of horn or 
 whalebone, habit or use can have done little or nothing as 
 tar as we can judge, toward their development. On the 
 other hand, the transportal of the lower eye of a fiat- 
 hsh to the upper side of the head, and the formation of a 
 prehensile tail, may be attributed almost wholly to con- 
 
236 MISCELLANEOUS OBJECTIONS TO THE 
 
 tinued use, together with inheritance. With respect to 
 the mammae of the higher animals, the most probable con¬ 
 jecture is that primordially the cutaneous glands over 
 the whole surface of a marsupial sack secreted a nutritious 
 fluid; and that these glands were improved in function 
 through natural selection, and concentrated into a confined 
 area, in which case they would have formed a mamma. 
 There is no more difficulty in understanding how the 
 branched spines of some ancient Echinoderm, which 
 served as a defence, became developed through natural 
 selection into tridactyle pedicellariae, than in understand¬ 
 ing the development of the pincers of crustaceans, through 
 slight, serviceable modifications in the ultimate and pe¬ 
 nultimate segments of a limb, which was at first used solely 
 for locomotion. In the avicularia and vibracula of the 
 Polyzoa we have organs widely different in appearance 
 developed from the same source; and with the vibracula 
 we can understand how the successive gradations might 
 have been of service. With the pollinia of orchids, the 
 threads which originally served to tie together the pollen- 
 grains, can be traced cohering into caudicles; and the steps 
 can likewise be followed by which viscid matter, such as 
 that secreted by the stigmas of ordinary flowers, and still 
 subserving nearly but not quite the same purpose, became 
 attached to the free ends of the caudicles—all these grada¬ 
 tions being of manifest benefit to the plants in question. 
 With respect to climbing plants, I ne*d not repeat what 
 has been so lately said. 
 
 It has often been asked, if natural selection be so potent, 
 why has not this or that structure been gained by certain 
 species, to which it would apparently have been advan¬ 
 tageous? But it is unreasonable to expect a precise answer 
 to such questions, considering our ignorance of the past 
 history of each species, and of the conditions which at the 
 present day determine its numbers and range. In most 
 cases only general reasons, but in some few cases special 
 reasons, can be assigned. Thus to adapt a species to new 
 habits of life, many co-ordinated modifications are almost 
 indispensable, and it may often have happened that the 
 requisite parts did not vary in the right manner or to the 
 right degree. Many species must have been prevented 
 from increasing in numbers through destructive agencies, 
 
THEOR T OF JSTA TURAL SELECTIO2T. 23 7 
 
 stood in no relation to certain structures, which we 
 imagine would have been gained through natural selection 
 from appearing to us advantageous to the species In this 
 case, as the struggle for life did not depend™ schsHuc 
 ures they could not have been acquired through natural 
 selection In many cases complex and long-enduring con¬ 
 i’ 10 i nS ’ ofte , n °f i a peculiar nature, are necessary for the 
 development of a structure; and the requisite conditions 
 may seldom have concurred. The belief that any given 
 
 we think, often erroneously, would S have 
 been beneficial to a species, would have been"gained under 
 all circumstances through natural selection, if opposed to 
 what we can understand of its manner of action. Mr 
 
 somethin^ 8 bnt ^ na . tural selection has effected 
 something, but he considers it as “demonstrably insuf- 
 
 fts le faencf aC T ntf r% thephen ° menawhich 1 ex Plain by 
 its agency. His chief arguments have now been con¬ 
 sidered, and the others will hereafter be considered. They 
 
 Hnn“ t0 u n ‘t e f 0 par , tak n e little of the character of demonstraf 
 tion, and to have little weight in comparison with those in 
 
 favoi of the power of natural selection, aided by the other 
 agencies often specified. Iam bound to add, that some of 
 
 vaLed^ a “d arguments here used by me, have been ad- 
 10 ‘ th ° s ame purpose m au able article lately pub¬ 
 lished in the ‘Medico-Chirurgical Review.” P 
 
 At the present day almost all naturalists admit evolution 
 
 throuVh°“f l r -r iVai,t Relieves species change 
 
 Hough an internal force or tendency,” about which "it 
 is not pretended that anything is known. That species 
 have a capacity for change will be admitted by all evolu¬ 
 tionists; but there is no need, as it seems to me, to invoke 
 
 bdiiv T ?a i /, 0rCe ^ ey , ond the tend ency to ordinary varia¬ 
 bility which through the aid of selection, by man has given 
 
 me to many well-adapted domestic races, and wh?ch 
 
 gHe 1 nt T a ' d ,° f , natural election, would equally well 
 give rise by graduated steps to natural races or species 
 
 ihe final result will generally have been, as already exl 
 
 plained, an advance, but m some few cases a retrogression 
 in organization. 5 
 
 Mr. Mivart is further inclined to believe and some 
 naturalists agree with him, that new species manifest 
 themselves “ with suddenness and by modifications appear 
 
238 MISCELLANEOUS OBJECTIONS TO THE 
 
 ino- at once.” For instance, he supposes that the differ¬ 
 ences between the extinct three-toed Hippanon and the 
 horse arose suddenly. He thinks it difficult to believe that 
 the wing of a bird “was developed m any other way than 
 by a comparatively sudden modification of a marked and 
 important kind and apparently he would extend the 
 same view to the wings of bats and pterodactyles. I Ins 
 conclusion, which implies great breaks or discontinuity in 
 the series, appears to me improbable m the highest degree. 
 
 Every one who believes in slow and gradual evolution, 
 will of course admit that specific changes may have been 
 as abrupt and as great as any single variation which we 
 meet with under nature, or even under domestication. 
 But as species are more variable when domesticated or cul¬ 
 tivated than under their natural conditions, it is not piob- 
 able that such great and abrupt variations have often 
 occurred under nature, as are known occasionally to anso 
 under domestication. Of these latter variations several 
 may be attributed to reversion; and the character which 
 thus reappear were, it is probable, in many cases ar hist 
 rained in a gradual manner. A still greater number must 
 be called monstrosities, such as six-fingered men, porcupine 
 men, Ancon sheep, Niata cattle, etc.; and as they are 
 widely different in character from natural species, they 
 throw very little light on our subject. Excluding such 
 cases of abrupt variations, the few wlucn remain would at 
 best constitute, if found in a state of natuie, doubtful 
 species, closely related to their parental types. . 
 
 My reasons for doubting whether natural species hare 
 changed as abruptly as have occasionally domestic races, 
 and for entirely disbelieving that they have changed in the 
 wonderful manner indicated by Mr. Mivart, are as follows. 
 According to our experience, abrupt and strongly marked 
 variations occur in our domesticated productions, sing y 
 and at rather long intervals of time. If such occurrec 
 under nature, they would be liable, as formerly explained, 
 to be lost by accidental causes of destruction and by subse¬ 
 quent intercrossing; and so it is known to be under o- 
 mestieation, unless abrupt variations of this kind are spec¬ 
 ially preserved and separated by the care of man. Hence, 
 in order that a new species should suddenly appear m the 
 manner supposed by Mr. Mivart, it is almost necessary to 
 
THEOR T OF NA TURAL SEL ECTION. 
 
 239 
 
 believe, in opposition to all analogy, that several wonder¬ 
 fully changed individuals appeared simultaneously within 
 the same district. This difficulty, as in the case of uncon¬ 
 scious selection by man, isavoided on the theory of gradual 
 evolution through the preservation of a large number of 
 individuals, which varied more of less in any favorable 
 dnection, and of the destruction of a large number which 
 varied in an opposite manner. 
 
 That many species have been evolved in an extremelv 
 gradual manner, there can hardly be a doubt. The species 
 and even the genera of many large natural families are so 
 closely allied together that it is difficult to distinguish not 
 a few of them On every continent, in proceeding from 
 north to south, from lowland to upland, etc., we meet with 
 a host of closely related or representative species; as we 
 likewise do on certain distinct continents, which we have 
 reason to believe were formerly connected. But in making 
 these and the following remarks, I am compelled to allude tS 
 subjects hereafter to be discussed. Look at the many out- 
 - round a continent, and see how many of their 
 
 inhabitants can be raised only to the rank of doubtful 
 species. So it is if we look to past times, and compare the 
 species which have just passed away with those still living 
 
 • Vlt i. 11 ^ t ^ e - Sa ?? e ar ^ as; or if we com pare the fossil species 
 imbedded in the sub-stages of the same geological forma- 
 
 tmn. It is indeed manifest that multitudes of species 
 are related in the closest manner to other species that still 
 exist or ha Ve lately existed; and it will hardly be main¬ 
 tained that such species have been developed in an abrupt 
 or sudden manner. Nor should it be forgotten, when we 
 look to the special parts of allied species, instead of to dis¬ 
 tinct species, that numerous and wonderfully fine grada¬ 
 tions can be traced, connecting together widely different 
 
 Many large groups of facts are intelligible only on the 
 principle that species have been evolved by very small steps. 
 
 or instance, the fact that the species included in the 
 larger genera are more closely related to each other and 
 present a greater number of varieties than do the species 
 
 _ i m ... _ a e also grouped in 
 
 little clusters, like varieties round species; and they present 
 
 other analogies with varieties, as was shown in our second 
 
240 
 
 MISCELLANEOUS OBJECTIONS TO TEE 
 
 chapter. On this same principle we can understand how 
 it is that specific characters are more variable than generic 
 characters; and how the parts which are developed m an 
 extraordinary degree or manner are more variable than 
 other parts of the same species. Many analogous facts, all 
 pointing in the same direction, could be added. 
 
 Although very many species have almost certainly been 
 produced by steps not greater than those separating line 
 varieties; yet it may be maintained that some have been 
 developed in a different and abrupt manner. Such an 
 admission, however, ought not to be made without stiong 
 evidence being assigned. The vague and in some respects 
 false analogies, as they have been shown to be by Mr. 
 Chauncey Wright, which have been advanced m favor of 
 this view, such as the sudden crystallization of inoiganic 
 substances, or the falling of a facetted spheroid from one 
 facet to another, hardly deserve consideration. One class 
 of facts, however, namely, the sudden appearance of new 
 and distinct forms of life in our geological formations sup¬ 
 ports at first sight the belief in abrupt development. But 
 the value of this evidence depends entirely on the perfec¬ 
 tion of the geological record, in relation to periods remote 
 in the history of the world. If the record is as frag¬ 
 mentary as many geologists strenuously assert, theie is 
 nothing strange in new forms appearing as if suddenly 
 developed. 
 
 Unless we admit transformations as prodigious as tnose 
 advocated by Mr. Mivart, such as the sudden development 
 of the wings of birds or bats, or the sudden conversion of 
 a ITipparion into a horse, hardly any light is thrown by the 
 oelief in abrupt modifications on the deficiency of connect¬ 
 ing links in our geological formations. But against the 
 belief in such abrupt changes, embryology enters a strong 
 protest. It is notorious that the wings of birds and bats, 
 and the legs of horses or other quadrupeds, are undis- 
 tinguishable at an early embryonic period, and that they 
 become differentiated by insensibly fine steps. Embryo- 
 logical resemblances of ail kinds can be accounted for,. as 
 we shall hereafter see, by the progenitors of^ our existing 
 species having varied after early youth, and having trans¬ 
 mitted their newly-acquired characters to their offspring, 
 at a corresponding age. The embryo is thus left almost 
 
THEORY OF NATURAL SELECTION. 
 
 241 
 
 unaffected, and serves as a record of the past condition of 
 the species. Hence it is that existing species during the 
 early stages of their development so often resemble ancient 
 and extinct forms belonging to the same class. On this 
 view of the meaning of _ embryological resemblances, and 
 a v view, it is incredible that an animal 
 should have undergone such momentous and abrupt trans¬ 
 formations as those above indicated, and yet should not 
 bear even a trace in its embryonic condition of any sudden 
 modification, every detail in its structure being developed 
 by insensibly fine steps. 
 
 He who believes that some ancient form was transformed 
 suddenly through an internal force or tendency into, for 
 instance, one furnished with wings, will be almost com¬ 
 pelled to assume, in opposition to all analogy, that many 
 individuals varied simultaneously. It cannot be denied 
 that such abrupt and great changes of structure are widely 
 different from those which most species apparently have 
 undergone. He will further be compelled to believe that 
 many structures beautifully adapted to all the other parts 
 of the same creature and to the surrounding conditions, 
 have been suddenly produced; and of such complex and 
 wonderful co-adaptations, he will not be able to assign a 
 shadow of an explanation. He will be forced to admit 
 that these great and sudden transformations have left no 
 trace of their action on the embryo. To admit all this is, 
 as it seems to me, to enter into the realms o£ miracle, and 
 to leave those of science. 
 
242 
 
 INSTINCT. 
 
 CHAPTER Yin. 
 
 INSTINCT. 
 
 Instincts comparable with habits, but different in their origin- 
 instincts graduated — Aphides and ants — Instincts variable— 
 Domestic instincts, their origin—Natural instincts of the cuckoo, 
 molothrus, ostrich and parasitic bees—Slave-making ants — 
 Hive-bee, its cell-making instinct — Changes of instinct and 
 structure not necessarily simultaneous—Difficulties of the theory 
 of the Natural Selection of instincts—Neuter or sterile insects— 
 Summary. 
 
 Many instincts are so wonderful that their development 
 will probably appear to the reader a difficulty sufficient to 
 overthrow my whole theory. I may here premise, that I 
 have nothing to*do with the origin of the mental powers, 
 any more than I have with that of life itself. We are con¬ 
 cerned only with the diversities of instinct and of the 
 other mental faculties in animals of the same class. 
 
 I will not attempt any definition of instinct. It would 
 be easy to show that several distinct mental actions are 
 commonly embraced by this term; but every one under¬ 
 stands what is meant, when it is said that instinct impels 
 the cuckoo to migrate and to [lay her eggs in other birds’ 
 nests. An action, which we ourselves require experience 
 to enable us to perform, when performed by an animal, 
 more especially by a very young one, without experience, 
 and when performed by many individuals in the same way, 
 without their knowing for what purpose it is performed, is 
 usually said to be instinctive. But I could show that none 
 of these characters are universal. A little dose of judg¬ 
 ment or reason, as Pierre Huber expresses it, often comes 
 into play, even with animals low in the scale of nature.. 
 
 Frederick Cuvier and several of the older metaphysicians 
 have compared instinct with habit. This comparison 
 gives, I think, an accurate notion of the frame of mind 
 
INSTINCT. 
 
 243 
 
 under which an instinctive action is performed, but not 
 necessarily of its origin. How unconsciously many habitual 
 actions are performed, indeed not rarely in direct oppo¬ 
 sition to our conscious will ! yet they may be modified by 
 the will or reason. Habits easily become associated with 
 othei habits, with certain periods of time and states of the 
 body. When once acquired, they often remain constant 
 throughout life. Several other points of resemblance 
 between instincts and habits could be pointed out. As in 
 repeating a well-known song, so in instincts, one action 
 follows another by a sort of rhythm* if a person be inter¬ 
 rupted m a song, or in repeating anything by rote, he is 
 geneially foiced to go back to recover the habitual train of 
 thought; so P. Huber found it was with a caterpillar, 
 which makes a very complicated hammock; for if lie took 
 a caterpillar which had completed its hammock uji to, say, 
 the sixth stage of construction, and put it into a hammock 
 completed up only to the third stage, the caterpillar simply 
 re-performed the fourth, fifth and sixth stages of con¬ 
 struction. If, however, a caterpillar were taken out of a 
 hammock made up, for instance, to the third stage, and 
 were put. into one finished up to the sixth stage, so that 
 much of its work was already done for it, far from deriving 
 any benefit from this, it was much embarrassed, and in 
 order to complete its hammock, seemed forced to start 
 from the third stage, where it had left off, and thus tried 
 to complete the already finished work. 
 
 If we suppose any habitual action to become inherited— 
 and it can be shown that this does sometimes happen— 
 then the resemblance between what originally was a habit 
 and an instinct becomes so close as not to be distinguished 
 If Mozart, instead of playing the piano-forte at three years 
 old with wonderfully little practice, had played a tune with 
 no practice at all, he might truly be said to have done so 
 instinctively. But it would be a serious error to suppose 
 that the greater number of instincts have been acquired by 
 habit m one generation, and then transmitted by inherit¬ 
 ance to succeeding generations. It can be clearly shown 
 that the most wonderful instincts with which we are 
 acquainted, namely, those of the hive-bee and of many ants, 
 could not possibly have been acquired by habit. 
 
 It will be universally admitted that instincts are as im- 
 
INSTINCT. 
 
 244 
 
 portant as corporeal structures for the welfare of each 
 species, under its present conditions of life. Under 
 changed conditions of life, it is at least possible that slight 
 modifications of instinct might be profitable to a species; 
 and if it can be shown that instincts do vary ever so little, 
 then I can see no difficulty in natural selection preserving 
 and continually accumulating variations of instinct to any 
 extent that was profitable. It is thus, as I believe, that all 
 the most complex and wonderful instincts have originated. 
 As modifications of corporeal structure arise from, and are 
 increased by, use or habit, and are diminished or lost by 
 disuse, so I do not doubt it has been with instincts. But 
 I believe that the effects of habit are in many cases of sub¬ 
 ordinate importance to the effects of the natural selection 
 of what may be called spontaneous variations of instincts— 
 that is of variations produced by the same unknown causes 
 which produce slight deviations of bodily structure. 
 
 No complex instinct can possibly be produced through 
 natural selection, except by the slow and gradual accumu¬ 
 lation of numerous slight, yet profitable, variations. Hence, 
 as in the case of corporeal structures, we ought to find in 
 nature, not the actual transitional gradations by which 
 each complex instinct has been acquired—for these could 
 be found only in the lineal ancestors of each species—but 
 we ought to find in the collateral lines of descent some 
 evidence of such gradations; or we ought at least to be 
 able to show that gradations of some kind are possible; and 
 this we certainly can do. I have been surprised to find, 
 making allowance for the instincts of animals having been 
 but little observed, except in Europe and North America, 
 and for no instinct being known among extinct species, how 
 very generally gradations, leading to the most complex in¬ 
 stincts, can be discovered. Changes of instinct may some¬ 
 times be facilitated by the same species having different in¬ 
 stincts at different periods of life, or at different seasons of 
 the year, or when placed under different circumstances, 
 etc.; in which case either the one or the other instinct 
 might be preserved by natural selection. And such in¬ 
 stances of diversity of instinct in the same species can be 
 shown to occur in nature. 
 
 Again, as in the case of corporeal structure, and con¬ 
 formably to my theory, the instinct of each species is good 
 
INSTINCT. 
 
 Mb 
 
 for itself; but has never, as far as we can judge, been pro¬ 
 duced for the exclusive good of others. One of the strong¬ 
 est instances of an animal apparently performing an 
 action for the sole good of another, with which I am 
 acquainted, is that of aphides voluntarily yielding, as was 
 first observed by Huber, their sweet excretion to ants: that 
 they do so voluntarily, the following facts show: I re¬ 
 moved all the ants from a group of about a dozen aphides 
 on a dock-plant, and prevented their attendance during 
 several hours. After this interval, I felt sure that the 
 aphides would want to excrete. I watched them for some 
 time through a lens, but not one excreted; I then tickled 
 and stroked them with a hair in the same manner, as well 
 as I could, as the ants do with their antennas; but not 
 one excreted. Afterward, I allowed an ant to visit them, 
 and it immediately seemed, by its eager way of running 
 about to be well awa^e what a rich flock it had discovered; 
 it then begun to play with its antennas on the abdomen 
 first of one aphis and then of another; and each, as soon as 
 it felt the antennas, immediately lifted up its abdomen and 
 excreted a limped drop of sweet juice, which was eagerly 
 devoured by the ant. Even the quite young aphides be¬ 
 haved in this manner, showing that the action was instinc¬ 
 tive, and not the result of experience. It is certain, from 
 the observations of Huber, that the aphides show no dis¬ 
 like to the ants: if the latter be not present they are at 
 last compelled to eject their excretion. But as the excre¬ 
 tion is extremely viscid, it is no doubt a convenience to 
 the aphides to have it removed; therefore probably they do 
 not excrete solely for the good of the ants. Although 
 there is no evidence that any animal performs an action 
 for the exclusive good of another species, yet each tries to 
 take advantage of the instincts of others, as each takes 
 advantage of the weaker bodily structure of other 
 species. So again certain instincts can not be considered as 
 absolutely perfect; but as details on this and other such 
 points are not indispensable, they may be here passed 
 over. 
 
 As some degree of variation in instincts under a state of 
 nature, and the inheritance of such variations, are indis¬ 
 pensable for the action of natural selection, as many 
 instances as possible ought to be given; but want of space 
 
INSTINCT. 
 
 246 
 
 prevents me. I can only assert that instincts certainly do 
 
 vary_for instance, tlie migratory instinct, both in extent 
 
 and. direction, and in its total loss. So it is with the nests 
 of birds, which vary partly in dependence on the situations 
 chosen, and on the nature and temperature of the country 
 inhabited, but often from causes wholly unknown to us. 
 Audubon has given several remarkable cases of differences 
 in the nests of the same species in the northern and south¬ 
 ern United States. Why, it has been asked, if instinct be 
 variable, has it not granted to the bee “ the ability to use 
 some other material when wax was deficients But what 
 other natural material could bees use? They will work, as 
 I have seen, with wax hardened with vermilion or solt- 
 ened with lard. Andrew Knight observed that his bees, 
 instead of laboriously collecting propolis, used a cement of 
 wax and turpentine, with which he had coveied dccoi- 
 ticated trees. It has lately been slio^wn that bees, instead 
 of searching for pollen, will gladly use a very different 
 substance, namely, oatmeal. Fear of any particular enemy 
 is certainly an instinctive quality, as may be seen in nest¬ 
 ling birds, though it is strengthened by experience, and by 
 the sight of fear of the same enemy in other animals. The 
 fear of man is slowly acquired, as I have elsewhere shown, 
 by the various animals which inhabit desert islands; and 
 we see an instance of this even in England, in the greatei 
 wildness of all our large birds in comparison with our small 
 birds; for the large birds have been most persecuted by 
 man/ We may safely attribute the greater wildness of our 
 large birds to this cause; for in uninhabited islands large 
 birds are not more fearful than small; and the magpie, so 
 wary in England, is tame in Korway, as is the hooded ciow 
 
 in Egypt. . . , . . 
 
 That the mental qualities of animals of the same kind, 
 born in a state of nature, vary much, could be shown by 
 many facts. Several cases could also be adduced of occa¬ 
 sional and strange habits in wild animals, which, if advan¬ 
 tageous to the species, might have given rise, through 
 natural selection, to new instincts. But I am well aware 
 that these general statements, without the facts in detail, 
 will produce but a feeble effect on the reader s mind, 
 can only repeat my assurance, that I do not speak without 
 good evidence. 
 
CHANGES OF HABIT OR INSTINCT. 
 
 247 
 
 INHERITED CHANGES OF HABIT OR IHSTIHCT IH DOMES¬ 
 TICATED AHIMALS. 
 
 . The possibility, or even probability, of inherited varia¬ 
 tions of instinct in a state of nature will be strengthened 
 by briefly considering a few cases under domestication. 
 We shall thus be enabled to see the part which habit and 
 the selection of so-called spontaneous variations have played 
 in modifying the mental qualities of our domestic animals. 
 It is notorious how much domestic animals vary in their 
 mental qualities. With cats, for instance, one naturally 
 takes to catching rats, and another mice, and these ten¬ 
 dencies are known to be inherited. One cat, according to 
 Mr. St. John, always brought home game birds, another 
 hares or rabbits, and another hunted on marshy ground and 
 almost nightly caught woodcocks or snipes. A number of 
 curious and authentic instances could be given of various 
 shades of disposition and of taste, and likewise of the oddest 
 tricks, associated with certain frames of minds or periods 
 of time, being inherited. But let us look to the familiar 
 case of the breeds of the dogs: it cannot be doubted that 
 young pointers (I have myself seen striking instances) will 
 sometimes point and even back other dogs the very first 
 time that they are taken out; retrieving is certainly in 
 some degree inherited by retrievers; and a tendency to run 
 round, instead of at, a flock of sheep, by shepherd dogs. 
 
 I cannot see that these actions, performed without experi¬ 
 ence by the young, and in nearly the same manner by each 
 individual, performed with eager delight by each breed, 
 and without the end being known—for the young pointer 
 can no more know that he points to aid his master, than 
 the white butterfly knows why she lavs her eggs on the leal 
 of the cabbage—I cannot see that these actions differ 
 essentially from true instincts. If we were to behold one 
 kind of wolf, when young and without any training, as 
 soon as it scented its prey, stand motionless like a statue, 
 and then slowly crawl forward with a peculiar gait; and 
 another kind of wolf rushing round, instead of at, a herd 
 of deer, and driving them. to . a distant point, we should 
 assuredly call these actions instinctive. Domestic instincts, 
 as they, may be called, are certainly far less fixed than 
 natural instincts; but they have been acted on by far less 
 
248 
 
 CHANGES OF HABIT OR INSTINCT 
 
 rigorous selections, and have been transmitted for ail 
 incomparably shorter period, under less fixed conditions of 
 
 life. 
 
 How strongly these domestic instincts, habits, and 
 dispositions are inherited, and how curiously thev 
 become mingled, is well shown when different breeds of 
 dogs are crossed. Thus it is known that a cross with a 
 bull-dog has affected for many generations the courage and 
 obstinacy of greyhounds; and a cross with a greyhound 
 has given to a whole family of shepherd-dogs a tendency 
 to hunt hares. These domestic instincts, when thus tested 
 by crossing, resemble natural instincts, which in a like 
 manner become curiously blended together, and foi a long 
 period exhibit traces of the instincts of either parent: for 
 example, Le Roy describes a dog, whose great-giandfather 
 was a wolf, and this dog showed a trace of its wild parent¬ 
 age only in one way, by not coming in a straight line to 
 his master, when called. 
 
 Domestic instincts are sometimes spoken of as actions 
 which have become inherited solely from long-continued 
 and compulsory habit; but this is not true. No one would 
 ever have thought of teaching, or probably could have 
 taught, the tumbler-pigeon to tumble—an action which, 
 as I have witnessed, is performed by young birds, that have 
 never seen a pigeon tumble. We may believe that some 
 one pigeon showed a slight tendency to this strange habit, 
 and that the long-continued selection of the best individ¬ 
 uals in successive generations made tumblers what they 
 now are; and near Glasgow there are house-tumblers, as I 
 hear from Mr. Brent, which can not fly eighteen inches 
 high without going head over heels. It may. be doubted 
 whether any one would have thought of training a dog to 
 point, had not some one dog naturally shown a tendency 
 in this line; and this is known occasionally to. happen, a3 
 I once saw, in a pure terrier: the act of pointing is prob¬ 
 ably, as many have thought, only the exaggerated pause of 
 an animal preparing to spring on its prey. When the first 
 tendency to point was once displayed, methodical selection 
 and the inherited effects of compulsory training in each 
 successive generation would soon complete the work; and 
 unconscious selection is still in progress, as each man tries 
 to procure, without intending to improve the breed, dogs 
 
IN DOMESTIC A TED ANIMALS. 
 
 249 
 
 which stand and hunt best. On the other hand, habit 
 alone in some cases has sufficed; hardly any animal is 
 more difficult to tame than the young of the wild rabbit; 
 scarcely any animal is tamer than the young of the tame 
 rabbit; but I can hardly suppose that domestic rabbits have 
 often been selected for tameness alone; so that we must 
 attribute at least the greater part of the inherited change 
 from extreme wildness to extreme tameness, to habit and 
 long-continued close confinement. 
 
 Natural instincts are lost under domestication: a re¬ 
 markable instance of this is seen in those breeds of fowls 
 which very rarely or never become “broody,” that is, never 
 wish to sit on their eggs. Familiarity alone prevents our 
 seeing how largely and how permanently the minds of our 
 domestic animals have been modified. It is scarcely pos¬ 
 sible to doubt that the love of man has become instinctive 
 in the dog. All wolves, foxes, jackals and species of the cat 
 genus, when kept tame, are most eager to attack poultry, 
 sheep and pigs; and this tendency has been found incur¬ 
 able in dogs which have been brought home as puppies from 
 countries such as Tierra del Fuego and Australia, where the 
 savages do not keep these domestic animals. How rarely, on 
 the other hand, do our civilized dogs, even when quite 
 young, require to be taught not to attack poultry, sheep and 
 pigs! No doubt they occasionally do make an attack, and 
 are then beaten; and if not cured, they are destroyed; 
 so that habit and some degree of selection have proba¬ 
 bly concurred in civilizing by inheritance our dogs. On 
 the other hand, young chickens have lost wholly by habit, 
 that fear of the dog and cat which no doubt was originally 
 instinctive in them, for I am informed by Captain Hutton 
 that the young chickens of the parent stock, the Gallus 
 bankiva, when reared in India under a hen, are at first ex¬ 
 cessively wild. So it is with young pheasants reared in 
 England under a hen. It is not that chickens have lost all 
 fear, but fear only of dogs and cats, for if the hen gives 
 the danger chuckle they will run (more especially young 
 turkeys) from under her and conceal themselves in the 
 surrounding grass or thickets; and this is evidently done 
 for the instinctive purpose of allowing, as we see in wild 
 ground-birds, their mother to fly away. But this instinct 
 retained by our chickens has become useless under domes- 
 
250 
 
 SPECIAL INSTINCTS . 
 
 tication, for the mother hen has almost lost by disuse the 
 power of flight. 
 
 Hence, we may conclude that under domestication in¬ 
 stincts have been acquired and natural instincts have been 
 lost, partly by habit and partly by man selecting and 
 accumulating, during successive generations, peculiar 
 mental habits and actions, which at first appeared from 
 what we must in our ignorance call an accident. In some 
 cases compulsory habit alone has sufficed to produce in¬ 
 herited mental changes. In other cases compulsory habit 
 has done nothing, and all has been the result of 
 selection, pursued both methodically and unconsciously; 
 but in most cases habit and selection have probably 
 concurred. 
 
 SPECIAL INSTINCTS. 
 
 We shall, perhaps, best understand how instincts in a 
 state of nature have become modified^ by selection by con¬ 
 sidering a few cases. I will select only three, namely, the 
 instinct which leads the cuckoo to lay her eggs in other 
 birds' nests; the slave-making instinct of certain ants, and 
 the cell-making power of the hive-bee. These two latter 
 instincts have generally and justly been ranked by natural¬ 
 ists as the most wonderful of all known instincts. 
 
 INSTINCTS OF THE CUCKOO. 
 
 It is supposed by some naturalists that the more imme¬ 
 diate cause of the instinct of the cuckoo is that she lays 
 her eggs, not daily, but at intervals of two or three days, 
 so that if she were to make her own nest and sit on her 
 own eggs, those first laid would have to be left for some 
 time unincubated or there would be eggs and young birds 
 of different ages in the same nest. If this were the case 
 the process of laying and hatching might be inconveni¬ 
 ently long, more especially as she migrates at a very 
 early period, and the first hatched young would probably 
 have to be fed by the male alone. But the American 
 cuckoo is in this predicament, for she makes her own nest 
 and has eggs and young successively hatched, all at the 
 same time. It has been both asserted and denied that 
 
INSTINCTS OF TIIE CUCKOO. 
 
 251 
 
 the American cuckoo occasionally lays her eggs in other 
 birds' nests; but I have lately heard from Dr. Merrill, 
 of Iowa, that he once found in Illinois a young cuckoo, 
 together with a young jay in the nest of a blue jay (Gar- 
 rulus cristatus); and as both were nearly full feathered, 
 there could be no mistake in their identification. I could 
 also give several instances of various birds which have 
 been known occasionally to lay their eggs in other birds' 
 nests. Now let us suppose that the ancient progenitor of 
 our European cuckoo had the habits of the American 
 cuckoo, and that she occasionally laid an egg in another 
 bird's nest. If the old bird profited by this occasional 
 habit through being enabled to emigrate earlier or through 
 any other cause; or if the young were made more vigorous 
 by advantage being taken of the mistaken instinct of 
 another species than when reared by their own mother, 
 encumbered as she could hardly fail to be by having eggs 
 and young of different ages at the same time, then the old 
 birds or the fostered young would gain an advantage. And 
 analogy would lead us to believe that the young thus reared 
 would be apt to follow by inheritance the occasional and 
 aberrant habit of their mother, and in their turn would be 
 apt to lay their eggs in other birds' nest, and thus be more 
 successful in rearing their young. By a continued process 
 of this nature, I believe that the strange instinct of our 
 cuckoo has been generated. It has, also, recently been 
 ascertained on sufficient evidence, by Adolf Muller, that 
 the cuckoo occasionally lays her eggs on the bare ground, 
 sits on them and feeds her voung. This rare event is prob¬ 
 ably a case of reversion to the long-lost, aboriginal instinct 
 of nidification. 
 
 It has been objected that I have not noticed other re¬ 
 lated instincts and adaptations of structure in the cuckoo, 
 which are spoken of as necessarily co-ordinated. But in 
 all cases, speculation on an instinct known to us only in a 
 single species, is useless, for we have hitherto had no 
 facts to guide us. Until recently the instincts of the 
 European and of the non-parasitic American cuckoo alone 
 were known; now, owing to Mr. Ramsay’s observations, we 
 have learned something about three Australian species, 
 which lay their eggs in other birds' nests. The chief 
 points to be referred to are three: first, that the eommor 
 
SPECIAL INSTINCTS. 
 
 252 
 
 cuckoo, with rare exceptions, lays only one egg in a nest, 
 so that the large and voracious young bird receives ample 
 food. Secondly, that the eggs are remarkably small, not 
 exceeding those of the skylark—a bird about one-foui th as 
 large as the cuckoo. That the small size of the egg is a 
 real case of adaptation we may infer from the fact of the 
 non-parasitic American cuckoo laying full-sized eggs. 
 Thirdly, that the young cuckoo, soon after birth, has the 
 .'instinct, the strength and a properly shaped back for eject¬ 
 ing its foster-brothers, which then perish from cold and 
 huno-er. This has been boldly called a beneficent arrange¬ 
 ment, in order that the young cuckoo may get sufficient 
 food, and that its foster-brothers may perish before they 
 
 *iad acquired much feeling! # 
 
 Turning now to the Australian species, though these 
 birds generally lay only one egg in a nest, it is not rare to find 
 two and even three eggs in the same nest. In the bronze 
 cuckoo the eggs vary greatly in size, from eight to ,en 
 lines in length. Now, if it had been of an advantage to 
 this species to have laid eggs even smaller than those now 
 laid, so as to have deceived certain foster-parents, or, as is 
 more probable, to have been hatched within a shorter 
 period (for it is asserted that there is a relation between 
 the size of eggs and the period of their incubation), then 
 there is no difficulty in believing that a race or species 
 might have been formed which would have laid smaller and 
 smaller eggs; for these would have been more safely hatched 
 and reared? Mr. Ramsay remarks that two of the Australian 
 cuckoos, when they lay their eggs in an open nest, mani¬ 
 fest a decided preference for nests containing eggs similar 
 in color to their own. The European species apparently 
 manifests some tendency toward a similar instinct, but not 
 rarely departs from it, as is shown by her laying her dull 
 and pale-colored eggs in the nest of the hedge-warblei 
 with bright greenish-blue eggs. Had our cuckoo invari¬ 
 ably displayed the above instinct, it would assuredly have 
 been added to those which it is assumed must all have 
 been acquired together. The eggs of the Australian bronze 
 cuckoo vary, according to Mr. Ramsay, to an extraordinary 
 degree in color; so that in this respect, as well as in size, 
 natural selection might have secured and fixed any advan¬ 
 tageous variation. 
 
INSTINCTS OF THE MOLOTHRUS. 
 
 253 
 
 In the case of the European cuckoo, the offspring of the 
 foster-parents are commonly ejected from the nest within 
 three days after the cuckoo is hatched; and as the latter 
 at this age is in a most helpless condition, Mr. Gfould was 
 formerly inclined to believe that the act of ejection was 
 performed by the foster-parents themselves. But he has 
 now received a trustworthy account of a young cuckoo 
 which was actually seen, while still blind and" not able even 
 to hold up its own head, in the act of ejecting its foster- 
 brothers. One of these was replaced in the nest by the 
 observer, and was again thrown out. With respect to the 
 means by which this strange and odious instinct was ac¬ 
 quired, if it were of great importance for the young cuckoo, 
 as is probably the case, to receive as much food as possible 
 soon after birth, I can see no special difficulty in its having 
 gradually acquired, during successive generations, the blind 
 desire, the strength, and structure necessary for the work 
 of ejection; for those cuckoos which had such habits and 
 structure best developed would be the most securely reared. 
 The first step toward the acquisition of the proper instinct 
 might have been mere unintentional restlessness on the 
 part of the young bird, when somewhat advanced in age 
 and strength; the habit having been afterward improved, 
 and transmitted to an earlier age. I can see no more diffi¬ 
 culty in this than in the unhatched young of other birds 
 acquiring the instinct to break through their own shells; 
 or than in young snakes acquiring in their upper jaws, as 
 Owen has remarked, a transitory sharp tooth for cutting 
 through the tough egg-shell. For if each part is liable to 
 individual variations at all ages, and the variations tend to 
 be inherited at a corresponding or earlier age—proposi¬ 
 tions which cannot be disputed—then the instincts and 
 structure of the young could be slowly modified as surely 
 as those of the adult; and both cases must stand or fall 
 together with the whole theory of natural selection. 
 
 borne species of Molothrus, a widely distinct genus of 
 American birds, allied to our starlings, have parasitic 
 habits like those of the cuckoo; and the species present an 
 interesting gradation in the perfection of their instincts. 
 The sexes of Molothrus badius are stated by an excellent 
 observer, Mr. Hudson, sometimes to live promiscuously 
 together in flocks, and sometimes to pair. They either 
 
254 
 
 SPECIAL INSTINCTS. 
 
 build a nest of their own or seize on one belonging to some 
 other bird, occasionally throwing out the nestlings of the 
 stranger. They either lay their eggs in the nest thus appro¬ 
 priated, or oddly enough build one for themselves on the top 
 of it. They usually sit on their own eggs and rear their own 
 young; but Mr. Hudson says it is probable that they are occa¬ 
 sionally parasitic, for he has seen the young of this species 
 following old birds of a distinct kind and clamoring to be 
 fed by them. The parasitic habits of another species of 
 Molothrus, the M. bonariensis, are much more highly de¬ 
 veloped than those of the last, but are still far from per¬ 
 fect. This bird, as far as it is known, invariably lays its 
 eggs in the nests of strangers; but it is remarkable that 
 several together sometimes commence to build an irregular 
 untidy nest of their own, placed in singular ill-adapted 
 situations, as on the leaves of a large thistle. They never, 
 however, as far as Mr, Hudson has ascertained, complete a 
 nest for themselves. They often lay so many eggs—from 
 fifteen to twenty—in the same foster-nest, that few or none 
 can possibly be hatched. They have, moreover, the extra¬ 
 ordinary habit of pecking holes in the eggs, whether of 
 their own species or of their foster parents, which they find 
 in the appropriated nests. They drop also many eggs on 
 the bare ground, which are thus wasted. A third species, 
 the M. pecoris of North America, has acquired instinct?- 
 as perfect as those of the cuckoo, for it never lays more 
 than one egg in a foster-nest, so that the } 7 oung bird is 
 securely reared. Mr. Hudson is a strong disbeliever in 
 evolution, but he appears to have been so much struck by 
 the imperfect instincts of the Molothrus bonariensis that 
 he quotes my words, and asks, “ Must we consider these 
 habits, not as especially endowed or created instincts, but 
 as small consequences of one general law, namely, 
 transition ?” 
 
 Various birds, as has already been remarked, occasionally 
 iay their eggs in the nests of other birds. This habit is 
 not very uncommon with the Gallinaceas, and throws some 
 light on the singular instinct of the ostrich. In this 
 family several hen birds unite and lay first a few eggs in 
 one nest and then in another; and these are hatched by 
 tbe males. This instinct may probably be accounted for by 
 the fact of the hens laying a large number of eggs, but, as 
 
SLA VK-MAKING INSTINCT . 
 
 255 
 
 with the cuckoo, at intervals of two or three days. The 
 instinct, however, of the American ostrich, as in the case 
 of the Molotlirus bonariensis, has not as yet been per¬ 
 fected; for a surprising number of eggs lie strewed over 
 the plains, so that in one day’s hunting I picked up no less 
 than twenty lost and wasted eggs. 
 
 Many bees are parasitic, and regularly lay their eggs in 
 the nests of other kinds of bees. This case is more re¬ 
 markable than that of the cuckoo; for these bees have not 
 only had their instincts but their structure modified in 
 accordance with their parasitic habits; for they do not 
 possessess the pollen-collecting apparatus which would have 
 been indispensable if they had stored up food for their own 
 young. Some species of Sphegidae (wasp-like insects) are 
 likewise parasitic; and M. Fabre has lately shown good 
 reason for believing that, although the Tachytes nigra gen¬ 
 erally makes it own burrow and stores it with paralyzed 
 prey for its own larvae, yet that, when this insect finds a 
 burrow already made and stored by another sphex, it takes 
 advantage of the prize, and becomes for the occasion par¬ 
 asitic. In this case, as with that of the Molotlirus or 
 cuckoo, I can see no difficulty in natural selection making 
 an occasional habit permanent, if of advantage to the 
 species, and if the insect whose nest and stored food are 
 feloniously appropriated, be not thus exterminated. 
 
 SLAVE-MAKING INSTINCT. 
 
 This remarkable instinct was first discovered in the For¬ 
 mica (Polyerges) rufescens by Pierre Huber, a better 
 observer even than his celebrated father. This ant is ab¬ 
 solutely dependent on its slaves; without their aid, the 
 species would certainly become extinct in a single year. 
 The males and fertile females do no work of any kind, and 
 the workers or sterile females, though most energetic and 
 courageous in capturing slaves, do no other work. They 
 are incapable of making their own nests, or of feeding 
 their own larvae. When the old nest is found incon¬ 
 venient, and they have to migrate, it is the slaves which 
 determine the migration, and actually carry their masters 
 in their jaws. So utterly helpless are the masters, that 
 when Huber shut up thirty of them without a slave, but 
 
256 
 
 SPECIAL INSTINCTS. 
 
 with plenty of food which they like best, and with their 
 own larvas and pupae to stimulate them to work, they did 
 nothing; they could not even feed themselves, and many 
 perished of hunger. Huber then introduced a single slave 
 (F. fusca), and she instantly set to work, fed and saved 
 the survivors; made some cells and tended the larvae, and 
 put all to rights. What can be more extraordinary than 
 these well-ascertained facts ? If we had not known of any 
 other slave-making ant, it would have been hopeless to 
 speculate how so wonderful an instinct could have been, 
 perfected. 
 
 Another species, Formica sanguinea, was likewise first 
 discovered by P. Huber to be a slave-making ant. This 
 species is found in the southern parts of England, and its 
 habits have been attended to by Mr. F. Smith, of the Brit¬ 
 ish Museum, to whom I am much indebted for information 
 on this and other subjects. Although fully trusting to the 
 statements of Huber and Mr. Smith, I tried to approach 
 the subject in a skeptical frame of mind, as any one may 
 well be excused for doubting the existence of so extraordi¬ 
 nary an instinct as that of making slaves. Hence, I will 
 give the observations which I made in some little detail. 
 I opened fourteen nests of F. sanguinea, and found a few 
 slaves in all. Males and fertile females of the slave species 
 (F. fusca) are found only in their own proper communi¬ 
 ties, and have never been observed in the nests of F. san¬ 
 guinea. The slaves are black and not above half the size 
 of their red masters, so that the contrast in their appear¬ 
 ance is great. When the nest is slightly disturbed, the 
 slaves occasionally come out, and like their masters are much 
 agitated and defend the nest: when the nest is much dis¬ 
 turbed, and the larvaB and pupae are exposed, the slaves 
 work energetically together with their masters in carrying 
 them away to a place of safety. Hence, it is clear that 
 the slaves feel quite at home. During the months of June 
 and July, on three successive years, I watched for many 
 hours several nests in Surrey and Sussex, and never saw a 
 slave either leave or enter a nest. As, during these 
 months, the slaves are very few in number, I thought that 
 they might behave differently when more numerous; but 
 Mr. Smith informs me that he has watched the nests at 
 various hours during May, June and August, both in Sur- 
 
SLA VE-MAKING INSTINCT. 
 
 257 
 
 rey and Hampshire, and has never seen the slaves, though 
 present in large numbers in August, either leave or enter 
 the nest. Hence, he considers them as strictly household 
 slaves. The masters, on the other hand, may be con¬ 
 stantly seen bringing in materials for the nest, and food of 
 all kinds. During the year 1860, however, in the month 
 of July, I came across a community with an unusually 
 large stock of slaves, and I observed a few slaves mingled 
 with their masters leaving the nest, and marching along 
 the same road to a tall Scotch fir-tree, twentv-five yards 
 distant, which they ascended together, probably in search 
 of aphides or cocci. According to Huber, who had ample 
 opportunities for observation, the slaves in Switzerland 
 habitually work with their masters in making the nest, 
 and they alone open and close the doors in the morning and 
 evening; and, as Huber expressly states, their principle 
 office is to search for aphides. This difference in the usual 
 habits of the masters and slaves in the two countries, prob¬ 
 ably depends merely on the slaves being captured in greater 
 numbers in Switzerland than in England. 
 
 One day I fortunately witnessed a migration of F. san- 
 guina from one nest to another, and it was a most interest¬ 
 ing spectacle to behold the masters carefully carrying their 
 slaves in their jaws instead of being carried by them, as in 
 the case of F. rufescens. Another day my attention was 
 struck by about a score of the slave-makers haunting the 
 same spot, and evidently not in search of food; they 
 approached and were vigorously repulsed by an independ¬ 
 ent community of the slave-species (F. fusca); sometimes 
 as many as three of these ants clinging to the legs of the 
 slave-making F. sanguinea. The latter ruthlessly killed 
 their small opponents and carried their dead bodies as 
 food to their nest, twenty-nine yards distant; but they were 
 prevented from getting any pupae to rear as slaves. I then 
 dug up a small parcel of the pupae of F. fusca from another 
 nest, and put them down on a bare spot near the place of 
 combat; they were eagerly seized and carried off by the 
 tyrants, who perhaps fancied that, after all, they had been 
 victorious in their late combat. 
 
 At the same time I laid on the same place a small parcel 
 of the pupae of another species, F. flava, with a few of 
 these little yellow ants still clinging to the fragments of 
 
SPECIAL INSTINCTS . 
 
 258 
 
 their nest. This species is sometimes, though rarely, 
 made into slaves, as has been described by Mr. Smith. 
 Although so small a species, it is very courageous, and I 
 have seen it ferociously attack other ants. In one instance 
 I found to my surprise an independent community of F. 
 flava under a stone beneath a nest of the slave-making h. 
 sanguinea; and when I had accidentally disturbed both 
 nests, the little ants attacked their big neighbors with sun 
 prising courage. Now I was curious to ascertain whether 
 F. sanguinea could distinguish the pupae of F. fusca, 
 which they habitually make into slaves, from those of the 
 little and furious F. flava, which they rarely capture, and it 
 was evident that they did at once distinguish them; for we 
 have seen that they eagerly and instantly seized the pupae 
 of F. fusca, whereas they were much terrified when they 
 came across the pupae, or even the earth from the nest, of 
 F. flava, and quickly ran away; but in about a quarter of 
 an hour, shortly after all the little yellow ants had crawled 
 awav, they took heart and carried off the pupae. 
 
 One evening I visited another community of F. san¬ 
 guinea, and found a number of these ants returning home 
 and entering their nests, carrying the dead bodies of F. 
 fusca (showing that it was not a migration) and numerous 
 pupae. I traced a long file of ants burdened with booty, 
 for about forty yards back, to a very thick clump of heath, 
 whence I saw the last individual of h. sanguinea emeige, 
 carrying a pupa; but I was not able to find the desolated 
 nest in the thick heath. The nest, however, must have 
 been close at hand, for two or three individuals of F. fusca 
 were rushing about in the greatest agitation, and one >vas 
 perched motionless with its own pupa in its mouth on the 
 top of a spray of heath, an image of despair over its ravaged 
 
 home. 
 
 Such are the facts, though they did not need confirma¬ 
 tion by me, in regard to the wonderful instinct of making 
 slaves. Let it be observed what a contrast the instinctive 
 habits of F. sanguinea present with those of. the conti¬ 
 nental F. rufescens. The latter does not build its own 
 nest, does not determine its own migrations, does not col¬ 
 lect food for itself or its young, and cannot even feed 
 itself: it is absolutely dependent on its numerous slaves. 
 Formica sanguinea, on the other hand, possesses much 
 
CELL-MAKING INSTINCT. 
 
 259 
 
 fewer slaves, and in the early part of the summer extremely 
 few: the masters determine when and where a new nest 
 shall be formed, and when they migrate, the masters carry 
 the slaves. Both in Switzerland and England the slaves 
 seem to have the exclusive care of the larvse, and the mas¬ 
 ters alone go on slave-making expeditions. In Switzerland 
 the slaves and masters work together, making and bringing 
 materials for the nest; both, but chiefly the slaves, tend 
 and milk, as it may be called, their aphides; and thus both 
 collect food for the community. In England the masters 
 alone usually leave the nest to collect building materials 
 and food for themselves, their slaves and larv®. So that 
 the masters in this country receive much less service from 
 their slaves than they do in Switzerland. 
 
 By what steps the instinct of F. sanguinea originated I 
 will not pretend to conjecture. But as ants which are not 
 slave-makers will, as I have seen, carry off the pupae of 
 other species, if scattered near their nests, it is possible 
 that such pup® originally stored as food might become 
 developed; and the foreign ants thus unintentionally reared 
 would then follow their proper instincts, and do what work 
 they could. If their presence proved useful to the species 
 which had seized them—if it were more advantageous to 
 this species, to capture workers than to procreate them— 
 the habit of collecting pup®, originally for food, might by 
 natural selection be strengthened and rendered permanent 
 for the very different purpose of raising slaves. When the 
 instinct was once acquired, if carried out to a much less 
 extent even than in our British F. sanguinea, which, as we 
 have seen, is less aided by its slaves than the same species 
 in Switzerland, natural selection might increase and modify 
 the instinct—always supposing each modification to be of 
 use to the species—until an ant w^as formed as abjectly 
 dependent on its slaves as is the Formica rufescens. 
 
 CELL-MAKING INSTINCT OF TIIE HIYE-BEE. 
 
 I will not here enter on minute details on this subject, 
 but will merely give an outline of the conclusions at which 
 I have arrived. He must be a dull man who can examine 
 the exquisite structure of a comb, so beautifully adapted 
 to its end, without enthusiastic admiration. We hear from 
 
260 
 
 SPECIAL INSTINCTS. 
 
 mathematicians that bees have practically solved a recon¬ 
 dite problem, and have made their cells of the proper 
 shape to hold the greatest possible amount of honey, with 
 the least possible consumption of precious wax in their 
 construction. It has been remarked that a skillful work¬ 
 man with fitting tools and measures, would find it very 
 difficult to make cells of wax of the true form, though this 
 is effected by a crowd of bees working in a dark hive. 
 Granting whatever instincts you please, it seems at first 
 quite inconceivable how they can make all the necessary 
 angles and planes, or even perceive when they are correctly 
 made. But the difficulty is not nearly so great as at first 
 appears: all this beautiful work can be shown, I think, to 
 follow from a few simple instincts. 
 
 I was led to investigate this subject by Mr. Waterhouse, 
 who has shown that the form of the cell stands in close re¬ 
 lation to the presence of adjoining cells; and the following 
 view may, perhaps, be considered only as a modification of 
 his theory. Let us look to the great principle of gradation, 
 and see whether Nature does not reveal tous her method of 
 work. At one end of a short series we have humble-bees, 
 which use their old cocoons to hold honey, sometimes 
 adding to them short tubes of wax, and likewise making 
 separate and very irregular rounded cells of wax. . At the 
 other end of the series we have the cells of the hive-bee, 
 placed in a double layer: each cell, as is well known, is 
 an hexagonal prism, with the basal edges of its six sides 
 beveled so as to join an inverted pyramid, of three rhombs. 
 These rhombs have certain angles, and the three which 
 form the pyramidal base of a single cell on one side of the 
 comb enter into the composition of the bases of three ad¬ 
 joining cells on the opposite side. In the series between 
 the extreme perfection "of the cells of the hive-bee and the 
 simplicity of those of the humble-bee we have the cells of 
 the Mexican Melipona domestica, carefully described and 
 figured by Pierre Iluber. The Melipona itself is interme¬ 
 diate in structure between the hive and humble-bee, but 
 more nearly related to the latter; it forms a nearly regular 
 waxen comb of cylindrical cells, in which the young are 
 hatched, and, in addition, some large cells of wax for hold¬ 
 ing honey. These latter cells are nearly, spherical and of 
 nearly equal sizes, and are aggregated into an irregular 
 
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CELL-MAKING INSTINCT. 
 
 261 
 
 mass* But the important point to notice is, that these 
 cells are always made at that degree of nearness to each 
 other that they would have intersected or broken into each 
 other if the spheres had been completed; but this is never 
 permitted, the bees building perfectly flat walls of wax be¬ 
 tween the spheres which thus tend to intersect. Hence, 
 each cell consists of an outer spherical portion, and of two" 
 three, or more flat surfaces, according as the cell adjoins 
 two, three, or more other cells. When one cell rests on 
 three other cells, which, from the spheres being nearly of 
 the same size, is very frequently and necessarily the case, 
 the three flat surfaces are united into a pyramid; and this 
 pyramid, as Huber has remarked, is manifestly a gross imi¬ 
 tation of the three-sided pyramidal base of the cell of the 
 hi\ e-bee. As in the cells of the hive-bee, so here, the three 
 plane surfaces in any one cell necessarily enter into the 
 construction of three adjoining cells. It is obvious that 
 the Melipona saves wax, and what is more important, 
 labor, by this manner of building; for the flat walls be¬ 
 tween the adjoining cells are not double, but are of the 
 same thickness as the outer spherical portions, and yet 
 each flat portion forms a part of two cells. 
 
 Reflecting on this case, it occurred to me that if the Meli¬ 
 pona had made its spheres at some given distance from 
 each other, and had made them of equal sizes and had 
 arranged them symmetrically in a double layer, the resulting- 
 structure would have been as perfect as the comb of the 
 hive-bee. Accordingly I wrote to Professor Miller, of Cam¬ 
 bridge, and this geometer has kindly read over the follow¬ 
 ing statement, drawn up from his information, and tells 
 me that it is strictly correct: 
 
 If a number of equal spheres be described with their 
 centers placed in two parallel layers; with the center of 
 each sphere at the distance of radius X */ 2, or radius 
 X 1.41421 (or at some lesser distance), from the centers of 
 the six surrounding spheres in the same layer; and at the 
 same distance from the centers of the adjoining spheres in 
 the other and parallel layer; then, if planes of intersec¬ 
 tion between the several spheres in both layers be formed, 
 there will result a double layer of hexagonal prisms united 
 together by pyramidal bases formed of three rhombs; and 
 the rhombs and the sides of the hexagonal prisms will have 
 
262 
 
 SPECIAL INSTINCTS . 
 
 every angle identically the same with the best measure¬ 
 ments which have been made of the cells of the hive-bee. 
 But I hear from Professor Wyman, who has made numer¬ 
 ous careful measurements, that the accuracy of the work¬ 
 manship of the bee has been greatly exaggerated; so much 
 so, that whatever the typical form of the cell may be, it is 
 rarely, if ever, realized. 
 
 Hence we may safely conclude that, if we could slightly 
 modify the instincts already possessed by the Melipona, 
 and in themselves not very wonderful, this bee would make 
 a structure as wonderfully perfect as that of the hive-bee. 
 We must suppose the Melipona to have the power of form¬ 
 ing her cells truly spherical, and of equal sizes; and this 
 would not be very surprising, seeing that she already does 
 so to a certain extent, and seeing what perfectly cylindri¬ 
 cal burrows many insects make in wood, apparently by 
 turning round on a fixed point. We must suppose the 
 Melipona to arrange her cells in level layers, as she already 
 does her cylindrical cells; and we must further suppose, 
 and this is the greatest difficulty, that she can somehow 
 judge accurately at what distance to stand from her fellow- 
 laborers when several are making their spheres; but she is 
 already so far enabled to judge of distance, that she always 
 describes her spheres so as to intersect to a certain extent; 
 and then she unites the points of intersection by perfectly 
 flat surfaces. By such modifications of instincts which in 
 themselves are not very wonderful—hardly more wonderful 
 than those which guide a bird to make its nest—I believe 
 that the hive-bee has acquired, through natural selection, 
 her inimitable architectural powers. 
 
 But this theory can be tested by experiment. Following 
 the example of Mr. Tegetmeier, I separated two combs, 
 and put between them a long, thick, rectangular strip of 
 wax: the bees instantly began to excavate minute circular 
 pits in it; and as they deepened these little pits, they made 
 them wider and wider until they were converted into 
 shallow basins, appearing to the eye perfectly true or parts 
 of a sphere, and of about the diameter of a cell. It was 
 most interesting to observe that, wherever several bees had 
 begun to excavate these basins near together, they had 
 begun their work at such a distance from each other that 
 by the time the basins had acquired the above-stated width 
 

 CELL-MAKING INSTINCT. 263 
 
 (i.e. about the width of an ordinary cell), and were in depth 
 about one-sixth of the diameter of the sphere of which they 
 formed a part, the rims of the basins intersected or broke 
 into each other. As soon as this occurred, the bees ceased 
 to evcavate, and began to build up flat walls of wax on the 
 lines of intersection between the basins, so that each hexa¬ 
 gonal prism was built upon the scalloped edge of a smooth 
 basin, instead of on the straight edges of a three-sided 
 pyramid as in the case of ordinary cells. 
 
 . ^ then put into the hive, instead of a thick, rectangular 
 piece of wax, a thin and narrow, knife-edged ridge, colored 
 with vermilion. The bees instantly began on both sides 
 to excavate little basins near to each other, in the same 
 way as before; but the ridge of wax was so thin, that the 
 bottoms of the basins, if they had been excavated to the 
 same depth as in the former experiment, would have 
 broken into each other from the opposite sides. The bees, 
 however, did not suffer this to happen, and they stopped 
 their excavations in due time; so that the basins, as soon 
 as they had been a little deepened, came to have flat bases; 
 and these flat bases, formed by thin little plates of the ver¬ 
 milion wax left ungnawed, were situated, as far as the eye 
 could judge, exactly along the planes of imaginary inter¬ 
 section between the basins on the opposite side of the ridge 
 of wax. In some parts, only small portions, in other 
 parts, large portions of a rhombic plate were thus left be¬ 
 tween the opposed basins, but the work, from the unnat¬ 
 ural state of things, had not been neatly performed. The 
 bees must have worked at very nearly the same rate in 
 circularly gnawing away and deepening the basins on both 
 sides of the ridge of vermilion wax, in order to have thus 
 succeeded in leaving flat plates between the basins, by 
 stopping work at the planes of intersection. 
 
 Considering how flexible thin wax is, I do not see that 
 there is any difficulty in the bees, while at work on the 
 two sides of a strip of wax, perceiving when they have 
 gnawed the wax away to the proper thinness, and then 
 stopping their work. In ordinary combs it has appeared 
 to me that the bees do not always succeed in working at 
 exactly the same rate from the opposite sides; for I have 
 noticed half-completed rhombs at the base of a just com¬ 
 menced cell, which were slightly concave on one side. 
 
264 
 
 SPECIAL INSTINCTS. 
 
 where I suppose that the bees had excavated too quickly, 
 and convex on the opposed side where the bees had worked 
 less quickly. In one well-marked instance, I put the comb 
 back into the hive, and allowed the bees to go on working 
 for a short time, and again examined the cell, and I found 
 that the rhombic plate had been completed, and had 
 become perfectly flat: it was absolutely impossible, from 
 the extreme thinness of the little plate, that they could 
 have affected this by gnawing away the convex side; and 
 I suspect that the bees in such cases stand on opposite sides 
 and push and bend the ductile and warm wax (which as I 
 have tried is easily done) into its proper intermediate 
 plane, and thus flatten it. 
 
 From the experiment of the ridge of vermilion wax we 
 can see that, if the bees were to build for themselves a 
 thin wall of wax, they could make their cells of the proper 
 shape, by standing at the proper distance from each other, 
 by excavating at the same rate, and by endeavoring to 
 make equal spherical hollows, but never allowing the 
 spheres to break into each other. Now bees, as may be 
 clearly seen by examining the edge of a growing comb, do 
 make a rough, circumferential wall or rim all round the 
 comb; and they gnaw this away from the opposite sides, 
 always working circularly as they deepen each cell. They 
 do not make the whole three-sided pyramidal base of any 
 one cell at the same time, but only that one rhombic plate 
 which stands on the extreme growing margin, or the two 
 plates, as the case may be; and they never complete the 
 upper edges of the rhombic plates, until the hexagonal 
 walls are commenced. Some of these statements differ 
 from those made by the justly celebrated elder Huber, but 
 I am convinced of their accuracy; and if I had space, I 
 could show that they are conformable with my theory. 
 
 Huber s statement, that the very first cell is excavated 
 out of a little parallel-sided wall of wax, is not, as far as I 
 have seen, strictly correct; the first commencement having 
 always been a little hood of wax; but I will not here enter 
 on details. We see how important a part excavation plays 
 in the construction of the cells; but it would be a great 
 error to suppose that the bees cannot build up a rough wall of 
 wax in the proper position—that is, along the plane of inter¬ 
 section between two adjoining spheres. I have several 
 
CELL-MAKING INSTINCT. 261 
 
 ep e oimen S showing dearly that they can do this. Even 
 in the rude circumferential rim or wall of wax round a 
 growing comb, flexures may sometimes be observed cor¬ 
 responding in position to the planes of the rhombic basal 
 plates of future cells. But the rough wall of wax has h 
 
 on e ?oth Se sid°es Tbfm ° ff> by bei ?f W gnawed a^ay 
 on noth sides, ihe manner in which the bees build is 
 
 cm ions; they always make the first rough wall from ten to 
 
 twenty times thicker than the excessively-thin finished wall 
 
 stand e how (W h 'u 1 " ltimatel J be left. We shall under¬ 
 stand how they work, by supposing masons first to pile un 
 
 a broad ridge of cement, and then to begin cutting it awav 
 
 tC^walMsYff Slde ; s 1 neai '. tbe ground, till a smooth, very 
 nnrt.ri t ft m the raiddle i ‘he masons always piling 
 
 summit of thp 7 T eD Sr d f d n in? fresh ceraen t on thf 
 summit of the ridge. We shall thus have a thin wall 
 
 steadily growing upward but always crowned by a gigantic 
 
 coping. From all the cells, both those just commenced 
 
 of laT° H C0 £ 1 P leted ’ b . em £ thus crowned by a strong coping 
 of wax, the bees can cluster and crawl over the comb with? 
 out injuring the delicate hexagonal walls. These walls as 
 Professor Miller has kindly ascertained for me, vary greatly 
 in thickness; being, on an average of twelve measure^ 
 ments made near the border of the comb. toTof an 
 inch m thickness; whereas the basal rhomboidafplates are 
 
 mian\VT rly ln e the P ro P OTtion of three to two,having a 
 mean thickness, from twenty-one measurements, of i , g 0 f 
 
 an inch.. By the above singular manner of building 
 strength is continually given to the comb, with the utmoft 
 ultimate economy of wax. UbC 
 
 It seems at first to add to the difficulty of understanding 
 how the cells are made, that a multitude of bees alTwwk 
 
 ?o!n fc cr h fn ; 0ne ti bee af ?T workin S a short time at one cell 
 to , anoth ® r ’ 80 ^at, as Huber has stated, a score of 
 dividuals work even at the commencement of the first 
 
 ft! »d 1 Wa ? fu le v P raotlcall - y to sh °w this fact, by covering 
 w dges of - the b exa gonal walls of a single cell, or the ex“ 
 .rerne margin of the circumferential rim of a growing 
 -omb, with an extremely thin layer of melted vermilion 
 ™tei 1 I “ vanab ly found that the color was most deli- 
 
 iave doneTwbb b' 6 bees ~ as . de li cate ly as a painter couid 
 ia\e done it with his brush—Dy atoms of the colored wax 
 
266 
 
 SPECIAL INSTINCTS. 
 
 having been taken from the spot on which it had beea 
 placed, and worked into the growing edges of the cells all 
 round. The work of construction seems to be a sort of 
 balance struck between many bees, all instinctively stand¬ 
 ing at the same relative distance from each other, all trying 
 to sweep equal spheres, and then building up, or leaving 
 ungnawed, the planes of intersection between these spheres. 
 It was really curious to note in cases of difficulty, as when 
 two pieces of comb met at an angle, how often the bees 
 would pull down and rebuild in different ways the same 
 cell, sometimes recurring to a shape which they had at first 
 rejected. 
 
 When bees have a place on which they can stand in their 
 proper positions for working—for instance, on a slip of 
 wood, placed directly under the middle of a comb growing 
 downward, so that the comb has to be built over one face 
 of the slip—in this case the bees can lay the foundations of 
 one wall of a new hexagon, in its strictly proper place, 
 projecting beyond the other completed cells. It suffices 
 that the bees should be enabled to stand at their proper 
 relative distances from each other and from the walls of 
 the last completed cells, and then, by striking imaginary 
 spheres, they can build up a wall intermediate between two 
 adjoining spheres; but as far as 1 have seen, they never 
 gnaw away and finish off the angles of a cell till a large part 
 both of that cell and of the adjoining cells has been built. 
 This capacity in bees of laying down under certain circum¬ 
 stances a rough wall in its proper place between two just 
 commenced cells, is important, as it bears on a fact, which 
 seems at first subversive of the foregoing theory; namely, 
 that the cells on the extreme margin of wasp-combs are 
 sometimes strictly hexagonal; but I have not space here to 
 enter on this subject. Nor does there seem to me any 
 great difficulty in a single insect (as in the case of a queen- 
 wasp) making hexagonal cells, if she were to work alter¬ 
 nately on the inside and outside of two or three cells com¬ 
 menced at the same time, always standing at the proper 
 relative distance from the parts of the cells just begun, 
 sweeping spheres or cylinders, and building up interme¬ 
 diate planes. 
 
 As natural selection acts only by the accumulation of 
 slight modifications of structure or instinct, each profitable 
 
CELL-MAKING INSTINCT. 267 
 
 to the individual under its conditions of life, it may reason¬ 
 ably be asked, how a long and graduated succession of 
 modified architectural instincts, all tending toward the pres¬ 
 ent perfect plan of construction, could have profited the 
 progenitors of the hive-bee? I think the answer is not 
 difficult: cells constructed like those of the bee or the wasp 
 gain in strength, and save much in labor and space, and in 
 the materials of which they are constructed. With respect 
 to the formation of wax, it is known that bees are often 
 liaid pressed to get sufficient nectar, and I am informed 
 by Mr. Tegetmeier that it has been experimentally proved 
 that from twelve to fifteen pounds of dry sugar are con¬ 
 sumed by a hive of bees for the secretion of a pound of 
 wax; so that a prodigious quantity of fluid nectar must 
 be collected and consumed by the bees in a hive for the 
 secretion of the wax necessary for the construction of their 
 combs. Moreover, many bees have to remain idle for 
 many days during the process of secretion. A large 
 store of honey is indispensable to support a large stock of 
 bees during the winter; and the security of the hive is 
 known mainly to depend on a large number of bees being 
 supported. Hence the saving of wax by largely saving 
 honey, and the time consumed in collecting the honey, 
 must be an important element of success to any family 
 of bees. Of course the success of the species may be de¬ 
 pendent on the number of its enemies, or parasites, or on 
 quite distinct causes, and so be altogether independent 
 of the quantity of honey which the bees can collect. But 
 let us suppose that this latter circumstance determined, as 
 it probably often has determined, whether a bee allied 
 to our humble-bees could exist in large numbers in any 
 countiy; and let us further suppose that the community 
 lived through the winter, and consequently required a store 
 of honey: there can in this case be no doubt that it would 
 be an advantage to our imaginary humble-bee if a slight 
 modification in her instincts led her to make her waxen 
 cells near together, so as to intersect a little; for a wall in 
 common even to two adjoining cells would save some little 
 labor and wax. Hence, it would continually be more and 
 moi e ad\antageous to our humble bees, if they were to 
 make their cells more and more regular, nearer together, 
 and aggregated into a mass, like the cells of the Melipona; 
 
OBJECTIONS TO THE THEORY 
 
 268 
 
 for in this case a large part of the bounding surface of each 
 cell would serve to bound the adjoining cells, and much 
 labor and wax would be saved. Again, from the same 
 cause, it would be advantageous to the Melipona, if she 
 were to make her cells closer together, and more regular 
 in every way than at present; for then, as we have seen, 
 the spherical surfaces would wholly disappear and be re¬ 
 placed by plane surfaces; and the Melipona would make a 
 comb as perfect as that of the hive-bee. Beyond this stage 
 of perfection in architecture, natural selection could not 
 lead; for the comb of the liive-bee, as far as we can see, is 
 absolutely perfect in economizing labor and wax. 
 
 Thus, as I believe, the most wonderful of all known in¬ 
 stincts, that of the hive-bee, can be explained by natural 
 selection having taken advantage of numerous, successive, 
 slight modifications of simpler instincts; natural selection 
 having, by slow degrees, more and more perfectly led the 
 bees to sweep equal spheres at a given distance from each 
 other in a double layer, and to build up and excavate the 
 wax along the planes of intersection; the bees, of course, 
 no more knowing that they swept their spheres at one par¬ 
 ticular distance from each other, than they know what are 
 the several angles of the hexagonal prisms and of the basal 
 rhombic plates; the motive power of the process of natural 
 selection having been the construction of cells of duo 
 strength and of the proper size and shape for the larvae, 
 this being effected with the greatest possible economy of 
 labor and wax; that individual swarm which thus made 
 the best cells with least labor, and least waste of honey in 
 the secretion of wax, having succeeded best, and having 
 transmitted their newly-acquired economical instincts to 
 new swarms, which in their turn will have had the best 
 chance of succeeding in the struggle for existence. 
 
 OBJECTIONS TO THE THEORY OP NATURAL SELECTION AS 
 
 APPLIED TO INSTINCTS! NEUTER AND STERILE INSECTS. 
 
 It has been objected to the foregoing view of^ the origin 
 of instincts that “ the variations of structure and of instinct 
 must have been simultaneous and accurately adjusted to each 
 other, as a modification in the one without an immediate 
 corresponding change in the other would have been fatal.” 
 
OF NATURAL SELECTION. 269 
 
 The force of this objection rests entirely on the assumption 
 that the changes in the instincts and structure are abrupt, 
 lo take as an illustration the case of the larger titmouse, 
 (Parus major) alluded to in a previous chapter; this bird 
 often holds the seeds of the yew between its feet on a 
 branch, and hammers with its beak till it gets at the 
 kernel. Now what special difficulty would there be in natu¬ 
 ral selection preserving all the slight individual variations 
 m the shape of the beak, which were better and better 
 adapted to break ojoen the seeds, until a beak was formed, 
 as well constructed for this purpose as that of the nut¬ 
 hatch, at the same time that habit, or compulsion, or 
 spontaneous variations of taste, led the bird to become 
 more and more of a seed-eater? In this case the beak is 
 supposed to be slowly modified by natural selection, subse¬ 
 quently to, but in accordance with, slowly changing habits 
 or taste; but let the feet of the titmouse vary and grow 
 larger from correlation with the beak, or from any other 
 unknown cause, and it is not improbable that such larger 
 feet would lead the bird to climb more and more until it 
 acquiied the remarkable climbing instinct and power of 
 the nuthatch. In this case a gradual change of structure 
 is supposed to lead to changed instinctive habits. To take 
 one more case: few instincts are more remarkable than that 
 which leads the swift of the Eastern Islands to make its 
 nest wholly of inspissated saliva. Some birds build their 
 nests of mud, believed to be moistened with saliva; and 
 one of the swifts of North America makes its nest (as I 
 have seen) of sticks agglutinated with saliva, and even with 
 flakes of this substance. . Is it then very improbable that 
 the natuial selection of individual swifts, which secreted 
 more and more saliva, should at last produce a species with 
 instincts leading it to neglect other materials and to make 
 its nest exclusively of inspissated saliva? And so in other 
 cases. It must, however, be admitted that in many 
 instances we cannot conjecture whether it was instinct or 
 structure which first varied. 
 
 No doubt many instincts of very difficult explanation 
 could be opposed to the theory of natural selection—cases, 
 in which we cannot see how an instinct could have origin¬ 
 ated;^ cases, in which no intermediate gradations are known 
 to exist; cases of instincts of such trifling importance, that 
 
270 OBJECTIONS TO THE THEORY 
 
 they could hardly have been acted on by natural selection; 
 cases of instincts almost identically the same in animals so 
 remote in the scale of nature that we cannot account, foi 
 their similarity by inheritance from a common progenitor, 
 and consequently must believe that they were independ¬ 
 ently acquired through natural selection. I will not here 
 enter on these several cases, but will confine myself to one 
 special difficulty, which at first appeared tome insuperable, 
 and actually fatal to the whole theory. I allude to the 
 neuters or sterile females in insect communities; for these 
 neuters often differ widely in instinct and in structure from 
 both the males and fertile females, and yet, from being 
 sterile, they cannot propagate their kind. 
 
 The subject well deserves to be discussed at great length, 
 but I will here take only a single case, that of working or 
 sterile ants. How the workers have been rendered sterile 
 is a difficulty; but not much greater than that of any 
 other striking modification of structure;, for it can be 
 shown that some insects and other articulate animals 
 in a state of nature occasionally become sterile; and if 
 such insects had been social, and it had been profitable 
 to the community that a number should have been 
 annually born capable of work, but incapable of procrea¬ 
 tion, I can see no especial difficulty in this having been 
 effected through natural selection. But I must passover 
 this preliminary difficulty. The great difficulty lies in 
 the working ants differing widely from both the males 
 and the fertile females in structure, as in the shape 
 of the thorax, and in being destitute of wings and some¬ 
 times of eyes, and in instinct. As far as. instinct 
 alone is concerned, the wonderful difference in this lespect 
 between the workers and the perfect females would have 
 been better exemplified by the hive-bee. If a working ant 
 or other neuter insect had been an ordinary animal, I 
 should have unhesitatingly assumed that all its characters 
 had been slowly acquired through natural. selection; 
 namely, by individuals having been born with slight profit¬ 
 able modifications, which were inherited by the offspring, 
 and that these again varied and again were selected, and so 
 onward. But with the working ant we have an insect 
 differing greatly from its parents, yet absolutely sterile.; so 
 that it could never have transmitted successively acquired 
 
OF NA TURAL SELECTION. 
 
 271 
 
 modifications of structure or instinct to its progeny. It 
 may well be asked how it is possible to reconcile this case 
 with the theory of natural selection? 
 
 hirst, let it be remembered that we have innumerable in¬ 
 stances, both in our domestic productions and in those in 
 a state of nature, of all sorts of differences of inherited 
 structure which are correlated with certain ages and with 
 either sex. We have differences correlated not only with 
 one sex, but with that short period when the reproductive 
 system is active, as in the nuptial plumage of many birds, 
 and in the hooked jaws of the male salmon. We have even 
 slight differences in the horns of different breeds of cattle 
 in relation to an artificially imperfect state of the male 
 sex, for oxen of certain breeds have longer horns than the 
 oxen of other breeds, relatively to the length of the horns 
 in both the bulls and cows of these same breeds. Hence, 
 I can see no great difficulty in any character becoming cor¬ 
 related with the sterile condition of certain members of 
 insect communities; the difficulty lies in understanding 
 how such correlated modifications of structure could have 
 been slowly accumulated by natural selection. 
 
 This difficulty, though _ appearing insuperable, is 
 lessened, or, as I believe, disappears, when it is remem¬ 
 bered that selection may be applied to the family, as well 
 as to the individual, and may thus gain the desired end. 
 Breeders of cattle wish the flesh and fat to be well marbled 
 together. An animal thus characterized has been slaugh¬ 
 tered, but the breeder has gone with confidence to the 
 same stock and has succeeded. Such faith may be placed in 
 the power of selection that a breed of cattle, always yield¬ 
 ing oxen with extraordinarily long horns, could, it is prob¬ 
 able, be formed by carefully watching which individual 
 bulls and cows, when matched, produced oxen with the 
 longest horns; and yet no one ox would ever have propa¬ 
 gated its kind. Here is a better and real illustration: 
 According to M. Verlot, some varieties of the double 
 annual stock, from having been long and carefully selected 
 to the right degree, always produce a large proportion of 
 seedlings bearing double and quite sterile flowers, but they 
 likewise yield some single and fertile plants. These latter, 
 by which alone the variety can be propagated, may be 
 compared with the fertile male and female ants, and the 
 
272 
 
 OBJECTIONS TO THE THEORY 
 
 double sterile plants with, the neuters of the same com¬ 
 munity. As with the varieties of the stock, so with social 
 insects, selection has been applied to the family, and not 
 to the individual, for the sake of gaining a serviceable end. 
 Hence, we may conclude that slight modifications of 
 structure or of instinct, correlated with the sterile condi¬ 
 tion of certain members of the community, have proved 
 advantageous; consequently the fertile males and females 
 have flourished, and transmitted to their fertile offspring a 
 tendency to produce sterile members with the same modifi¬ 
 cations. This process must have been repeated many 
 times, until that prodigious amount of difference between 
 the fertile and sterile females of the same species has been 
 produced which we see in many social insects. 
 
 But we have not as yet touched on the acme of the dif¬ 
 ficulty; namely, the fact that the neuters of several ants 
 differ, not only from the fertile females and _ males, but 
 from each other, sometimes to an almost incredible degree, 
 and are thus divided into two or even three castes. The 
 castes, moreover, do not commonly graduate into each 
 other, but are perfectly well defined; being as distinct from 
 each other as are any two species of the same genus, or 
 rather as any two genera of the same family. Thus, in 
 Eciton, there are working and soldier neuters, with jaws 
 and instincts extraordinarily different: in Cryptocerus, the 
 workers of one caste alone carry a wonderful sort of shield 
 on their heads, the use of which is quite unknown; in the 
 Mexican Myrmecocystus, the workers of one caste never 
 leave the nest; they are fed by the workers of another 
 caste, and they have an enormously developed abdomen 
 which secretes a sort of honey, supplying the place of that 
 excreted by the aphides, or the domestic cattle as they may 
 be called, which our European ants guard and imprison. 
 
 It will indeed be thought that I have an overweening 
 confidence in the principle of natural selection, when I do 
 not admit that such wonderful and well-established facts 
 at once annihilate the theory. In the simpler case of 
 neuter insects all of one caste, which, as I believe, have 
 been rendered different from the fertile males and females 
 through natural selection, we may conclude from _ the 
 analogy of ordinary variations, that the successive, slight, 
 profitable modifications did not first arise in all the neuters 
 
OF NATURAL SELECTION 
 
 273 
 
 in the same nest, but in some few alone; and that by the 
 survival of the communities with females which produced 
 most neuters having the advantageous modification, all 
 the neuters ultimately came to be thus characterized. Ac¬ 
 cording to this view we ought occasionally to find in the 
 same nest neuter insects, presenting gradations of struct¬ 
 ure; and this we do find, even not rarely, considering how 
 few neuter insects out of Europe have been carefully ex¬ 
 amined. Mr. F. Smith has shown that the neuters of 
 several British ants differ surprisingly from each other in 
 size and sometimes in color; and that the extreme forms can 
 be linked together by individuals taken out of the same nest: 
 I have myself compared perfect gradations of this kind. 
 It sometimes happens that the larger or the smaller sized 
 workers are the most numerous; or that both large and 
 small are numerous, while those of an intermediate size 
 are scanty in numbers. Formica flava has larger and 
 smaller workers, with some few of intermediate size; and, 
 in this species, as Mr. F. Smith has observed, the larger 
 workers have simple eyes (ocelli), which, though small, can 
 be plainly distinguished, whereas the smaller workers have 
 their ocelli rudimentary. Having carefully dissected 
 several specimens of these workers, I can affirm that the 
 eyes are far more rudimentary in the smaller workers than 
 can be accounted for merely by their proportionately lesser 
 size; and I fully believe, though I dare not assert so posi¬ 
 tively, that the "workers of intermediate size have their 
 ocelli in an exactly intermediate condition. So that here 
 we have two bodies of sterile workers in the same nest, dif¬ 
 fering not only in size, but in their organs of vision, yet 
 connected by some few members in an intermediate 
 condition. I may digress by adding, that if the smaller 
 workers had been the most useful to the community, and 
 those males and females had been continuallv selected, 
 which produced more and more of the smaller workers, 
 until all the workers were in this condition, we should 
 then have had a species of ant with neuters in nearly the 
 same condition as those of Myrmica. For the workers of 
 Myrmicahave not even rudiments of ocelli, though the male 
 and female ants of this genus have well-developed ocelli. 
 
 I may give one other case: so confidently did I expect 
 occasionally to find gradations of important structures 
 
274 
 
 OBJECTIONS TO THE THEORY 
 
 between the different castes of neuters in the same species, 
 that I gladly availed myself of Mr. F. Smith's offer of 
 numerous specimens from the same nest of the driver ant 
 (Anomma) of West Africa. The reader will perhaps best 
 appreciate the amount of difference in these workers by 
 my giving, not the actual measurements, but a strictly 
 accurate illustration: the difference was the same as if we 
 were to see a set of workmen building a house, of whom 
 many were five feet four inches high, and many sixteen feet 
 high; but we must in addition suppose that the larger 
 workmen had heads four instead of three times as big as 
 those of the smaller men, and jaws nearly five times as big. 
 The jaws, moreover, of the working ants of the several 
 sizes differed wonderfully in shape, and in the form and 
 number of the teeth. But the' important fact for usis 
 that, though the workers can be grouped into castes of dif¬ 
 ferent sizes, yet they graduate insensibly into each other, 
 as does the widely different structure of their jaws. I speak 
 confidently on this latter point, as Sir J. Lubbock made 
 drawings for me, with the camera lucida, o* the jaws which 
 I dissected from the workers of the several sizes. Mr. 
 Bates, in his interesting “Naturalist on the A.mazons,” 
 has described analogous cases. 
 
 With these facts before me, I believe that natural selec¬ 
 tion, by acting on the fertile ants or parents, could form a 
 species"which should regularly produce neuters, all of large 
 size with one form of jaw, or all of small size with widely 
 different jaws; or lastly, and this is the greatest difficulty, 
 one set of workers of one size and structure, and simulta¬ 
 neously another set of workers of a different size and 
 structure; a graduated series having first been formed, as 
 in the case of the driver ant, and then the extreme forms 
 having been produced in greater and greater numbers, 
 through the survival of the parents which generated them, 
 until none with an intermediate structure were produced. 
 
 An analogous explanation has been given by Mr. Wallace, 
 of the equally complex case, of certain Malayan butterflies 
 regularly appearing under two or even three distinct 
 female forms; and by Fritz Muller, of certain Brazilian 
 crustaceans likewise appearing under two widely distinct 
 male forms. But this subject need not here be discussed. 
 
 I have now explained how, I believe, the w T onderful fact- 
 
SUMMARY. 
 
 m 
 
 of two distinctly defined castes of sterile workers existing 
 in the same nest, both widely different from each other 
 and from their parents, has originated. We can see how 
 useful their production may ha T7 e been to a social commu¬ 
 nity of ants, on the same principle that the division of 
 labor is useful to civilized man. Ants, however, work by 
 inherited instincts and by inherited organs or tools’, 
 while man works by acquired knowledge and manufactured 
 instruments. But I must confess, that, with all my faith 
 in natural selection, I should never have anticipated that 
 this principle could have been efficient in so high a degree, 
 had pot the case of these neuter insects led me to this"con- 
 clusion. I have, therefore, discussed this case, at some 
 little but wholly insufficient length, in order to show the 
 power of natural selection, and likewise because this is by 
 far the most serious special difficulty which my theory has 
 encountered. . The case, also, is very interesting, as it 
 proves that with animals, as with plants, any amount of 
 modification may be effected by the accumulation of 
 numerous, slight, spontaneous variations, which are in any 
 way profitable, without exercise or habit having been 
 brought into play. For peculiar habits, confined to the 
 workers of sterile females, however long they might be fol¬ 
 lowed, could not possibly affect the males and fertile 
 females, which alone leave descendants. I am surprised 
 that no one has hitherto advanced this demonstrative case 
 of neuter insects, against the well-known doctrine of in¬ 
 herited habit, as advanced by Lamarck. 
 
 SUMMARY. 
 
 I have endeavored in this chapter briefly to show that 
 the mental qualities of our domestic animals vary, and that 
 the variations are inherited. Still more briefly I have at¬ 
 tempted to show that instincts vary slightly in a state of 
 nature. No one will dispute that instincts are of the high¬ 
 est importance to each animal. Therefore, there is no real 
 difficulty, under changing conditions of life, in natural 
 selection accumulating to any extent slight modifications 
 of instinct which are in any way useful. In many cases 
 habit or use and disuse have probably come into play. I 
 do not pretend that the facts given in this chapter 
 
SUMMARY. 
 
 276 
 
 strengthen in any great degree my theory; but none of the 
 cases of difficulty, to the best of my judgment, annihilate 
 it. On the other hand, the fact that instincts are not 
 always absolutely perfect and are liable to mistakes; that 
 no instinct can be shown to have been produced for the 
 good of other animals, though animals take advantage of 
 the instincts of others; that the canon in natural history 
 of (e Natura non facit saltum,” is applicable to instincts as 
 well as to corporeal structure, and is plainly explicable on 
 the foregoing views, but is otherwise inexplicable—all tend 
 to corroborate the theory of natural selection. 
 
 This theory is also strengthened by some few other facts 
 in regard to instincts; as by that common case of closely 
 allied, but distinct, species, when inhabiting distant parts 
 of the world and living under considerable different con¬ 
 ditions of life, yet often retaining nearly the same instincts. 
 For instance, we can understand, on the principle of in¬ 
 heritance, how it is that the thrush of tropical South Amer¬ 
 ica lines its nest with mud, in the same peculiar manner as 
 does our British thrush; how it is that the Hornbills of 
 Africa and India have the same extraordinary instinct of 
 plastering up and imprisoning the females in a hole in a 
 tree, with only a small hole left in the plaster through 
 which the males feed them and their young when hatched; 
 how it is that the male wrens (Troglodytes) of Aorth 
 America build “ cock-nests,” to roost in, like the males of 
 our Kitty-wrens—a habit wholly unlike that of any other 
 known bird. Finally, it may not be a logical deduction, 
 but to my imagination it is far more satisfactory to look at 
 such instincts as the young cuckoo ejecting its foster- 
 brothers, ants making slaves, the larvae of ichneumonidae 
 feeding within the live bodies of caterpillars, not as spe¬ 
 cially endowed or created instincts, but as small conse¬ 
 quences of one general law leading to the advancement of 
 all organic beings—namely, multiply, vary, let the strong* 
 *»t live and the weakest die. 
 
HYBRIDISM. 
 
 m 
 
 CHAPTER IX. 
 
 HYBKIDISM. 
 
 Distinction between tbe sterility of first crosses and of hybrids— 
 Sterility various in degree, not universal, affected by close inter¬ 
 breeding, removed by domestication — Laws governing tbe 
 sterility of hybrids—Sterility not a special endowment, but inci¬ 
 dental on other differences, not accumulated by natural selec¬ 
 tion—Causes of the sterility of first crosses and of hybrids— 
 Parallelism between the effects of changed conditions of life and 
 of crossing—Dimorphism and trimorphism—Fertility of varieties 
 when crossed and of their mongrel offspring not universal—• 
 Hybrids and mongrels compared independently of their fertility 
 •—Summary. 
 
 The view commonly entertained by naturalists is that 
 species, when intercrossed, have been specially endowed 
 with sterlility, in order to prevent their confusion. This 
 view certainly seems at first highly probable, for species 
 living together could hardly have been kept distinct had 
 they been capable of freely crossing. The subject is in 
 many ways important for us, more especially as the sterility 
 of species when first crossed, and that of their hybrid off¬ 
 spring, cannot have been acquired, as I shall show, by the 
 preservation of successive profitable degrees of sterility. 
 It is an incidental result of differences in the reproductive 
 systems of the parent-species. 
 
 In treating this subject, two classes of facts, to a large 
 extent fundamentally different, have generally been con¬ 
 founded; namely, the sterility of species when first crossed, 
 and the sterility of the hybrids produced from them. 
 
 Pure species have of course their organs of reproduction 
 in a perfect condition, yet when intercrossed they produce 
 either few or no offspring. Hybrids, on the other hand, 
 have their reproductive organs functionally impotent, as 
 may be clearly seen in the state of the male element in 
 both plants and animals; though the formative organs 
 
278 
 
 HYBRIDISM. 
 
 themselves are perfect in structure, as far as the micro¬ 
 scope reveals. In the first case the two sexual elements 
 which go to form the embryo are perfect; in the second 
 case they are either not at all developed, or are imperfectly 
 developed. This distinction is important, when the cause 
 of the sterility, which is common to the two cases, has to 
 be considered. The distinction probably has been sluried 
 over, owing to the sterility in both cases being looked on 
 as a special endowment, beyond the province of our reason¬ 
 ing powers. 
 
 The fertility of varieties, that is of the forms known or 
 believed to be descended from common parents, when 
 crossed, and likewise the fertility of their mongrel off¬ 
 spring, is, with reference to my theory, of equal importance 
 with the sterility of species; for it seems to make a broad 
 and clear distinction between varieties and species. 
 
 DEGREES OF STERILITY. 
 
 First, for the sterility of species when crossed and of 
 their hybrid offspring. ‘ It is impossible to study the sev¬ 
 eral memoirs and works of those two conscientious and ad¬ 
 mirable observers, Kolreuter and Gartner, who almost 
 devoted their lives to this subject, without being deeply 
 impressed with the high generality of some degree of stei- 
 ility. Kolreuter makes the rule universal; but then he 
 cuts the knot, for in ten cases in which he found two forms, 
 considered by most authors as distinct species, quite fertile 
 together, he unhesitatingly ranks them as varieties. . Giiit- 
 ner, also, makes the rule equally universal; and he disputes 
 the entire fertility of Kolreuter’s ten cases. But in these 
 and in many other cases, Gartner is obliged carefully to 
 count the seeds, in order to show that there is any degiee 
 of sterility. He always compares the maximum number 
 of seeds produced by two species when first crossed, and 
 the maximum produced by their hybrid offspring, with 
 the average number produced by both pure parent-species 
 in a state°of nature. But causes of serious error here in¬ 
 tervene! a plant, to be hybridized, must be castrated, and, 
 what is often more important, must be secluded in order 
 to prevent pollen being brought to it by insects from other 
 plants. Nearly all the plants experimented on by Gartner 
 
DEGREES OF STERILITY. 
 
 279 
 
 were potted, and were kept in a chamber in his house. 
 That these processes are often injurious to the fertility of 
 a plant cannot be doubted; for Gartner gives in his table 
 about a score of cases of plants which he castrated, and 
 artificially fertilized with their own pollen, and (excluding 
 all cases such as the Leguminosse, in which there is an 
 acknowledged difficulty in the manipulation) half of these 
 twenty plants had their fertility in some degree impaired. 
 Moreover, as Gartner repeatedly crossed some forms, such 
 as the common red and blue pimpernels (Anagallis arvensis 
 and coerulea), which the best botanists rank as varieties, 
 and found them absolutely sterile, we may doubt whether 
 many species are really so sterile, when intercrossed, as he 
 believed. 
 
 It is certain, on the one hand, that the sterility of 
 various species when crossed is so different in degree and 
 graduates away so insensibly, and, on the other hand, that 
 the fertility of pure species is so easily affected by various 
 circumstances, that for all practical purposes it is most 
 difficult to say where perfect fertility ends and sterility 
 begins. I think no better evidence of this can be required 
 than that the two most experienced observers who have 
 ever lived, namely Kolreuter and Gartner, arrived at 
 diametrically opposite conclusions in regard to some of the 
 very same forms. It is also most instructive to compare— 
 but I have not space here to enter on details—the evidence 
 advanced by our best botanists on the question whether 
 certain doubtful forms should be ranked as species or 
 varieties, with the evidence from fertility adduced by dif¬ 
 ferent hybridizers, or by the same observer from experi¬ 
 ments made during different years. It can thus be shown 
 that neither sterility nor fertility affords any certain dis¬ 
 tinction between species and varieties. The evidence 
 from this source graduates away, and is doubtful in the 
 same degree as is the evidence derived from other consti¬ 
 tutional and structural differences. 
 
 > In regard to the sterility of hybrids in successive genera¬ 
 tions; though Gartner was enabled to rear some hybrids, 
 carefully guarding them from a cross with either pure 
 parent, for six or seven, and in one case for ten generations, 
 yet he asserts positively that their fertility never increases, 
 but generally decreases greatly and suddenly. With re- 
 
HYBRIDISM ; 
 
 280 
 
 spect to this decrease, it may first be noticed that when 
 any deviation in structure or constitution is common to 
 both parents, this is often transmitted in an augmented 
 degree to the offspring; and both sexual elements in hybrid 
 plants are already affected in some degree. But I believe 
 that their fertility has been diminished in nearly all these 
 cases by an independent cause, namely, by too close inter¬ 
 breeding. I have made so many experiments and collected 
 so many facts, showing on the one hand that an occasional 
 cross with a distinct individual or variety increases the 
 vigor and fertility of the offspring, and on the other hand 
 that very close interbreeding lessens their vigor and fertil¬ 
 ity, that I can not doubt the correctness of this conclusion. 
 Hybrids are seldom raised by experimentalists in great 
 numbers; and as the parent-species, or other allied hybrids, 
 o-enerally grow in the same garden, the visits, of insects 
 must be carefully prevented during the flowering season: 
 hence hybrids, if left to themselves, will generally be fer¬ 
 tilized during each generation by pollen from the same 
 flower; and this would probably be injurious to their fertil¬ 
 ity, already lessened by their hybrid origin. I am 
 strengthened in this conviction by a remarkable statement 
 repeatedly made by Gartner, namely, that if even the less 
 fertile hybrids be artificially fertilized with hybrid pollen 
 of the same kind, their fertility, notwithstanding the fre¬ 
 quent ill effects from manipulation, sometimes decidedly 
 increases, and goes on increasing. Now, in the process of 
 artificial fertilization, pollen is as often taken by chance 
 (as I know from my own experience) from the anthers of 
 another flower, as from the anthers of the flower itself 
 which is to be fertilized; so that a cross between two flow¬ 
 ers, though probably often on the same plant, would be 
 thus effected. Moreover, whenever complicated experi¬ 
 ments are in progress, so careful an observer as Gartner 
 would have castrated his hybrids, and this would have in¬ 
 sured in each generation a cross with pollen from a dis¬ 
 tinct flower, either from the same plant or from another 
 plant of the same hybrid nature. And thus, the strange 
 fact of an increase of fertility in the successive generations 
 of artificially fertilized hybrids, in contrast with those spon¬ 
 taneously self-fertilized, may, as I believe, be accounted 
 for by too close interbreeding having been avoided. 
 
DEGREES OF STERILITY. 
 
 281 
 
 Now let us turn to the results arrived at by a third most 
 experienced hybridizer, namely, the Hon. and Rev. W. 
 Herbert. He is as emphatic in his conclusion that some 
 hybrids are perfectly fertile—as fertile as the pure parent- 
 species—as are Kolreuter and Gartner that some degree of 
 sterility between distinct species is a universal law of 
 nature. He experimented on some of the very same species 
 as did Gartner. The difference in their results may, I 
 think, be in part accounted for by Herbert's great horticul¬ 
 tural skill, and by his having hot-houses at his command. 
 Of his many important statements I will here give only a 
 single one as an example, namely, that “ every ovule in a 
 pod of Crinum capense fertilized by C. revolutum pro¬ 
 duced a plant, which I never saw to occur in a case of its 
 natural fecundation." So that here we have perfect, or 
 even more than commonly perfect fertility, in a first cross 
 between two distinct species. 
 
 This case of the Crinum leads me to refer to a singular 
 fact, namely, that individual plants of certain species 
 of Lobelia, Yerbascum and Passiflora, can easily be fer¬ 
 tilized by the pollen from a distinct species, but not by 
 pollen from the same plant, though this pollen can be 
 proved to be perfectly sound by fertilizing other plants or 
 species. In the genus Hippeastrum, in Corydalis as 
 shown by Professor Hildebrand, in various orchids as 
 shown by Mr. Scott and Fritz Muller, all the individuals 
 are in this peculiar condition. So that with some species, 
 certain abnormal individuals, and in other species all the 
 individuals, can actually be hybridized much more readily 
 than they can be fertilized by pollen from the same indi¬ 
 vidual plant! To give one instance, a bulb of Hippeas¬ 
 trum aulicum produced four flowers; three were fertilized 
 by Herbert with their own pollen, and the fourth was sub¬ 
 sequently fertilized by the pollen of a compound hybrid 
 descended from three distinct species: the result was that 
 “the ovaries of the three first flowers soon ceased to grow, 
 aud after a few days perished entirely, whereas the pod 
 impregnated by the pollen of the hybrid made vigorous 
 growth and rapid progress to maturity, and bore good seed, 
 which vegetated freely." Mr. Herbert tided similar experi¬ 
 ments during many years, and always with the same result. 
 These cases serve to show on what slight and mysterious 
 
282 
 
 HYBRIDISM ,; 
 
 causes the lesser or greater fertility of a species sometimes 
 depends. 
 
 The practical experiments of horticulturists, though not 
 made with scientific precision, deserve some notice. It is 
 notorious in how complicated a manner the species of 
 Pelargonium, Fuchsia, Calceolaria, Petunia, Rhododen¬ 
 dron, etc., have been crossed, yet many of these hybrids 
 seed freely. For instance, Herbert asserts that a hybrid 
 from Calceolaria integrifolia and plantaginea, species most 
 widely dissimilar in general habit, “ reproduces itself as 
 perfectly as if it had been a natural species from the 
 mountains of Chili.” I have taken some pains to ascer¬ 
 tain the degree of fertility of some- of the complex crosses 
 of Rhododendrons, and I am assured that many of them 
 are perfectly fertile. Mr. C. Noble, for instance, informs 
 me that he raises stocks for grafting from a hybrid between 
 Rhod. ponticum and catawbiense, and that this hybrid 
 “ seeds as freely as it is possible to imagine.” Had hybrids, 
 when fairly treated, always gone on decreasing in fertility 
 in each successive generation, as G&rtner believed to be 
 the case, the fact would have been notorious to nursery¬ 
 men. Horticulturists raise large beds of the same hybrid, 
 and such alone are fairly treated, for by insect agency the 
 several individuals are allowed to cross freely with each 
 other, and the injurious influence of close interbreeding is 
 thus prevented. Any one may readily convince himself 
 of the efficiency of insect agency by examining the flowers 
 of the more sterile kinds of hybrid Rhododendrons, which 
 produce no pollen, for he will find on their stigmas plenty 
 of pollen brought from other flowers. 
 
 In regard to animals, much fewer experiments have been 
 carefully tried than with plants. If our systematic arrange¬ 
 ments can be trusted, that is, if the genera of animals are 
 as distinct from each others as are the genera of plants, 
 then we may infer that animals more widely distinct in 
 the scale of nature can be crossed more easily than in 
 the case of plants; but the hybrids themselves are, I 
 think, more sterile. It should, however, be borne in 
 mind that, owing to few animals breeding freely 
 under confinement, few experiments have been fairly 
 tried: for instance, the canary-bird has been crossed with 
 nine distinct species of finches, but, as not one of these 
 
DEGREES OF STERILITY. 283 
 
 breeds freely in confinement, we have no right to expect 
 that the first crosses between them and the canary, or that 
 their hybrids, should be perfectly fertile. Again, with 
 respect to the fertility in successive generations of the more 
 feitile hybiid animals, I hardly know of an instance in 
 which two families of the same hybrid have been raised at 
 the same time from different parents, so as to avoid the ill 
 effects of close interbreeding. On the contrary, brothers 
 and sisters have usually been crossed in each successive 
 generation, in opposition to the constantly repeated admon¬ 
 ition of every breeder. And in this case, it is not at all 
 surprising that the inherent sterility in the hybrids should 
 have gone on increasing. 
 
 Although I know of hardly any thoroughly well-authen¬ 
 ticated cases of perfectly fertile hybrid animals, I have 
 leason to believe that the hybrids from Cervulus vaginalis 
 and Reevesii, and from Phasianus colchicus with P. tor- 
 quatus, are perfectly fertile. M. Quatrefages states that 
 the hybrids from two moths (Bombyx cynthia and arrindia) 
 were proved in Paris to be fertile inter se for eight genera¬ 
 tions. It has lately been asserted that two such distinct 
 species as the hare and rabbit, when they can be got to 
 breed together, produce offspring, which are highly fertile 
 when crossed with one of the parent-species. The hybrids 
 from the common and Chinese geese (A. cygnoides), species 
 which are so different that they are generally ranked in 
 distinct genera, have often bred in this country with either 
 P m e paieut, and in one single instance they have bred 
 inter se. This was effected by Mr. Eyton, who raised two 
 hybrids from the same parents, but from different hatches; 
 and from these two birds he raised no less than eight 
 hybiids (grandchildren of the pure geese) from one nest. 
 In India, however, these cross-bred geese must be far more 
 
 i ^ ic TA1 . by two eminently capable judges, 
 
 namely Mr. Blyth and Captain Ilutton, that whole flocks 
 ot these crossed geese are kept in various parts of the coun¬ 
 ty , and as. they are kejit for profit, where neither pure 
 paient-species exists, they must certainly be highly or per¬ 
 fectly fertile. - 1 
 
 With our domesticated animals, the various races when 
 crossed together are quite fertile; yet in many cases they 
 aie descended from two or more wild species. From this 
 
284 
 
 LAWS GOVERNING THE STERILITY 
 
 fact we must conclude either that the aboriginal parent- 
 species at first produced perfectly fertile hybnds, or t a 
 the hybrids subsequently reared under domestication 
 became quite fertile. This latter alternative, which was 
 first propounded by Pallas, seems by far the most probable, 
 and can, indeed, hardly be doubted. It is, for instance, 
 almost certain that our dogs are descended from several 
 wild stocks; yet, with perhaps the exception of certain in¬ 
 digenous domestic dogs of South America, all are quite 
 fertile together; but analogy makes me greatly doubt, 
 whether the several aboriginal species would at first have 
 freely bred together and have produced quite fertile hybrids. 
 So again I have lately acquired decisive evidence that the 
 crossed offspring from the Indian humped and common 
 cattle are inter se perfectly fertile; and from the observa¬ 
 tions by Rutimeyer on their important osteological diffei- 
 ences, as well as from those by Mr. Blyth on their differences 
 in habits, voice, constitution, etc., these two forms must 
 be regarded as good and distinct species. The same remarks 
 may be extended to the two chief races of the pig. We 
 must, therefore, either give up the belief of the universal 
 sterility of species when crossed; or we must look at this 
 sterility in animals, not as an indelible characteristic, but 
 as one capable of being removed by domestication. _ 
 Finally, considering all the ascertained facts on the inter¬ 
 crossing of plants and animals, it may be concluded that 
 some degree of sterility, both in first crosses and in hybrids, 
 is an extremely general result; but that it cannot, under 
 our present state of knowledge, be considered as absolutely 
 
 universal. 
 
 LAWS GOVERNING THE STERILITY OF FIRST CROSSES AND 
 
 OF HYBRIDS. 
 
 We will now consider a little more in detail. the laws 
 governing the sterility of first crosses and of hybnds. ur 
 chief obiect will be to" see whether or not these laws indicate 
 that species have been specially endowed with this quality, 
 in order to prevent their crossing and blending together m 
 utter confusion. The following conclusions are drawn up 
 chiefly from Gartner’s admirable work on the hybridization 
 of plants. I have taken much pains to ascertain how far 
 they apply to animals, and, considering how scanty our 
 
285 
 
 OF FIRST CROSSES AND OF HYBRIDS. 
 
 knowledge is in regard to hybrid animals, I have been sur 
 prised to find how generally the same rules apply to both 
 kingdoms. 
 
 It has been already remarked, that the degree of fertility, 
 both of first crosses and of hybrids, graduates from zero to 
 perfect fertility. It is surprising in how many curious 
 ways this gradation can be shown; but only the barest 
 outline of the facts can here be given. When pollen from 
 a plant of one family is placed on the stigma of a plant of 
 a distinct family, it exerts no more influence than so much 
 inorganic dust. From this absolute zero of fertility, the 
 pollen of different species applied to the stigma of some 
 one species of the same genus, yields a perfect gradation 
 in the number of seeds produced, up to nearly complete or 
 even quite complete fertility; and, as we have seen, in cer¬ 
 tain abnormal cases, even to an excess of fertility, beyond 
 that which the plant’s own pollen produces. So in 
 hybrids themselves, there are some which never have pro¬ 
 duced, and probably never would produce, even with the 
 pollen of the pure parents, a single fertile seed: but in 
 some of these cases a first trace of fertility may be detected, 
 by the pollen of one of the pare parent-species causing the 
 flower of the hybrid to wither earlier than it otherwise 
 would have done; and the early withering of the flower is 
 well known to be a sign of incipient fertilization. From 
 this extreme degree of sterility we have self-fertilized 
 hybrids producing a greater and greater number of seeds 
 up to perfect fertility. 
 
 The hybrids raised from two species which are very diffi¬ 
 cult to cross, and which rarely produce any offspring, are 
 generally very sterile; but the parallelism between the 
 difficulty of making a first cross, and the sterility of the 
 hybrids thus produced—two classes of facts which are 
 generally confounded together—is by no means strict. 
 There are many cases, in which two pure species, as in the 
 genus Verbascum, can be united with unusual facility, and 
 produce numerous hybrid offspring, yet these hybrids are 
 remarkably sterile. On the other hand, there are species 
 which can be crossed very rarely, or with extreme difficulty, 
 but the hybrids, when at last produced, are very fertile. 
 Even within the limits of the same genus, for instance in 
 Dianthus, these two opposite cases occur. 
 
286 
 
 LAWS GOVERNING THE STERILITY 
 
 The fertility, both of first crosses and of hybrids, is more 
 easilv affected by unfavorable conditions, than is that of 
 pure"species. But the fertility of first crosses is likewise 
 innately variable; for it is not always the same in degree 
 when the same two species are crossed under the same cir¬ 
 cumstances; it depends in part upon the constitution of 
 the individuals which happen to have been chosen for the 
 experiment. So it is with hybrids, for their degree of fer¬ 
 tility is often found to differ greatly in the several indi¬ 
 viduals raised from seed out of the same capsule and ex¬ 
 posed to the same conditions. 
 
 By the term systematic affinity is meant, the general re¬ 
 semblance between species in structure and constitution. 
 Now the fertility of first crosses, and of the hybrids pro¬ 
 duced from them, if largely governed by their systematic 
 affinity. This is clearly shown by hybrids never having 
 been raised between species ranked by systematists in dis¬ 
 tinct families; and on the other hand, by very closely 
 allied species generally uniting with facility. But the cor¬ 
 respondence between systematic affinity and the facility of 
 crossing is by no means strict. A multitude of cases could 
 be given of very closely allied species which will not unite, 
 or only with extreme difficulty; and on the other hand of 
 very distinct species which unite with the utmost facility. 
 In the same family there may be a genus, as Dianthus, in 
 which very many species can most readily be crossed; and 
 another genus, as Silene, in which the most persevering 
 efforts have failed to produce between extremely close 
 species a single hybrid. Even within the limits of the 
 same genus, "we meet with this same difference; for in¬ 
 stance, the many species of Nicotiana have been more 
 largely crossed than the species of almost any other genus; 
 but Gartner found that N. acuminata, which is not a par¬ 
 ticularly distinct species, obstinately failed to fertilize, or 
 to be fertilized, by no less than eight other species of Nico¬ 
 tiana. Many analogous facts could be given. 
 
 No one has been able to point out what kind or what 
 amount of difference, in any recognizable character, is suf¬ 
 ficient to prevent two species crossing. _ It can be shown 
 that plants most widely different in habit and general ap¬ 
 pearance, and having strongly marked differences in every 
 part of the flower, even in the pollen, in the fruit, and in 
 
OF FIRST CROSSES AND OF HYBRIDS . 28? 
 
 the cotyledons, can be crossed. Annual and perennial 
 plants, deciduous and evergreen trees, plants inhabiting 
 different stations and fitted for extremely different climates, 
 can often be crossed with ease. 
 
 By a reciprocal cross between two species, I mean the 
 case, for instance, of a female ass being first crossed by a 
 stallion, and then a mare by a male ass; these cwo species 
 may then be said to have been reciprocally crossed. 
 I here is often . the widest possible difference in the 
 facility of making reciprocal crosses. Such cases are 
 highly important, for they prove that the capacity in 
 any two species to cross is often completely independent 
 of their sytematic affinity, that is of any difference 
 in their structure or constitution, excepting in their 
 reproductive systems. The diversity of the result in recip¬ 
 rocal crosses between the same two species was long ago 
 observed by Kolreuter. To give an instance: Mirabilis 
 jalapa can easily be. fertilized by the pollen of M. long- 
 iflora, and the hybrids thus produced are sufficiently fer¬ 
 tile; but Kolreuter tried more than two hundred times, 
 during eight folio wing years, to fertilize reciprocally M. long- 
 iflora with the pollen of M. jalapa, and utterly failed. 
 Several other equally striking cases could begiven." Thuret 
 has observed the same fact with certain sea-weeds or Fuci. 
 Gartner, moreover, found that this difference of facility in 
 making reciprocal crosses is extremely common in a lesser 
 degree. He has observed it even between closely related 
 forms (as IVfatthiola annua and glabra) which many 
 botanists rank only as varieties. It is also a remarkable 
 fact that hybrids raised from reciprocal crosses, though of 
 course compounded of the very same two species, the one 
 species having first been used as the father and then as the 
 mother, though they rarely differ in external characters, 
 yet generally differ in fertility in a small, and occasionally 
 in a high degree. 
 
 Several other singular rules could be given from Gart- 
 nei: for instance, some species have a remarkable power of 
 crossing with other species; other species of the same 
 genus have a remarkable power of impressing their like¬ 
 ness on their hybrid offspring; but these two powers do not 
 at all necessarily go together. There are certain hybrids 
 which, instead of having, as is usual, an intermediate 
 
288 
 
 LAWS GOVERNING THE STERILITY 
 
 character between their two parents, always closely resem¬ 
 ble one of them; and such hybrids, though externally so 
 like one of their pure parent-species, are with rare excep¬ 
 tions extremely sterile. So again among hybrids which 
 are usually intermediate in structure between their parents, 
 exceptional and abnormal individuals sometimes are born, 
 which closely resemble one of their pure parents; and these 
 hybrids are almost always utterly sterile, even when the 
 other hybrids raised from seed from the same capsule have 
 a considerable degree of fertility* These facts show how 
 completely the fertility of a hybrid may be independent of 
 its external resemblance to either pure parent. 
 
 Considering the several rules now given, which govern 
 the fertility of first crosses and of hybrids, we see that 
 when forms, which must be considered as good and distinct 
 species, are united, their fertility graduates from zero to 
 perfect fertility, or even to fertility under certain con¬ 
 ditions in excess; that their fertility, besides being emi¬ 
 nently susceptible to favorable and unfavorable conditions, 
 is innately variable; that it is by no means always the same 
 in degree in the first cross and in the hybrids produced 
 from this cross; that the fertility of hybrids is not related 
 to the degree in which they resemble in external appearance 
 either parent; and lastly, that the facility of making a first 
 cross between any two species is not always governed by 
 their systematic affinity or degree of resemblance to each 
 other. This latter statement is clearly proved by the dif¬ 
 ference in the result of reciprocal crosses between the same 
 two species, for, according as the one species or the other 
 is used as the father or the mother, there is generally some 
 difference, and occasionally the widest possible dif¬ 
 ference, in the facility of effecting an union. The 
 hybrids, moreover, produced from reciprocal crosses often 
 differ in fertility. 
 
 Now, do these complex and singular rules indicate 
 that species have been endowed with sterility simply to 
 prevent their becoming confounded in nature? I think 
 not. For why should the sterility be so extremely differ¬ 
 ent in degree, when various species are crossed, all of which 
 we must suppose it would be equally important to keep 
 from blending together? Why should the degree of 
 sterility be innately variable in the individuals of the same 
 
OF FIRST CROSSES AND OF HYBRIDS. 
 
 289 
 
 species? Why should some species cross with facility and 
 yet produce very sterile hybrids; and other species cross 
 with extreme difficulty, and yet produce fairly fertile 
 hybrids? Why should there often be so great a differ¬ 
 ence in the result of a reciprocal cross between the same 
 two species? Why, it may even be asked, has the pro¬ 
 duction of hybrids been permitted ? To grant to species 
 the special power of producing hybrids, and then to stop 
 their further propagation by different degrees of sterility, 
 not strictly related to the facility of the first union between 
 their parents, seems a strange arrangement. 
 
 The foregoing rules and facts, on the other hand, appear 
 to me clearly to indicate that the sterility, both of first 
 crosses and of hybrids, is simply incidental or dependent on 
 unknown differences in their reproductive systems; the 
 differences being of so peculiar and limited a nature, that, 
 in reciprocal crosses between the same two species, the 
 male sexual element of the one will often freely act on the 
 female sexual element of the other, but not in a reversed 
 direction. It will be advisable to explain a little more 
 fully, by an example, what I mean by sterility being inci¬ 
 dental on other differences, and not a specially endowed 
 quality. As the capacity of one plant to be grafted or 
 budded on another is unimportant for their welfare in a 
 state of nature, I presume that no one will suppose that 
 this capacity is a specially endowed quality, but will admit 
 that it is incidental on differences in the laws of growth of 
 the two plants. We can sometimes see the reason why one 
 tree will not take on another from differences in their rate of 
 growth, in the hardness of their wood, in the period of the 
 flow or nature of their sap, etc.; but in a multitude of 
 cases we can assign no reason whatever. Great diversity 
 in the size of two plants, one being woody and the other 
 herbaceous, one being evergreen and the other deciduous, 
 and adaptation to widely different climates, do not always 
 prevent the two grafting together. As in hybridization, so 
 with grafting, the capacity is limited by systematic affinity, 
 for no one has been able to graft together trees belonging 
 to quite distinct families; and, on the other hand, closely 
 allied species and varieties of the same species, can usually, 
 but not invariably, be grafted with ease. But this capacity, 
 as in hybridization, is by no means absolutely governed by 
 
2 9.0 LAWS GO VERNING THE ST ERIE 1TY 
 
 systematic affinity. Although many distinct genera within 
 the same family have been grafted together, in other cases 
 species of the same genus will not take on each other. I lie 
 pear can be grafted far more readily on the quince, which 
 is ranked as a distinct genus, than on the apple, which is a 
 member of the same genus. Even different varieties ot 
 the pear take with different degrees of facility on the 
 quince; so do different varieties of the apricot and peach 
 
 on certain varieties of the plum. . . 
 
 As Gartner found that there was sometimes an innate 
 difference in different individuals of the same two 
 species in crossing; so Sageret believes this to be the 
 case with different individuals of the same two species 
 in being grafted together. As in reciprocal crosses, the 
 facility of effecting an union is often very far from equal, 
 so it sometimes is in grafting. The common goosebeny, 
 for instance, cannot be grafted on the currant, whereas 
 the currant will take, though with difficulty, on the 
 
 & ° We have seen that the sterility of hybrids which have 
 their reproductive organs in an imperfect condition, is a 
 different case from the difficulty of uniting two pure spe¬ 
 cies which have their reproductive organs perfect; yet 
 these two distinct classes of cases run to a large extent 
 parallel. Something analogous occurs m grafting; tor 
 Thouin found that three species of Robima, which seeded 
 freely on their own roots, and which could be grafted with 
 no great difficulty on a fourth species, when thus grafted 
 were rendered barren. On the other hand, certain species 
 of Sorbus, when grafted on other species, yielded twice 
 as much fruit as when on their own roots. We are re¬ 
 minded by this latter fact of the extraordinary cases oi 
 hippeastrum, passiflora, etc., which seed much moie fiee y 
 when fertilized with the pollen of a distinct species than 
 when fertilized with pollen from the same plant. 
 
 We thus see that, although there is a clear and gieat dr - 
 ference between the mere adhesion of grafted stocks an 
 the union of the male and female elements in the act ot 
 reproduction, yet that there is a rude degree of parallelism 
 in the results of grafting and of crossing distinct species. 
 And as we must look at the curious and complex laws & ov * 
 erning the facility with which trees can be grafted on each 
 
291 
 
 OF FIRST CROSSES AND OF HYBRIDS. 
 
 other as incidental on unknown differences in their vege¬ 
 tative systems, so I believe that the still more complex 
 laws governing the facility of first crosses are incidental on 
 unknown differences in their reproductive systems. These 
 diffeiences in both cases follow, to a certain extent, as 
 might have been expected, systematic affinity, by which 
 term every kind of resemblance and dissimilarity between 
 organic beings is attempted to be expressed. The facts by 
 no means seem to indicate that the greater or lesser diffi¬ 
 culty of either grafting or crossing various species has been 
 a special endowment; although in the case of crossing, the 
 difficulty is as important for the endurance and stability of 
 specific forms as in the case of grafting it is unimportant 
 for their welfare. 
 
 origin and causes of the sterility of first crosses 
 
 AND OF HYBRIDS. 
 
 At one time it appeared to me probable, as it has to others, 
 that the sterility of first crosses and of hybrids might have 
 been slowly acquired through the natural selection of 
 slightly lessened degrees of fertility, which, like any other 
 variation, spontaneously appeared in certain individuals of 
 one variety when crossed with those of another variety. 
 For it would clearly be advantageous to two varieties or 
 incipient species if they could be kept from blending, on 
 the same principle that, when man is selecting at the 
 same time two varieties, it is necessary that he should 
 keep them separate. In the first place, it may be re¬ 
 marked that species inhabiting distinct regions are often 
 sterile when crossed; now it could clearly have been of 
 no advantage to such separated species to have been 
 rendered mutually sterile, and consequently this could 
 not have been effected through natural selection; but 
 it may perhaps be argued, that, if a species was rendered 
 sterile with some one compatriot, sterility with other spe¬ 
 cies would follow as a necessary contingencv. In the 
 second place, it is almost as much opposed to the theory of 
 natural selection as to that of special creation, that in re- 
 cipiocal ciosses the male element of one form should have 
 been rendered utterly impotent on a second form, while at 
 the same time the male element of khis second form is en- 
 
292 CA USES OF THE STERILITY 
 
 abled freely to fertilize the first form; for this peculiar 
 state of the reproductive system could hardly have been 
 
 advantageous to either species. _ . , 
 
 In considering the probability of natural selection having 
 come into action, in rendering species mutually sterile, the 
 greatest difficulty will be found to lie in the existence of 
 many graduated steps, from slightly lessened fertility to ab¬ 
 solute sterility. It may he admitted that it would profit an 
 incipient species, if it were rendered in some slight degiee 
 sterile when crossed with its parent form or with some 
 other variety; for thus fewer bastardized and deteriorated 
 offspring would be produced to commingle their blood with 
 the new species in process of formation. But he who will 
 take the trouble to reflect on the steps by which this first 
 degree of sterility could be increased through natural selec¬ 
 tion to that high degree which is common with so many 
 species, and which is universal with species which have 
 been differentiated to a generic or family rank, will find 
 the subject extraordinarily complex. After mature reflec¬ 
 tion it seems to me that this could not have been effected 
 through natural selection. Take the case of any two spe¬ 
 cies which, when crossed, produced few and sterile off¬ 
 spring; now, what is there which could favor the survival 
 of those individuals which happened to be endowed m a 
 slightly higher degree with mutual infertility, and whic 
 thus approached by one small step toward absolute sterility. 
 Yet an advance of this kind, if the theory of natuial se¬ 
 lection be brought to bear, must have incessantly occurred 
 with many species, for a multitude are mutually quite 
 barren. With sterile neuter insects we have reason to be¬ 
 lieve that modifications in their structure and fertility 
 have been slowly accumulated by natural selection, trom 
 an advantage having been thus indirectly given to the com¬ 
 munity to which they belonged over other communities of 
 the same species; but an individual animal not belonging 
 to a social community, if rendered slightly sterile when 
 crossed with some other variety, would not thus itself gain 
 any advantage or indirectly give any advantage to the other 
 individuals of the same variety, thus leading to their pieser- 
 
 vation. ... ,. • 
 
 But it would be superfluous to discuss this question in 
 
 detail: for with plants wa have conclusive evidence that 
 
OF FIRST CROSSES AND OF HYBRIDS. 393 
 
 the sterility of crossed species must be due to some princi- 
 pie, quite independent of natural selection. Both Gartner 
 and Kolreuter have proved that in genera including numer¬ 
 ous species, a series can be formed from species which when 
 crossed yield fewer and fewer seeds, to species which never 
 produce a single seed, but yet are affected by the pollen of 
 certain other species, for the germen swells. It is here 
 manifestly impossible to select the more sterile individuals 
 which have already ceased to yield seeds; so that this acme 
 ot sterility, when the germen alone is effected, cannot have 
 been gained through selection; and from the laws govern¬ 
 ing the various grades of sterility being so uniform through¬ 
 out the animal and vegetable kingdoms, we may infer that 
 the cause, whatever it may be, is the same or nearly the 
 same m all cases. 
 
 We will now look a little closer at the probable nature 
 of the differences between species which induce sterility in 
 first ciosses and in hybrids. In the case of first crosses, 
 the greater or less difficulty in effecting an union and in 
 obtaining offspring apparently depends on several distinct 
 causes. There must sometimes be a physical impossibility 
 m the male element reaching the ovule, as would be the 
 case with a plant having a pistil too long for the pollen- 
 tubes to reach the ovarium. It has also been observed that 
 when the pollen of one species is placed on the stigma of a 
 allied species, though the pollen-tubes protrude, 
 they do not penetrate the stigmatic surface. Again, the 
 male element may reach the female element, but be inca¬ 
 pable of causing an embryo to be developed, as seems to 
 have been tbe case with some of Thureffs experiments on 
 uci. -No explanation can be given of these facts, any 
 more than why certain trees can not be grafted on others. 
 Lastly, an embryo may be developed, and then perish at 
 an early period. This latter alternative has not been suf¬ 
 ficiently attended to; but I believe, from observations com¬ 
 municated to me by Mr. Hewitt, who has had great ex¬ 
 perience m hybridizing pheasants and fowls, that the early 
 death of the embryo is a very frequent cause of sterility in 
 first crosses.. Mr. Salter has recently given the results of 
 an examination of about 500 eggs produced from various 
 crosses between three species of Gallus and their hybrids: 
 
294 
 
 CA USES OF THE STERILIT7 
 
 the majority of these eggs had been fertilized; and ia the 
 majority of the fertilized eggs, the embryos had either been 
 partially developed and had then perished, or had become 
 nearly mature, but the young chickens had been unable 
 to break through the shell. Of the chickens which were 
 born, more than four-fifths died within the first few days, 
 or at latest weeks, “ without any obvious cause, apparently 
 from mere inability to live;” so that from the 500 eggs only 
 twelve chickens were reared. With plants, hybridized em¬ 
 bryos probably often perish in a like manner; at least it is 
 known that hybrids raised from very distinct species are 
 sometimes weak and dwarfed, and perish at an early age; 
 of which fact Max Wichura has recently given some strik¬ 
 ing cases with hybrid willows. It may be here worth 
 noticing that in some cases of parthenogenesis, the em¬ 
 bryos within the eggs of silk moths which had not been 
 fertilized, pass through their early stages of development 
 and then perish like the embryos produced by a cross be¬ 
 tween distinct species. Until becoming acquainted with 
 these facts, I was unwilling to believe in the frequent early 
 death of hybrid embryos; for hybrids, when once born, are 
 generally healthy and long-lived, as we see in the case of 
 the common mule. Hybrids, however, are differently cir¬ 
 cumstanced before and after birth: when born and living 
 in a country where their two parents live, they are gener¬ 
 ally placed under suitable conditions of life. But a hybrid 
 partakes of only half of the nature and constitution of its 
 mother; it may therefore, before birth, as long as it is 
 nourished within its mother’s womb, or within the egg or 
 seed produced by the mother, be exposed to conditions in 
 some degree unsuitable, and consequently be liable to 
 perish at an early period; more especially as all very young 
 beings are eminently sensitive to injurious or unnatural 
 conditions of life. But after all, the cause more probably 
 lies in some imperfection in the original act of impregna¬ 
 tion, causing the embryo to be imperfectly developed, 
 rather than in the conditions to which it is subsequently 
 exposed. 
 
 In regard to the sterility of hybrids, in which the sexual 
 elements are imperfectly developed, the case is somewhat 
 different. I have more than once alluded to a large body 
 of facts showing that, when animals and plants are 
 
OF FIRST CROSSES AND OF HYBRIDS. 295 
 
 removed from their natural conditions, they are extremely 
 liable to have their reproductive systems seriously affected. 
 This, in fact, is the great bar to the domestication of ani¬ 
 mals. Between the sterility thus superinduced and that of 
 hybrids, there are many points of similarity. In both 
 cases the sterility j.s independent of general health, and is 
 often accompanied by excess of size or great luxuriance. 
 In both cases the sterility occurs in various degrees; in 
 both, the male element is the most liable to be affected; 
 but sometimes the female more than the male. In both, 
 the tendency goes to a certain extent with systematic affi¬ 
 nity, for whole groups of animals and plants are rendered 
 impotent by the same unnatural conditions; and whole 
 groups of species tend to produce sterile hybrids. On the 
 other hand, one species in a group will sometimes resist 
 great changes of conditions with unimpaired fertility; and 
 certain species in a group will produce unusually fertile 
 hybrids. No one can tell till he tries, whether any partic¬ 
 ular animal will breed under confinement, or any exotic 
 plant seed freely under culture; nor can he tell till he 
 tries, whether any two species of a genus will produce more 
 or less sterile hybrids. Lastly, when organic beings are 
 placed during several generations under conditions not 
 natural to them, they are extremely liable to vary, which 
 seems to be partly due to their reproductive systems having 
 been specially affected, though in a lesser degree than when 
 sterility ensues. So it is with hybrids, for their offspring 
 in successive generations are eminently liable to vary, as 
 every experimentalist has observed. 
 
 Thus we see that when organic beings are placed under 
 new and unnatural conditions, and when hybrids are pro¬ 
 duced by the unnatural crossing of two species, the repro¬ 
 ductive ^ system, independently of the general state of 
 health, is affected in a very similar manner. In the one 
 case, the conditions of life have been disturbed, though 
 often in so slight a degree as to be inappreciable by us; in 
 the other case, or that of hybrids, the external conditions 
 have remained the same, but the organization has been dis¬ 
 turbed by two distinct structures and constitutions, includ¬ 
 ing of course the reproductive systems, having been 
 blended into one. For it is scarcely possible that two 
 organizations should be compounded into one, without 
 
296 
 
 CA USES OF THE STERILITY 
 
 some disturbance occurring in the development, or periodi¬ 
 cal action, or mutual relations of the different parts and 
 organs one to another or to the conditions of life. When 
 hybrids are able to breed inter se, they transmit to their 
 offspring from generation to generation the same com¬ 
 pounded organization, and hence we need not be surprised 
 that their sterility, though in some degree variable, does 
 not diminish; it is even apt to increase, this being gener¬ 
 ally the result, as before explained, of too close interbreed¬ 
 ing. The above view of the sterility of hybrids being 
 caused by two constitutions being compounded into one 
 has been strongly maintained by Max Wichura. 
 
 It must, however, be owned that we cannot understand, 
 on the above or any other view, several facts with respect 
 to the sterility of hybrids; for instance, the unequal fer¬ 
 tility of hybrids produced from reciprocal crosses; or the 
 increased sterility in those hybrids which occasionally and 
 exceptionally resemble closely either pure parent. Nor do 
 I pretend that the foregoing remarks go to the root of the 
 matter; no explanation is offered why an organism, when 
 placed under unnatural conditions, is rendered sterile. All 
 that I have attempted to show is, that in two cases, in 
 some respects allied, sterility is the common result—in the 
 one case from the conditions of life having been disturbed, 
 in the other case from the organization having been dis¬ 
 turbed by two organizations being compounded into one. 
 
 A similar parallelism holds good with an allied yet very 
 different class of facts. It is an old and almost universal 
 belief, founded on a considerable body of evidence, which I 
 have elsewhere given, that slight changes in the conditions 
 of life are beneficial to all living things. We see this acted 
 on by farmers and gardeners in their frequent exchanges 
 of seed, tubers, etc., from one soil or climate to another, 
 and back again. During the convalescence of animals, 
 great benefit is derived from almost any change in their 
 habits of life. Again, both with plants and animals, there 
 is the clearest evidence that a cross between individuals of 
 the same species, which differ to a certain extent, gives 
 vigor and fertility to the offspring; and that close inter¬ 
 breeding continued during several generations between the 
 nearest relations, if these be kept under the same conditions 
 of life, almost always leads to decreased size, weakness, or 
 sterility- 
 
OF FIRST CROSSES AND OF H YBR1DS. a9? 
 
 Hence it seems that, on the one hand, slight changes in 
 the conditions of life benefit all organic beings, and on the 
 othei hand, that slight crosses, that is, crosses between the 
 males and females of the same species, which have been 
 subjected to slightly different conditions, or which have 
 slightly varied, give vigor and fertility to the offspring 
 - 3 , ^s we h ave seen, organic beings long habituated to 
 ceitam uniform conditions under a state of nature, when 
 subjected, as under confinement, to a considerable change 
 in their conditions, very frequently are rendered more or 
 less sterile; and we know that a cross between two forms 
 that have become widely or specifically different, produce 
 hybrids which are almost always in some degree sterile I 
 am fully persuaded that this double parallelism is by no 
 means an accident or an illusion. He who is able to ex¬ 
 plain why the elephant, and a multidude of other animals 
 are incapable of breeding when kept under only partial 
 confinement m their native country, will be able to explain 
 the primary cause of hybrids being so generally sterile, 
 lie will at the same time be able to explain how it is that 
 the races of some of our domesticated animals, which have 
 often been subjected to new and net uniform conditions, 
 are quite fertile together, although they are descended from 
 distinct species, which would probably have been sterile if 
 aboriginally crossed. The above two parallel series of facts 
 seem to be connected together by some common but un- 
 known bond, which is essentially related to the principle 
 of life; this principle, according to Mr. Herbert Spencer, 
 being that life depends on, or consists in, the incessant 
 action and reaction of various forces, which, as throughout 
 nature, are always tending toward an equilibrium; and 
 when this tendency is slightly disturbed by any change, 
 the vital forces gam in power. * ’ 
 
 RECIPROCAL DIMORPHISM AKD TRIMORPHISM. 
 
 This subject may be here briefly discussed, and will be 
 found to throw some light on hybridism. Several plants 
 belonging to distinct orders present two forms, which 
 exist in about equal numbers and which differ in no respect 
 except m their reproductive organs; one form having a 
 °ng pistil with short stamens, the other a short pistil 
 
298 
 
 reciprocal dimorphism 
 
 with long stamens; the two having differently sized pollen- 
 grains. With trimorpliic plants there are three forms 
 likewise differing in the lengths of their pistils and stamens, 
 in the size and color of the pollen-grains, and m some 
 other respects; and as in each of the three forms there are 
 two sets of stamens, the three forms possess altogethei six 
 sets of stamens and three kinds of pistils. These organs 
 are so proportioned in length to each other that half the 
 stamens in two of the forms stand on a level with the 
 stigma of the third form. Now I have shown, and the 
 result has been confirmed by other observers, that in 
 order to obtain full fertility with these plants, it is neces- 
 sary that the stigma of the one form should be fertilized 
 by pollen taken from the stamens of corresponding height 
 in another form. So that with dimorphic species two 
 unions, which may be called legitimate, are fully lei tile, 
 and two, which may be called illegitimate, are more or less 
 infertile. With trimorpliic species six unions are legiti¬ 
 mate. or fully fertile, and twelve are illegitimate, or moie 
 
 or less infertile. , .. . . 
 
 The infertility which may be observed m various dimor¬ 
 phic and trimorpliic plants, when they are illegitimately 
 fertilized, that is by pollen taken from stamens not cor¬ 
 responding in height with the pistil, differs much m degree, 
 up to absolute and utter sterility; just in the same manner 
 as occurs in crossing distinct species. As the degree of 
 sterility in the latter case depends in an eminent degiee on 
 the conditions of life being more or less favorable, so I 
 have found it with illegitimate unions. It is well known 
 that if pollen of a distinct species be placed on the stigma 
 of a flower, and its own pollen be afterward, even after 
 a considerable interval of time, placed on the same stigma, 
 its action is so strongly prepotent that it generally annihi¬ 
 lates the effect of the foreign pollen; so it is with the pollen 
 of the several forms of the same species, for legitimate 
 pollen is strongly prepotent over illegitimate pollen, when 
 both are placed on the same stigma. I ascertained this 
 by fertilizing several flowers, first illegitimately, and twenty- 
 four hours afterward legitimately, with pollen taken 
 from a peculiarly colored variety, and all the seedling 
 were similarly colored; this shows that the legitimate pollen, 
 though applied twenty-four hours subsequently, had 
 
AND TRIMORPHISM. 
 
 299 
 
 wholly destroyed or prevented the action of the previously 
 applied illegitimate pollen. Again, as in making recipro¬ 
 cal crosses between the same two species, there is occa¬ 
 sionally a great difference in the result, so the same thing 
 occurs with trimorphic plants; for instance, the mid- 
 sty led form of Lythrum salicaria was illegitimately fer¬ 
 tilized with the greatest ease by pollen from the longer 
 stamens of the short-styled form, and yielded many seeds; 
 but the latter form did not yield a single seed when fer¬ 
 tilized by the longer stamens of the mid-styled form. 
 
 In all these respects, and in others which might be 
 added, the forms of the same undoubted species, when 
 illegitimately united, behave in exactly the same manner as 
 do two distinct species when crossed. This led me carefully 
 to observe during four years many seedlings, raised from 
 several illegitimate unions. The chief result is that these 
 illegitimate plants, as they may be called, are not 
 fully fertile. It is possible to raise from dimorphic species, 
 both long-styled and short-syled illegitimate plants, and 
 from trimorphic plants all three illegitimate forms. These 
 can then be properly united in a legitimate manner. When 
 this is done, there is no apparent reason why they should 
 not yield as. many seeds as did their parents when legiti¬ 
 mately fertilized. But such is not the case. They are all 
 infertile, in various degrees; some being so utterly and in¬ 
 curably sterile that they did not yield during four seasons 
 a single seed or even seed-capsule. The sterility of these 
 illegitimate plants, when united with each other in a legiti¬ 
 mate manner, may be strictly compared with that of 
 hybrids when crossed inter se. If, on the other hand, a 
 hybrid is crossed with either pure parent-species, the ster¬ 
 ility is usually much lessened: and so it is when an illegiti¬ 
 mate plant is fertilized by a legitimate plant. In the 
 same manner as the sterility of hybrids does not always run 
 parallel with the difficulty of making the first cross between 
 the two parent-species, so that sterility of certain illegiti¬ 
 mate plants was unusually great, while the sterility of the 
 union from which they were derived was by no means 
 great. With hybrids raised from the same seed-capsule 
 the degree of sterility is innately variable, so it is in a 
 marked manner with illegitimate plants. Lastly, many 
 hybrids are profuse and persistent flowerers, while other 
 
300 
 
 RECIPROCAL DIMORPHISM 
 
 and more sterile hybrids produce few flowers, and are weak, 
 miserable dwarfs; exactly similar cases occur with the 
 illegitimate offspring of various dimorphic and trimorphie 
 plants. 
 
 Altogether there is the closest indentity in character and 
 behavior between illegitimate plants and hybrids. It is 
 hardly an exaggeration to maintain that illegitimate plants 
 are hybrids, produced within the limits of the same species 
 by the improper union of certain forms, while ordinary 
 hybrids are produced from an improper union between so- 
 called distinct species. We have also already seen that 
 there is the closest similarity in all respects between first 
 illegitimate unions and first crosses between distinct species. 
 This will perhaps be made more fully apparent by an illus¬ 
 tration; we may suppose that a botanist found two well- 
 marked varieties (and such occur) of the long-styled form 
 of the trimorphie Lythrum salicaria, and that he deter¬ 
 mined to try by crossing whether they were specifically 
 distinct. He would find that they yielded only about one- 
 fifth of the proper number of seed, and that they behaved 
 in all the other above specified respects as if they had 
 been two distinct species. But to make the case sure, he 
 would raise plants from his supposed hybridized seed, and 
 he would find that the seedlings were miserably dwarfed 
 and utterly sterile, and that they behaved in all other 
 respects like ordinary hybrids. He might then maintain 
 that he had actually proved, in accordance with the com¬ 
 mon view, that his two varieties were as good and as dis¬ 
 tinct species as any in the world; but he would be com¬ 
 pletely mistaken. 
 
 The facts now given on dimorphic and trimorphie plants 
 are important, because they show us, first, that the physio¬ 
 logical test of lessened fertility, both in first crosses and in 
 hybrids, is no safe criterion of specific distinction; secondly, 
 because we may conclude that there is some unknown bond 
 which connects the infertility of illegitimate unions with 
 that of their illegitimate offspring, and we are led to 
 extend the same view to first crosses and hybrids; thirdly, 
 because we find, and this seems -to me of especial impor¬ 
 tance, that two or three forms of the same species may 
 exist and may differ in no respect whatever, either in 
 structure or in constitution, relatively to external con- 
 
AND TRIMORPHISM. 
 
 301 
 
 ditions, and yet be sterile when united in certain ways. 
 For we must remember that it is the union of the sexual 
 elements of individuals of the same form, for instance, of 
 two long-styled forms, which results in sterility; while it 
 is the union of the sexual elements proper to two distinct 
 forms which is fertile. Hence the case appears at first sight 
 exactly the reverse of what occurs, in the ordinary unions 
 of the individuals of the same species and with crosses 
 between distinct species. It is, however, doubtful whether 
 this is really so; but I will not enlarge on this obscure 
 subject. 
 
 We may, however, infer as probable from the considera¬ 
 tion of dimorphic and trimorphic plants, that the sterility 
 of distinct species when crossed and of their hybrid pro- 
 geny, depends exclusively on the nature of their sexual 
 elements, and not on any difference in their structure or 
 general constitution. We are also led to this same con¬ 
 clusion by considering reciprocal crosses, in which the 
 male of one species cannot be united, or can be united 
 with great difficulty, with the female of a second species, 
 while the converse cross can be effected with perfect 
 facility. That excellent observer, Gartner, likewise con¬ 
 cluded that species when crossed are sterile owing to dif¬ 
 ferences confined to their reproductive systems. 
 
 FERTILITY OF VARIETIES WHEN CROSSED, AND OF THEIR 
 MONGREL OFFSPRING, NOT UNIVERSAL. 
 
 It may be urged as an overwhelming argument that 
 there must be some essential distinction between species 
 and varieties, inasmuch as the latter, however much they 
 may differ from each other in external appearance, cross 
 with perfect facility, and yield perfectly fertile offspring. 
 With some exceptions, presently to be given, I fully admit 
 that this is the rule. But the subject is surrounded by 
 difficulties, for, looking to varieties produced under nature", 
 if two forms hitherto reputed to be varieties be found in 
 any degree sterile together, they are at once ranked by 
 most naturalists as species. For Instance, the blue and red 
 pimpernel, which are considered by most botanists as 
 varieties, are said by Gartner to be quite sterile when 
 crossed, and he consequently ranks them as undoubted 
 
302 
 
 FERTILITY OF VARIETIES 
 
 species. If we thus argue in a circle, the fertility of all 
 varieties produced under nature will assuredly have to be 
 
 ^'ifwe turn to varieties, produced, or supposed to have 
 been produced, under domestication, we aie still involvei 
 in some doubt. For when it is stated, for instance, 
 that certain South American indigenous domestic dogs do 
 not readily unite with European dogs, the explanation 
 which will occur to every one, and probably the true one, 
 is that they are descended from aboriginally distinct 
 species. Nevertheless the perfect fertility of so many do¬ 
 mestic races, differing widely from each othei in appear¬ 
 ance, for instance, those of the pigeon, or of the cabbage, 
 is a remarkable fact; more especially when we reflect how 
 many species there are, which, though resembling each 
 other most closely, are utterly sterile when intercrossed. 
 Several considerations, however, render the fertility ot do¬ 
 mestic varieties less remarkable. In the first place, it may 
 be observed that the amount of external difference between 
 two species is no sure guide to their degree of mutual 
 sterility, so that similar differences in the case of varieties 
 would be no sure guide. It is certain that with species the 
 cause lies exclusively in differences in their sexual consti¬ 
 tution Now the varying conditions to which domesticated 
 aniinais and cultivated plants have been subjected, have 
 had so little tendency toward modifying the. reproductive 
 system in a manner leading to mutual sterility, that we 
 have good grounds for admitting the directly opposite doc¬ 
 trine of Pallas, namely, that such conditions generally 
 eliminate this tendency; so that the domesticated descend¬ 
 ants of species, which in their natural state probably won d 
 have been in some degree sterile when crossed, become per¬ 
 fects fertile together. With plants., so far is cultivation 
 from giving a tendency toward sterility between distinct 
 species, that in several well-authenticated cases already 
 alluded to, certain plants have been affected in an opposite 
 manner, for they have become self-impotent, while, still 
 retaining the capacity of fertilizing, and. being fertilized 
 by, other species. If the Pallasian doctrine of the elimi¬ 
 nation of sterility through long-continued domestication be 
 admitted, and it can hardly be rejected, it becomes in the 
 highest degree improbable that similar conditions long-con- 
 
WHEN CROSSED. 
 
 303 
 
 tinued should likewise induce this tendency; though in 
 certain cases, with species having a peculiar constitution, 
 sterility might occasionally be thus caused. Thus, as I 
 believe, we can understand why, with domesticated ani¬ 
 mals, varieties have not been produced which are mutually 
 sterile; and why with plants only a few such cases, imme¬ 
 diately to be given, have been observed. 
 
 The real difficulty in our present subject is not, as it 
 appears to. me, why domestic varieties have not become 
 mutually infertile when crossed, but why this has so 
 generally occurred with natural varieties, as soon as 
 they have been permanently modified in a sufficient de¬ 
 gree to take rank as species. We are far from precisely 
 knowing the cause; nor is this surprising, seeing how 
 profoundly ignorant we are in regard to the normal 
 and abnormal action of the reproductive system. But 
 we can see that species, owing to their struggle for exist¬ 
 ence with numerous competitors, will have been exposed 
 during long periods of time to more uniform conditions, 
 than have domestic varieties; and this may well make 
 a wide difference in the result. For we know how 
 commonly wild animals and plants, when taken from 
 their natural conditions and subjected to captivity, 
 are rendered sterile; and the reproductive functions 
 of organic beings which have always lived under natural 
 conditions would probably in like manner be emi¬ 
 nently sensitive to the influence of an unnatural cross. 
 Domesticated productions, on the other hand, which, as 
 shown by the mere fact of their domestication, were not 
 originally highly sensitive to changes in their conditions of 
 life, and which can now generally resist with undimin¬ 
 ished fertility repeated changes of conditions, might be 
 expected to. produce varieties, which would be little liable 
 to have their reproductive powers injuriously affected by 
 the act of crossing with other varieties which had origi¬ 
 nated in a like manner. 
 
 I have as yet spoken as if the varieties of the same species 
 were invariably fertile when intercrossed. But it is impos¬ 
 sible to resist the evidence of the existence of a certain 
 amount of sterility in the few following cases, which I will 
 briefly abstract. The evidence is at least as good as that 
 from which we believe in the sterility of a multitude of 
 
304 
 
 FERTILITY OF VARIETIES 
 
 species. The evidence is also derived from hostile wit¬ 
 nesses, who in all other ca«es consider fertility and sterility 
 as safe criterions of specific distinction. . Gartner kept, 
 during several years, a dwarf kind of maize with yellow 
 seeds, and a tall variety with red seeds growing near each 
 other in his garden; and although these plants have sepa- 
 ated sexes, they never naturally crossed. He then fertil¬ 
 ized thirteen flowers of the one kind with pollen of the 
 other; but only a single head produced any seed, and this 
 one head produced only five grains. Manipulation in this 
 case could not have been injurious, as the plants have sepa¬ 
 rated sexes. Ho one, I believe, has suspected that these 
 varieties of maize are distinct species; and.it is important; 
 to notice that the hybrid plants thus raised were them¬ 
 selves perfectly fertile; so that even Gartner did not ven¬ 
 ture to consider the two varieties as specifically distinct. 
 
 Girou de Buzareingues crossed three varieties of gourd, 
 which like the maize has separate sexes, and he asserts that 
 their mutual fertilization is by so much the less easy as 
 their differences are greater. How far these experiments 
 may be trusted, I know not; but the forms experimented 
 on are ranked by Sageret, who mainly founds his classifi¬ 
 cation by the test of infertility, as varieties, and Naudin 
 has come to the same conclusion. 
 
 The following case is far more remarkable, and seems at 
 first incredible; but it is the result of an astonishing num¬ 
 ber of experiments made during many years on nine species 
 of Verbascum, by so good an observer and so hostile a wit¬ 
 ness as Gartner: namely, that the yellow and white varie¬ 
 ties when crossed produce less seed than the similarly 
 colored varieties of the same species. Moreover, he asserts 
 that, when yellow and white varieties of one species are 
 crossed with yellow and white varieties of a distinct 
 species, more seed is produced by the crosses between the 
 similarly colored flowers, than between those which are dif¬ 
 ferently colored. Mr. Scott also has experimented on the 
 species and varieties of Verbascum; and although unable 
 to confirm Gartner’s results on the crossing of the distinct 
 species, he finds that the dissimilarly, colored varieties of 
 the same species yield fewer seeds, in the proportion of 
 eighty-six to 100, than the similarly colored varieties. Yet 
 these varieties differ in no respect, except in the color of 
 
WHEN CROSSED. 305 
 
 their flowers; and one variety can sometimes be raised 
 from the seed of another. « 
 
 Kdlreuter, whose accuracy has been confirmed by 
 every subsequent observer, has proved the remarkable 
 fact that one particular variety of the common tobacco 
 was more fertile than the other varieties, when crossed 
 with a widely distinct species. He experimented on five 
 forms which are commonly reputed to be varieties, and 
 which he tested by the severest trial, namely, by recipro¬ 
 cal crosses, and he found their mongrel offspring perfectly 
 fertile. But one of these five varieties, when used either 
 as the father or mother, and crossed with the Nico- 
 tiana glutinosa, always yielded hybrids not so sterile as 
 those which were produced from the four other varieties 
 when crossed with N. glutinosa. Hence, the reproductive 
 system of this one variety must have been in some manner 
 and in some degree modified. 
 
 From these facts it can no longer be maintained that 
 varieties when crossed are invariably quite fertile. From 
 the great difficulty of ascertaining the infertility of varie~ 
 ties in a state of nature, for a supposed variety, if proved 
 to be infertile in any degree, would almost universally be 
 ranked as a species; from man attending only to external 
 characters in his domestic varieties, and from such 
 varieties not having been exposed for very long periods to 
 uniform conditions of life; from these several considera¬ 
 tions we may conclude that fertility does not constitute a 
 fundamental distinction between varieties and species when 
 crossed. The general sterility of crossed species may 
 safely be looked at, not as a special acquirement or endow¬ 
 ment, but as incidental on changes of an unknown nature 
 in their sexual elements. 
 
 HYBRIDS AND MONGRELS COMPARED, INDEPENDENT! Tr 
 
 OF THEIR FERTILITY. 
 
 Independently of the question of fertility, the offspring 
 of species and of varieties when crossed may be compared 
 in several other respects. Gartner, whose strong wish it 
 was to draw a distinct line between species and varieties, 
 could find very few, and, as it seems to me, quite unim¬ 
 portant differences between the so-called hybrid offspring 
 
306 HYBRIDS AND MONGRELS COMPARED. 
 
 of species, and the so-called mongrel offspring of varieties. 
 And, on v the other hand, they agree most closely in many 
 important respects. 
 
 I shall here discuss this subject with extreme brevity. 
 The most important distinction is, that in the first genera¬ 
 tion mongrels are more variable than hybrids; but Gartner 
 admits that hybrids from species which have long been cul¬ 
 tivated are often variable in the first generation; and I 
 have myself seen striking instances of this fact. Gartner 
 further admits that hybrids between very closely allied 
 species are more variable than those from very distinct 
 species; and this shows that the difference in the degree of 
 variability graduates away. When mongrels and the more 
 fertile hybrids are propagated for several generations, an 
 extreme amount of variability in the offspring in both 
 cases is notorious; but some few instances of both hybrids 
 and mongrels long retaining a uniform character could be 
 given. The variability, however, in the successive gener¬ 
 ations of mongrels is, perhaps, greater than in hybrids. 
 
 This greater variability in mongrels than in hybrids 
 does not seem at all surprising. For the parents of 
 mongrels are varieties, and mostly domestic varieties 
 (very few experiments having been tried on natural varie¬ 
 ties), and this implies that there has been recent variabil¬ 
 ity, which would often continue and would augment 
 that arising from the act of crossing. The slight 
 variability of hybrids in the first generation, in contrast 
 with that in the succeeding generations, is a curious fact 
 and deserves attention. For it bears on the view which I 
 have taken of one of the causes of ordinary variability, 
 namely, that the reproductive system, from being eminently 
 sensitive to changed conditions of life, fails under these 
 circumstances to perform its proper function of producing 
 offspring closely similar in all respects to the parent form. 
 Now, hybrids in the first generation are descended from 
 species (excluding those long cultivated) which have not 
 had their reproductive systems in any way affected, and 
 they are not variable; but hybrids themselves have the re¬ 
 productive systems seriously affected and their descendants 
 are highly variable. 
 
 But to return to our comparison of mongrels and 
 hybrids: Gartner states that mongrels are more liable, 
 
HYBRIDS AND MONGRELS COMPARED. 3 q 7 
 
 than hybrids to revert to either parent form; but this, if it 
 be true, is certainly only a difference in degree. More¬ 
 over, Gartner expressly states that the hybrids from long 
 cultivated plants are more subject to reversion than 
 
 lybuds fiom species in their natural state; and this prob¬ 
 ably explains the singular difference in the results arrived 
 at by different observers. Thus Max Wichura doubts 
 whether hybrids ever revert to their parent forms, and he 
 experimented on uncultivated species of willows, while 
 Naudin, on the other hand, insists in the strongest terms 
 on the almost universal tendency to reversion in hybrids 
 and he experimented chiefly on cultivated plants. Gartner 
 further states that when any two species, although most 
 closely allied to each other, are crossed with a third species, 
 the hybiids are widely different from each other; whereas 
 if two \ery distinct varieties of one species are crossed with 
 another species, the hybrids do not differ much. But this 
 conclusion, as far as I can make out, is founded on a 
 single experiment, and seems directly opposed to the 
 results of several experiments made by Kolreuter. 
 
 Such alone are the unimportant differences which 
 Gaitnei is able to point out between hybrid and mongrel 
 plants. On the other hand, the degrees and kinds of re¬ 
 semblance in mongrels and in hybrids to their respective 
 parents, more especially in hybrids produced from nearly 
 related species, follow, according to Gartner, the same 
 laws. When two species are crossed, one has sometimes a 
 prepotent power of impressing its likeness on the hybrid, 
 bo I believe it to be with varieties of plants; and with ani¬ 
 mals, one variety certainly often has this prepotent power 
 over another variety. Hybrid plants produced from a 
 lecipiocal cross generally resemble each other closely, and 
 so it is with mongrel plants from a reciprocal cross. Both 
 hybrids and mongrels can be reduced to either pure parent 
 
 foim by repeated crosses in successive generations with 
 either parent. 
 
 These several remarks are apparently applicable to ani¬ 
 mals, but the subject is here much complicated, partly 
 owing to the existence of secondary sexual characters, but 
 more especially owing to prepotency in transmitting like¬ 
 ness running more strongly in one'sex than in the other, 
 both when one species is crossed with another and when 
 
308 HYBRIDS AND MONGRELS COMPARED. 
 
 one variety is crossed with another variety. For instance, 
 X think those authors are right who maintain that the ass 
 has a prepotent power over the horse, so that both the 
 mule and the hinny resemble more closely the ass than the 
 horse; but that the prepotency runs more strongly in the 
 male than in the female ass, so that the mule, which is an 
 offspring of the male ass and mare, is more like an ass than 
 is the hinny, which is the offspring of the female ass and 
 stallion. 
 
 Much stress has been laid by some authors on the sup¬ 
 posed fact, that it is only with mongrels that the offspring 
 are not intermediate in character, but closely resemble one 
 of their parents; but this does sometimes occur with 
 hybrids, yet I grant much less frequently than with mon¬ 
 grels. Looking to the cases which I have collected of 
 cross-bred animals closely resembling one parent, the re¬ 
 semblances seem chiefly confined to characters almost mon¬ 
 strous in their nature, and which have suddenly appeared 
 —such as albinism, melanism, deficiency of tail or horns, 
 or additional fingers and toes; and do not relate to char¬ 
 acters which have been slowly acquired through selection. 
 A tendency to sudden reversions to the perfect character 
 of either parent would, also, be much more likely to occur 
 with mongrels, which are descended from varieties often 
 suddenly produced and semi-monstrous in character, than 
 with hybrids, which are descended from species slowly and 
 naturally produced. On the whole, I entirely agree with 
 Dr. Prosper Lucas, who, after arranging an enormous 
 body of facts with respect to animals, comes to the con¬ 
 clusion that the laws of resemblance of the child to its 
 parents are the same, whether the two parents differ little 
 or much from each other, namely, in the union of individ¬ 
 uals of the same variety, or of different varieties, or of 
 distinct species. 
 
 Independently of the question of fertility and sterility, 
 in all other respects there seems to be a general and close 
 similarity in the offspring of crossed species, and of crossed 
 varieties” If we look at species as having been specially 
 created, and at varieties as having been produced by sec¬ 
 ondary laws, this similarity would be an astonishing fact. 
 But it harmonizes perfectly with the view that there is no 
 essential distinction between species and varieties. 
 
SUMMARY. 
 
 309 
 
 SUMMARY OF CHAPTER. 
 
 First crosses between forms, sufficiently distinct to be 
 ranked as species, and their hybrids, are very generally, 
 but not universally, sterile. The sterility is of all degrees, 
 and is often so slight that the most careful experimental¬ 
 ists have arrived at diametrically opposite conclusions iu 
 ranking forms by this test. The sterility is innately vari¬ 
 able in individuals of the same species, and is eminently, 
 susceptible to action of favorable and unfavorable condi¬ 
 tions. The degree of sterility does not strictly follow 
 systematic affinity, but is governed by several curious and 
 complex laws. It is generally different, and sometimes 
 widely different in reciprocal crosses between the same two 
 species. It is not always equal in degree in a first cross 
 and in the hybrids produced from this cross. 
 
 In the same manner as in grafting trees, the capacity in 
 one species or variety to take on another, is incidental on 
 differences, generally of an unknown nature, in their vege¬ 
 tative systems, so in crossing, the greater or less facility of 
 one species to unite with another is incidental on unknown 
 differences in their reproductive systems. There is no 
 more reason to think that species have been specially en¬ 
 dowed with various degrees of sterility to prevent their 
 crossing and blending in nature, than to think that trees 
 have been specially endowed with various and somewhat 
 analogous degrees of difficulty in being grafted together in 
 order to prevent their inarching in our forests. 
 
 The sterility of first crosses and of their hybrid progeny 
 has not been acquired through natural selection. In the 
 case of first crosses it seems to depend on several circum¬ 
 stances; in some instances in chief part on the early death 
 of the embryo. In the case of hybrids, it apparently de¬ 
 pends on their whole organization having been disturbed 
 by being compounded from two distinct forms; the ster¬ 
 ility being closely allied to that which so frequently affects 
 pure species, when exposed to new and unnatural con¬ 
 ditions of life. He who will explain these latter cases will 
 be able to explain the sterility of hybrids. This view is 
 strongly supported by a parallelism of another kind: 
 namely, that, firstly, slight changes in the conditions of 
 life add to the vigor and fertility of all organic beings; and 
 
310 
 
 SUMMARY. 
 
 secondly, that the crossing of forms, which have been ex¬ 
 posed to slightly different conditions of life, or which have 
 varied, favors the size, vigor and fertility of their offspring. 
 The facts given on the sterility of the illegitimate unions 
 of dimorphic and trimorphic plants and of their illegitimate 
 progeny, perhaps render it probable that some unknown 
 bond in all cases connects the degree of fertility of first 
 unions with that of their offspring. The consideration of 
 these facts on dimorphism, as well as of the results of re¬ 
 ciprocal crosses, clearly leads to the conclusion that the 
 primary cause of the sterility of crossed species is confined 
 to differences in their sexual elements. But why, in the 
 case of distinct species, the sexual elements should so gen¬ 
 erally have become more or less modified, leading to their 
 mutual infertility, we do not know; but it seems to stand 
 in some close relation to species having been exposed for 
 long periods of time to nearly uniform conditions of life. 
 
 It is not surprising that the difficulty in crossing any 
 two species, and the sterility of their hybrid offspring, 
 should in most cases correspond, even if due to distinct 
 causes: for both depend on the amount of difference be¬ 
 tween the species which are crossed. Nor 'it surprising 
 that the facility of effecting a first cross, and the fertility 
 of the hybrids thus produced, and the capacity of being 
 grafted together—though this latter capacity evidently 
 depends on widely different circumstances—should all run, 
 to a certain extent, parallel with the systematic affinity of 
 the forms subjected to experiment; for systematic affinity 
 includes resemblances of all kinds. 
 
 First crosses between forms known to be varieties, or 
 sufficiently alike to be considered as varieties, and their 
 mongrel offspring, are very generally, but not, as is so 
 often stated, invariably fertile. Nor is this almost uni¬ 
 versal and perfect fertility surprising, when it is remem¬ 
 bered how liable we are to argue in a circle with respect to 
 varieties in a state of nature; and when we remember that 
 the greater number of varieties have been produced under 
 domestication by the selection of mere external differences, 
 and that they have not been long exposed to uniform con¬ 
 ditions of life. It should also be especially kept in mind, 
 that long-continued domestication tends to eliminate ster¬ 
 ility, and is therefore little likely to induce this same 
 
SUMMARY. 
 
 311 
 
 quality. Independently of the question of fertility, 
 in all other respects there is the closest general resemblance 
 between hybrids and mongrels, in their variability, in their 
 power of absorbing each other by repeated crosses, and in 
 their inheritance of characters from both parent-forms. 
 Finally, then, although we are as ignorant of the precise 
 cause of the sterility of first crosses and of hybrids as we 
 are why animals and plants removed from their natural 
 conditions become sterile, yet the facts given in this 
 chapter do not seem to me opposed to the belief tha« 
 species aboriginally existed as varieties. 
 
312 
 
 IMPERFECTION OF TEE 
 
 
 
 CHAPTER X. 
 
 ON THE IMPERFECTION OF THE GEOLOGICAL RECORD. 
 
 On the absence of intermediate varieties at the present day—On the 
 nature of extinct intermediate varieties; on their number—On 
 the lapse of time, as inferred from the rate of denudation and or 
 deposition—On the lapse of time as estimated by years On the 
 poorness of our palaeontological collections—On the intermittence 
 of geological formations—On the denudation of granitic areas— 
 On the absence of intermediate varieties in any one formation— 
 On the sudden appearance of groups of species—On their sudden 
 appearance in the lowest known fossiliferous strata Antiquity 
 of the habitable earth. 
 
 1 ^ the sixth chapter I enumerated the chief objections 
 which might be justly urged against the views maintained 
 in this volume. Most of them have now been discussed. 
 One, namely, the distinctness of specific forms and their 
 not being blended together by innumerable transitional 
 links, is a very obvious difficulty. I assigned reasons why 
 such links do not commonly occur at the present day under 
 the circumstances apparently most favorable for their pres¬ 
 ence, namely, on an extensive and continuous area with 
 graduated physical conditions. I endeavored to show, that 
 the life of each species depends in a more important manner 
 on the presence of other already defined organic forms, than 
 on climate, and, therefore, that the really governing condi¬ 
 tions of life do not graduate away quite insensibly like 
 heat or moisture. I endeavored, also, to show that inter¬ 
 mediate varieties, from existing in lesser numbers than 
 the forms which they connect, will generally be beaten out 
 and exterminated during the course of further modifica¬ 
 tion and improvement. The main cause, however, of 
 innumerable intermediate links not now occurring every¬ 
 where throughout nature, depends on the very process of 
 natural selection, through which new varieties continually 
 take the places of and supplant their parent-forms. But 
 
GEOLOGICAL RECORD. 
 
 313 
 
 just in proportion as this process of extermination has 
 acted on an enormous scale, so must the number of inter¬ 
 mediate varieties, which have formerly existed, be truly 
 enormous. Why then is not every geological formation 
 and every stratum full of such intermediate links? Geo¬ 
 logy assuredly does not reveal any such finely-graduated 
 organic chain; and this, perhaps, is the most obvious and 
 serious objection which can be urged against the theory. 
 The explanation lies, as I believe, in the extreme imper¬ 
 fection of the geological record. 
 
 In the first place, it should always be borne in mind 
 what sort of intermediate forms must, on the theory, have 
 formerly existed. I have found it difficult, when looking 
 at any two species, to avoid picturing to myself forms 
 directly intermediate between them. But this is a wholly 
 false view; we should always look for forms intermediate 
 between each species and a common but unknown pro¬ 
 genitor; and the progenitor will generally have differed, in 
 some respects from all its modified descendants. To give 
 a simple illustration: the fantail and pouter pigeons are 
 both descended from the rock-pigeon; if we possessed all 
 the intermediate varieties which have ever existed, we 
 should have an extremely close series between both and 
 the rock-pigeon; but we should have no varieties directly 
 intermediate between the fantail and pouter; none, for 
 instance, combining a tail somewhat expanded with a crop 
 somewhat enlarged, the characteristic features of these two 
 breeds. These two breeds, moreover, have become so 
 much modified, that, if we had no historical or indirect 
 evidence regarding their origin, it would not have been 
 possible to have determined, from a mere comparison of 
 their structure with that of the rock-pigeon, 0. livia, 
 whether they had descended from this species or from 
 some other allied form, such as C. oenas. 
 
 So, with natural species, if we look to forms very dis¬ 
 tinct, for instance to the horse and tapir, we have no 
 reason to suppose that links directly intermediate between 
 them ever existed, but between each and an unknown 
 common parent. The common parent will have had in its 
 whole organization much general resemblance to the tapir 
 and to the horse; but in some points of structure may 
 have differed considerably from both, even perhaps more 
 
314 
 
 THE LAPSE OF TIME. 
 
 
 than they differ from each other. Hence,, in all such 
 cases, we should be unable to recognize the parent-form of 
 any two or more species, even if we closely compared the 
 structure of the parent with that of its modified descend¬ 
 ants, unless at the same time we had a nearly perfect chain 
 of the intermediate links. 
 
 It is just possible, by the theory, that one of two 
 living forms might have descended from the other; for 
 instance, a horse from a tapir; and in this case direct 
 intermediate links will have existed between them. But 
 such a case would imply that one form had remained 
 for a very long period unaltered, while its descend¬ 
 ants had undergone a vast amount of change; and the 
 principle of competition between organism and organism, 
 between child and parent, will render this a very rare 
 event; for in all cases the new and improved forms of life 
 tend to supplant the old and unimproved forms. 
 
 By the theory of natural selection all living species have 
 been connected with the parent-species of each genus, by 
 differences not greater than we see between the natural and 
 domestic varieties of the same species at the present day; 
 and these parent-species, now generally extinct, have in 
 their turn been similarly connected with more ancient 
 forms; and so on backward, always converging to the 
 common ancestor of each great class. So that the number 
 of intermediate and transitional links, between all living 
 and extinct species, must have been inconceivably great. 
 But assuredly, if this theory be true, such have lived upon 
 the earth. 
 
 ON THE LAPSE OP TIME, AS INFERRED FROM THE RATE 
 OF DEPOSITION AND EXTENT OF DENUDATION. 
 
 Independently of our not finding fossil remains of such 
 infinitely numerous connecting links, it may be objected 
 that time cannot have sufficed for so great an amount of 
 organic change, all changes having been effected slowly. 
 It is hardly possible for me to recall to the reader who is 
 not a practical geologist, the facts leading the mind feebly 
 to comprehend the lapse of time. He who can read Sir 
 Charles Lyell's grand work on the Principles of Geology, 
 which the future historian will recognize as having pro* 
 
TEE LAPSE OF TIME. 3 ^ 
 
 duced a 1 evolution in natural science, and yet does not 
 admit now \ast have been the past periods of time, may at 
 once close this volume. Not that it suffices to study the 
 .riinciples of Geology, or to read special treatises by differ¬ 
 ent observeis on separate formations, and to mark how 
 eacli author attempts to give an inadequate idea of the 
 duiation of. each formation, or even of each stratum. We 
 can best gain some idea of past time by knowing the agen¬ 
 cies at work; and learning how deeply the surface of & the 
 land has been denuded, and how much sediment has been 
 deposited. As Lyell has well remarked, the extent and 
 thickness of our sedimentary formations are the result and 
 the measure of the denudation which the earth/s crust has 
 elsewhere undergone. Therefore a man should examine 
 for himself the great piles of superimposed strata, and 
 watch the rivulets bringing down mud, and the waves 
 wearing away the sea-cliffs, in order to comprehend some¬ 
 thing about the duration of past time, the monuments of 
 which we see all around us. 
 
 It is good to wander along the coast, when formed of 
 moderately hard rocks, and mark the process of degrada¬ 
 tion. .The tides in most cases reach the cliffs only for a 
 short time twice a day, and the waves eat into them only 
 when they are charged with sand or pebbles; for there is 
 good evidence that pure water effects nothing in wearing 
 away rock. At last the base of the cliff is undermined, 
 huge fragments fall down, and these, remaining fixed, have 
 to be worn away atom by atom, until after being reduced 
 in size they can be rolled about by the waves, and then 
 they are more quickly ground into pebbles, sand or mud. 
 But . how often do we see along the bases of re¬ 
 treating. cliffs rounded boulders, all thickly clothed 
 by marine productions, showing how little they are 
 abraded, and how seldom they are rolled about! More¬ 
 over, if. we follow for a few miles any line of 
 rocky cliff, which is undergoing degradation, w r e find that 
 it is only here and there, along a short length or round a 
 promontory, that the cliffs are at the present time suffering. 
 
 I he appearance of the surface and the vegetation show that 
 elsewhere years have elapsed since the waters washed their 
 base. 
 
 We have, however, x’ecently learned from the obserya- 
 
TI1E LAPSE OF TIME. 
 
 316 
 
 tions of Ramsay, in the van of many excellent observers— 
 of Jukes, Geikie, Croll and others, that subaerial degrada¬ 
 tion is a much more important agency than coast-action 
 or the power of the waves. The whole surface of the land 
 is exposed to the chemical action of the air and of the ram- 
 water, with its dissolved carbonic acid, and in colder coun¬ 
 tries to frost; the disintegrated matter is carried down even 
 gentle slopes during heavy rain, and to a greater extent 
 than might be supposed, especially m and districts, by the 
 wind: it is then transported by the streams and rivers, 
 which, when rapid deepen their channels, and triturate the 
 fragments. On a rainy day, even in a gently undulating 
 country, we see the effects of subaenal degradation m the 
 muddy rills which flow down every slope. Messrs. Ramsay 
 and Whitaker have shown, and the observation is a most 
 striking one, that the great lines of escarpment m the 
 Wealden district and those ranging across England, which 
 formerly were looked at as ancient sea-coasts, can not have 
 been thus formed, for each line is composed of one and the 
 same formation, while our sea-cliffs are everywhere formed 
 by the intersection of various formations. This being the 
 case, we are compelled to admit that the escarpments owe 
 their origin in chief part to the rocks of which they are 
 composed, having resisted subaerial denudation better 
 than the surrounding surface; this surface consequently 
 has been gradually lowered, with the lines of harder rock 
 left projecting. Nothing impresses the mind with the vast 
 duration of time, according to our ideas of time, more 
 forcibly than the conviction thus gained that subaenal 
 agencies, which apparently have so little power, and which 
 seem to work so slowly, have produced great results. 
 
 When thus impressed with the. slow -rate at which the 
 land is worn away through subaerial and littoral action, it 
 is good, in order to appreciate the past duration of time, 
 to consider, on the one hand, the masses of rock which 
 have been removed over many extensive areas, and on 
 the other hand the thickness of our sedimentary forma¬ 
 tions. I remember having been much struck when view¬ 
 ing volcanic islands, which have , been worn by the waves 
 and pared all round into perpendicular cliffs of one 01 wo 
 thousand feet in height; for the gentle slope of the lava- 
 streams, due to their formerly liquid state, showed at a 
 
THE LAPSE OF TIME. 
 
 317 
 
 glance how far the hard, rocky beds had once extended 
 into the open ocean. The same story is told still more 
 plainly by faults—those great cracks along which the strata 
 have been upheaved on one side, or thrown down on the 
 other, to the height or depth of thousands of feet; for since 
 the crust cracked, and it makes no great difference whether 
 the upheaval was sudden, or, as most geologists now believe, 
 was slow and effected by many starts, the surface of the 
 land has been so completely planed down that no trace of 
 these vast dislocations is externally visible. The Craven 
 fault, for instance, extends for upward of thirty miles, and 
 along this line the vertical displacement of the strata varies 
 from 600 to 3,000 feet. Professor Ramsay has published 
 an account of a downthrow in Anglesea of 2,300 feet; and 
 he informs me that he fully believes that there is one in 
 Merionethshire of 12,000 feet; yet in these cases there is 
 nothing on the surface of the land to show such prodigious 
 movements; the pile of rocks on either side of the crack 
 having been smoothly swept away. 
 
 On the other hand, in all parts of the world the piles of 
 sedimentary strata are of wonderful thickness. In the 
 Cordillera, I estimated one mass of conglomerate at ten 
 thousand feet; and although conglomerates have probably 
 been accumulated at a quicker rate than finer sediments, 
 yet from being formed of worn and rounded pebbles, each 
 of which bears the stamp of time, they are good to show 
 how slowly the mass must have been heaped together. 
 Professor Ramsay has given me the maximum thickness, 
 from actual measurement in most cases, of the successive 
 formations in different parts of Great Britain; and this is 
 
 the result: 
 
 Feet. 
 
 Palaeozoic strata (not including igneous beds). 57,154 
 
 Secondary strata. 13,190 
 
 Tertiary strata. 2,240 
 
 —making altogether 72,584 feet; that is, very nearly thir¬ 
 teen and three-quarters British miles. Some of the for¬ 
 mations, which are represented in England by thin beds, 
 are thousands of feet in thickness on the Continent. More¬ 
 over, between each successive formation we have, in the 
 opinion of most geologists, blank periods of enormous 
 length. So that the lofty pile of sedimentary rocks in 
 
318 
 
 TEE LAPSE OF TIME. 
 
 Britain gives but an inadequate idea of the time which has 
 elapsed during their accumulation. The consideration of 
 these various facts impresses the mind almost in the same 
 manner as does the vain endeavor to grapple with the idea 
 of eternity. 
 
 Nevertheless this impression is partly false. Mr. Croll, 
 in an interesting paper, remarks that we do not err “in 
 forming too great a conception of the length of “ geological 
 periods/' but in estimating them by years. When geolo¬ 
 gists look at large and complicated phenomena, and then 
 at the figures representing several million years, the two 
 produce a totally different effect on the mind, and the 
 figures are at once pronounced too small. In regard to 
 subaerial denudation, Mr. Croll shows, by calculating the 
 known amount of sediment annually brought down by 
 certain rivers, relatively to their areas of drainage, that 
 1,000 feet of solid rock, as it became gradually disintegrated, 
 would thus be removed from the mean level of the whole 
 area in the course of six million years. This seems an 
 astonishing result, and some considerations lead to the 
 suspicion that it may be too large, but if halved or quartered 
 it is still very surprising. Few of us, however, know what 
 a million really means: Mr. Croll gives the following illus¬ 
 tration: Take a narrow strip of paper, eighty-three feet 
 four inches in length, and stretch it along the wall of a 
 large hall; then mark off at one end the tenth of an inch. 
 This tenth of an inch will represent one hundred years, 
 and the entire strip a million years. But let it be borne 
 in mind, in relation to the subject of this work, what 
 a hundred years implies, represented as it is by a 
 measure utterly insignificant in a hall of the above 
 dimensions. Several eminent breeders, during a single 
 lifetime, have so largely modified some of the higher 
 animals, which propagate their kind much more slowly 
 than most of the lower animals, that they have formed 
 what well deserves to be called a new sub-breed. Few men 
 have attended with due care to any one strain for more 
 than half a century, so that a hundred years represents the 
 work of two breeders in succession. It is not to be sup¬ 
 posed that species in a state of nature ever change so 
 quickly as domestic animals under the guidance of method¬ 
 ical selection. The comparison would be in every way 
 
THE LAPSE OF TIME . 
 
 319 
 
 fairer with the effects which follow from unconscious 
 selection, that is, the preservation of the most useful or 
 beautiful animals, with no intention of modifying the 
 breed; but by this process of unconscious selection, various 
 breeds have been sensibly changed in the course of two or 
 three centuries. 
 
 Species, however, probably change much more slowly, 
 and within the same country only a few change at the same 
 time. This slowness follows from all the inhabitants of 
 the same country being already so well adapted to each 
 other, that new places in the polity of nature do not occur 
 until after long intervals, due to the occurrence of physical 
 changes of some kind, or through the immigration of new 
 forms. Moreover, variations or individual differences of 
 the right nature, by which some of the inhabitants might 
 be better fitted to their new places under the altered 
 circumstance, would not always occur at once. Un¬ 
 fortunately we have no means of determining, according 
 to the standard of years, how long a period it takes to 
 modify a species; but to the subject of time we must 
 return. 
 
 ON THE POORNESS OP PALAEONTOLOGICAL COLLECTIONS. 
 
 Now let us turn to our richest geological museums, and 
 what a paltry display we behold! That our collections are 
 imperfect is admitted by every one. The remark of that 
 admirable palaeontologist, Edward Forbes, should never be 
 forgotten, namely, that very many fossil species are known 
 and named from single and often broken specimens, or 
 from a few specimens collected on some one spot. Only 
 a small portion of the surface of the earth has been 
 geologically explored, and no part with sufficient care, as 
 the important discoveries made every year in Europe 
 prove. No organism wholly soft can be preserved. Shells 
 and bones decay and disappear when left on the bottom of 
 the sea, where sediment is not accumulating. We prob¬ 
 ably take a quite erroneous view, when we assume that 
 sediment is being deposited over nearly the whole bed of 
 the sea, at a rate sufficiently quick to imbed and preserve 
 fossil remains. Throughout an enormously large propor¬ 
 tion of the ocean, the bright blue tint of the water be- 
 
320 
 
 THE POORNESS OF 
 
 speaks its purity. The many cases on record of a forma¬ 
 tion conformably covered, after an immense interval of 
 time, by another and later formation, without the under¬ 
 lying bed having su ffered in the interval any wear and tear, 
 seem explicable only on the view of the bottom of the sea 
 not rarely lying for ages in an unaltered condition. 
 The /emaitis which do become imbedded, if in sand 
 or gravel, will, when the beds are upraised, generally 
 be dissolved by the percolation of rain water charged 
 with carbolic acid. Some of the many kinds of animals 
 which live on the beach between high and low water 
 mark seem to be rarely preserved. For instance, the 
 several species of the Clithamalinse (a sub-family of sessile 
 cirripedes) coat the rocks all over the world in infinite 
 numbers they are all strictly littoral, with the exception of 
 a single Mediterranean species, which inhabits deep water, 
 and this has been found fossil in Sicily, whereas not one 
 other species has hitherto been found in any tertiary for¬ 
 mation: yet it is known that the genus Chthamalus existed 
 during the Chalk period. Lastly, many great deposits, 
 requiring a vast length of time for their accumulation, are 
 entirely destitute of organic remains, without our being 
 able to assign any reason: one of the most striking in¬ 
 stances is that of the Flysch formation, which consists of 
 shale and sandstone, several thousand, occasionally even 
 six thousand feet in thickness, and extending for at least 
 300 miles from Vienna to Switzerland; and although this 
 great mass has been most carefully searched, no fossils, 
 except a few vegetable remains, have been found. 
 
 With respect to the terrestrial productions which lived 
 during the Secondary and Palaeozoic periods, it is super¬ 
 fluous to state that our evidence is fragmentary in an 
 extreme degree. For instance, untill recently not a land- 
 shell was known belonging to either of these vast periods, 
 with the exception of one species discovered by Sir C. Lyell 
 and Dr. Dawson in the carboniferous strata of North 
 America; but now land-shells have been found in the lias. 
 In regard to mammiferous remains, a glance at the histor¬ 
 ical table published in Lyelbs Manual will bring home the 
 truth, how accidental and rare is their preservation, far 
 better than pages of detail. Nor is their rarity surprising, 
 when we remember how large a proportion of the bones of 
 
PALEONTOLOGICAL COLLECTIONS. 
 
 321 
 
 tertiary mammals have been discovered either in caves or in 
 lacustrine deposits; and that not a cave or true lacustrine 
 bed is known belonging to the age of our secondary or 
 palaeozoic formations. 
 
 But the imperfection in the geological record largely re¬ 
 sults from another and more important cause than an} r of 
 the foregoing; namely, from the several formations being 
 separated from each other bv wide intervals of time. This 
 doctrine has been emphatically admitted by many geologists 
 and palaeontologists, who, like E. Forbes, entirely disbe¬ 
 lieve in the change of species. When we see the forma¬ 
 tions tabulated in written works, or when we follow them 
 in nature, it is difficult to avoid believing that thev are 
 closely consecutive. But we know, for instance, from Sir 
 B. Murchison's great work on Russia, what wide gaps there 
 are in that country between the superimposed formations; 
 so it is in North America, and in many other parts of the 
 world. The most skillful geologist, if his attention had 
 been confined exclusively to these large territories, would 
 never have suspected that during the periods which were 
 blank and barren in his own country, great piles of sedi¬ 
 ment, charged with new and peculiar forms of life, had 
 elsewhere been accumulated. And if, in every separate 
 territory, hardly any idea can be formed of the length of 
 time which has elapsed between the consecutive forma¬ 
 tions, we may infer that this could nowhere be ascertained. 
 The frequent and great changes in the mineralogical com¬ 
 position of consecutive formations, generally implying 
 great changes in the geography of the surrounding lands, 
 whence the sediment was derived, accord with the belief of 
 vast intervals of time having elapsed between each for¬ 
 mation. 
 
 We can, I think, see why the geological formations 
 of each region are almost invariable intermittent; that is, 
 have not followed each other in close sequence. Scarcely 
 any fact struck me more when examining many hundred 
 miles of the South American coasts, which have been up¬ 
 raised several hundred feet within the recent period, than 
 the absence of any recent deposits sufficiently extensive to 
 last for even a short geological period. Along the whole 
 west coast, which is inhabited by a peculiar marine fauna, 
 tertiary beds are so poorly developed that no record of sev- 
 
THE POORNESS OF 
 
 322 
 
 eral successive and peculiar marine faunas will probably ba 
 preserved to a distant age. A little reflection, will explain 
 why, along the rising coast of the western side of South 
 America, no extensive formations with recent or tertiary 
 remains can anywhere be found, though the supply of sedi¬ 
 ment must for ages have been great, from the enormous 
 degradation of the coast rocks and from the muddy streams 
 entering the sea. The explanation, no.doubt, is that the 
 littoral and sublittoral deposits are continually worn away, 
 as soon as they are brought up by. the slow and gradual 
 rising of the land within the grinding action of the coast 
 
 waves. ( , , 
 
 We may, I think, conclude that sediment must be ac¬ 
 cumulated in extremely thick, solid, or extensive masses, 
 in order to withstand the incessant action of the.waves, 
 when first upraised and during successive oscillations of 
 level, as well as the subsequent subaerial degradation. 
 Such thick and extensive accumulations of sediment may 
 be formed in two wavs; either in profound depths of the 
 sea, in which case the bottom will, not be inhabited by so 
 many and such varied forms of life, as the more shallow 
 seas; and the mass when upraised will, give an. imperfect 
 record of the organisms which existed in the neighborhood 
 during the period of its accumulation. Or sediment may 
 be deposited to any thickness and. extent over a shallow 
 bottom, if it continue slowly to subside. In this latter case, 
 as long as the rate of subsidence and the supply of sedi¬ 
 ment nearly balance each other, the sea will remain shallow 
 and favorable for many and varied forms, and thus a rich 
 fossilifercus formation, thick enough, when upraised, to 
 resist a large amount of denudation, may be formed. . 
 
 I am convinced that nearly all our ancient formations, 
 which are throughout the greater part of their thickness 
 rich in fossils, have thus been formed during subsidence. 
 Since publishing my views on this subject in 1845, I have 
 watched the progress of geology, and have been surprised 
 to note how author after author, in treating of this or that 
 great formation, has come to the conclusion that it was 
 accumulated during subsidence. I may add, that the only 
 ancient tertiary formation on .the west coast of South 
 America, which has been bulky enough to resist such de¬ 
 gradation as it has as yet suffered, but which will hardly 
 
PALEONTOLOGICAL COLLECTIONS. 323 
 
 last to a distant geological age, was deposited during a 
 downward oscillation of level, and thus gained considerable 
 thickness. 
 
 All geological facts tell us plainly that each area has 
 undergone numerous slow oscillations of level, and appar- 
 ently these oscillations have affected wide spaces. Conse¬ 
 quently, formations rich in fossils and sufficiently thick 
 and extensive to resist subsequent degradation, will have 
 been formed over wide spaces during periods of sub¬ 
 sidence, but only where the supply of sediment was 
 sufficient to keep the sea shallow and to embed and 
 preserve the remains before they had time to decay. On 
 the other hand, as long as the bed of the sea remains sta¬ 
 tionary, thick deposits cannot have been accumulated in 
 the shallow parts,, which are the most favorable to life. 
 Still less can this have happened during the alternate 
 periods of-elevation; or, to speak more accurately, the beds 
 which were then accumulated will generally have been de¬ 
 stroyed by being upraised and brought within the limits of 
 the coast-action. 
 
 These remarks apply chiefly to littoral and sublittoral 
 depositsc In the case of an extensive and shallow sea, such 
 as that within a large part of the Malay Archipelago, 
 where the depth varies from thirty or forty to sixty fath¬ 
 oms, a widely extended formation might be formed during 
 a period of elevation, and yet not suffer excessively from 
 denudation during its slow upheaval; but the thickness 
 of the formation could not be great, for owing to the ele- 
 vatory movement it would be less than the depth in which 
 it was formed; nor would the deposit be much consoli¬ 
 dated, nor be capped by overlying formations, so that it 
 would run a good chance of being worn away by atmos¬ 
 pheric degradation and by the action of the sea during 
 subsequent oscillations of level. It has, however, been 
 suggested by Mr. Hopkins, that if one part of the area, 
 after rising and before being denuded, subsided, the 
 deposit formed during the rising movement, though not 
 thick, might afterward become protected by fresh accumu¬ 
 lations, and thus be preserved for a long period. 
 
 Mr„ Hopkins also expresses his belief that sedimentary 
 beds of considerable horizontal extent have rarely been 
 completely destroyed. But all geologists, excepting the 
 
TUE POORNESS OF 
 
 t 
 
 324 
 
 few who believe that our present metamorphic schists and 
 plutonic rocks once formed the primordial nucleus of the 
 globe, will admit that these latter rocks have been stripped 
 of their covering to an enormous extent. For it is 
 scarcelv possible that such rocks could have been solidified 
 and crystallized while uncovered; but if the metamorphic 
 faction, occurred at profound depths of the ocean, the 
 former protecting mantle of rock may not have been very 
 thick. Admitting then that gneiss, mica-schist, granite, 
 diorite, etc., were once necessarially covered up, how can 
 we account for the naked and extensive areas of such rocks 
 in many parts of the world, except on the belief that they 
 have subsequently been completely denuded of all over¬ 
 ling strata? That such extensive areas do exist cannot 
 be doubted'; the granitic region of Parime is described 
 by Humboldt as being at least nineteen times as large 
 as Switzerland, South of the Amazon, Bone colors 
 an area composed of rocks of this nature as equal to that 
 of Spain, France* Italy, part of Germany, and the British 
 Islands, all conjoined. This region has not been carefully 
 explored, but from the concurrent testimony of travelers, 
 the granitic area is very large: thus Yon Eschwege gives a 
 detailed section of these rocks, > stretching from Rio de 
 Janeiro for 260 geographical miles inland in a straight 
 line; and I traveled for 150 miles in another direction, and 
 saw" nothing but granitic rocks. Numerous specimens, 
 collected along the whole coast, from near Rio Janeiro to 
 the mouth of the Plata, a distance of 1,100 geographical 
 miles, were examined by me, and they all belonged to 
 this class. Inland, along the whole northern bank of 
 the Plata, I saw, besides modern tertiary beds, only one 
 small patch of slightly metamorphosed rock, which alone 
 could have formed a part of the original capping of the 
 granitic series. Turning to a well-known region, namely, 
 to the United States and Canada, as shown in Professor H. 
 D. Rogers’ beautiful map, I have estimated the areas by 
 cutting out and weighing the paper, and I find that the 
 metamorphic (excluding the “ semi-metamorphic ”) and 
 granite rocks exceed, in the proportion of 19 to 12.5, 
 the whole of the newer Paleozoic formations. In many 
 regions the metamorphic and granite rocks would be found 
 much more widely extended than they appear to be, if all 
 
PALEONTOLOGICAL COLLECTIONS. 325 
 
 the sedimentary beds were removed which rest uncon- 
 formably on them, and which could not have formed part 
 of the original mantle under which they were crystallized. 
 Hence, it is probable that in some parts of the world whole 
 
 formations have been completely denuded, with not a wreck 
 leit behind. 
 
 One remark is here worth a passing notice. During 
 periods of elevation the area of the land and of the adioin- 
 lng shoal parts of the sea will be increased and new sta¬ 
 tions will often be formed—all circumstances favorable, as 
 P**®^*^ ,y explained, for the formation of new varieties 
 and species; but during such periods there will generally 
 be a blank m the geological record. On the other hand, 
 during subsidence, the inhabited area and number of 
 inhabitants will decrease (excepting on the shores of a 
 continent when first broken up into an archipelago), and 
 consequently during subsidence, though there will be 
 much extinction, few new varieties or species will be 
 formed; and it is during these very periods of subsidence 
 that the deposits which are richest in fossils have been 
 accumulated. 
 
 OH" THE ABSENCE OF NUMEROUS INTERMEDIATE VARIE¬ 
 TIES IN ANY SINGLE FORMATION. 
 
 From these several considerations it cannot be doubted 
 that the geological record, viewed as a whole, is extremely 
 imperfect; but if we confine our attention to any one 
 formation, it becomes much more difficult to understand 
 why we do not therein find closely graduated varieties 
 between the allied species which lived at its commence¬ 
 ment and. at its close. Several cases are on record of the 
 same species presenting varieties in the upper and lower 
 parts of the same formation. Thus Trautschold gives a 
 number of instances with Ammonites, and Hilgendorf has 
 described a most curious case of ten graduated forms of 
 rlanorbis multiformis in the successive beds of a fresh¬ 
 water formation in Switzerland. Although each formation 
 has indisputably required a vast number of years for its 
 deposition, several reasons can be given why each should 
 not commonly include a graduated series of links between 
 the species which lived at its commencement and close, but 
 
326 ABSENCE OF INTERMEDIATE VARIETIES 
 
 I cannot assign due proportional weight to the following 
 considerations. 
 
 Although each formation may mark a very long lapse of 
 years, each probably is short compared with the period 
 requisite to change one species into another. I am aware 
 that two palaeontologists, whose opinions are worthy of 
 much deference, namely Bronn and Woodward, have con¬ 
 cluded that the average duration of each formation is twice 
 or thrice as long as the average duration of specific forms. 
 But insuperable difficulties, as it seems to me, prevent us 
 from coming to any just conclusion on this head. When 
 we see a species first appearing in the middle of any forma¬ 
 tion, it would be rash in the extreme to infer that it had 
 not elsewhere previously existed. So again, when we find 
 a species disappearing before the last layers have been de¬ 
 posited, it would be equally rash to suppose that it then 
 became extinct. We forget how small the area of Europe 
 is compared with the rest of the world; nor have the sev¬ 
 eral stages of the same formation throughout Europe been 
 correlated with perfect accuracy. 
 
 We may safely infer that with marine animals of all 
 kinds there has been a large amount of migration due to 
 climatal and other changes; and when we see a species first 
 appearing in any formation, the probability is that it only 
 then first immigrated into that area. It is well-known, 
 for instance, that several species appear somewhat earlier 
 in the palaeozoic beds of North America than in those of 
 Europe; time having apparently been required for their 
 migration from the American to the European seas. In 
 examining the latest deposits, in various quarters of the 
 world, it has everywhere been noted, that some few still 
 existing species are common in the deposit, but have 
 become extinct in the immediately surrounding sea; or, 
 conversely, that some are now abundant in the neighbor¬ 
 ing sea, but are rare or absent in this particular deposit. 
 It is an excellent lesson to reflect on the ascertained 
 amount of migration of the inhabitants of Europe during 
 the glacial epoch, which forms only a part of one whole 
 geological period; and likewise to reflect on the changes 
 of level, on the extreme change of climate, and on the 
 great lapse of time, all included within this same glacial 
 period. Yet it may be doubted whether, in any quarter of 
 
IN ANT SINGLE FORMATION. 33 ? 
 
 the world, sedimentary deposits, including fossil remains ,, 
 have gone on accumulating within the same area during 
 the whole of this period. It is not, for instance, probable 
 that, sediment was deposited during the whole of the 
 glacial period near the mouth of the Mississippi, within 
 that limit of depth at which marine animals can best 
 flouiish. for we know that great geographical changes 
 occurred in other parts of America during this space of 
 time. When such beds as were deposited in shallow water 
 near the mouth of the Mississippi during some part of the 
 glacial period shall have been upraised, organic remains 
 will probably first appear and disappear at different levels, 
 owing to the migrations of species and to geographical 
 changes. And in the distant future, a geologist, examin¬ 
 ing these beds, would be tempted to conclude that the 
 average duration of life of the embedded fossils had been 
 less than that of the glacial period, instead of having been 
 really far greater, that is, extending from before the glacial 
 epoch to the present day. 
 
 . ** order to get a perfect gradation between two forms 
 in tne upper and lower parts of the same formation, the 
 deposit must have gone on continuously accumulating 
 dining a.long period, sufficient for the slow process of 
 modification; hence, the deposit must be a very thick 
 one; and the species undergoing change must have lived 
 m the same district throughout the whole time,, But 
 we have seen that a thick formation, fossiliferous 
 throughout its entire thickness, can accumulate only 
 during, a period of subsidence; and to keep the depth 
 approximately the same, which is necessary that the 
 same marine species may live on the same space, the sun- 
 ply of sediment must nearly counterbalance the amount 
 of subsidence. But this same movement of subsi¬ 
 dence, will tend to submerge the area whence the sediment 
 is derived, and thus diminish the supply, while the down¬ 
 ward movement continues 0 In fact, this nearly exact bal¬ 
 ancing between the supply of sediment and the amount of 
 subsidence is probably a rare contingency; for it has been 
 observed by more than one palasontologist that very thick 
 deposits are usually barren of organic remains, except near 
 their upper or lower limits. 
 
 It would seem that each separate formation, like the 
 
328 ABSENCE OF INTERMEDIATE VARIETIES 
 
 whole pile of formation in any country, has generally been 
 intermittent in its accumulation. When we see, as is so 
 often the case, a formations composed of beds of widely 
 different mineralogical composition, we may reasonably 
 suspect that the process of deposition has been more or less 
 interrupted. Nor will the closest inspection of a forma¬ 
 tion give us any idea of the length of time which its depo¬ 
 sition may have consumed^ Many instances could be 
 given of beds, only a few feet in thickness, representing 
 formations which are elsewhere thousands of feet in thick¬ 
 ness, and which must have required an enormous period 
 for their accumulation; yet no one ignorant of this fact 
 would have even suspected the vast lapse of time repre¬ 
 sented by the thinner formation 0 Many cases could be 
 given of the lower beds of a formation having been up¬ 
 raised, denuded, submerged, and then recovered by the 
 upper beds of the same formation—facts, showing what 
 wide, yet easily overlooked, intervals have occurred in its 
 accumulation. In other cases we have the plainest evi¬ 
 dence in great fossilized trees, still standing upright as 
 they grew, of many long intervals of time and changes of 
 level during the process of deposition, which would not 
 have been suspected, had not the trees been preserved: thus 
 Sir Co Lyell and Dr„ Dawson found carboniferous beds 
 1,400 feet thick in Nova Scotia, with ancient root-bearing 
 strata, one above the other, at no less than sixty-eiglit dif¬ 
 ferent levels. Hence, when the same species occurs at the 
 bottom, middle, and top of a formation, the probability is 
 that it has not lived on the same spot during the whole 
 period of deposition, but has disappeared and reappeared, 
 perhaps many times, during the same geological period. 
 Consequently if it were to undergo a considerable amount 
 of modification during the deposition of any one geological 
 formation, a section would not include all the fine inter¬ 
 mediate gradations which must on our theory have existed, 
 but abrupt, though perhaj^s slight, changes of form. 
 
 It is all-important to remember that naturalists have no 
 go'den rule by which to distinguish species and varieties; 
 they grant some little variability to each species, but when 
 they meet with a somewhat greater amount of difference 
 between any two forms, they rank botli as species, unless 
 they are enabled to connect them together by the closest 
 
IN ANY SINGLE FORMATION. 330 
 
 intermediate gradations; and this, from the reasons just 
 assigned, we can seldom hope to effect in any one geolog- 
 
 2K “YT i S !?PP 0 ! m g B and c to be two species, and^a 
 t ilia. A, to be found m an older and underlying bed* even 
 if A were strictly intermediate between B and C, it would 
 simply be ranked as a third and distinct species, unless at 
 the same time it could be closely connected by intermedi¬ 
 ate varieties with either one or both forms. Nor should it 
 be forgotten, as before explained, that A might be the 
 
 he P °| B . a ? d C > and ? efc would not necessarily 
 
 be stnctly intermediate between them in all respects. So 
 
 that we might obtain the parent-species and its several 
 modified descendants from the lower and upper beds of the 
 same formation, and unless we obtained numerous transi¬ 
 tional gradations, we should not recognize their blood-rela- 
 
 tionship, and should consequently rank them as distinct 
 species. 
 
 It is notorious on what excessively slight differences 
 many paleontologists have founded their species; and they 
 do tins the more readily if the specimens come from differ¬ 
 ent sub-stages of the same formation. Some experienced 
 conchologists are now sinking many of the very fine species of 
 7? y rh }g l 'y an d others into the rank of varieties; and on 
 this view we do find the kind of evidence of change which 
 on the theory we ought to find. Look again at the later 
 tertiary deposits, which include many shells believed by 
 the majority of naturalists to be identical with existing 
 species; but some excellent naturalists, as Agassiz and 
 Pictet, maintain that all these tertiary species are specific¬ 
 ally distinct, though the distinction is admitted to be very 
 slight; so that here, unless we believe that these eminent 
 naturahsts have been misled by their imaginations, and 
 that these late tertiary species really present no difference 
 whatever from their living, representatives, or unless we 
 
 111 °PP?. slfclon to the judgment of most naturalists, 
 that these tertiary species are all truly distinct from the 
 recent, we have evidence of the frequent occurrence of slight 
 modifications of the kind required. If we look to rather 
 wider intervals of time, namely, to distinct but consecu- 
 
 S a a #a S f ? reat forma tion, we find that the 
 
 embeddeii fossils though universally ranked as specific¬ 
 ally different, yet are far more closely related to each other 
 
330 ABSENCE OF INTERMEDIATE VARIETIES 
 
 than are the species found in more widely separated foima- 
 tions; so that here again we have undoubted evidence of 
 change in the direction required by the theoiy; but to this 
 latter subject I shall return in the following chapter. 
 
 With animals and plants that propagate rapidly and do 
 not wander much, there is reason to suspect, as we 
 have formerly seen, that their varieties are geneially at 
 first local; and that such local varieties do not spread 
 widely and supplant their parent-form until they have 
 been modified and perfected in some considerable degree. 
 According to this view, the chance of discovering in a 
 formation in any one country all the early stages of tiansn 
 tion between any two forms, is small, for the successive 
 changes are supposed to have been local or confined to 
 some one spot. Most marine animals have a wide lange, 
 and we have seen that with plants it is those which have 
 the widest range, that oftenest present varieties; so that, 
 with shells and other marine animals, it is probable that 
 those which had the widest range, far exceeding the limits 
 of the known geological formations in Europe, have often¬ 
 est given rise, first to local varieties and ultimately to new 
 species; and this again would greatly lessen the chance of 
 our being able to trace the stages of transition in any one 
 geological formation. 
 
 It is a more important consideration, leading to the same 
 result, as lately insisted on by Dr. Falconer, namely, that 
 the period during which each species underwent modifica¬ 
 tion, though long as measured by years, was probably short 
 in comparison with that during which it remained without 
 undergoing any change. 
 
 It should not be forgotten, that at the present day, with 
 perfect specimens for examination, two forms can 
 seldom be connected by intermediate varieties, and thus 
 proved to be the same species, until many specimens are 
 collected from many places; and with fossil species this 
 can rarelv be done. We shall, perhaps, best perceive the 
 improbability of our being enabled to connect species by 
 numerous, fine, intermediate, fossil links, by asking 0111 - 
 selves whether, for instance, geologists at some futuie 
 period will be able to prove that our different breeds of 
 cattle, sheep, horses, and dogs are descended from a single 
 stock or from several aboriginal stocks; or again, whether 
 
IN ANT SINGLE FORMA I ION. 33l 
 
 certain sea-shells inhabiting the shores of North America, 
 which are ranked by some conchologists as distinct species 
 from their European representatives, and by other con¬ 
 chologists as only varieties, are really varieties, or are, as 
 it is called, specifically distinct. This could be effected 
 by the future geologist only by his discovering in a fossil 
 state numerous intermediate gradations; and such success 
 is improbable in the highest degree. 
 
 It has been asserted over and over again, by writers who 
 believe in the immutability of species, that geology yields 
 no linking forms. This assertion, as we shall see in the 
 next chapter, is certainly erroneous. As Sir J. Lubbock 
 has remarked, “ Every species is a link between other allied 
 forms.” If we take a genus having a score of species, 
 recent and extinct, and destroy four-fifths of them, no one 
 doubts that the remainder will stand much more distinct 
 from each other. If the extreme forms in the genus 
 happen to have been thus destroyed, the genus itself will 
 stand more distinct from other allied genera. What geo¬ 
 logical research has not revealed, is the former existence of 
 ififinitely numerous gradations, as fine as existing varieties, 
 connecting together nearly all existing and extinct species. 
 But this ought not to be expected; yet this has been 
 repeatedly advanced as a most serious objection against 
 my views. 
 
 It may be worth while to sum up the foregoing remarks 
 on the causes of the imperfection of the geological record 
 under an imaginary illustration. The Malay Archipelago 
 is about the size of Europe from the North Cape to the 
 Mediterranean, and from Britain to Bussia ; and therefore 
 equals all the geological formations which have been 
 examined with any accuracy, excepting those of the United 
 States of America. I fully agree with Mr. God win-Austen, 
 that the present condition of the Malay Archipelago, with 
 its numerous large islands separated by wide and shallow 
 seas, probably represents the former state of Europe, 
 while most of our formations were accumulating. The 
 ; Malay Archipelago is one of the richest regions in organic 
 beings; yet. if all the species were to be collected which 
 have ever lived there, how imperfectly would they repre¬ 
 sent the natural history of the world ! 
 
 But we have every reason to believe that the terrestrial 
 
3 32 ABSENCE OF INTERMEDIATE VARIETIES 
 
 productions of the archipelago would be preserved in an 
 extremely imperfect manner in the formations which we 
 suppose to be there accumulating. Not many of the 
 strictly littoral animals, or of those which lived on naked 
 submarine rocks, would be embedded; and those embedded 
 in gravel or sand would not endure to a distant epoch. 
 Wherever sediment did not accumulate on the bed of the 
 sea, or where it did not accumulate at a sufficient rate to 
 protect organic bodies from decay, no remains could be 
 preserved. 
 
 Formations rich in fossils of many kinds, and of thick¬ 
 ness sufficient to last to an age as distant in futurity as the 
 secondary formations lie in the past, would generally be 
 formed in the archipelago only during periods of subsi¬ 
 dence. These periods of subsidence would be separated 
 from each other by immense intervals of time, during 
 which the area would be either stationary or rising; while 
 rising, the fossiliferous formations on the steeper shores 
 would be destroyed, almost as soon as accumulated, by the 
 incessant coast-action, as we now see on the shores of South 
 America. Even throughout the extensive and shallow 
 seas within the archipelago, sedimentary beds could hardly 
 be accumulated of great thickness during the periods of 
 elevation, or become capped and protected by subsequent 
 deposits, so as to have a good chance of enduring to a very 
 distant future. During the periods of subsidence, there 
 would probably be much extinction of life; during the 
 periods of elevation, there would be much variation, but 
 the geological record would then be less perfect. 
 
 It may be doubted whether the duration of any one great 
 period of subsidence over the whole or part of the archi¬ 
 pelago, together with a contemporaneous accumulation of 
 sediment, would exceed the average duration of the same 
 specific forms; and these contingencies are indispensable 
 for the preservation of all the transitional gradations be¬ 
 tween any two or more species. If such gradations were 
 not all fully preserved, transitional varieties would merely 
 appear as so many new, though closely allied species. It 
 is also probable that each great period of subsidence would 
 be interrupted by oscillations of level, and that slight cli- 
 matical changes would intervene during such lengthy 
 periods; and in these cases the inhabitants of the arch;- 
 
IN ANY SINGLE FORMATION . 
 
 833 
 
 pelago would migrate, and no closely consecutive record of 
 their modifications could be preserved in any one forma¬ 
 tion. 
 
 Very many of the marine inhabitants of the archipelago 
 now range thousands of miles beyond its confines; and 
 analogy plainly leads to the belief that it would be chiefly 
 these far-ranging species, though only some of them, 
 which would oftenest produce new varieties; and the vari¬ 
 eties would at first be local or confined to one place, but if 
 possessed of airy decided advantage, or when further modi¬ 
 fied. and improved, they would slowly spread and supplant 
 their parent-forms. When such varieties returned to their 
 ancient homes, as they would differ from their former state 
 in a nearly uniform, though perhaps extremely slight degree, 
 and as they would be found imbedded in slightly differ¬ 
 ent sub-stages of the same formation, they would, accord¬ 
 ing to the principles followed by many paleontologists, be 
 ranked as new and distinct species. 
 
 If then there be some degree of truth in these remarks, 
 we have no right to expect to find, in our geological for¬ 
 mations, an infinite number of those fine transitional forms 
 which, on our theory, have connected all the past and 
 present species of the same group into one long and branch¬ 
 ing chain of life. We ought only to look for a few links, 
 and such assuredly we do find—some more distantlv, some 
 more closely, related to each other; and these links, let 
 them be ever so close, if found in different stages of the 
 same formation, would, by many palaeontologists, be 
 ranked as distinct species. But I do not pretend that I 
 should ever have suspected how poor was the record in the 
 best preserved geological sections, had not the absence of 
 innumerable transitional links between the species which 
 lived at the commencement and close of each formation, 
 pressed so hardly on my theory. 
 
 ON THE SUDDEN APPEARANCE OF WHOLE GROUPS OF 
 
 ALLIED SPECIES. 
 
 The abrupt manner in which whole groups of species 
 suddenly appear in certain formations, has been urged by 
 several palaeontologists—for instance, by Agassiz, Pictet, 
 and Sedgwick—as a fatal objection to the belief in the 
 
SUDDEN APPEARANCE OF 
 
 334 
 
 transmutation of species. If numerous species, belonging 
 to the same genera or families, have really started into life 
 at once, the fact would be fatal to the theory of evolution 
 through natural selection. For the development by this 
 means of a group of forms, all of which are descended from 
 some one progenitor, must have been an extremely slow 
 process; and the progenitors must have lived long before 
 their modified descendants. But we continually overrate 
 the perfection of the geological record, and falsely infer, 
 because certain genera or families have not been found be¬ 
 neath a certain stage, that they did not exist before that 
 stage. In all cases positive palaeontological evidence may 
 be implicitly trusted; negative evidence is worthless, as 
 experience has so often shown. We continually forget how 
 large the world is, compared with the area over which our 
 geological formations have been carefully examined; we 
 forget that groups of species may elsewhere have long 
 existed, and have slowly multiplied, before they invaded 
 the ancient archipelagoes of Europe and the Unites States. 
 We do not make due allowance for the intervals of time 
 which have elapsed between our consecutive formations, 
 longer perhaps in many cases than the time requiied foi 
 the accumulation of each formation. These intervals will 
 have given time for the multiplication of species from some 
 one parent-form: and in the succeeding formation, such 
 groups or species will appear as if suddenly created. 
 
 I may here recall a remark formerly made, namely, that 
 it might require a long succession of ages to adapt an or¬ 
 ganism to some new and peculiar line of life, for instance, 
 to fly through the air; and consequently that the transi¬ 
 tional forms would often long remain confined to some one 
 region; but that, when this adaptation had once been 
 effected, and a few species had thus acquired a great ad¬ 
 vantage over other organisms, a comparatively short time 
 would be necessary to produce many divergent forms, 
 which would spread rapidly and widely throughout the 
 world. Professor Pictet, in his excellent Review of this 
 work, in commenting on early transitional forms, and 
 taking birds as an illustration, cannot see how the succes¬ 
 sive modifications of the anterior limhs of a supposed pro¬ 
 totype could possibly have been of any advantage. But 
 look at the penguins of the Southern Ocean; have not 
 
GEO UPS OF ALLIED SPECIES . 335 
 
 these birds their front limbs in tliis precise intermediate 
 state of “neither true arms nor true wings?” Yet these 
 birds hold their place victoriously in the battle for life; for 
 they exist in infinite numbers and of many kinds. I do 
 not suppose, that we here see the real transitional grades 
 through which the wings, of birds have passed; but what 
 special difficulty is there in believing that it might profit 
 the modified descendants of the penguin, first to become 
 enabled to flap along the surface of the sea like the logger- 
 headed duck, and ultimately to rise from its surface and 
 glide through the air? 
 
 I will now give a few examples to illustrate the fore¬ 
 going i.emaiks, and to show how liable we are to error in 
 supposing that whole groups of species have suddenly been 
 pioduced. Even in so short an interval as that between 
 the first and second editions of PictePs great work on 
 Palaeontology, published in 1844-4G and in 1853-57, the 
 conclusions on the . first appearance and disappearance of 
 several gioups of animals have been considerably modified* 
 and a third edition would require still further changes. I may 
 recall the well-known fact that in geological treatises, pub- 
 hshed not many years ago, mammals were always spoken 
 of as having abruptly come in at the commencement of the 
 tertiary series. And now one of the richest known ac¬ 
 cumulations of fossil mammals belongs to the middle of the 
 secondary series; and true mammals have been discovered 
 in.the new red sandstone at nearly the commencement of 
 this great series. Cuvier used to urge that no monkey 
 occurred in any tertiary stratum; but now extinct species 
 have been discovered in India, South America and in 
 Euiope, as far back as the miocene stage. Had it not 
 been for the rare accident of the preservation of footsteps 
 in the new red sandstone of the United States, who would 
 have ventured to suppose that no less than at least thirty 
 different bird-like animals, some of gigantic size, existed 
 duimg that period? Uot a fragment of bone has been dis¬ 
 covered. in these beds. Uot long ago, palaeontologists 
 maintained that the whole class of birds came suddenly 
 into existence during the eocene period; but now we know, 
 on the authority of Professor Owen, that a bird certainly 
 h\ed during the deposition of the upper greensand; and 
 still moie recently, that strange bird, the Archeopteryx, 
 
336 
 
 SUDDEN APPEARANCE OE 
 
 with a long lizard-like tail, bearing a pair of feathers on 
 each joint, and with its wings furnished with two free 
 claws, has been discovered in the oolitic slates of Solenho- 
 fen. Hardly any recent discovery shows more forcibly 
 than this how little we as yet know of the former inhab¬ 
 itants of the world. 
 
 I may give another instance, which, from having passed 
 under my own eyes, has much struck me. In a memoir on 
 Fossil Sessile Cirripedes, I stated that, from the large num¬ 
 ber of existing and extinct tertiary species; from the ex¬ 
 traordinary abundance of the individuals of many species 
 all over the world, from the Arctic regions to the equator, 
 inhabiting various zones of depths, from the upper tidal 
 limits to fifty fathoms; from the perfect manner in which 
 specimens are preserved in the oldest tertiary beds; from 
 the ease with which even a fragment of a valve can be 
 recognized; from all these circumstances, I inferred that, 
 had sessile cirripedes existed during the secondary periods, 
 they would certainly have been preserved and dis¬ 
 covered; and as not one species had then been, discov¬ 
 ered in beds of this age, I concluded that this great 
 group had been suddenly developed at the commencement 
 of the tertiary series. This was a sore trouble to me, 
 adding, as I then thought, one more instance of the 
 abrupt appearance of a great group of species. But my 
 work had hardly been published, when a skillful palaeon- 
 togist, M. Bosquet, sent me a drawing of a perfect speci¬ 
 men of an unmistakable sessile cirripede, which he had 
 himself extracted from the chalk of Belgium. And, as 
 if to make the case as striking as possible, this cirripede 
 was a Ohthamalus, a very common, large, and ubiquitous 
 genus, of which not one species has as yet been found even 
 in any tertiary stratum. Still more recently, a Pyrgoma, 
 a member of a distinct subfamily of sessile cirripedes, has 
 been discovered by Mr. Woodward in the upper chalk; so 
 that we now have abundant evidence of the existence of 
 this group of animals during the secondary period. 
 
 The case most frequently insisted on by palaeontologists 
 of the apparently sudden appearance of a whole group of 
 species, is that of thet eleostean fishes., low down, according 
 to Agassiz, in the Chalk period. This group includes the 
 large majority of existing species. But certain Jurassic 
 
GROUPS OF ALLIED SPECIES . 
 
 33 ? 
 
 and Triassic forms are now commonly admitted to be 
 teleostean; and even some palaeozoic forms have thus been 
 classed by one high authority. If the teleosteans had 
 really appeared suddenly in the northern hemisphere at 
 the commencement of the chalk formation, the fact would 
 have been highly remarkable; but it would not have formed 
 an insuperable difficulty, unless it could likewise have been 
 shown that at the same period the species were suddenly 
 and simultaneously developed in other quarters of the 
 world. It is almost superfluous to remark that hardly any 
 fossil-fish are known from south of the equator; and by 
 running through Pictet's Palaeontology it will be seen that 
 very few species are known from several formations in 
 Europe. Some few families of fish now have a confined 
 range; the teleostean fishes might formerly have had a 
 similarly confined range, and after having been largely 
 developed in some one sea, have spread widely. Nor have 
 we any right to suppose that the seas of the world have 
 always been so freely open from south to north as they are 
 at present. Even at this day, if the Malay Archipelago 
 were converted into land, the tropical parts of the Indian 
 Ocean would form a large and perfectly inclosed basin, in 
 which any great group of marine animals might be multi¬ 
 plied; and here they would remain confined, until some of 
 the species became adapted to a cooler climate, and were 
 enabled to double the southern capes of Africa or Australia, 
 and thus reach other and distant seas. 
 
 From these considerations, from our ignorance of the 
 geology of other countries beyond the confines of Europe 
 and the United States, and from the revolution in oar 
 palaeontological knowledge effected by the discoveries of 
 the last dozen years, it seems to me to be about as rash 
 to dogmatize on the succession of organic forms throughout 
 the world, as it would be for a naturalist to land for five 
 minutes on a barren point in Australia, and then to discuss 
 the number and range of its productions. 
 
 OK THE SUDDEK APPEARAKCE OF GROUPS O v ALLIED 
 SPECIES IK THE LOWEST KKOWK FOSSILIFEROUS STRATA. 
 
 There is another and allied difficulty, which is much 
 , more serious, I allude to the manner in which species 
 
338 
 
 GROUPS OF ALLIED SPECIES 
 
 belonging to several of the main divisions of the animal 
 kingdom suddenly appear in the lowest known fossiliferous 
 rocks. Most of the arguments which have convinced me 
 that all the existing species of the same group are descended 
 from a single progenitor, apply with equal force to the 
 earliest known species. For instance, it cannot be doubted 
 that all the Cambrian and Silurian trilobites are descended 
 from some one crustacean, which must have lived long 
 before the Cambrian age, and which probably differed 
 greatly from any known animal. Some of the most ancient 
 animals, as the Nautilus, Lingula, etc., do not differ much 
 from living species; and it cannot on our theory be sup¬ 
 posed, that these old species were the progenitors of all the 
 species belonging to the same groups which have subse¬ 
 quently appeared, for they are not in any degree inter¬ 
 mediate in character. 
 
 Consequently, if the theory be true, it is indisputable 
 that before the lowest Cambrian stratum was deposited 
 long periods elapsed, as long as, or probably far longer 
 than, the whole interval from the Cambrian age to the 
 present day; and that during these vast periods the world 
 swarmed with living creatures. Here we encounter a 
 formidable objection; for it seems doubtful whether the 
 earth, in a fit state for the habitation of living creatures, 
 has lasted long enough. Sir W. Thompson concludes that 
 the consolidation of the crust can hardly have occurred less 
 than twenty or more than four hundred million years ago, 
 but probably not less than ninety-eight or more than two 
 hundred million years. These very wide limits show how 
 doubtful the data are; and other elements may have here¬ 
 after to be introduced into the problem. Mr. Croll esti¬ 
 mates that about sixty million years have elapsed since the 
 Cambrian period, but this, judging from the small amount 
 of organic change since the commencement of the Glacial 
 epoch, appears a very short time for the many and great 
 mutations of life, which have certainly occurred since the 
 Cambrian formation; and the previous one hundred and 
 forty million years can hardly be considered as sufficient 
 for the development of the varied forms of life which 
 already existed during the Cambrian period. It is, how¬ 
 ever, probable, as Sir William Thompson insists, that the 
 world at a very early period was subjected to more rapid 
 
/iY LO WERT EOSSILIFERO t)8 STRATA. 339 
 
 ; , tS P u hysical con< 3’tions than those 
 induce changes at a « ° 1 chal !? es woultl have tended to 
 which then existed. COrreSp ° Ddl ^ rate in organisms 
 
 To the question why we do not find rich fossil iferons 
 H Pp lts belonging to these assumed earliest periods prior to 
 the Cambrian system, I can give no satisfactory Answer 
 Seveial eminent geologists, with Sir R. Murchison at their 
 head, were until recently convinced that we beheld in the 
 
 dTwn of Sr'othe ‘r ,’r 6St Siluri “ stratum the" first 
 i 0 lite Othei highly competent judges, as Lyell and 
 
 ha ^ e dls P uted tlils conclusion. We should not 
 foiget than only a small portion of the world is known with 
 accuracy. Not very long ago M. Barrande added another 
 and lower stage, abounding with new and peculiar s wr it 
 eneath the. then known Silurian system; and now still 
 ower down m the Lower Cambrian formation Mr Hicks 
 has found South Wales beds rich in trilobites and con 
 taming various molluscs and annelids. The presence of 
 p losphatio nodules and bituminous matter, even in some 
 ot the lowest azotm rocks, probabty indicates life at these 
 
 formaLou 1 of p® e f st . ence of tde E ozoon in the Laurentian 
 formation of Canada is generally admitted. There are three 
 
 gieat^series of strata beneath the Silurian system in Can¬ 
 ada, m the lowest of which the Eozoon is found. Sir W 
 
 for g surms t s eS th t aif t cf he n lt United tllickuess >nay possibly 
 
 base of tlm nal L a • the ? uoceedm S rocks, from the 
 oase ot the palaeozoic series to the present time 
 
 Ye are thus carried back to a period so remote that the 
 
 appearance of the so-called primordial fauna (of Barrande) 
 
 evtnt ” The 6 EoLo°T d r ed fV? comparatively modern 
 event The Eozoon belongs to the most lowly organized 
 
 bUt iS i h!ghly 0 ^nized°for its 
 
 has rema, tetl el^t ? 1 tleSS ni l mbers - a,ld - as Dr. Dawson 
 has rema ked, ceitainly preyed on other minute organic 
 
 mgs, which must have lived in great numbers Thus 
 
 he words, which I wrote in 1859, about the existence of 
 
 mg beings long before the Cambrian period and which 
 
 are almost the same with those since used bv Sir W Lo<ran* 
 
 have proved true Nevertheless, the difficulty of assigning 
 
 any good reason for the absence of vast piles of strata rich 
 
 in fossils beneath the Cambrian system is very great. It 
 
340 
 
 GROUPS OF ALLIED SPECIES 
 
 does not seem probable that the most ancient beds ha\e 
 been quite worn away by denudation, or that their fossils 
 have been wholly obliterated by metamorphic action, for 
 if this had been the case we should have found only small 
 remnants of the formations next, succeeding them in age, 
 and these would always have existed in a partially meta¬ 
 morphosed condition. But the descriptions which we 
 possess of the Silurian deposits over immense territories in 
 Russia and in North America, do not support the view 
 that the older a formation is the more invariably it has 
 suffered extreme denudation and metamorphism. 
 
 The case at present must remain inexplicable, and may 
 be truly urged as a valid argument against the views here 
 entertained. To show that it may hereafter receive some 
 explanation, I will give , the following hypothesis. From 
 the nature of the organic remains which do not appear to 
 have inhabited profound depths, in the several formations 
 of Europe and of the United States; and from the amount 
 of sediment, miles in thickness, of which the formations 
 are composed, we may infer that from first to last large 
 islands or tracts of land, whence the sediment was derived, 
 occurred in the neighborhood of the now existing conti¬ 
 nents of Europe and North America, ihis same view has 
 since been maintained by Agassiz and others. But we do 
 not know what was the state of things in the intervals 
 between the several successive formations; whether Europe 
 and the United States during these intervals existed. as 
 dry land, or as a submarine surface near land, on which 
 sediment was not deposited, or as the bed of an open and 
 unfathomable sea. 
 
 Looking to the existing oceans, which are thrice as ex¬ 
 tensive as the land, we see them studded with many islands; 
 but hardly one truly oceanic island (with the exception of 
 New Zealand, if this can be called a truly oceanic island) 
 is as yet known to afford even a remnant of any palaeozoic 
 or secondary formation. Hence, we may perhaps infer, 
 that during the palaeozoic and secondary periods, neither 
 continents nor continental islands existed where our oceans 
 now extend; for had they existed, palaeozoic and second- 
 arv formations would in all probability have been accumu¬ 
 lated from sediment derived from their wear and tear; 
 and these would have been at least partially upheaved by 
 
IN LO WEST F0SSIL1FER0 VS STRA TA. 345 . 
 
 the oscillations of level, which must have intervened 
 during these enormously long periods. If, then, we may 
 infer anything from these facts, we may infer that, where 
 our oceans now extend, oceans have extended from the 
 remotest period of which we have any record; and on 
 the other h*$nd, that where continents now exist, 
 large tracts of land have existed, subjected, no doubt, to 
 gieat oscillations of level, since the Cambrian period. The 
 colored map appended to my volume on Coral Reefs, led 
 
 great oceans are still mainly areas 
 01 subsidence, the great archipelagoes still areas of oscilla¬ 
 tions of level, and the continents areas of elevation. JBut 
 we have no reason to assume that things have thus re¬ 
 mained from the beginning of the world. Our continents 
 seem to have been formed by a preponderance, during 
 many oscillations of level, of the force of elevation. But 
 may not the areas of preponderant movement have 
 changed in the lapse of ages? At a period long antecedent 
 to the Cambrian epoch, continents may have existed where 
 oceans are now spread out, and clear and open oceans 
 may have existed where, our continents now stand. Nor 
 should we be justified in assuming that if, for instance, 
 the bed of the Pacific Ocean were now converted into a 
 continent we should there find sedimentary formations, in 
 recognizable condition, older than the Cambrian strata, 
 supposing such to have been formerly deposited; for it 
 might well happen that strata which had subsided some 
 miles nearer to the center of the earth, and which had 
 been pressed on by an enormous weight of superincumbent 
 water, might have undergone far more metamorphic action 
 than strata which have always remained nearer to the sur¬ 
 face. The immense areas in some parts of the world, for 
 instance in South America, of naked metamorphic rocks, 
 which must have been heated under great pressure, have 
 always seemed to me to require some special explana¬ 
 tion; and we may perhaps believe that we see in these 
 large areas the many formations long anterior to the Cam¬ 
 brian epoch in a completely metamorphosed and denuded 
 condition. 
 
 The several difficulties here discussed, namely, that, 
 though we find in our geological formations many links 
 between the species which now exist and which formerly 
 
342 
 
 GROUPS OF ALLIED SPECIES. 
 
 existed, we do not find infinitely numerous fine transitional 
 forms closely joining them ail together. The sudden man¬ 
 ner in which several groups of species first appear in our 
 European formations, the almost entire absence, as at 
 nresent known, of formations rich in fossils beneath 
 the Cambrian strata, are all undoubtedly of the most 
 serious nature. We see this in the fact that the most em¬ 
 inent palaeontologists, namely, Cuvier, Agassiz, Bariande, 
 Pictet/Falconer, E. Forbes, etc., and all our greatest geol¬ 
 ogists, as Lyell, Murchison, Sedgwick etc., have unani¬ 
 mously, often vehemently, maintained the immutability of 
 species But Sir Charles Lyell now gives the support of 
 his high authority to the opposite side, and most geologists 
 and palaeontologists are much shaken in their formei belief.. 
 Those who believe that the geological record is in any de¬ 
 gree perfect, will undoubtedly at once reject the theory, 
 For my part, following out Lyell’s metaphor, I look at the 
 geological record as a history of the world imperfectly kept 
 Ld written in a changing dialect. Of this history we pos¬ 
 sess the last volume alone, relating only to two or three 
 countries. Of this volume, only here and there a short 
 chapter has been preserved, and of each page, only here 
 and there a few lines. Each word of the slowly-changing 
 language, more or less different in the successive chapters, 
 may represent the forms of life, which are entombed in 
 on/ consecutive formations, and which falsely appear 
 to have been abruptly introduced. On this view the 
 difficulties above discussed are greatly diminished or even 
 
 disappear. 
 
 
ORGANIC BEINGS. 
 
 343 
 
 CHAPTER XL 
 
 ON THE GEOLOGICAL SUCCESSION OF ORGANIC BEINGS. 
 
 ^ S ^ 0W an( ^ successive appearance of new species—On tlieir 
 different rates of change—Species once lost do not reappear— 
 Groups of species follow the same general rules in their appear¬ 
 ance and disappearance as do single species—On extinction—On 
 simultaneous changes in the forms of life throughout the 
 world On the affinities of extinct species to each other and to 
 living species -On the state of development of ancient forms— 
 On the succession of the same types within the same areas— 
 Nummary of preceding and present chapter. 
 
 Let us now see whether the several facts and laws 
 relating to the geological succession of organic beings 
 accord best with the common view of the immutability of 
 species, or with that of their slow and gradual modifica¬ 
 tion, through variation and natural selection. 
 
 New species have appeared very slowly, one after another, 
 both on the land and in the waters. Lyell has shown that 
 it is hardly possible to resist the evidence on this head in 
 the case of the several tertiary stages; and every year tends 
 to fill up the blanks between the stages, and to make the 
 proportion between the lost and existing forms more 
 gradual. In some of . the most recent beds, though 
 undoubtedly of high antiquity if measured by years, only 
 one or two species are extinct, and only one or two are new, 
 having appeared there for the first time, either locally, or' 
 as far as we know, on the face of the earth. The second¬ 
 ary formations are more broken; but, as Bronn has 
 remarked, neither the appearance nor disappearance of the 
 many species embedded in each formation has been simul¬ 
 taneous. 
 
 Species belonging to different genera and classes have 
 not changed at the same rate, or in the same degree. In 
 the older tertiary beds a few living shells may still be 
 found in the midst of a multitude of extinct forms. 
 
344 
 
 TEE GEOLOGICAL SUCCESSION 
 
 Falconer lias given a striking instance of a similar fact, 
 for an existing crocodile is associated with many lost 
 mammals and reptiles in the sub-Himalayan deposits. 
 The Silurian Lingula differs but little from the living 
 species of this genus; whereas most of the other Silurian 
 Molluscs and all the Crustaceans have changed greatly. 
 The productions of the land seem to have changed at a 
 quicker rate than those of the. sea, of which a striking 
 instance has been observed in Switzerland. There is some 
 reason to believe that organisms high in the scale, change 
 more quickly than those that are low: though there are 
 exceptions to this rule. The amount of organic change, 
 as Pictet has remarked, is not the same in each successive 
 so-called formation. Yet if we compare any but the most 
 closely related formations, all the species will.be found to 
 have undergone some change. When a species has once 
 disappeared from the face of the earth, we have no reason 
 to believe that the same identical form ever reappears. 
 The strongest apparent exception to this latter rule is that 
 of the so-called “ colonies ” of M. Barrande, which intrude 
 for a period in the midst of an older formation, and then 
 allow the pre-existing fauna to reappear; but LyelTs expla¬ 
 nation, namely, that it is a case of temporary migration 
 from a distinct geographical province, seems satisfactory. 
 
 These several facts accord well with our theory, which 
 includes no fixed law of development, causing all the 
 inhabitants of an area to change abruptly, or simultane¬ 
 ously, or to ail equal degree. The process of modification 
 must be slow, and will generally affect only a few species 
 at the same time; for the variability of each species is 
 independent of that of all others. Whether such varia¬ 
 tions or individual differences as may arise will be accu¬ 
 mulated through natural selection in a greater or less 
 degree, thus causing a greater or less amount of perma¬ 
 nent modification, will depend on many complex contin¬ 
 gencies—on the variations being of a beneficial nature, on 
 the freedom of intercrossing, on the slowly changing 
 physical conditions of the country, on the immigration of 
 new colonists, and on the nature of the other inhabitants 
 with which the varying species come into competition. 
 Hence it is by no means surprising that one species should 
 retain the same identical form much longer than others; 
 
OF ORGANIC BEINGS. 
 
 345 
 
 or, if changing, should change in a less degree. We find 
 similar relations between the existing inhabitants of dis¬ 
 tinct countries; for instance, the land-shells and coleopter¬ 
 ous insects of Madeira have come to differ considerably 
 from their nearest allies on the continent of Europe, 
 whereas the marine shells and birds have remained 
 unaltered. We can perhaps understand the apparently 
 t quicker rate of change in terrestrial and in more highly 
 'organized productions compared with marine and lower 
 productions, by the more complex relations of the higher 
 beings to their organic and inorganic conditions of life, as 
 explained in a former chapter. When many of the inhab¬ 
 itants of any area have become modified and improved, we 
 can understand, on the principle of competition, and from 
 the all-important relations of organism to organism in the 
 struggle for life, that any form which did not become in 
 some degree modified and improved, would be liable to 
 extermination. Hence, we see why all the species in the 
 same region do at last, if we look to long enough intervals 
 of time, become modified, for otherwise they would become 
 extinct. 
 
 In members of the same class the average amount of 
 change, during long and equal periods of time, may, per¬ 
 haps, be nearly the same; but as the accumulation of 
 enduring formations, rich in fossils, depends on great 
 masses of sediment being deposited on subsiding areas, our 
 formations have been almost necessarily accumulated at 
 wide and irregularly intermittent intervals of time; conse¬ 
 quently the amount of organic change exhibited by the fos¬ 
 sils embedded in consecutive formations is not equal. 
 Each formation, on this view, does not mark a new and 
 complete act of creation, but only an occasional scene, 
 taken almost at hazard, in an ever slowly changing drama. 
 
 We can clearly understand why a species when once lost 
 should never reappear, even if the very same conditions of 
 life, organic and inorganic, should recur. For though the 
 offspring of one species might be adapted (and no doubt 
 this has occurred in innumerable instances) to fill the 
 place of another species in the economy of nature, and 
 thus supplant it; yet the two forms—the old and the 
 new—"would not be identically the same; for both would 
 almost certainly inherit different characters from their dk- 
 
346 
 
 TEE GEOLOGICAL SUCCESSION 
 
 tinct progenitors; and organisms already differing would 
 vary in a different manner. For instance, it is possible, if 
 all our fantail pigeons were destroyed, that fanciers might 
 make a new breed hardly distinguishable from the present 
 breed; but if the parent rock-pigeon were likewise destroyed, 
 and under nature we have every reason to believe that 
 parent forms are generally supplanted and exterminated by 
 their improved offspring, it is incredible that a fantail, 
 identical with the existing breed, could be raised from any 
 other species of pigeon, or even from any other well estab¬ 
 lished race of the domestic pigeon, for the successive varia¬ 
 tions would almost certainly be in some degree different, 
 and the newly-formed variety would probably inherit from 
 its progenitor some characteristic differences. 
 
 Groups of species, that this, genera and families, follow 
 the same general rules in their appearance and disappear¬ 
 ance as do single species, changing more or less quickly, 
 and in a greater or lesser degree. A group, when it has 
 once disappeared, never reappears; that is, its existence, as 
 long as it lasts, is continuous. I am aware that there are 
 some apparent exceptions to this rule, but the exceptions 
 are surprisingly few, so few that E. Forbes, Pictet, and 
 Woodward (though all strongly opposed to such views as I 
 maintain) admit its truth; and the rule strictly accords 
 with the theory. For all the species of the same group, 
 however long it may have lasted, are the modified descend¬ 
 ants one from the other, and all from a common progeni¬ 
 tor. In the genus Lingula, for instance, the species 
 which have successively appeared at all ages must have 
 been connected by an unbroken series of generations, from 
 the lowest Silurian stratum to the present day. 
 
 We have seen in the last chapter that whole groups of 
 species sometimes falsely appear to have been abruptly 
 developed; and I have attempted to give an explanation of 
 this fact, which if true would be fatal to my views. But 
 such cases are certainly exceptional; the general rule being 
 a gradual increase in number, until the group reaches its 
 maximum, and then, sooner or later, a gradual decrease. 
 If the number of the species included within a genus, or 
 the number of the genera within a family, be represented 
 by a vertical line of varying thickness, ascending through 
 the successive geological formations, in which the species 
 
OF ORGANIC BEINGS. 
 
 347 
 
 are found, the line will sometimes falsely appear to begin 
 at its lower end, not in a sharp point, but abruptly; it 
 then gradually thickens upward, often keeping of equal 
 thickness for a space, and ultimately thins out in the 
 upper beds, marking the decrease and final extinction of 
 the species. This gradual increase in number of the species 
 of a group is strictly conformable with the theory, for the 
 species of the same genus, and the genera of the same 
 family, can increase only slowly and progressively; the 
 process of modification and the production of a number of 
 allied forms necessarily being a slow and gradual process, 
 one species first giving rise to two or three varieties, these 
 being slowly converted into species, which in their turn 
 produce by equally slow steps other varieties and species, 
 and so on, like the branching of a great tree from a single 
 stem, till the group becomes large. 
 
 <W EXTI^CTICW. 
 
 We have as yet only spoken incidentally of the disap¬ 
 pearance of species and. of groups of species. On the 
 theory of natural selection, • the extinction of old forms 
 and the production of new and improved forms are inti¬ 
 mately connected together,. The old notion of all the 
 inhabitants of the earth having been swept away by catas¬ 
 trophes at successive periods is very generally given up, even 
 by those geologists, as Elie de Beaumont, Murchison, Bar- 
 rande, etc., whose general views would naturally lead 
 them to this conclusion. On the contrary, we have every 
 reason to believe, from the study of the tertiary formations, 
 that species and groups of species gradually disappear, one 
 after another, first from one spot, then from another, and 
 finally from the world. In some few cases, however, as by 
 the breaking of an isthmus and the consequent irruption 
 of a multitude of new inhabitants into an adjoining sea, 
 or by. the final subsidence of an island, the process of ex¬ 
 tinction may have been rapid. Both single species and 
 whole groups of species last for very unequal periods; some 
 groups, as we have seen, have endured from the earliest 
 known dawn of life to the present day; some have disap¬ 
 peared before the close of the palaeozoic period. No fixed 
 law seems to determine the length of time during which 
 
348 
 
 EXTINCTION. 
 
 any single species or any single genus endures. There is 
 reason to believe that the extinction of a whole group of 
 species is generally a slower process than their production: 
 if their appearance and disappearance be represented, as 
 before, by a vertical line of varying thickness the line is 
 found to taper more gradually at its upper end, which 
 marks the progress of extermination, than at its lower end, 
 which marks the first appearance and the early increase in 
 number of the species. In some cases, however, the extermi¬ 
 nation of whole groups, as of ammonites, toward the close 
 of the secondary period, has been wonderfully sudden. 
 
 The extinction of species has been involved in the most 
 gratuitous mystery. Some authors have even supposed 
 that, as the individual has a definite length of life, so have 
 species a definite duration. No one can have marvelled 
 more than I have done at the extinction of species. When 
 I found in La Plata the tooth of a horse embedded with 
 the remains of Mastodon, Megatherium, Toxodon and 
 other extinct monsters, which all co-existed with still 
 living shells at a very late geological period, I. was. filled 
 with astonishment; for, seeing that the horse, since its in¬ 
 troduction by the Spaniards into South America, has run 
 wild over the whole country and has increased in numbers 
 at an unparalleled rate, I asked myself what could so. re¬ 
 cently have exterminated the former horse under conditions 
 of life apparently so favorable. But my astonishment was 
 groundless. Professor Owen soon perceived that the tooth, 
 though so like that of the existing horse, belonged to an 
 extinct species. Had this horse been still living, but in 
 some degree rare, no naturalist would have felt the least 
 surprise at its rarity; for rarity is the attribute of a vast 
 number of species of all classes, in all countries. If we 
 ask ourselves why this or that species is rare, we. answer 
 that something is unfavorable in its conditions of life; but 
 what that something is we can hardly ever tell. On the 
 supposition of the fossil horse still existing as a rare species, 
 we might have felt certain, from the analogy of all other 
 mammals, even of the slow-breeding elephant, and from the 
 history of the naturalization of the domestic horse in 
 South America, that under more favorable conditions it 
 would in a very few years have stocked the whole con¬ 
 tinent. But we could not have told what the unfavorable 
 
EXTINCTION. 
 
 340 
 
 conditions were which checked its increase, whether some 
 one or several contingencies, and at what period of the 
 horse’s life, and in what degree they severally acted. If 
 the conditions had gone on, however slowly, becoming less 
 and less favorable, we assuredly should not have perceived 
 the fact, yet the fossil horse would certainly have become 
 rarer and rarer, and finally extinct—its place being seized 
 on by some more successful competitor. 
 
 It is most difficult alwavs to remember that the increase 
 of every creature is constantly being checked by unper¬ 
 ceived hostile agencies; and that these same unper¬ 
 ceived agencies are amply sufficient to cause rarity, and 
 finally extinction. So little is this subject understood, 
 that I have heard surprise repeatedly expressed at such 
 great monsters as the Mastodon and the more ancient Din- 
 osaurians having become extinct; as if mere bodily strength 
 gave victory in the battle of life. Mere size, on the con¬ 
 trary, would in some cases determine, as has been remarked 
 by Owen, quicker extermination, from the greater amount 
 of requisite food. Before man inhabited India or Africa, 
 some cause must have checked the continued increase of 
 the existing elephant. A highly capable judge. Dr. Fal¬ 
 coner, believes that it is chiefly insects which, from inces¬ 
 santly harassing and weakening the elephant in India, 
 check its increase; and this was Bruce’s conclusion with 
 respect to the African elephant in Abyssinia. It is certain 
 that insects and blood-sucking bats d:termine tbe existence 
 of the larger naturalized quadrupeds in several parts of 
 South America. 
 
 We see in many cases in the more recent tertiary forma¬ 
 tions that rarity precedes extinction; and we know that 
 this has been the progress of events with those animah 
 which have been exterminated, either locally or wholly, 
 through man’s agency. I may repeat what I published in 
 1845 , namely, that to admit that species generally become 
 rare before they become extinct—to feel no surprise at the 
 rarity of a species, and yet to marvel greatly when the spe¬ 
 cies ceases to exist, is much the same as to admit that sick¬ 
 ness in the individual is the forerunner of death—to feel 
 no surprise at sickness, but, when the sick man dies, to 
 wonder and to suspect that he died by some deed of 
 violence. 
 
350 
 
 EXTINCTION. 
 
 The theory of natural selection is grounded on the belief 
 that each new variety and ultimately each new species, is 
 produced and maintained by having some advantage over 
 those with which it comes into competition; and the con¬ 
 sequent extinction of the less-favored forms almost inevita¬ 
 bly follows. It is the same with our domestic productions; 
 when a new and slightly improved variety has been raised, 
 it at first supplants the less improved varieties in the same 
 neighborhood; when much improved it is transported far 
 and near, like our sliort-horn cattle, and takes the place of 
 other breeds in other countries. Thus the appearance of 
 new forms and the disappearance of old forms, both those 
 naturally and those artificially produced, are bound 
 together. In flourishing groups, the number of new spe¬ 
 cific forms which have been produced within a given time 
 has at some periods probably been greater than the number 
 of the old specific forms which have been exterminated; 
 but we know that species have not gone on indefinitely in¬ 
 creasing, at least during the later geological epochs, so 
 that, looking to later times, we may believe that the pro¬ 
 duction of new forms has caused the extinction of about 
 the same number of old forms. 
 
 The competition will generally be most severe, as for¬ 
 merly explained and illustrated by examples, between the 
 forms which are most like each other in all respects. Hence 
 the improved and modified descendants of a species will 
 generally cause the extermination of the parent-species; 
 and if many new forms have been developed from any 
 one species, the nearest allies of that species, i. e. 
 the species of the same genus, will be the most liable 
 to extermination. Thus, as I believe, a number of new 
 species descended from one species, that is a new genus, 
 comes to supplant an old genus, belonging to the same 
 family. But it must often have happened that a new 
 species belonging to some one group has seized on the place 
 occupied by a species belonging to a distinct group, and 
 thus have caused its extermination. If many allied forms 
 be developed from the successful intruder, many will have 
 to yield their places; and it will generally be the allied 
 forms, which will suffer from some inherited inferiority :n 
 common. But whether it be species belonging to the 
 same or to a distinct class, which have yielded their places 
 
EXTINCTION. 
 
 351 
 
 to other modified and improved species, a few of the suf¬ 
 ferers may often be preserved for a long time, from being 
 fitted to some peculiar line of life, or from inhabiting some 
 distant and isolated station, where they will have escaped 
 severe competition. For instance, some species of Trigo- 
 nia, a great genus of shells in the secondary formations, 
 survive in the Australian seas; and a few members of the 
 great and almost extinct group of Ganoid fishes still inhabit 
 our fresh waters. Therefore, the utter extinction of a 
 group is generally, as we have seen, a slower process than 
 its production. 
 
 With respect to the apparently sudden extermination of 
 whole families or orders, as of Trilobites at the close of the 
 palaeozoic period, and of Ammonites at the close of the 
 secondary period, we must remember what has been already 
 said on the probable wide intervals of time between our 
 consecutive formations; and in these intervals there may 
 have been much slow extermination. Moreover, when, by 
 sudden immigration or by unusually rapid development, 
 many species of a new group have taken possession of an 
 area, many of the older species will have been exterminated 
 in a correspondingly rapid manner; and the forms which 
 thus yield their places will commonly be allied, for they 
 will partake of the same inferiority in common. 
 
 Thus, as it seems to me, the manner in which single 
 species and whole groups of species become extinct accords 
 well with the theorv of natural selection. We need not 
 marvel at extinction; if we must marvel, let it be at our 
 own presumption in imagining for a moment that we un¬ 
 derstand the many complex contingencies on which the 
 existence of each species depends. If we forget for an 
 instant that each species tends to increase inordinately, 
 and that some check is always in action, yet seldom per¬ 
 ceived by us, the whole economy of nature will be utterly 
 obscured. Whenever we can precisely say why this species 
 is more abundant in individuals than that; why this 
 species and not another can be naturalized in a given coun¬ 
 try; then, and not until then, we may justly feel surprise 
 why we cannot account for the extintion of any particular 
 species or group of species. 
 
FORMS OF LIFE CHANGING 
 
 ON THE FORMS OF LIFE CHANGING ALMOST SIMULTA¬ 
 NEOUSLY THROUGHOUT THE WORLD. 
 
 Scarcely any pala3ontological discovery is more striking 
 than the fact that the forms of life change almost simul¬ 
 taneously throughout the world. Thus our European 
 Chalk formation can be recognized in many distant regions, 
 under the most different climates, where not a frag¬ 
 ment of the mineral chalk itself can be found; namely, in 
 North America, in equatorial South America, in Tierra 
 del Fuego, at the Cape of Good Hope, and in the peninsula 
 of India. For at these distant points, the organic remains 
 in certain beds present an unmistakable resemblance to 
 those of the Chalk. It is not that the same species are 
 met with; for in some cases not one species is identically 
 the same, but they belong to the same families, genera, 
 and sections of genera, and sometimes are similarly char¬ 
 acterized in such trifling points as mere superficial sculp¬ 
 ture. Moreover, other forms, which are not found in the 
 Chalk of Europe, but which occur in the formations either 
 above or below, occur in the same order at these distant 
 points of the world. In the several successive palaeozoic 
 formations of Russia, Western Europe, and North America, 
 a similar parallelism in the forms of life has been observed 
 by several authors; so it is, according to Lyell, with the 
 European and North American tertiary deposits. Even if 
 the few fossil species which are common to the Oid and 
 New Worlds were kept wholly out of view, the general 
 parallelism in the successive forms of life, in the palaeozoic 
 and tertiary stages, would still be manifest, and the several 
 formations could be easily correlated. 
 
 These observations, however, relate to the marine inhabi¬ 
 tants of the world: we have not sufficient data to judge 
 whether the productions of the land and of fresh water at 
 distant points change in the same parallel manner. We 
 may.doubt whether they have thus changed: if the Mega¬ 
 therium, Mylodon, Macrauchenia, and Toxodon had been 
 brought to Europe from La Plata, without any information 
 in regard to their geological position, no one would have 
 suspected that they had co-existed with sea-shells all still 
 living; but as these anomalous monsters co-existed with 
 the Mastodon and Horse, it might at least have been in- 
 
THROUGHOUT THE WORLD. 353 
 
 ferred that they had lived during one of the later tertiary 
 stages. 
 
 When the marine forms of life are spoken of as having 
 changed simultaneously throughout the world, it must not 
 be supposed that this expression relates to the same year, 
 or to the same century, or even that it has a very strict 
 geological sense; for if all the marine animals now living 
 in Europe, and all those that lived in Europe during the 
 pleistocene period (a very remote period as measured by 
 years, including the whole glacial epoch) were compared 
 with those now existing in South America or in Australia, 
 the most skillful naturalist would hardly be able to say 
 whether the present or the pleistocene inhabitants of 
 Europe resembled most closely those of the southern hemi¬ 
 sphere.. So, again, several highly competent observers 
 maintain that the existing productions of the United States 
 are more closely related to those which lived in Europe 
 during certain late tertiary stages, than to the present in¬ 
 habitants of Europe; and if this be so, it is evident that 
 fossiliferous beds now deposited on the shores of North 
 America would hereafter be liable to be classed with some¬ 
 what older European beds. Nevertheless, looking to a 
 remotely future epoch, there can be little doubt that all 
 the more modern marine formations, namely, the upper 
 pliocene, the pleistocene and strictly modern beds of 
 Europe, North and South America, and Australia, from 
 containing fossil remains in some degree allied, and from 
 not including those forms which are found only in the 
 older underlying deposits, would be correctly ranked as 
 simultaneous in a geological sense. 
 
 The fact of the forms of life changing simultaneously in 
 the above large sense, at distant parts of the world, has 
 greatly struck those admirable observers, MM. de Verneuil 
 and d'Archiac. After referring to the parallelism of the 
 palaeozoic forms of life in various parts of Europe, they add, 
 “If, struck by this strange sequence, we turn our atten¬ 
 tion to North America, and there discover a series of ana¬ 
 logous phenomena, it will appear certain that all these 
 modifications of species, their extinction, and the intro¬ 
 duction of new ones, can not be owing to mere changes in 
 marine currents or other causes more or less local and 
 temporary, but depend on general laws which govern the 
 
 l 
 
354 
 
 FORMS OF LIFE CUANGING 
 
 whole animal kingdom.” M. Barrande has made forcible 
 remarks to precisely the same effect. It is, indeed, quite 
 futile to look to changes of currents, climate, or other phy¬ 
 sical conditions, as the cause of these great mutations in 
 the forms of life throughout the world, under the most 
 different climates. We must, as Barrande has remarked, 
 look to some special law. We shall see this more clearly 
 when we treat of the present distribution of organic beings, 
 and find how slight is the relation between the physical 
 conditions of various countries and the nature of their 
 inhabitants. 
 
 This great fact of the parallel succession of the forms of 
 life throughout the world, is explicable on the theory of 
 natural selection. New species are formed by having some 
 advantage over older forms; and the forms, which are 
 already dominant, or have some advantage over the other 
 forms in their own country, give birth to the greatest 
 number of new varieties or incipient species. We have 
 distinct evidence on this head, in the plants which are 
 dominant, that is, which are commonest and most widely 
 diffused, producing the greatest number of new varieties. 
 It is also natural that the dominant, varying and far- 
 spreading species, which have already invaded, to a certain 
 extent, the territories of other species, should be those 
 which would have the best chance of spreading still further, 
 and of giving rise in new countries to other new varieties 
 and species. The process of diffusion would often be very 
 slow, depending on climatal and geographical changes, on 
 strange accidents, and on the gradual acclimatization of 
 new species to the various climates through wdrich they 
 might have to pass, but in the course of time the domi¬ 
 nant forms would generally succeed in spreading and would 
 ultimately prevail. The diffusion would, it is probable, be 
 slower with the terrestrial inhabitants of distinct conti¬ 
 nents than with the marine inhabitants of the continuous 
 sea. We might therefore expect to find, as we do find, a 
 less strict degree of parallelism in the succession of the 
 productions of the land than with those of the sea. 
 
 Thus, as it seems to me, the parallel, and, taken in a 
 large sense, simultaneous, succession of the same forms of 
 life throughout the world, accords well with the principle 
 of new species having been formed by dominant species 
 
THROUGHOUT THE WORLD. 
 
 355 
 
 spreading widely and varying; the new species thus pro¬ 
 duced being themselves dominant, owing to their having 
 had some advantage over their already dominant parents, 
 as well as over other species, and again spreading, varying, 
 and producing new forms. The old forms which are 
 beaten and which yield their places to the new and victori¬ 
 ous forms, will generally be allied in groups, from inherit¬ 
 ing some inferiority in common; and, therefore, as new 
 and improved groups spread throughout the world, old 
 groups disappear from the world; and the succession of 
 forms everywhere tends to correspond both in their first 
 appearance and final disappearance. 
 
 There is one other remark connected with this subject 
 worth making. I have given my reasons for believing 
 that most of our great formations, rich in fossils, were 
 deposited during periods of subsidence; and that blank 
 intervals of vast duration, as far as fossils are concerned, 
 occurred during the periods when the bed of the sea was 
 either stationary or rising, and likewise when sediment 
 was not thrown down quickly enough to imbed and pre¬ 
 serve organic remains. During these long and blank inter¬ 
 vals I suppose that the inhabitants of each region 
 underwent a considerable amount of modification and 
 extinction, and that there was much migration from other 
 parts of the world. As we have reason to believe that large 
 areas are affected by the same movement, it is probable 
 that strictly contemporaneous formations have often been 
 accumulated over very wide spaces in the same quarter 
 of the world; but we are very far from having any 
 right to conclude that this has invariably been the case, 
 and that large areas have invariably been affected by the 
 same movements. When two formations have been depos¬ 
 ited in two regions during nearly, but not exactly, the 
 same _ period, we should find in both, from the causes 
 explained in the foregoing paragraphs, the same general 
 succession in the forms of life ; but the species would not 
 exactly correspond ; for there will have been a little more 
 time in the one region than in the other for modification, 
 extinction and immigration. 
 
 I suspect that cases of this nature occur in Europe. 
 Mr. Prestwich, in his admirable Memoirs on the eocene 
 deposits of England and France, is able to draw a close 
 
356 
 
 AFFINITIES OF EXTINCT SPECIES. 
 
 general parallelism between the successive stages in the 
 two countries; but when he compares certain stages in 
 England with those in France, although he finds in both a 
 curious accordance in the numbers of the species belonging 
 to the same genera, yet the species themselves differ in a 
 manner very difficult to account for considering the prox¬ 
 imity of the two areas, unless, indeed, it be assumed that 
 an isthmus separated two seas inhabited by distinct, but 
 contemporaneous faunas. Lyell has made similar obser¬ 
 vations on some of the later tertiary formations. Barrande, 
 also, shows that there is a striking general parallelism in the 
 successive Silurian deposits of Bohemia and Scandinavia; 
 nevertheless he finds a suprising amount of difference 
 in the species. If the several formations in these regions 
 have not been deposited during the same exact periods 
 —a formation in one region often corresponding with a 
 blank interval in the other—and if in both regions the 
 species have gone on slowly changing during the accumu¬ 
 lation of the several formations and during the long inter¬ 
 vals of time between them; in this case the several 
 formations in the two regions could be arranged in the 
 same order, in accordance with the general succession of 
 the forms of life, and the order would falsely appear to be 
 strictly parallel; nevertheless the species would not be 
 all the same in the apparently corresponding stages in the 
 two regions. 
 
 ON THE AFFINITIES OF EXTINCT SPECIES TO EACH OTHER, 
 
 AND TO LIVING FORMS. 
 
 Let us now look to the mutual affinities of extinct and 
 living species. All fall into a few grand classes ; and thia 
 fact is at once explained on the principle of descent. 
 The more ancient any form is, the more, as a general 
 rule, it differs from living forms. But, as Buckland long 
 ago remarked, extinct species can all be classed either in 
 still existing groups, or between them. That the extinct 
 forms of life help to fill up the intervals between existing 
 genera, families and orders, is certainly true; but as this 
 statement has often been ignored or even denied, it may 
 be well to make some remarks on this subject, and to give 
 some instances, If we confine our attention either to the 
 
AFFINITIES OF EXTINCT SPECIES. 357 
 
 living or to the extinct species of the same class, the series 
 is fai less perfect than if we combine both into one general 
 system.. In the writings of Professor Owen we continually 
 meet with the expression of generalized forms, as applied 
 to extinct animals; and in the writings of Agassiz, of 
 prophetic or synthetic types; and these terms imply that 
 such forms are, in fact, intermediate or connecting links 
 Another distinguished palaeontologist, M. Gaudry, has 
 shown in the most striking manner that many of the fossil 
 mammals diseo\ered by him in Attica serve to break down 
 the intervals between existing genera. Cuvier ranked the 
 Kummants and Pachyderms as two of the most distinct 
 orders of mammals; but so many fossil links have been dis¬ 
 entombed that Owen has had to alter the whole classifica¬ 
 tion, and has placed certain Pachyderms in the same 
 sub-order with ruminants; for example, he dissolves by 
 gradations the apparently wide interval between the pig 
 and the. camel. The ITngulata or hoofed quadrupeds are 
 now divided into the even-toed or odd-toed divisions; but 
 the Maciauchenia of South America connects to a certain 
 extent these two grand divisions. No one will deny that 
 the Hipparion is intermediate between the existing horse 
 and certain other ungulate forms. What a wonderful con¬ 
 necting link in the chain of mammals is the Xypotherium 
 from South Ameiica, as the name given to it by Professor 
 Ge.rvais expresses, and which cannot be placed in any ex¬ 
 isting order. The Sirenia form a very distinct group of the 
 mammals, and one of the most remarkable peculiarities in 
 existing dugong and lamentin is the entire absence of hind 
 lrmbs, without even a rudiment being left; but the extinct 
 Halitherium had., according to Professor Plower, an ossified 
 \tnigh-bo.ne^ articulated to a well-defined acetabulum in 
 the pelvis, and it thus makes some approach to ordinary 
 hoofed quadrupeds, to which the Sirenia are in other re¬ 
 spects allied. The cetaceans or whales are widely different 
 from all other mammals, but the tertiary Zeugiodon and 
 Squalodon, which have been placed by some naturalists in 
 an order by themselves, are considered by Professor Huxley 
 to be undoubtedly cetaceans, “and to constitute connect¬ 
 ing links with the aquatic carnivora/* 
 
 Even the wide interval between birds arid reptiles has 
 been shown by the naturalist [just quoted to bC martially 
 
S58 
 
 AFFINITIES OF EXTINCT SPECIE8. 
 
 bridged over in the most unexpected manner, on the one 
 hand, by the ostrich and extinct Archeopteryx, and on the 
 other hand by the Compsognathus, one of the Dinosaurians 
 -that group which includes the most gigantic of all ter¬ 
 restrial reptiles. Turning to the Invertebrata, Barrande 
 asserts, a higher authority could not be named, that he is 
 every day taught that, although palaeozoic animals can cer¬ 
 tainly be classed under existing groups, yet that at this 
 ancient period the groups were not so distinctly separated 
 from each other as they now are. 
 
 Some writers have objected to any extinct species, or 
 group of species, being considered as intermediate between 
 any two living species, or groups of species. If by this 
 term it is meant that an extinct form is directly interme¬ 
 diate in all its characters between two living forms or 
 groups, the objection is probably valid. But in a natural 
 classification many fossil species certainly stand between 
 living species, and some extinct genera between living 
 genera, even between genera belonging to distinct families. 
 The most common case, especially with respect to very dis¬ 
 tinct groups, such as fish and reptiles, seems to be that, 
 supposing them to be distinguished at the present day by a 
 score of characters, the ancient members are separated by a 
 somewhat lesser number of characters, so that the two 
 groups formerly made a somewhat nearer approach to each 
 other than they now do. 
 
 It is a common belief that the more ancient a form is, by 
 so much the more it tends to connect by some of its char¬ 
 acters groups now widely separated from each other. This 
 remark no doubt must be restricted to those groups which ; 
 have undergone much change in the course of geological 
 ages; and it would be difficult to prove the truth of the 
 proposition, for every now and then even a living animal, 
 as the Lepidosiren, is discovered having affinities directed 
 toward very distinct groups. Yet if we compare the older 
 reptiles and Batrachians, the older fish, the older cephalo- 
 pods, and the eocene mammals, with the recent members 
 of the same classes, we must admit that there is truth in 
 the remark. 
 
 Let us see how far these several facts and inferences 
 accord with the theory of descent with modification. As 
 the subject is somewhat complex, I must request the reader 
 
AFFINITIES OF EXTINCT SPECIES. 339 
 
 to turn to the diagram in the fourth chapter. We may 
 suppose that the numbered letters in italics represent 
 genera, and the dotted lines diverging from them the spe¬ 
 cies in each genus. The diagram is much too simple, too 
 few genera and too few species being given, but this is un¬ 
 important for .us. The horizontal lines may represent suc¬ 
 cessive geological formations, and all the forms beneath 
 the uppermost line may be considered as extinct. The 
 three existing genera a 1 *, qp 44 , will form a small 
 family; b 44 and f x 4 , a closely allied family or subfamily, 
 and tA 4 > e 44 , m 14 , a third family. These three families, 
 together with the many extinct genera on the several lines 
 of descent diverging from the parent form (A) will form 
 an order, for all will have inherited something in common 
 from their ancient progenitor. On the principle of the 
 continued tendency to divergence of character, which was 
 foimerly illustrated by this diagram, the more recent any 
 form is the more it will generally differ from its ancient 
 progenitor. Hence, we can understand the rule that the 
 most ancient fossils differ most from existing forms. We 
 must not, however, assume that divergence of character is 
 a necessary contingency; it depends solely on the descend¬ 
 ants fiom a species being thus enabled to seize on many 
 and different places in the economy of nature. Therefore 
 it is .quite possible, as we have seen in the case of some 
 feuunan forms, that a species might go on being slightly 
 modified in relation to its slightly altered conditions of 
 life, and yet retain throughout a vast period the same gen- 
 eial chaiacteiistics. This is represented in the diagram by 
 the letter f 14 . J 
 
 All the many forms, extinct and recent, descended 
 from (A), make, as before remarked, one order; and this 
 order, from the continued effects of extinction and divero-- 
 ence of character, has become divided into several sub¬ 
 families and families, some of which are supposed to have 
 perished at different periods, and some to have endured to 
 the present day. 
 
 By looking at the diagram we can see that if many of 
 the extinct forms supposed to be imbedded in the successive 
 formations, were discovered at several points low down in 
 the seiies, the three existing families on the uppermost 
 line would be rendered less distinct from each other. If, 
 
360 
 
 AFFINITIES OF EXTINCT SPECIES. 
 
 for instance, the genera a 1 , (P, a 10 , /*, in*, m*, in 9 , were dis¬ 
 interred, these three families would be so closely linked 
 together that they probably would have to be united into 
 one great family, in nearly the same manner as has occurred 
 with ruminants and certain pachyderms. Yet he who 
 objected to consider as intermediate the extinct genera, 
 which thus link together the living genera of three fami¬ 
 lies, would be partly justified, for they are intermediate, 
 not directly, but only by a long and circuitous course 
 through many widely different forms. If many extinct 
 forms were to be discovered above one of the middle hori¬ 
 zontal lines or geological formations—for instance, above 
 No. VI.—but none from beneath this line, then only two 
 of the families (those on the left hand, a u , etc., and b li , 
 etc.) would have to be united into one; and there would 
 remain two families, which would be less distinct from 
 each other than they were before the discovery of the 
 fossils. So again, if the three families formed of eight 
 genera (a li to in u ), on the uppermost line, be supposed to 
 differ from each other by half-a-dozen important char¬ 
 acters, then the families which existed at a period marked 
 VI would certainly have differed from each other by a less 
 number of characters; for they would at this early stage of 
 descent have diverged in a less degree from their common 
 progenitor. Thus it comes that ancient and extinct 
 genera are often in a greater or less degree intermediate in 
 character between their modified descendants, or between 
 their collateral relations. 
 
 Under nature the process will be far more complicated 
 than is represented in the diagram; for the groups will 
 have been more numerous; they will have endured for 
 extremely unequal lengths of time, and will have been 
 modified in various degrees. As we possess only the last 
 volume of the geological record, and that in a very broken 
 condition, we have no right to expect, except in rare cases, 
 to fill up the wide intervals in the natural system, and 
 thus to unite distinct families or orders. All that we have 
 a right to expect is, that those groups which have, within 
 known geological periods, undergone much modification, 
 should in the older formations make some slight approach 
 to each other; so that the older members should differ less 
 from each other in some of their characters than do the 
 
AFFINITIES OF ESTINC1 SPECIES. gg. 
 
 I - i • -J _ same groups; and this by the 
 
 concurrent evidence of our best palaeontologists is fre¬ 
 quently the case. 6 
 
 Thus, on the theory of descent with modification, the 
 mam facts with respeot to the mutual affinities of the 
 extinct forms of life to each other and to living' forms 
 are explained in a satisfactory manner. And they are 
 wholly inexplicable on any other view. 
 
 On this same theory, itis evident that thefaunadurineany 
 one great period in the earth’s history will be intermediate 
 in general character between that which preceded and 
 that which succeeded it. Thus the species which lived 
 at the sixth great stage of descent in the diagram are the 
 modified offspring of those which lived at the fifth stage 
 and are the parents of those which became still more 
 modified at the seventh stage; hence they could hardly fail 
 to be nearly intermediate in character between the forms 
 of life above and below. We must, however, allow for the 
 entire extinction of some preceding forms, and in any one 
 region for the immigration of new forms from other 
 legions, and for a large amount of modification during the 
 long and blank intervals between the successive formations 
 Subject to these allowances, the fauna of each geological 
 penod undoubtedly is intermediate in character, between 
 the preceding and succeeding faunas. I need give only 
 one instance, namely, the manner in which the fossils of the 
 Devonian system, when this system was first discovered 
 were at once recognized by paleontologists as intermediate 
 m character between those of the overlying carboniferous 
 and underlying Silurian systems. But each fauna is not 
 necessarily exactly intermediate, as unequal intervals of 
 time have elapsed between consecutive formations 
 it is no real objection to the truth of the statement that 
 the fauna of each period as a whole is nearly intermediate 
 m character between the preceding and succeeding faunas, 
 that certain genera offer exceptions to the rule. For instance, 
 the species of mastodons and elephants, when arranged by 
 f?r*. falconer in two series-in the first place according to 
 then mutual affinities, and in the second place according to 
 their periods of existence—do not accord in arrangement, 
 lhe species extreme in character are not the oldest or the 
 aiost recent; nor are those which are intermediate in char- 
 
363 AFFINITIES OF EXTINCT SPECIES. 
 
 acter, intermediate in age. But supposing for an instant, in 
 this and other such cases, that the record of the first appear¬ 
 ance and disappearance of the species was complete, which 
 is far from the case, we have no reason to believe that forms 
 successively produced necessarily endure for corresponding 
 lengths of time. A very ancient form may occasionally have 
 lasted much longer than a form elsewhere subsequently 
 produced, especially in the case of terrestrial productions 
 inhabiting separated districts. To compare small things 
 with great; if the principle living and extinct races of the 
 domestic pigeon were arranged in serial affinity, this ar¬ 
 rangement would not closely accord with the order in time 
 of their production, and even less with the order of tlieir 
 disappearance; for the parent rock-pigeon still lives; and 
 many varieties between the rock-pigeon and the carriei 
 have become extinct; and carriers which are extreme in 
 the important character of length of beak originated earlier 
 than short-beaked tumblers, which are at the opposite end 
 of the series in this respect. 
 
 Closely connected with the statement, that the organic 
 remains "from an intermediate formation are in some degiee 
 intermediate in character, is the fact, insisted on by all 
 paleontologists, that fossils from two consecutive forma¬ 
 tions are far more closely related to each other, than are 
 the fossils from two remote formations. Pictet gives as 
 a well-known instance, the general resemblance of the 
 organic remains from the several stages of the Chalk 
 formation, though the species are distinct in each stage. 
 This fact alone, from its . generality, seems to have 
 shaken Professor Pictet in his belief in the immutability 
 of species. He who is acquainted with the distribution 
 of existing species over the globe, will not attempt to 
 account for the close resemblance of distinct species in 
 closely consecutive formations, by the physical conditions 
 of the ancient areas having remained nearly the same. 
 Let it be remembered that the forms of life, at least those 
 inhabiting the sea, have changed almost simultaneously 
 throughout the world, and therefore under the most 
 different climates and conditions. Consider the prodig¬ 
 ious viscisitudes of climate during the pleistocene period, 
 which includes the whole glacial epoch, and note how 
 little the specific forms of the inhabitants of the sea have 
 been affected. 
 
AFFINITIES OF EXTINCT SPECIES. 363 
 
 On the theory of descent, the full meaning of the fossil 
 remains from closely consecutive formations being closely 
 related, though ranked as distinct species, is obvious. As 
 the accumulation of each formation has often been inter¬ 
 rupted, and as long blank intervals have intervened 
 between successive formations, we ought not to expect to 
 find, as I attempted to show in the last chapter, in anv one 
 or in any two formations, all the intermediate varieties 
 between the species which appeared at the commencement 
 and close of these periods: but we ought to find after 
 intervals, very long as measured by years, but only moder¬ 
 ately long as measured geologically, closely allied forms, 
 or, as they have been called by some authors, representa¬ 
 tive species; and these assuredly we do find. We find, in 
 short,. such evidence of the slow and scarcely sensible 
 mutations of specific forms, as we have the right to 
 expect. 
 
 Otf THE STATE OF DEVELOPMENT OF ANCIENT COMPARED 
 
 WITH LIVING FORMS. 
 
 We have seen in the fourth chapter that the degree of 
 differentiation and specialization of the parts in organic 
 beings, when arrived at maturity, is the best standard, as 
 yet suggested, of their degree of perfection or highness. 
 We have also seen that, as the specialization of parts is an 
 advantage to each being, so natural selection will tend to 
 render the organization of each being more specialized and 
 perfect, and in this sense higher; not but that it may leave 
 many creatures with simple and unimproved structures 
 fitted for simple conditions of life, and in some cases will 
 even degrade or simplify the organization, yet leaving 
 such degraded beings better fitted for their new walks of 
 life. In another and more general manner, new species 
 become superior to their predecessors; for they have to 
 beat in the. struggle for life all the older forms, with which 
 they come into close competition. We may therefore con¬ 
 clude that if under a nearly similar climate the eocene 
 inhabitants of the world could be put into competition 
 with the existing inhabitants, the former would be beaten 
 and exterminated by the latter, as would the secondary by 
 the eocene, and the palaeozoic by the secondary forms. So 
 
ae4 
 
 STATE OF DEVELOPMENT OF 
 
 that by this fundamental test of victory in the battle for 
 life, as well as by the standard of the specialization of 
 organs, modern forms ought, on the theory of natural 
 selection, to stand higher than ancient forms. Is this 
 the case? A large majority of palaeontologists would 
 answer in the affirmative; and it seems that this answer 
 must be admitted as true, though difficult of proof. 
 
 It is no valid objection to this conclusion, that certain 
 Brachiopods have been but slightly modified from an 
 extremely remote geological epoch; and that certain land 
 and fresh-water shells have remained nearly the same, from 
 the time when, as far as is known, they first appeared. 
 It is not an insuperable difficulty that Foraminifera 
 have not, as insisted on by Dr. Carpenter, progressed in 
 organization since even the Laurentian epoch; for some 
 organisms would have to remain fitted for simple condi¬ 
 tions of life, and what could be better fitted for this end 
 than these lowly organized Protozoa? Such objections as 
 the above would be fatal to my view, if it included advance 
 in organization as a necessary contingent. They would 
 likewise be fatal, if the above Foraminifera, for instance, 
 could be proved to have first come into existence during 
 the Laurentian epoch, or the above Brachiopods during the 
 Cambrian formation; for in this case, there would not have 
 been time sufficient for the development of these organ¬ 
 isms up to the standard which they had then reached. 
 When advanced up to any given point, there is no neces¬ 
 sity, on the theory of natural selection, for their further 
 continued process; though they will, during each succes¬ 
 sive age, have to be slightly modified, so as to hold their 
 places in relation to slight changes in their conditions. 
 The foregoing objections hinge on the question whether we 
 really know how old the world is, and at what period the 
 various forms of life first appeared; and this may well be 
 disputed. 
 
 The problem whether organization on the whole has 
 advanced is in many ways excessively intricate. The geo¬ 
 logical record, at all times imperfect, does not extend far 
 enough back to show with unmistakable clearness that 
 wikhin the known history of the world organization has 
 largely advanced. Even at the present day, looking to 
 members of the same class, naturalists are not unanimous 
 
ANCIENT AND LIVING NORMS. 
 
 305 
 
 wt Ch f f °/. mS °, Ught t0 be ranked as h'ghest: thus, some 
 look at the selaceans or sharks, from their approach in 
 
 some important points of structure to reptiles, as the high¬ 
 est fish; others look at the teleosteans as'the highest. The 
 ganoids stand intermediate between the selaceans and 
 teleosteans; tne latter at the present day are largely pre¬ 
 ponderant in number; but formerly selaceans and ganoids 
 alone existed; and m this case, according to the standard 
 of highness chosen, so will it be said that fishes have 
 advanced or retrograded in organization. To attempt to 
 compare members of distinct types in the scale of highness 
 seems hopeless; who will decide whether a cuttle-fish be 
 higher than a bee—that insect which the great Von Baer 
 believed to be ‘ m fact more highly organized than a fish, 
 although upon another type?” In the complex struggle 
 foi life it is quite credible that crustaceans, not very high 
 in their own class, might beat cephalopods, the highest 
 mollucs; and such crustaceans, though not highly devel¬ 
 oped, would stand very high in the scale of invertebrate 
 animals if judged by the most decisive of all trials—the 
 law ot battle. Beside these inherent difficulties in decid¬ 
 ing which forms are the most advanced in organization, 
 we ought not solely to compare the highest members of a 
 class at any two periods—though undoubtedly this is one 
 and perhaps the most important element in striking a bal¬ 
 ance—but we ought to compare all the members, high and 
 low, at two periods. At an ancientepoch the highest and low¬ 
 est molluscoidal animals, namely, cephalopods and brachio- 
 pods, swarmed m numbers; at the present time both groups 
 are greatly reduced while others, intermediate in organi¬ 
 zation, have largely increased; consequently some natu¬ 
 ralists maintain that molluscs were formerly more highly 
 developed than at present; but a stronger case can be made 
 out on the opposite side, by considering the vast reduction 
 biachiopods, and the fact that our existing cephalopods, 
 though few in number, are more highly organized than 
 their ancient representatives. We ought also to compare 
 ie lelative proportional numbers, at any two periods, of 
 the high and low classes throughout the world: if for 
 instance, at the present day fifty thousand kinds of verte¬ 
 brate animals exist, and if we knew that at some former 
 period only ten thousand kinds existed, we ought to look 
 
366 STATE OF DEVELOPMENT OF 
 
 at this increase in number in the highest class, which im¬ 
 plies a great displacement of lower forms, as^ a decided 
 advance in the organization of the world. W e thus see 
 how hopelessly difficult it is to compare with peifect faii- 
 ness, under such extremely complex relations, the standaid 
 of organization of the imperfectly-known faunas of succes¬ 
 sive periods. -,,111 
 
 We shall appreciate this difficulty more clearly by look¬ 
 ing to certain existing faunas and floras. From the extra¬ 
 ordinary manner in which European productions have 
 recently spread over New Zealand, and have seized on 
 places which must have been previously occupied by the 
 indigenes, we must believe, that if all the animals and 
 plants of Great Britain were set free in New Zealand, a 
 multitude of British forms would in the course of time 
 become thoroughly naturalized there, and would exter¬ 
 minate many of the natives. On the other hand, from the 
 fact that hardly a single inhabitant of the southern hemi¬ 
 sphere has become wild in any part of Europe, we may 
 well doubt whether, if all the productions of New Zealand 
 were set free in Great Britain, any consideiable number 
 would be enabled to seize on places now occupied by our 
 native plants and animals. Under this point of view, the 
 productions of Great Britain stand much higher in the 
 scale than those of New Zealand. Yet the most skillful 
 naturalist, from an examination of the species of tne two 
 countries, could not have foreseen this result. 
 
 Agassiz and several other highly competent judges insist 
 that ancient animals resemble to a certain extent the em¬ 
 bryos of recent animals belonging to the same classes; and 
 that the geological succession of extinct forms is nearly 
 parallel with the embryological development of existing 
 forms. This view accords admirably well with our theory. 
 In a future chapter I shall attempt to show that the adult 
 differs from its embryo, owing to variations having super¬ 
 vened at a not early age, and having been inherited at a 
 corresponding age. This process, while it leaves the em¬ 
 bryo almost unaltered, continually adds, in the course of 
 successive generations, more and more difference to the 
 adult. Thus the embryo comes to be left as a sort of 
 picture, preserved by nature, of the former and less modi¬ 
 fied condition of the species. This view may be true, and 
 
ANCIENT AND LIVING FORMS 
 
 367 
 
 may never be capable of proof. Seeing, for instance, 
 that the oldest known mammals, reptiles, and fishes strictly 
 belong to their proper classes, though some of these old 
 forms are in a slight degree less distinct from each other 
 than are the typical members of the same groups at the 
 present day, it would be vain to look for animals having 
 the common embryological character of the vertebrata, 
 until beds rich in fossils are discovered far beneath the 
 lowest Cambrian strata—a discovery of which the chance 
 is small. 
 
 (W THE SUCCESSION OF THE SAME TYPES WITHIN THE 
 THE SAME AREAS, DURING THE LATER TERTIARY 
 PERIODS. 
 
 Mr. Clift many years ago showed that the fossil mam¬ 
 mals from the Australian caves were closely allied to the 
 living marsupials of that continent. In South America, a 
 similar relationship is manifest, even to an uneducated 
 eye, in the gigantic pieces of armor, like those of the arma¬ 
 dillo, found in several parts of La Plata; and Professor 
 Owen has shown in the most striking manner that most of 
 the fossil mammals, buried there in such numbers, are re¬ 
 lated to South American types. This relationship is even 
 more clearly seen in the wonderful collection of fossil bones 
 made by MM. Lund and Clausen in the caves of Brazil. I 
 was so much impressed with these facts that I stronglv in¬ 
 sisted, in 1839 and 1845, on this “law of the succession of 
 types/—on “this wonderful relationship in the same con¬ 
 tinent between the dead and the living.” Professor Owen 
 has subsequently extended the same generalization to the 
 mammals of the Old World. We see the same law in this 
 author’s restorations of the extinct and gigantic birds of 
 New.Zealand. We see it also in the birds of the caves of 
 Brazil. . Mr. Woodward has shown that the same law holds 
 good with sea-shells, but, from the wide distribution of 
 most molluscs, it is not well displayed by them. Other 
 cases could be added, as the relation between the extinct 
 and living land-shells of Madeira; and between the extinct 
 and^ living brackish water-shells of the Aralo-Caspian Sea. 
 
 Now, what does this remarkable law of the succession of 
 the same types within the same areas mean? He would be a 
 
368 
 
 SUCCESSION OF THE 
 
 bold man who, after comparing the present climate of 
 Australia and of parts of South America, under the same 
 latitude, would attempt to account, on the one hand 
 through dissimilar physical conditions, for the dissimilarity 
 of the inhabitants of these two continents ; and, on the 
 other hand through similarity of conditions, for the uni¬ 
 formity of the same types in each continent during the 
 later tertiary periods. Nor can it be pretended that it is 
 an immutable law that marsupials should have been chiefly 
 or solely produced in Australia ; or that Edentata and 
 other American types should have been solely produced in 
 South America. For we know that Europe in ancient 
 times was peopled by numerous marsupials ; and I have 
 shown in the publications above alluded to, that in Amer¬ 
 ica the law of distribution of terrestrial mammals was for¬ 
 merly different from what it now is. North America for¬ 
 merly partook strongly of the present character of the 
 southern half of the continent ; and the southern half was 
 formerly more closely allied, than it is at present, to the 
 northern half. In a similar manner we know, from Fal¬ 
 coner and Cautley’s discoveries, that Northern India was 
 formerly more closely related in its mammals to Africa 
 than it is at the present time. Analogous, facts could be 
 given in relation to the distribution of marine animals. 
 
 On the theory of descent with modification, the great law 
 of the long enduring, but not immutable, succession of the 
 same types within the same areas, is at once explained ; for 
 the inhabitants of each quarter of the world will obviously 
 tend to leave in that quarter, during the next succeeding 
 period of time, closely allied though in some degree modi¬ 
 fied descendants. If the inhabitants of one continent for¬ 
 merly differed greatly from those of another continent, so 
 will their modified descendants still differ in nearly the 
 same manner and degree. But after very long intervals of 
 time, and after great geographical changes, permitting 
 much intermigration, the feebler will yield to the more 
 dominant forms, and there will be nothing immutable in 
 the distribution of organic beings. 
 
 It may be asked in ridicule whether I suppose that the 
 megatherium and other allied huge monsters, which for- 
 merely lived in South America, have left behind them the 
 sloth, armadillo, and ant-eater, as their degenerate descend. 
 
SAME TYPES IN TIIE SAME AREAS. 
 
 369 
 
 ants. This cannot for an instant be admitted. These 
 huge animals have become wholly extinct, and have left no 
 progeny. But in the caves of Brazil there are many 
 extinct species which are closely allied in size and in all 
 other characters to the species still living in South America; 
 and some of these fossils may have been the actual progeni¬ 
 tors of the living species. It must not be forgotten that, 
 on our theory, all the species of the same genus are the 
 descendants of some one species; so that, if six genera, 
 each having eight species, be found in one geological for¬ 
 mation, and in a succeeding formation there be six other 
 allied or representative genera, each with the same number 
 of species, then we may conclude that generally only one 
 species of each of the older genera has left modified 
 descendants, which constitute the new genera containing 
 the several species; the other seven species of each old 
 genus having died out and left no progeny. Or, and this 
 will be a far commoner case, two or three species in two or 
 three alone of the six older genera will be the parents of 
 the new genera : the other species and the other old genera 
 having become utterly extinct. In failing orders, with the 
 genera and species decreasing in numbers as is the case 
 with the Edentata of South America, still fewer genera 
 and species will leave modified blood-descendants. 
 
 SUMMARY OF THE PRECEDING AND PRESENT CHAPTERS 
 
 I have attempted to show that the geological record is 
 extremely imperfect; that only a small portion of the 
 globe has been geologically explored with care; that only 
 certain classes of organic beings have been largely preserved 
 in a fossil state; that the number both of specimens and of 
 species, preserved in our museums, is absolutely as nothing 
 compared with the number of generations which must have 
 passed away even during a single formation ; that, owing 
 to subsidence being almost necessary for the accumulation 
 of deposits rich in fossil species of many kinds, and thick 
 enough to outlast future degradation, great intervals of 
 time must have elapsed between most of our successive for¬ 
 mations ; that there has probably been more extinction 
 during the periods of subsidence, and more variation 
 during the periods of elevation, and during the latter 
 
370 
 
 SUMMARY OF TEF 
 
 the record will have been least perfectly kept; that each 
 single formation has not been continuously deposited; 
 that the duration of each formation is probably short com¬ 
 pared with the average duration of specific forms; that 
 migration has played an important part in the first appear¬ 
 ance of new forms in any one area and formation ; that 
 widely ranging species are those which have varied most 
 frequently, and have oftenest given rise to new species ; that 
 varieties have at first been local; and lastly, although each 
 species must have passed through numerous transitional 
 stages, it is probable that the periods, during which each 
 underwent modification, though many and long as meas¬ 
 ured by years, have been short in comparison with the 
 periods during which each remained in an unchanged con¬ 
 dition. These causes, taken conjointly, will to a large 
 extent explain why—though we do find many links—we do 
 not find interminable varieties, connecting together all 
 extinct and existing forms by the finest graduated steps. 
 It should also be constantly borne in mind that any linking 
 variety between two forms, which might be found, would 
 be ranked, unless the whole chain could be perfectly 
 restored, as a new and distinct species; for it is not pre¬ 
 tended that we have any sure criterion hv which species 
 and varieties can be discriminated. 
 
 He who rejects this view of the imperfection of the geo¬ 
 logical record, will rightly reject the whole theory. For he 
 may ask in vain where are the numberless transitional 
 links which must formerly have connected the closely 
 allied or representative species, found in the successive 
 stages of the same great formation? He may disbelieve in 
 the immense intervals of time which must have elapsed 
 between our consecutive formations; he may overlook how 
 important a part migration has played, when the forma¬ 
 tions of any one great region, as those of Europe, are con¬ 
 sidered; he may urge the apparent, but often falsely 
 apparent, sudden coming in of whole groups of species. 
 He may ask where are the remains of those infinitely nu¬ 
 merous organisms which must have existed long before the 
 Cambrian system was deposited? We now know that at 
 least one animal did then exist; but I can answer this last 
 question only by supposing that where our oceans now 
 extend they have extended for an enormous period, and 
 
PRECEDiNG AND PRESENT CHAPTERS. 37 j 
 
 where our oscillating continents now stand they have stood 
 since the commencement of the Cambrian system: but. 
 that, long before that epoch, the world presented a widely 
 c lfieient aspect; and that the older continents, formed of 
 01 mations older than any known to us, exist now only as 
 
 remnants in a metamorphosed condition, or lie still buried 
 under the ocean. 
 
 Passing from these difficulties, the other great leading 
 tacts m palaeontology agree admirably with the theory of 
 descent with modification through variation and natural 
 selection. \Ve can thus understand how it is that new 
 species come in slowly and successively; how species of 
 ctmerent classes do not necessarily change together, or at 
 the same rate, or in the same degree; yet in the long run 
 that all undergo modification to some extent. The ex¬ 
 tinction of old forms is the almost inevitable consequence 
 of the production of new forms. We can understancTwhy 
 w len a species has once disappeared, it never reappears, 
 vxi oups of species increase in numbers slowly, and endure 
 for unequal periods of time; for the process cf modifica- 
 lon is necessarily slow, and depends on many complex 
 contingencies. The dominant species belonging to large 
 and dominant groups tend to leave many modified descend¬ 
 ants, which form new sub-groups and groups. As these 
 are formed, the species of the less vigorous groups, from 
 their inferiority inherited from a common progenitor, tend 
 to become extinct together, and to leave no modified off¬ 
 spring on the face of the earth. But the utter extinction 
 of a whole group of species has sometimes been a slow pro¬ 
 cess, from the survival of a few descendants, lingering in 
 protected and isolated situations. When a group has once 
 wholly disappeared, it does not reappear; for the link of 
 generation has been broken. 
 
 We can understand how it is that dominant forms which 
 spread widely and yield the greatest number of varieties 
 tend to people the world with allied, but modified, de¬ 
 scendants; and these will generally succeed in displacing 
 the groups which are their inferiors in the struggle for 
 existence. Hence, after long intervals of time, the pro- 
 ductions of the world appear to have changed simultane- 
 
 We can understand how it is that all the forms of life. 
 
SUMMAR Y OF CHAPTERS. 
 
 372 
 
 ancient and recent, make together a few grand classes. 
 We can understand, from the continued tendency to di¬ 
 vergence of character, why the more ancient a foi m is, the 
 more it generally differs from those now living; why 
 ancient and extinct forms often tend to fill up gaps be¬ 
 tween existing forms, sometimes blending two groups, pre¬ 
 viously classed as distinct, into one; but more commonly 
 bringing them only a little closer together. The more 
 ancient a form is, the more often it stands in some degree 
 intermediate between groups now distinct; for the moie 
 ancient a form is, the more nearly it will be related to, and 
 consequently resemble, the common progenitor of groups, 
 since become widely divergent. Extinct forms are seldom 
 directly intermediate between existing forms; but are in¬ 
 termediate only by a long and circuitous couise thiough 
 other extinct and different forms. We can clearly see why 
 the organic remains of closely consecutive formations are 
 closely^allied; for they are closely linked together by gen¬ 
 eration. We can clearly see why the remains of an inter¬ 
 mediate formation are intermediate in character.. 
 
 The inhabitants of the world at eacli successive period 
 in its history have beaten their predecessors in the race for 
 life, and are, in so far, higher in the scale, and their 
 structure has generally become more specialized; and this 
 may account for the common belief held by so many palae¬ 
 ontologists, that organization on the whole has progressed. 
 Extinct and ancient animals resemble to a certain extent the 
 embryos of the more recent animals belonging to the same 
 classes, and this wonderful fact receives a simple explana¬ 
 tion according to our views. The succession of the same 
 types of structure within the same areas during The later 
 geological periods ceases to be mysterious, and is intelligible 
 
 on the principle of inheritance. 
 
 If, then, the geological record be as imperfect as many 
 believe, and it may at least be asserted that the record cannot 
 be proved to be much more perfect, the main objections to 
 the theory of natural selection are greatly diminished or 
 disappear. On the other hand, all the chief laws of 
 paleontology plainly proclaim, as it seems to me, that 
 species have been produced by ordinary generation: old 
 forms having been supplanted by new and improved forms 
 of life, the products of Variation and the Survival of the 
 Eittest. 
 
GEOGRAPHICAL DISTRIBUTION ,. 
 
 • 
 
 CHAPTER XII. 
 
 GEOGRAPHICAL DISTRIBUTION. 
 
 Present distribution cannot be accounted for by differences in 
 physical conditions — Importance of barriers—Affinity of the 
 productions of the same continent—Centers of creation—Means 
 of dispersal by changes of climate and of the level of the land, 
 and by occasional means—Dispersal during the Glacial period— 
 Alternate Glacial periods in the North and South. 
 
 In considering the distribution of organic beings 
 over the face of the globe, the first great fact which strikes 
 us is, that neither the similarity nor the dissimilarity of 
 the inhabitants of various regions can be wholly accounted 
 for by climatal and other physical conditions. Of late, 
 almost every author who has studied the subject has come 
 to this conclusion. The case of America alone would 
 almost suffice to prove its truth; for if we exclude the 
 arctic and northern temperate parts, all authors agree that 
 one of the most fundamental divisions in geographical 
 distribution is that between the New and the Old Worlds; 
 yet if we travel over the vast American continent, from 
 the central parts of the United States to its extreme south¬ 
 ern point, we meet with the most diversified conditions; 
 humid districts, arid deserts, lofty mountains, grassy 
 plains, forests, marshes, lakes and great rivers, under 
 almost every temperature. There is hardly a climate or 
 condition in the Old World which cannot be paralleled in 
 the New—at least so closely as the same species generally 
 require. No doubt small areas can be pointed out in the 
 Old World hotter than any in the New World; but these 
 are not inhabited by a fauna different from that of the sur¬ 
 rounding districts; for it is rare to find a group of organ¬ 
 isms confined to a small area, of which the conditions are 
 peculiar in only a slight degree. Notwithstanding this 
 
374 
 
 GEOGRAPHICAL DISTRIBUTION. 
 
 general parallelism in the conditions of Old and New 
 Worlds, how widely different are their living productions. 
 
 Iii the southern hemisphere, if we compare large tracts 
 of land in Australia, South Africa, and western oout 1 
 America, between latitudes 25 and 35 degrees, we sha 
 find parts extremely similar in all tlieir conditions, yet it 
 would not be possible to point out three faunas and floras 
 more utterly dissimilar. Or, again, we may compare the 
 productions of South America south of latitude 3o degiees 
 with those north of 25 degrees, which consequently are 
 separated by a space of ten degrees of latitude, and ai e 
 exposed to considerably different conditions; yet they are 
 incomparably more closely related to each other than they 
 are to the productions of Australia or Africa under nearly 
 the same climate. Analogous facts could be given with 
 
 respect to the inhabitants of the sea. < 
 
 A second great fact which strikes us m our general 
 review is, that barriers of any kind, or obstacles to tree 
 migration, are related in a close and important manner 
 to the differences between the productions ot various 
 regions. We see this in the great difference m nearly 
 all the terrestrial productions of the Isew and Old 
 Worlds, excepting in the northern parts, where the land 
 almost ioins, and where, under a slightly different climate, 
 there might have been free migration for the northern 
 temperate forms, as there now is for the strictly arctic pio- 
 ductions. We see the same fact in the great difference 
 between the inhabitants of Australia, Africa and bouth 
 America under the same latitude; for these countries aie 
 almost as much isolated from each other as is possible. On 
 each continent, also, we see the same fact; for on the op¬ 
 posite sides of lofty and continuous mountain-ranges, ot 
 great deserts and even of large rivers, we find different 
 productions; though as mountain-chains, deserts, etc., aie 
 not as impassable, or likely to have endured so long, as the 
 oceans separating continents, the differences are very in¬ 
 ferior in degree to those characteristic of distinct con¬ 
 tinents. . 
 
 Turning to the sea, we find the same law. 1 he marine 
 
 inhabitants of the eastern and western shores of boutli 
 America are very distinct, with extremely few shells, Crus¬ 
 tacea, or echinodermata in common; but Dr. (xuntner nas 
 
 
GEOGRAPHICAL DISTRIBUTION. 
 
 375 
 
 recently shown that about thirty per cent, of the fishes are 
 the same on the opposite sides of the isthmus of Panama; 
 and this fact has led naturalists to believe that the isthmus 
 was formerly open. Westward of the shores of America, 
 a wide space of open ocean extends, with not an island as 
 a halting-place for emigrants; here we have a barrier of 
 another kind, and as soon as this is passed we meet in the 
 eastern islands of the Pacific with another and totally dis¬ 
 tinct fauna. So that three marine faunas range northward 
 and southward in parallel lines not far from each other, 
 under corresponding climate; but from being separated 
 from each other by impassable barriers, either of land or 
 open sea, they are almost wholly distinct. On the other 
 hand, proceeding still further westward from the eastern 
 islands of the tropical parts of the Pacific, we encounter 
 no impassable barriers, and we have innumerable islands as 
 halting-places, or continuous coasts, until, after traveling 
 over a hemisphere, we come to the shores of Africa; and 
 over this vast space we meet with no well-defined and dis¬ 
 tinct marine faunas. Although so few marine animals are 
 common to the above-named three approximate faunas of 
 Eastern and Western America and the eastern Pacific 
 islands, yet many fishes range from the Pacific into the 
 Indian Ocean, and many shells are common to the eastern 
 islands of the Pacific and the eastern shores of Africa on 
 almost exactly opposite meridians of longitude. 
 
 A third great fact, partly included in the foregoing 
 statement, is the affinity of the productions of the same 
 continent or of the same sea, though the species themselves 
 are distinct at different points and’stations. It is a law of 
 the widest generality, and every continent offers innum¬ 
 erable instances. Nevertheless, the naturalist, in travel¬ 
 ing, for instance, from north to south, never fails to be 
 struck by the manner in which successive groups of beings, 
 specifically distinct, though nearly related, replace each 
 other. He hears from closely allied, yet distinct kinds of 
 birds, notes nearly similar, and sees their nests similarly con¬ 
 structed, but not quite alike, with eggs colored in nearly the 
 same manner. The plains near the Straits of Magellan are 
 inhabited by one species of Rhea (American ostrich), and 
 northward the plains of La Plata by another species of the 
 same genus; and not by a true ostrich or emu, like those 
 
376 GEOGRAPHICAL DISTRIBUTION. 
 
 inhabiting Africa and Australia under the same latitude. 
 On these same plains of La Plata we see the agouti 
 and bizcacha, animals having nearly the same habits as 
 our hares and rabbits, and belonging to the same order of 
 rodents, but they plainly display an American type of 
 structure. We ascend the lofty peaks of the Cordillera, 
 and we find an alpine species of bizcacha; we look to the 
 waters, and we do not find the beaver or muskrat, but the 
 ' coypu and capybara, rodents of the South American type. 
 Innumerable other instances could be given. If we look to 
 the islands off the American shore, however much they may 
 differ in geological structure, the inhabitants _ are essen¬ 
 tially American, though they may be all peculiar species. 
 We may look back to past ages, as shown in the last 
 chapter, and we find American types then prevailing on the 
 American continent and in the American seas. We see in 
 these facts some deep organic bond, throughout space and 
 time, over the same areas of land and water, independently 
 of physical conditions. The naturalist must be dull who 
 is not led to inquire what this bond is. 
 
 The bond is simply inheritance, that cause which alone, 
 as far as we positively know, produces organisms quite like 
 each other, or, as we see in the case of varieties, nearly 
 alike. The dissimilarity of the inhabitants of different 
 regions may be attributed to modification through variation 
 and natural selection, and probably in a subordinate degree 
 to the definite influence of different physical conditions. 
 The degrees of dissimilarity will depend on the migration 
 of the more dominant forms of life from one region into 
 another having been more or less effectually prevented, at 
 periods more or less remote—on the nature and number of 
 the former immigrants—and on the action of the inhab¬ 
 itants on each other in leading to the preservation of differ¬ 
 ent modifications; the relation of organism to organism in 
 the struggle for life being, as I Jiave already often re¬ 
 marked, the most important of all relations. Thus the 
 high importance of barriers comes into play by checking 
 migration; as does time for the slow process of modifica¬ 
 tion through natural selection. Widely-ranging species, 
 abounding in individuals, which have already triumphed 
 over many competitors in their own widely-extended homes, 
 will have the best chance of seizing on new places, when 
 
GEOGRAPHICAL DISTRIBUTION. 
 
 377 
 
 they spread out into new countries. In their new homes 
 they will be exposed to new conditions, and will frequently 
 undergo further modification and improvement; and thus 
 they will become still further victorious, and will produce 
 groups of modified descendants. On this principle of in¬ 
 heritance with modification we can understand how it is 
 that sections of genera, whole genera, and even families, 
 are confined to the same areas, as is so commonly and noto¬ 
 riously the case. 
 
 There is no evidence, as was remarked in the last 
 chapter, of the existence of any law of necessary develop¬ 
 ment. As the variability of each species is an independent 
 property, and will be taken advantage of by natural selec¬ 
 tion, only so far as it profits each individual in its complex 
 struggle for life, so the amount of modification in different 
 species will be no uniform quantity. If a number of species, 
 after having long competed with each other in their old 
 home, were to migrate in a body into a new and afterward 
 isolated country, they would be little liable to modification; 
 for neither migration nor isolation in themselves effect any 
 thing. These principles come into play only by bringing 
 organisms into new relations with each other and in a lesser 
 degree with the surrounding physical conditions. As wc 
 have seen in the last chapter that some forms have retained 
 nearly the same character from an enormously remote 
 geological period, so certain species have migrated over 
 vast spaces, and have not become greatly or at all modified. 
 
 According to these views, it is obvious that the several 
 species of the same genus, though inhabiting the most 
 distant quarters of the world, must originally have pro¬ 
 ceeded from the same source, as they are descended 
 from the same progenitor. In the case of those 
 species which have undergone, during whole geological 
 periods, little modification, there is not much difficulty in 
 believing that they have migrated from the same region; 
 for during the vast geographical and climatical changes 
 which have supervened since ancient times, almost any 
 amount of migration is possible. But in many other cases, 
 in which we have reason to believe that the species of a 
 genus have been produced within comparatively recent 
 times, there is great difficulty on this head. It is also 
 obvious that the individuals of the same species,, though 
 
378 
 
 SINGLE CENTERS OF CREATION 
 
 now inhabiting distant and isolated regions, must have 
 proceeded from one spot, where their parents were first 
 produced: for, as has been explained, it is incredible that 
 individuals indentically the same should have been pro¬ 
 duced from parents specifically distinct. 
 
 SINGLE CENTERS OF SUPPOSED CREATION. 
 
 We are thus brought to the question which has been 
 largely discussed by naturalists, namely, whether species 
 have been created at one or more points of the earth's sur¬ 
 face. Undoubtedly there are many cases of extreme diffi¬ 
 culty in understanding how the same species could possi¬ 
 bly have migrated from some one point to the several dis¬ 
 tant and isolated points, where now found. Nevertheless 
 the simplicity of the view that each species was first pro¬ 
 duced within a single region captivates the mind. He who 
 rejects it, rejects the vera causa of ordinary generation 
 with subsequent migration, and calls in the agency of a 
 miracle. It is universally admitted, that in most cases the 
 area inhabited by a species is continuous; and that when a 
 plant or animal inhabits two points so distant from each 
 other, or with an interval of such a nature, that the space 
 could not have been easily passed over by migration, the 
 fact is given as something remarkable and exceptional. 
 The incapacity of migrating across a wide sea is more clear 
 in the case of terrestrial mammals than perhaps with any 
 other organic beings; and, accordingly, we find no inex¬ 
 plicable instances of the same mammals inhabiting distant 
 points of the world. No geologist feels any difficulty in 
 Great Britain possessing the same quadrupeds with the 
 rest of Europe, for they were no doubt once united. But 
 if the same species can be produced at two separate points, 
 why do we not find a single mammal common to Europe 
 and Australia or South America? The conditions of life 
 are nearly the same, so that a multitude of European 
 animals and plants have become naturalized in America 
 and Australia; and some of the aboriginal plants are 
 identically the same at these distant points of the 
 northern and southern hemispheres? The answer, as 
 I believe, is, that mammals have not been able to 
 migrate, whereas gome plants, from their varied means 
 
SINGLE CENTERS OF CREATION. 
 
 m 
 
 of dispersal, have migrated across the wide and broken 
 interspaces. The great and striking influence of barriers 
 of all kinds, is intelligible only on the view that the great 
 majority of species have been produced on one side, and 
 have not been able to migrate to the opposite side. Some 
 few families, many subfamilies, very many genera, a still 
 greater number of. sections of genera, are confined to a 
 single region; and it has been observed by several natural¬ 
 ists that the most natural genera, or those genera in which 
 the species are most closely related to each other, are gen¬ 
 erally confined to the same country, or if they have a wide 
 range that their range is continuous. What a strange 
 anomaly it would be if a directly opposite rule were to 
 prevail when we go down one step lower in the series, 
 namely, to the individuals of the same species, and 
 these had not been, at least at first, confined to some one 
 region! 
 
 Hence, it seems to me, as it has to many other natu¬ 
 ralists, that the view of each species having been produced 
 in one area alone, and having subsequently migrated from 
 that area as far as its powers of migration and subsistence 
 under past and present conditions permitted, is the most 
 probable. Undoubtedly many cases occur in which we 
 cannot explain how the same species could have passed from 
 one point to the other. But the geographical and climatical 
 changes which have certainly occurred within recent geo¬ 
 logical times, must have rendered discontinuous the for¬ 
 merly continuous range of many species. So that we are 
 reduced to consider whether the exceptions to continuity of 
 range are so numerous, and of so grave a nature, that we 
 ought to give up the belief, rendered probable by general 
 considerations, that each species has been produced within 
 one area, and has migrated thence as far as it could. It 
 would be hopelessly tedious to discuss all the exceptional 
 cases of the same species, now living at distant and sep¬ 
 arated points, nor do I for a moment pretend that any 
 explanation could be offered of many instances. But, 
 after some preliminary remarks, I will discuss a few of the 
 most striking classes of facts, namely, the existence of the 
 same species on the summits of distant mountain ranges, 
 and at distant points in the Arctic and Antarctic regions; 
 and secondly (in the following chapter), the wide distri- 
 
SINGLE CENTERS OF CREATION. 
 
 380 
 
 bution of fresh water productions; and thirdly, the 
 occurrence of the same terrestrial species on islands and 
 on the nearest mainland, though separated by hundreds of 
 miles of open sea. If the existence of the same species at 
 distant and isolated points of the earth , s surface can in 
 many instances be explained on the view of each species 
 having migrated from a single birthplace, then, consider¬ 
 ing our ignorance with respect to former climatical and geo¬ 
 graphical changes, and to the various occasional means of 
 transport, the belief that a single birthplace is the law 
 seems to me incomparably the safest. 
 
 In discussing this subject we shall be enabled at the 
 same time to consider a point equally important for us, 
 namely, whether the several species of a genus which must 
 on our theory all be descended from a common progenitor, 
 can have migrated, undergoing modification during their 
 migration from some one area. If, when most of the spe¬ 
 cies inhabiting one region arc different from those of another 
 region, though closely allied to them, it can be shown that 
 migration from the "one region to the other has probably 
 occurred at some former period, our general view will be much 
 strengthened; for the explanation is obvious on the principle 
 of descent with modification. A volcanic island, for in¬ 
 stance, upheaved and formed at the distance of a few 
 hundreds of miles from a continent, would probably receive 
 from it in the course of time a few colonists, and their 
 descendants, though modified, would still be related by 
 inheritance to the inhabitants of that continent. Cases of 
 this nature are common, and are, as we shall hereafter see, 
 inexplicable on the theory of independent creation. This 
 view of the relation of the species of one region to those of 
 another, does not differ much from that advanced by Mr. 
 Wallace, who concludes that “ every species has come into 
 existence coincident both in space and time with a pre¬ 
 existing closely allied species.” And it is now well known 
 that he attributes this coincidence to descent with modi¬ 
 fication. 
 
 The question of single or multiple centres of creation 
 differs from another though allied question, namely, 
 whether all individuals of the same species are descended 
 from a single pair, or single hermaphrodite, or whether, as 
 some authors suupose, from many individuals simultane- 
 
MEANS OF DISPERSAL. 
 
 381 
 
 ously created. With organic beings which never intercross, 
 if such exist, each species must be descended from a suc¬ 
 cession of modified varieties, that have supplanted each 
 other, but have never blended with other individuals or 
 varieties of the same species; so that, at each successive 
 stage of modification, all the individuals of the same form 
 will be descended from a single parent. But in the great 
 majority of cases, namely, with all organisms which habit¬ 
 ually unite for each birth, or which occasionally intercross, 
 the individuals of the same species inhabiting the same 
 area will be kept nearly uniform by intercrossing; so that 
 many individuals will go on simultaneously changing, and 
 the whole amount of modification at each stage will not be 
 due to descent from a single parent. To illustrate what I 
 mean: our English race-horses differ from the horses of 
 every other breed; but they do not owe their difference and 
 superiority to descent from any single pair, but to continued 
 care in the selecting and training of many individuals 
 during each generation. 
 
 Before discussing the three classes of facts, which I have 
 selected as presenting the greatest amount of difficulty on 
 the theory of “ single centers of creation,” I must say a 
 few words on the means of dispersal. 
 
 MEANS OF DISPERSAL. 
 
 Sir C. Lyell and other authors have ably treated this 
 subject. I can give here only the briefest abstract of the 
 more important facts. Change of climate must have had 
 a powerful influence on migration. A region now impass¬ 
 able to certain organisms from the nature of its climate, 
 might have been a high road for migration, when the 
 climate was different. I shall, however, presently have to 
 discuss this branch of the subject in some detail. "Changes 
 of level in the land must also have been highly influential: 
 a narrow isthmus now separates two marine faunas; sub¬ 
 merge it, or let it formerly have been submerged, 
 and the two faunas will now blend together, or may 
 formerly have blended. Where the sea now extends, 
 land may at a former period have connected islands or pos¬ 
 sibly even continents together, and thus have allowed terres¬ 
 trial productions to pass from one to the other. No geologist 
 
382 
 
 MEANS OF DISPERSAL. 
 
 disputes that great mutations of level have occurred within 
 the period of existing organisms. Edward Forbes insisted 
 that all the islands in the Atlantic must have been recently 
 connected with Europe or Africa, and Europe likewise 
 with America. Other authors have thus hypothetically 
 bridged over every ocean, and united almost every island 
 with some mainland. If, indeed, the arguments used by 
 Eorbes are to be trusted, it must be admitted that 
 scarcely a single island exists which has not recently 
 been united to some continent. This view cuts the 
 Gordian knot of the dispersal of the same species to the 
 most distant points, and removes many a difficulty; but to 
 the best of my judgment we are not authorized in admit¬ 
 ting such enormous geographical changes within the period 
 of existing species. It seems to me that we have abundant 
 evidence of great oscillations in the level of the land or 
 sea; but not of such vast changes in the position and ex¬ 
 tension of our continents, as to have united them within 
 the recent period to each other and to the several interven¬ 
 ing oceanic islands. I freely admit the former existence 
 of many islands, now buried beneath the sea, which may 
 have served as halting-places for plants and for many 
 animals during their migration. In the coral-producing 
 oceans such sunken islands are now marked by rings of 
 coral or atolls standing over them. Whenever it is fully 
 admitted, as it will some day be, that each species has 
 proceeded from a single birthplace, and when in the course 
 of time we know something definite about the means of 
 distribution, we shall be enabled to speculate with security 
 on the former extension of the land. But I do not believe 
 that it will ever be proved that within the recent period 
 most of our continents which now stand quite separate, 
 have been continuously, or almost continuously united 
 with each other, and with the many existing oceanic 
 islands. Several facts in distribution—such as the great 
 difference in the marine faunas on the opposite sides of 
 almost every continent—the close relation of the tertiary 
 inhabitants of several lands and even seas to their present 
 inhabitants—the degree of affinity between the mammals 
 inhabiting islands with those of the nearest continent, 
 being in part determined (as we shall hereafter see) by the 
 depth of the intervening ocean—these and other such 
 
MEANS OF DISPERSAL. 
 
 383 
 
 facts are opposed to the admission of such prodigious geo¬ 
 graphical revolutions within the recent period, as are 
 necessary on the view advanced by Forbes and admitted by 
 his followers. The nature and relative proportions of the 
 inhabitants of oceanic islands are likewise opposed to the 
 belief of their former continuity of continents. Nor does 
 the almost universally volcanic composition of such islands 
 favor the admission that they are the wrecks of sunken 
 continents; if they had originally existed as continental 
 mountain ranges, some at least of the islands would have 
 been formed, like other mountain summits, of granite, 
 metamorphic schists, old fossiliferous and other rocks, in¬ 
 stead of consisting of mere piles of volcanic matter. 
 
 I must now say a few words on what are called acci¬ 
 dental means, but which more properly should he called 
 occasional means of distribution. I shall here confine 
 myself to plants. In botanical works, this or that plant 
 is often stated to be ill adapted for wide dissemination; 
 but the greater or less facilities for transport across the 
 sea may be said to be almost wholly unknown. Until 
 I tried, with Mr. Berkeley^ aid, a few experiments, it 
 was not even known how far seeds could resist the in¬ 
 jurious action of sea-water. To my surprise I found 
 that out of eighty-seven kinds, sixty-four germinated 
 after an immersion of twenty-eight days, and a few 
 survived an immersion of 137 days. It deserves notice 
 that certain orders were far more injured than others: nine 
 Leguminosse were tried, and, with one exception, they 
 resisted the salt-water badly; seven species of the allied 
 orders, Hydrophyllaceas and Polemoniaceaj, were all killed 
 by a month's immersion. For convenience sake I chiefly 
 tried small seeds without the capsules or fruit; and as all 
 of these sunk in a few days, they could not have been 
 floated across wide spaces of the sea, whether or not they 
 were injured by salt water. Afterward I tried some larger 
 fruits, capsules, etc., and some of these floated for a long 
 time. It is well known what a difference there is in the 
 buoyancy of green and seasoned timber; and it occurred 
 to me that floods would often wash into the sea dried 
 plants or branches with seed-capsules or fruit attached to 
 them. Hence I was led to dry the stems and branches of 
 ninety-four plants with ripe fruit, and to place them on 
 
384 
 
 MEANS OF DISPERSAL. 
 
 sea-water. The majority sunk quickly, but some which, 
 while green, floated, for a very short time, when dried, 
 floated much longer; for instance, ripe hazel-nuts sunk 
 immediately, but when dried they floated for ninety days, 
 and afterward when planted germinated; an asparagus- 
 plant with ripe berries floated for twenty-three days, wdien 
 dried it floated for eighty-five days, and the seeds after¬ 
 ward germinated; the ripe seeds of Helosciadium sunk in 
 two days, when dried they floated for above ninety days, 
 and afterward germinated. Altogether, out of the ninety- 
 four dried plants, eighteen floated for above twenty-eight 
 days; and some of the eighteen floated for a very much longer 
 period. So that as -§4 kinds of seeds germinated after an 
 immersion of twenty-eight days; and as distinct species 
 with ripe fruit (but not all the same species as in the forego¬ 
 ing experiment) floated, after being dried, for above twenty- 
 eight days, we may conclude, as far as anything can be 
 inferred from these scanty facts, that the seeds of y 1 ^ 
 kinds of plants of any country might be floated by sea- 
 currents during twenty-eight days, and would retain their 
 power of germination. In Johnston's Physical Atlas, the 
 average rate of the several Atlantic currents is thirty-three 
 miles per diem (some currents running at the rate of sixty 
 miles per diem); on this average, the seeds of plants 
 belonging to one country might be floated across 924 miles 
 of sea to another country, and when stranded, if blown by 
 an inland gale to a favorable spot, would germinate. 
 
 Subsequently to my experiments, M. Martens tried sim¬ 
 ilar ones, but in a much better manner, for he placed the 
 seeds in a box in the actual sea, so that they were alter¬ 
 nately wet and exposed to the air like really floating 
 plants. He tried ninety-eight seeds, mostly different from 
 mine, but he chose many large fruits, and likewise seeds, 
 from plants which live near the sea; and this would have 
 favored both the average length of their flotation and their 
 resistance to the injurious action of the salt-water. On 
 the other hand, he did not previously dry the plants or 
 branches with the fruit; and this, as we have seen, would 
 have caused some of them to have floated much longer. 
 The result was that -£-f of his seeds of different kinds 
 floated for forty-two days, and were then capable of ger¬ 
 mination. But I do not doubt that plants exposed to the 
 
MEANS OF DISPERSAL. 
 
 385 
 
 waves would float for a less time than those protected from 
 violent movement as in our experiments. Therefore, it 
 would perhaps be safer to assume that the seeds of about 
 ■jW plants of a flora, after having been dried, could be 
 floated across a space of sea 900 miles in width, and would 
 then germinate. The facts of the larger fruits often float¬ 
 ing longer than the small, is interesting; as plants with 
 large seeds or fruit which, as Alph. de Candolle has shown, 
 generally have restricted ranges, could hardly be trans¬ 
 ported by any other means. 
 
 Seeds may be occasionally transported in another 
 manner. Drift timber is thrown up on most islands, 
 even on those in the midst of the widest oceans; and the 
 natives of the coral islands in the Pacific procure stones 
 for their tools, solely from the roots of drifted trees, these 
 stones being a valuable royal tax. I find that when irregu¬ 
 larly shaped stones are embedded in the roots of trees, 
 small parcels of earth are frequently inclosed in their inter¬ 
 stices and behind them, so perfectly that not a particle 
 could be washed away during the longest transport: out of 
 one small portion of earth thus completely inclosed by the 
 roots of an oak about fifty years old, three dicotyledonous 
 plants germinated: I am certain of the accuracy of this 
 observation. Again, I can show that the carcasses of birds, 
 when floating on the sea, sometimes escape being immedi¬ 
 ately devoured: and many kinds of seeds in the crops of 
 floating birds long retain their vitality: peas and vetches, 
 for instance, are killed by even a few days* immersion in 
 sea-water; but some taken out of the crop of a pigeon, 
 which had floated on artificial sea-water for thirty days, to 
 my surprise nearly all germinated. 
 
 Living birds can hardly fail to be highly effective agents 
 in the transportation of seeds. I could give many facts 
 showing how frequently birds of many kinds are blown by 
 gales to vast distances across the ocean. We may safely 
 assume that under such circumstances their rate of flight 
 would often be thirty-five miles an hour; and some authors 
 have given a far higher estimate. I have never seen an 
 instance of nutritious seeds passing through the intestines 
 of a bird; but hard seeds of fruit pass uninjured through 
 even the digestive organs of a turkey. In the course of 
 two months, I picked up in my garden twelve kinds of 
 
386 
 
 MEANS OE DISPERSAL. 
 
 seeds, out of the excrement of small birds, and these 
 seemed perfect, and some of them, which were tried, ger¬ 
 minated. But the following fact is more important: the 
 crops of birds do not secrete gastric juice, and do not, as I 
 know by trial, injure in the least the germination of seeds; 
 now, after a bird has found and devoured a large supply of 
 food, it is positively asserted that all the grains do not pass 
 into the gizzard for twelve or even eighteen hours. A 
 bird in this interval might easily be blown to the distance 
 of five hundred miles, and hawks are known to look out 
 for tired birds, and the contents of their torn crops might 
 thus readily get scattered. Some hawks and owls bolt 
 their prey whole, and, after an interval of from twelve to 
 twenty hours, disgorge pellets, which, as I know from ex¬ 
 periments made in the Zoological Gardens, include seeds 
 capable of germination. Some seeds of the oat, wheat, 
 millet, canary, hemp, clover, and beet germinated after 
 having been from twelve to twenty-one hours in the 
 stomachs of different birds of prey; and two seeds of beet 
 grew after having been thus retained for two days and 
 fourteen hours. Fresh-water fish, I find, eat seeds of many 
 land and water plants; fish are frequently devoured by 
 birds, and thus the seeds might be transported from place 
 to place. I forced many kinds of seeds into the stomachs 
 of dead fish, and then gave their bodies to fishing-eagles, 
 storks, and pelicans; these birds, after an interval of many 
 hours, either rejected the seeds in pellets or passed.them in 
 their excrement; and several of these seeds retained the 
 power of germination. Certain seeds, however, were 
 always killed by this process. 
 
 Locusts are sometimes blown to great distances from the 
 land. I myself caught one 370 miles from the .coast of 
 Africa, and have heard of others caught at greater distances. 
 The Rev. R. T. Lowe informed Sir C. Lyell that in No¬ 
 vember, 1844, swarms of locusts visited the island of 
 Madeira. They were in countless numbers, as thick as 
 the flakes of snow in the heaviest snowstorm, and extended 
 upward as far as could be seen with a telescope. During 
 two or three days they slowly careered round and round in 
 an immense ellipse, at least five or six miles in diameter, 
 and at night alighted on the taller trees, which were com¬ 
 pletely coated with them. They then disappeared over the 
 
MEANS OF DISPERSAL. 
 
 387 
 
 sea, as suddenly as they had appeared, and have not since 
 visited the island. Now, in parts of Natal it is believed by 
 some farmers, though on insufficient evidence, that injuri¬ 
 ous seeds are introduced into their grass-land in the dung 
 left by the great flights of locusts which often visit that 
 country. In consequence of this belief Mr. Weale sent me 
 in a letter a small packet of the dried pellets, out of which 
 I extracted under the microscope several seeds, and raised 
 from them seven grass plants, belonging to two species, of 
 two genera. Hence a swarm of locusts, such as that 
 which visited Madeira, might readily be the means of in¬ 
 troducing several kinds of plants into an island lying far 
 from the mainland. 
 
 Although the beaks and feet of birds are generally clean, 
 earth sometimes adheres to them: in one case I removed 
 sixty-one grains, and in another case twenty-two grains of 
 dry argillaceous earth from the foot of a partridge, and in 
 the earth there was a pebble as large as the seed of a vetch. 
 Here is a better case: the leg of a woodcock was sent to 
 me by a friend, with a little cake of dry earth attached to 
 the shank, weighing only nine grains; and this contained 
 a seed of the toad-rush (Juncus bufonius) which germin¬ 
 ated and flowered. Mr. Swaysland, of Brighton, who dur¬ 
 ing the last forty years has paid close attention to our 
 migratory birds, informs me that he has often shot wag¬ 
 tails (Motacillse), wheatears, and whinchats (Saxicolae), on 
 their first arrival on our shores, before they had alighted; 
 and he has several times noticed little cakes of earth 
 attached to their feet. Many facts could be given showing 
 how generally soil is charged with seeds. For instance. 
 Professor Newton sent me the leg of a red-legged partridge 
 (Caccabis rufa) which had been wounded and could not 
 fly, with a ball of hard earth adhering to it, and weighing 
 six and a half ounces. The earth had been kept for three 
 years, but when broken, watered and placed under a bell 
 glass, no less than eighty-two plants sprung from it: these 
 consisted of twelve monocotyledons, including the common 
 oat, and at least one kind of grass, and of seventy dicotyle¬ 
 dons, which consisted, judging from the young leaves, of 
 at least three distinct species. With such facts before us, 
 can we doubt that the many birds which are annually 
 blown by gales across great spaces of ocean, and which an- 
 
388 
 
 MEAN'S OF DISPERSAL. 
 
 nually migrate—for instance, tlie millions of quails across 
 the Mediterranean—must occasionally transport a few 
 seeds imbedded in dirt adhering to their feet or beaks? 
 But I shall have to recur to this subject. 
 
 As icebergs are known to be sometimes loaded with earth 
 and stones, and have even carried brushwood, bones, 
 and the nest of a land-bird, it can hardly be doubted that 
 they must occasionally, as suggested by Lyell, have trans¬ 
 ported seeds from one part to another of the arctic and 
 antarctic regions ; and during the Glacial period from one 
 part of the now temperate regions to another. In the 
 Azores, from the large number of plants common to 
 Europe, in comparison with the species on the other 
 islands of the Atlantic, which stand nearer to the main¬ 
 land, and (as remarked by Mr. H. C. Watson) from their 
 somewhat northern character, in comparison with the lati¬ 
 tude, I suspected that these islands had been partly stocked 
 by ice-born seeds during the Glacial epoch. At my request 
 Sir 0. Lyell wrote to M. Hartung to inquire whether he 
 had observed erratic bowlders on these islands, and he 
 answered that he had found large fragments of granite and 
 other rocks, which do not occur in the archipelago. Hence 
 we may safely infer that icebergs formerly landed their 
 rocky burdens on the shores of these mid-ocean islands, 
 and it is at least possible that they may have brought 
 thither some few seeds of northern plants. 
 
 Considering that these several means of transport, and 
 that other means, which without doubt remain to be dis¬ 
 covered, have been in action year after year for tens of 
 thousands of years, it would, I think, be a marvelous fact 
 if many plants had not thus become widely transported. 
 These means of transport are sometimes called accidental, 
 but this is not strictly correct: the currents of the sea are 
 not accidental, nor is the direction of prevalent gales of 
 wind. It should be observed that scarcely any means of 
 transport would carry seeds for very great distances: for 
 seeds do not retain their vitality when exposed for a great 
 length of time to the action of sea water; nor could they 
 be long carried in the crops or intestines of birds. These 
 means, however, would suffice for occasional transport 
 across tracts of sea some hundred miles in breadth, or from 
 island to island, cr from a continent to a neighboring 
 
 
MEANS OF DISPERSAL. 3go 
 
 island, but not from one distant continent to another. 
 X'he floias of distant continents would not by such means 
 become mingled; but would remain as distinct as they now 
 are. The currents, from their course, would never brin-r 
 seeds from North America to Britain, though they mio-ht 
 and do biing seeds from the AVbst Indies to our western 
 shores, where, if not killed by their very long immersion 
 in salt water, they could not endure our climate. Almost 
 every year, one or two land-birds are blown across the 
 whole Atlantic Ocean, from North America to the western 
 shores of Ireland and England; but seeds could be trans¬ 
 ported by these rare wanderers only by one means, namely 
 by dirt adhering to their feet or beaks, which is in itself a 
 rare accident. Even in this case, how small would be the 
 chance of a seed falling on favorable soil, and coming to 
 maturity! But it would be a great error to argue that 
 because a well-stocked island, like Great Britain, has not, 
 as far as is known (and it would be very difficult to prove 
 this), received within the last few centuries, through occa¬ 
 sional means of transport, immigrants from Europe or any 
 other, continent, that a poorly-stocked island, though 
 standing more remote from the mainland, would not 
 .. , . _ similai means. Out of a hundred 
 
 kinds of seeds 01 animals transported to an island, even if 
 far less well-stacked than Britain, perhaps not more than 
 one would be so well fitted to its new home, as to become 
 naturalized. But this is no valid argument against what 
 would be effected by occasional means of transport, 
 during the long lapse of geological time, while the island 
 was being upheaved, and before it had become fully stocked 
 with inhabitants. On almost bare land, with few or no 
 destiuctive insects or birds living there, nearly every seed 
 which chanced to arrive, if fitted for the climate, would 
 germinate and survive. 
 
 DISPERSAL DURING THE GLACIAL PERIOEk 
 
 The identity of many plants and animals, on mountain- 
 summits, separated from each other bv hundreds of miles of 
 lowlands, where Alpine species could*' not possibly exist, is 
 one of the most striking cases known of the same species 
 Imng at distant points, without the apparent possibility 
 
390 
 
 DISPERSAL DURING 
 
 of their having migrated from one point to the other. It 
 is indeed a remarkable fact to see so many plants of the 
 same species living on the snowy regions of the Alps or 
 Py renees, and in the extreme northern parts of Europe; 
 but it is far more remarkable, that the plants on the White 
 Mountains, in the United States of America, are all the 
 same with those of Labrador, and nearly all the same, as 
 we hear from Asa Gray, with those on the loftiest mount¬ 
 ains of Europe. Even as long ago as 1747, such facts led 
 Gmelin to conclude that the same species must have been 
 independently created at many distinct points; and we 
 might have remained in this same belief, had not Agassiz 
 and others called vivid attention to the Glacial period, 
 which, as we shall immediately see, atfords a simple expla¬ 
 nation of these facts. We have evidence of almost every 
 conceivable kind, organic and inorganic, that, within a 
 very recent geological period, central Europe and North 
 America suffered under an arctic climate. The ruins of a 
 house burned by fire do not tell their tale more plainly than 
 do the mountains of Scotland and Wales, with their scored 
 flanks, polished surfaces, and perched bowlders, of the icy 
 streams with which their valleys were lately filled. So 
 greatly has the climate of Europe changed, that in North¬ 
 ern Italy, gigantic moraines, left by old glaciers, are now 
 clothed by the vine and maize. Throughout a large part 
 of the United States, erratic bowlders and scored rocks 
 plainly reveal a former cold period. 
 
 The former influence of the glacial climate on the dis¬ 
 tribution of the inhabitants of Europe, as explained by 
 Edward Forbes, is substantially as follows. But we shall 
 follow the changes more readily, by supposing a new glacial 
 period slowly to come on, and then pass awa} T , as formerly 
 occurred. As the cold came on, and as each more south¬ 
 ern zone became fitted for the inhabitants of the north, 
 these would take the places of the former inhabitants of 
 the temperate regions. The latter, at the same time, 
 would travel further and further southward, unless they 
 were stopped by barriers, in which case they would perish. 
 The mountains would become covered with snow and ice, 
 and their former Alpine inhabitants would descend to the 
 plains. By the time that the cold had reached its maxi¬ 
 mum, we should have an arctic fauna and flora, covering 
 
THE GLACIAL PERIOD . 
 
 391 
 
 the central parts of Europe, as far south as the Alps and 
 Pyrenees, and even stretching into Spain. The now 
 temperate regions of the United States would likewise be 
 covered by arctic plants and animals and these would be 
 nearly the same with those of Europe; for the present 
 circumpolar inhabitants, which we suppose to have every¬ 
 where traveled southward, are remarkably uniform round 
 the world. 
 
 As the warmth returned, the arctic forms would retreat 
 northward, closely followed up in their retreat by the pro¬ 
 ductions of the more temperate regions. And as the snow 
 melted from the bases of the mountains, the arctic forms 
 would seize on the cleared and thawed ground, always 
 ascending, as the warmth increased and the snow still 
 further disappeared, higher and higher, while their breth¬ 
 ren were pursuing their northern journey. Hence, when 
 the warmth had fully returned, the same species, which 
 had lately lived together on the European and North 
 American lowlands, would again be found in the arctic 
 regions of the Old and New Worlds, and on many isolated 
 mountain summits far distant from each other. 
 
 Thus we can understand the identity of many plants at 
 points so immensely remote as the mountains of the United 
 States and those of Europe. We can thus also understand 
 the fact that the Alpine plants of each mountain-range are 
 more especially related to the arctic forms living due 
 north or nearly due north of them: for the first migration 
 when the cold came on, and the re-migration on the return¬ 
 ing warmth, would generally have been due south and 
 north. The Alpine plants, for example, of Scotland, as 
 remarked by Mr. H. 0. Watson, and those of the Pyrenees, 
 as remarked by Ramond, are more especially allied to the 
 plants of northern Scandinavia; those of the United 
 States to Labrador; those of the mountains of Siberia to 
 the arctic regions of that country. These views, grounded 
 as they are on the perfectly well-ascertained occurrence of a 
 former Glacial period, seem to me to explain in so satis¬ 
 factory a manner the present distribution of the Alpine 
 and Arctic productions of Europe and America, that when 
 in other regions we find the same species on distant mount¬ 
 ain-summits, we may almost conclude, without other 
 evidence, that a colder climate formerly permitted their 
 
392 
 
 DISPERSAL DURING 
 
 migration across the intervening lowlands, now become 
 too warm for their existence. 
 
 As the arctic forms moved first southward and after- 
 waid backward to the north, in unison with the changin 0, 
 climate, they will not have been exposed during their long 
 migrations to any great diversity of temperature; and as 
 they all migrated in a body together, their mutual rela¬ 
 tions will not have been. much disturbed. Hence, in 
 accoidance with the principles inculcated in this volume, 
 these forms will not have been liable to much modification. 
 But with the Alpine productions, left isolated from the 
 moment of the returning warmth, first at the bases and 
 ultimately on the summits of the mountains, the case will 
 have been soniewhat different; for it is not likely that all 
 the same arctic species will have been left on mountain 
 ranges far distant from each other, and have survived there 
 ever since; they will also, in all probability, have become 
 mingled with ancient Alpine species, which must have 
 existed on the mountains before the commencement of the 
 Glacial epoch, and which during the coldest period will 
 have been temporarily driven down to the plains; they 
 will, also, have been subsequently exposed to somewhat 
 dilfeient climatical influences. Their mutual relations will 
 thus have been in some degree disturbed; consequently 
 they will have been liable to modification; and they have 
 been modified; for if we compare the present Alpine plants 
 and animals of the several great European mountain 
 1 anges, one with another, though many of the species 
 remain identically the same, some exist as varieties, some 
 as doubtful forms or sub-species and some as distinct yet 
 
 closely allied species representing each other on the several 
 ranges. 
 
 In the foregoing illustration I have assumed that at the 
 commencement of our imaginary Glacial period, the arctic 
 piodactions were as uniform round the polar regions as 
 they aie at the present da} 7 . But it is also necessary to 
 assume that many sub-arctic and some few temperate forms 
 were the same round the world, for some of the species 
 which now exist on the lower mountain slopes and on the 
 plains of North America and Europe are the same; and it 
 nia\ be asked how I account for this degree of uniformity 
 in the sub-arctic and temperate forms round the world, at 
 
THE GLACIAL PERIOD. 393 
 
 the commencement of the real Glacial period. At the 
 present day the sub-arctic and northern temperate pro¬ 
 ductions of the Old and New Worlds are separated from 
 each other by the whole Atlantic Ocean and by the north¬ 
 ern part of the Pacific. During the Glacial period, when 
 the inhabitants of the Old and New Worlds lived further 
 southward then they do at present, they must have been 
 still more completely separated from each other by wider 
 spaces of ocean; so that it may well be asked how the same 
 species could then or previously have entered the two con¬ 
 tinents. The explanation, I believe, lies in the nature of 
 the climate before the commencement of the Glacial period 
 At tins, the newer Pliocene period, the majority of the in¬ 
 habitants of the world were specifically the same as now, and 
 we have good reason to believe that the climate was warmer 
 than at the present day. Hence, we may suppose that the 
 organisms which now live under latitude 60 degrees, lived 
 during the Pliocene period further north, under the Polar 
 Circle, m latitude 66-67 degrees; and that the present arctic 
 productions then lived on the broken land still nearer to the 
 P° le ‘ ^ w ® look a t a terrestrial globe, we see under 
 
 the Polar Circle that there is almost continuous land from 
 western Europe through Siberia, to eastern America. And 
 this continuity of the circumpolar land, with the conse¬ 
 quent freedom under a more favorable climate for inter- 
 migration, will account for the supposed uniformity of the 
 sub-arctm and temperate productions of the Old and New 
 * or Ids, at a period anterior to the Glacial epoch. 
 
 Believing, from reasons before alluded to, that our con¬ 
 tinents have long remained in nearly the same relative 
 position, though subjected to great oscillations of level, I 
 am strongly inclined to extend the above view, and to infer 
 that during some still earlier and still warmer period, such 
 as the older Pliocene period, a large number of the same 
 plants and animals inhabited the almost continuous cir- 
 
 an ^_ tka t these plants and animals, both in 
 the Old and New Worlds, begun slowly to migrate south¬ 
 ward as the climate became less warm, long before the 
 commencement of the Glacial period. We now see, as I 
 believe, their descendants, mostly in a modified condition, 
 m the central parts of Europe and the United States. On 
 this view we can understand the relationship with very 
 
DISPERSAL DURING 
 
 394 
 
 little identity, between the productions of North America 
 and Europe—a relationship which is highly remarkable, 
 considering the distance of the two areas, and theii sepa¬ 
 ration by the whole Atlantic Ocean. We can further under¬ 
 stand the singular fact remarked on by several observers 
 that the productions of Europe and America dining the 
 later tertiary stages were more closely related to each other 
 than they are at the present time; for during these warmer 
 periods the northern parts of the Old and New Worlds will 
 have been almost continuously united by land, serving as a 
 bridge, since rendered impassible by cold, for intermigra¬ 
 tion of their inhabitants. . 
 
 During the slowly decreasing warmth of the Pliocene 
 period, as soon as the species in common, which inhabited 
 the New and Old Worlds, migrated south of the Polar Circle, 
 they will have been completely cut off from each other. 
 This separation, as far as the more temperate productions 
 are concerned, must have taken place long ages ago. As 
 the plants and animals migrated southward, they will 
 have* become mingled in the one great region with the 
 native American productions, and would have had to com¬ 
 pete with them; and in the other great region, with those 
 of the Old World. Consequently we have here everything 
 favorable for much modification—for far more modifica¬ 
 tion than with the Alpine productions, left isolated, within 
 a much more recent period, on the several mountain ranges 
 and on the arctic lands of Europe and North America. Hence, 
 it has come, that when we compare the now living produc¬ 
 tions of the temperate regions of the New and Old Worlds, 
 we find very few identical species (though Asa Gray has 
 lately shown that more plants are identical than was for¬ 
 merly supposed), but we find in every great class many 
 forms, which some naturalists rank as geographical laces, 
 and others as distinct species; and a host of closely allied 
 or representative forms which are ranked by all naturalists 
 as specifically distinct. 
 
 As on the land, so in the waters of the sea, a slow south¬ 
 ern migration of a marine fauna, which, during the Pliocene 
 or even a somewhat earlier period, was nearly uniform along 
 the continuous shores of the Polar Circle, will account, on 
 the theory of modification, for many closely allied forms 
 now living in marine areas completely sundered. Thus, 1 
 
TEE GLACIAL PERIOD. 395 
 
 think, we can understand, the presence of some closely 
 allied, still existing and extinct tertiary forms, on the 
 eastern and western shores of temperate North America; 
 and the still more striking fact of many closely allied crus¬ 
 taceans (as described in Dana’s admirable work), some fish 
 and other marine animals, inhabiting the Mediterranean 
 and the seas of Japan—these two areas being now com¬ 
 pletely separated by the breadth of a whole continent and 
 by wide spaces of ocean. 
 
 These cases of close relationship in species either now or 
 formerly inhabiting the seas on the eastern and western 
 shores of North America, the Mediterranean and Japan, 
 and the temperate lands of North America and Europe, 
 are. inexplicable on the theory of creation. We cannot 
 maintain that such species have been created alike, in cor¬ 
 respondence with the nearly similar physical conditions of 
 the areas; for if we compare, for instance, certain parts of 
 South America with parts of South Africa or Australia, we 
 see countries closely similar in all their physical conditions 
 with their inhabitants utterly dissimilar. 
 
 ALTERNATE GLACIAL PERIODS IN THE NORTH AND SOUTH. 
 
 But we must return to our more immediate subject. I 
 am convinced that Eorbes’ view may be largely extended. 
 In Europe we meet with the plainest evidence of the Glacial 
 period, from the western shores of Britain to the Ural 
 range, and southward to the Pyrenees. We may infer 
 from the frozen manimals and nature of the mountain 
 vegetation, that Siberia was similarly affected. In the Leb¬ 
 anon, according to Dr. Hooker, perpetual snow formerly 
 coveied the central axis, and fed glaciers which rolled 
 4,000 feet down the valleys. The same observer has 
 recently found great.moraines at a low level on the Atlas 
 range in North Africa. Along the Himalaya, at points 
 900 miles apart, glaciers have left the marks of their 
 foimer low descent; and in Sikkim, Dr. Hooker saw maize 
 growing on ancient and gigantic moraines. Southward of 
 the Asiatic continent, on the opposite side of the equator, 
 we know, from the excellent researches of Dr. J. Haast 
 and Di. Hector, that in New Zealand immense glaciers 
 foimeily descended to a low level; and the same plants 
 
39G 
 
 ALTERNATE GLACIAL PERIODS 
 
 found by Dr. Hooker on widely separated mountains in 
 this island tell the same story of a former cold period. 
 From facts communicated to me by the Rev. W. B. 
 Clarke, it appears also that there are traces of former gla¬ 
 cial action on the mountains of the south-eastern corner 
 of Australia. 
 
 Looking- to America; in the northern half, ice-borne 
 fragments of rock have been observed on the eastern side 
 of the continent, as far south as latitude thirty-six and 
 thirty-seven degrees, and on the shores of the Pacific, 
 where the climate is now so different, as far south as lati¬ 
 tude forty-six degrees. Erratic bowlders have, also, been 
 noticed on the Rocky Mountains. In the Cordillera of 
 South America, nearly under the equator, glaciers once 
 extended far below their present level. In Central Chili I 
 examined a vast mound of detritus with great bowlders, 
 crossing the Portillo valley, which, there can hardly be a 
 doubt, once formed a huge moraine; and Mr. D. Forbes 
 informs me that he found in various parts of the Cordillera, 
 from latitude thirteen to thirty degrees south, at about the 
 height of 12,000 feet, deeply-furrowed rocks, resembling 
 those with which he was familiar in Norway, and likewise 
 great masses of detritus, including grooved pebbles. Along 
 this whole space of the Cordillera true glaciers do not now 
 exist even at much more considerable heights. Further 
 south, on both sides of the continent, from latitude forty- 
 one degrees to the southernmost extremity, we have the 
 clearest evidence of former glacial action, in numerous 
 immense bowlders transported far from their parent 
 source. 
 
 From these several facts, namely, from the glacial action 
 having extended all round the northern and southern 
 hemispheres—from the period having been in a geological 
 sense recent in both hemispheres—from its having lasted 
 in both during a great length of time, as may be inferred 
 from the amount of work effected—and lastly, from gla¬ 
 ciers having recently descended to a low level along the 
 whole line of the Cordillera, it at one time appeared to me 
 that we could not avoid the conclusion that the tempera¬ 
 ture of the whole world had been simultaneously lowered 
 during the Glacial period. But now, Mr. Croll, in a series 
 of admirable memoirs, has attempted to show that a glacial 
 
IN THE NORTH AND SOUTH 
 
 39? 
 
 condition of climate is the result of various physical causes, 
 brought into operation by an increase in the eccentricity of 
 the earth's orbit. All these causes tend toward the same 
 end; but the most powerful appears to be the indirect in¬ 
 fluence of the eccentricity of the orbit upon oceanic cur- 
 lents. According to Mr. Croll, cold periods regularly recur 
 every ten or fifteen thousand years; and these at long in- 
 teivals aie extremely severe, owing to certain contingen¬ 
 cies, of which the most important, as Sir 0. Lyell has 
 shown, is the relative position of the land and water. Mr. 
 Croll believes that the last great glacial period occurred 
 about 240,000 years ago, and endured, with slight altera¬ 
 tions of climate, for about 160,000 years. With respect to 
 moie ancient glacial periods, several geologists are con¬ 
 vinced, from direct evidence, that such occurred during the 
 miocene and eocene formations, not to mention still more 
 ancient formations. But the most important result for us, 
 anived at by Mr. Croll, is that whenever the northern 
 hemisphere passes through a cold period the temperature 
 of the southern hemisphere is actually raised, with the 
 winters rendered much milder, chiefly through changes in 
 the direction of the ocean currents. So conversely it will 
 be with the northern hemisphere, while the southern passes 
 through a glacial period. This conclusion throws so much 
 light on geographical distribution that I am strongly in¬ 
 clined to trust in it; but I will first give the facts which 
 demand an explanation. 
 
 In South America, Dr. Hooker has shown that besides 
 many closely allied species, between forty and fifty of the 
 flowering plants of Tierra del Fuego, forming no inconsid¬ 
 erable. part of its scanty flora, are common to North 
 America and Europe, enormously remote as these areas in 
 opposite hemispheres are from each other. On the lofty 
 mountains of equatorial America a host of peculiar species 
 belonging to European genera occur. On the Organ 
 Mountains of Brazil some few temperate European, some 
 Antarctic and some Andean genera w r ere found by Gardner 
 which do not exist in the low intervening hot countries. 
 On the Silla of Caraccas the illustrious Humboldt long ago 
 found species belonging to genera characteristic of the 
 Cordillera. 
 
 In Africa, several forms characteristic of Europe, and 
 
398 
 
 ALTERNATE GLACIAL PERIODS 
 
 some few representatives of the flora of the Cape of 
 Good Hope, occur on the mountains of Abyssinia. At 
 the Cape of Good Hope a very few European species, 
 believed not to have been introduced by man, and on the 
 mountains several representative European forms are found 
 which have not been discovered in the intertropical parts 
 of Africa. Dr. Hooker has also lately shown that several 
 of the plants living on the upper parts of the lofty island 
 of Fernando Po, and on the neighboring Cameroon Mount¬ 
 ains, in the Gulf of Guinea, are closely related to those on 
 the mountains of Abyssinia, and likewise to those of tem¬ 
 perate Europe. It now also appears, as I hear from Hr. 
 Hooker, that some of these same temperate plants have 
 been discovered by the Rev. R. T. Lowe on the mountains 
 of the Cape Verde Islands. This extension of the same tem¬ 
 perate forms, almost under the equator, across the whole 
 continent of Africa and to the mountainsof the Cape Verde 
 archipelago, is one of the most astonishing facts ever re¬ 
 corded in the distribution of plants. 
 
 On the Himalaya, and on the isolated mountain ranges 
 of the peninsula of India, on the heights of Ceylon and op 
 the volcanic cones of Java, many plants occur either identi¬ 
 cally the same or representing each other, and at the same 
 time representing plants of Europe not found in the inter¬ 
 vening hot lowlands. A list of the genera of^ plants col¬ 
 lected on the loftier peaks of .Java, raises a picture of a 
 collection made on a hillock in Europe. Still more strik¬ 
 ing is the fact that peculiar Australian forms are repre¬ 
 sented by certain plants growing on the summits of the 
 mountains of Borneo. Some of these Australian forms, as 
 I hear from Dr. Hooker, extend along the heights of the 
 peninsula of Malacca, and are thinly scattered on the one 
 hand over India, and on the other hand as far north as 
 Japan. 
 
 On the southern mountains of Australia, Dr. F. Muller 
 has discovered several European species; other species, 
 not introduced by man, occur on the lowlands; and a long 
 list can be given, as I am informed by Dr. Hooker, of 
 European genera, found in Australia, but not in the inter¬ 
 mediate torrid regions. In the admirable “Introduction 
 to the Flora of New Zealand,” by Dr. Hooker, analogous 
 and striking facts are given in regard to the plants of that 
 
IN THE NORTH AND SOUTH . 
 
 399 
 
 large island. Hence, we see that certain plants growing on 
 the more lofty mountains of the tropics in all parts of the 
 world, and on the temperate plains of the north and south, 
 are either the same species or varieties of the same species. 
 It should, however, be observed that these plants are not 
 strictly arctic forms; for, as Mr. H. 0. Watson has re¬ 
 marked, “ in receding from polar toward equatorial lati¬ 
 tudes, the Alpine or mountain flora really become less and 
 less Arctic." Besides these identical and closely allied 
 forms, many species inhabiting the same widely sundered 
 areas, belong to genera not now found in the intermediate 
 tropical lowlands. 
 
 These brief remarks apply to plants alone; but some few 
 analogous facts could be given in regard to terrestrial 
 animals. In marine productions, similar cases likewise 
 occur; as an example, I may quote a statement by the 
 highest authority, Professor Dana, that “it is certainly a 
 wonderful fact that New Zealand should have a closer re¬ 
 semblance in its Crustacea to Great Britain, its antipode, 
 than to any other part of the world." Sir J. Richardson, 
 also, speaks of the reappearance on the shores of New 
 Zealand,. Tasmania, etc., of northern forms of fish. Dr. 
 Hooker informs me that twenty-five species of Algge are 
 common to New Zealand and to Europe, but have not 
 been found in the intermediate tropical seas. 
 
 From the foregoing facts, namely, the presence of tem¬ 
 perate forms on the highlands across the whole of equatorial 
 Africa, and along the Peninsula of India, to Ceylon and 
 the Malay Archipelago, and in a less well-marked manner 
 across the wide expanse of tropical South America, it ap¬ 
 pears almost certain that at some former period, no doubt 
 during the most severe part of a Glacial period, the low¬ 
 lands of these great continents were everywhere tenanted 
 under the equator by a considerable number of temperate 
 forms. At this period the equatorial climate at the level 
 of the sea was probably about the same with that now ex¬ 
 perienced at the height of from five to six thousand feet 
 under the same latitude, or perhaps even rather cooler. 
 During this, the coldest period, the lowlands under the 
 equator must have been clothed with a mingled tropical 
 and temperate vegetation, like that described by Hooker as 
 growing luxuriantly at the height of from four to five 
 
400 ALTERNATE GLACIAL PERIODS 
 
 thousand feet on the lower slopes of the Himalaya, but 
 with perhaps a still greater preponderance of temperate 
 forms. So again in the mountainous island of Fernando 
 Po, in the Gulf of Guinea, Mr. Mann found temperate 
 European forms begining to appear at the height of about 
 five thousand feet. On the mountains of Panama, at the 
 height of only two thousand feet, Dr. Seemann found the 
 vegetation like that of Mexico, “ with forms of the torrid 
 zone harmoniously blended with those of the temper¬ 
 ate.” 
 
 Now let us see whether Mr. Croll’s conclusion that when 
 the northern hemisphere suffered from the extreme cold of 
 the great Glacial period, the southern hemisphere was 
 actually warmer, throws any clear light on the present ap¬ 
 parently inexplicable distribution of various organisms in 
 the temperate parts of both hemispheres, and on the 
 mountains of the tropics. The Glacial period, as measured 
 by years, must have been very long; and when we remem¬ 
 ber over what vast spaces some naturalized plants and ani- 
 mals have spread within a few centuries, this period will 
 have been ample for any amount of migration. As the 
 cold became more and more intense, we know that Arctic 
 forms invaded the temperate regions; and, from the facts 
 -just given, there can hardly be a doubt that some of the 
 more vigorous, dominant and widest-spreading temperate 
 forms invaded the equatorial lowlands. The inhabitants 
 of these hot lowlands would at the same time have migrated 
 to the tropical and subtropical regions of the south, for the 
 southern hemisphere was at this period warmer. On the 
 decline of the Glacial period, as both hemispheres gradu¬ 
 ally recovered their former temperature, the northern tem¬ 
 perate forms living on the lowlands under the equator, 
 would have been driven to their former homes or have been 
 destroyed, being replaced by the equatorial forms return¬ 
 ing from the south. Some, however, of the northern 
 temperate forms would almost certainly have ascended any 
 adjoining high land, where, if sufficiently lofty, they would 
 have long survived like the Arctic forms on the mountains 
 of Europe. They might have survived, even if the climate 
 was not perfectly fitted for them, for the change of tem¬ 
 perature must have been very slow, and. plants undoubtedly 
 possess a certain capacity for acclimatization, as shown by 
 
IN THE NORTH AND SOUTH. 
 
 401 
 
 their transmitting to their offspring different constitutional 
 powers of resisting heat and cold. 
 
 In the regular course of events the southern hemisphere 
 would in its turn be subjected to a severe Glacial period, 
 with the northern hemisphere rendered warmer; and then 
 the southern temperate forms would invade the equatorial 
 lowlands. The northern forms which had before been left 
 on the mountains would now descend and mingle with the 
 southern forms. These latter, when the warmth returned, 
 would return to their former homes, leaving some few 
 species on the mountains, and carrying southward with 
 them some of the northern temperate forms which had 
 descended from their mountain fastnesses. Thus, we 
 should have some few species identically the same in the 
 northern and southern temperate zones and on the mount¬ 
 ains of the intermediate tropical regions. But the species 
 left during a long time on these mountains, or in opposite 
 hemispheres, would have to compete with many new forms 
 and would be exposed to somewhat different physical con¬ 
 ditions; hence, they would be eminently liable to modifica¬ 
 tion, and would generally now exist as varieties or as rep¬ 
 resentative species; and this is the case. We must, also, 
 bear in mind the occurrence in both hemispheres of former 
 Glacial periods; for these will account, in accordance with 
 the same principles, for the many quite distinct species in¬ 
 habiting the same widely separated areas, and belonging to 
 genera not now found in the intermediate torrid zones. 
 
 It is a remarkable fact, strongly insisted on by Hooker, 
 in regard to America, and by Alph. de Candolle in regard 
 to Australia, that many more identical or slightly modified 
 species have migrated from the north to the south, than in 
 a reversed direction. We see, however, a few southern 
 forms on the mountains of Borneo and Abyssinia. I sus¬ 
 pect that this preponderant migration from the north to 
 the south is due to the greater extent of land in the north, 
 and to the northern forms having existed in their own 
 homes in greater numbers, and having consequently been 
 advanced through natural selection and competition to a 
 higher stage of perfection, or dominating power, than the 
 southern forms. And thus, when the two sets became 
 commingled in the equatorial regions, during the alterna¬ 
 tions of the Glacial periods, the northern forms were tho 
 
403 
 
 ALTERNATE GLACIAL PERIODS 
 
 more powerful and were able to hold their places on the 
 mountains, and afterward to migrate southward with the 
 southern forms; but not so the southern in regard to the 
 northern forms. In the same manner, at the present day, 
 we see that very many European productions cover the 
 ground in La Plata, New Zealand, and to a lesser degree 
 in Australia, and have beaten the natives; whereas 
 extremely few southern forms have become naturalized in 
 any part of the northern hemisphere, though hides, wool, 
 and other objects likely to carry seeds have been largely 
 imported into Europe during the last two or three cen¬ 
 turies from La Plata and during the last forty or fifty years 
 from Australia. The Neilgherrie Mountains in India, 
 however, offer a partial exception; for here, as I hear from 
 Dr. Hooker, Australian forms are rapidly sowing them¬ 
 selves and becoming naturalized. Before the last great 
 Glacial period, no doubt the intertropical mountains were 
 stocked with endemic Alpine forms; but these have almost 
 everywhere yielded to the more dominant forms generated 
 in the larger areas and more efficient workshops of the 
 north. In many islands the native productions are nearly 
 equalled, or even outnumbered, by those which have 
 become naturalized; and this is the first stage toward their 
 extinction. Mountains are islands on the land, and their 
 inhabitants have yielded to those produced within the 
 larger areas of the north, just in the same way as the 
 inhabitants of real islands have everywhere yielded and are 
 still yielding to continental forms naturalized through 
 man’s agency. 
 
 The same principles apply to the distribution of terres¬ 
 trial animals and of marine productions, in the northern 
 and southern temperate zones, and on the intertropical 
 mountains. When, during the height of the Glacial 
 period, the ocean-currents were widely different to what 
 they now are, some of the inhabitants of the temperate seas 
 might have reached the equator; of these a few would per¬ 
 haps at once be able to migrate southward, by keeping to 
 the cooler currents, while others might remain and sur¬ 
 vive in the colder depths until the southern hemisphere 
 was in its turn subjected to a glacial climate and permitted 
 their further progress; in nearly the same manner as, 
 according to Forbes, isolated spaces inhabited by Arctic 
 
/A r T 1 IE NORTH AND SOUTH. 4o;} 
 
 productions exist to the present day in the deeper parts of 
 the northern temperate seas. 1 1 
 
 1 .T! f ™ m ., su PP osin £ that all the difficulties in 
 legard to the distribution and affinities of the identical and 
 allied species, which now live so widely separated in the 
 north and south, and sometimes on the intermediate mount¬ 
 ain-! anges, are removed on the views above given. The 
 exact lines of migration cannot be indicated. We cannot 
 say why certain species and not others have migrated- whv 
 ceitain species have been modified and have given rise to 
 new forms, while others have remained unaltered. We 
 cannot hope to explain such facts, until we ?an say why 
 one species and not another becomes naturalized by man's 
 agency in a foreign land; why one species ranges twice or 
 thrice as tar, and is twice or thrice as common, as another 
 species within their own homes. 
 
 . Various special difficulties also remain to be solved* for 
 instance, the occurrence, as shown by Dr. Hooker, of the 
 same plants at points so enormously remote as Kerguelen 
 and, New Zealand, and Fuegia; but icebergs, as suggested 
 by Lyell, may have been concerned in their dispersal. The 
 existence at these and other distant points of the southern 
 hemisphere, of species, which, though distinct, belong to 
 genera exclusively confined to the south, is a more remark¬ 
 able case. Some of these species are so distinct, that we 
 cannot suppose that there has been time since the com- 
 mencement of the last Glacial period for their migration 
 and subsequent modification to the necessary degree. The 
 acts seem to indicate that distinct species belonging to the 
 same genera have migrated in radiating lines from a 
 common center; and I am inclined to look in the southern 
 as in the northern hemisphere, to a former and warmer 
 period, before the commencement of the last Glacial 
 period, when the Antarctic lands, now covered with ice 
 supported a highly peculiar and isolated flora. It may be 
 suspected that before this flora was exterminated during the 
 last Glacial epoch, a few forms had been already widelv dis¬ 
 persed to various points of the southern hemisphere bv oc¬ 
 casional means of transport, and by the aid, as halting- 
 places, of now sunken islands. Thus the southern shores 
 of America Australia, and New Zealand may have become 
 slightly tinted by the same peculiar forms of lifew 
 
404 
 
 ALTERNATE GLACIAL PERIODS. 
 
 Sir C. Lyell in a striking passage lias speculated, in lan¬ 
 guage almost identical with mine, on the effects of great 
 alterations of climate throughout the world on geograph¬ 
 ical distribution. And we have now seen that Mr. CrolFs 
 conclusion that successive Glacial periods in the one hemi¬ 
 sphere coincide with warmer periods in the opposite hemi¬ 
 sphere, together with the admission of the slow modifica¬ 
 tion of species, explains a multitude of facts in the distri¬ 
 bution of the same and of the allied forms of life in all 
 parts of the globe. The living waters have flowed during 
 one period from the north and during another from the 
 south, and in both cases have reached the equator; but the 
 stream of life has flowed with greater force from the north 
 than in the opposite direction, and has consequently more 
 freely inundated the south. As the tide leaves its drift in 
 horizontal lines, rising higher’ on the shores where the tide 
 rises highest, so have the living waters left their living 
 drift on our mountain summits, in a line gently rising 
 from the Arctic lowlands to a great altitude under the 
 equator. The various beings thus left stranded may be 
 compared with savage races of man, driven up and surviv¬ 
 ing in the mountain fastnesses of almost every land, which 
 serves as a record, full of interest to us, of the former in¬ 
 habitants of the surrounding lowlands. 
 
FRESH-WATER PRODUCTIONS. 
 
 405 
 
 CHAPTER XIII. 
 
 geographical distribution— continued. 
 
 Distribution of fresb-water productions — On tbe inhabitants of 
 oceanic islands—Absence of Batrachians and of terrestrial Mam¬ 
 mals—On the relation of the inhabitants of islands to those of 
 the nearest mainlaind—On colonization from the nearest source 
 with subsequent modification—Summary of the last and present 
 chapter. 
 
 FRESH-WATER PRODUCTIONS. 
 
 As lakes and river systems are separated from each 
 other by barriers of land, it might have been thought 
 that fresh-water productions would not have ranged widely 
 within the same country, and as the sea is apparently a 
 still more formidable barrier, that they would never have 
 extended to distant countries. But the case is exactly the 
 reverse. Not only have many fresh-water species, belong¬ 
 ing to different classes, an enormous range, but allied 
 species prevail in a remarkable manner throughout the 
 world. When first collecting in the fresh waters of Brazil, 
 I well remember feeling much surprise at the similarity of 
 the fresh-water insects, shells, etc., and at the dissimilarity 
 of the surrounding terrestrial beings, compared with those 
 of Britain. 
 
 But the wide ranging power of fresh-water productions 
 can, I think, in most cases be explained by their having 
 become fitted, in a manner highly useful to them, for short 
 and frequent migrations from pond to pond, or from 
 stream to stream, within their own countries; and liability 
 to wide dispersal would follow from this capacity as an 
 almost necessary consequence. We can here consider only 
 a few cases; of these, some of the most difficult to explain 
 are presented by fish. It was formerly believed that the 
 same fresh-water species never existed* on two continents 
 
406 
 
 FRESH-WATER PRODUCTIONS. 
 
 distant from each other. But Dr. Gunther has lately 
 shown that the Galaxias attenuatus inhabits Tasmania, 
 New Zealand, the Falkland Islands and the mainland of 
 South America. This is a wonderful case, and probably 
 indicates dispersal from an Antarctic center during a 
 former warm period. This case, however, is rendered in 
 some degree less surprising by the species of this genus 
 having the power of crossing by some unknown means con¬ 
 siderable spaces of open ocean: thus there is one species 
 common to New Zealand and to the Auckland Islands, 
 though separated by a distance of about 230 miles.. On 
 the same continent fresh-water fish often range widely, 
 and as if capriciously; for in two adjoining river systems 
 some of the species may be the same and some wholly 
 different. 
 
 It is probable that they are occasionally transported by 
 what may be called accidental means. Thus fishes still 
 alive are not very rarely dropped at distant points by 
 whirlwinds; and it is known that the ova retain their 
 vitality for a considerable time after removal from the 
 water. Their dispersal may, however, be mainly attribu¬ 
 ted to changes in the level of the land within the recent 
 period, causing rivers to flow into each other. Instances, 
 also, could be given of this having occurred during floods, 
 without any change of level. The wide differences of the 
 fish on the opposite sides of most mountain-ranges, which 
 are continuous and consequently must, from , an early 
 period, have completely prevented the inosculation of the 
 river, systems on the two sides, leads to the same conclu¬ 
 sion. Some fresh-water fish belong to very ancient, forms, 
 and in such cases there will have been ample time for 
 great geographical changes, and consequently time and 
 means for much migration. Moreover, Dr. Gunther has 
 recently been led by several considerations to infer that 
 with fishes the same forms have a long endurance. . Salt¬ 
 water fish can with care be slowly accustomed to live in 
 fresh water; and, according to Valenciennes, there is 
 hardly a single group of which all the members are con¬ 
 fined to fresh water, so that a marine species belonging to 
 a fresh-water group might travel far along the shores of 
 the sea, and could, it is probable, become adapted without 
 much difficulty to the fresh waters of a distant land. 
 
FRESH-WATER PRODUCTIONS. 
 
 407 
 
 Some species of fresh-water shells have very wide ranges, 
 and allied species which, on our theory, are descended from 
 a common parent, and must have proceeded from a single 
 source, prevail throughout the world. Their distribution 
 at first perplexed me much, as their ova are not likely to 
 be transported by birds; and the ova, as well as the adults, 
 are immediately killed by sea-water. I could not ever, 
 understand how some naturalized species have spread 
 rapidly throughout the same country. But two facts, 
 which I have observed—and many others no doubt will be 
 discovered—throw some light on this subject. When ducks 
 suddenly emerge from a pond covered with duck-weed, I 
 have twice seen these little plants adhering to their backs; 
 and it has happened to me, in removing a little duck-weed 
 from one aquarium to another, that I have unintentionally 
 stocked the one with fresh-water shells from the other. 
 But another agency is perhaps more effectual: I suspended 
 the feet of a duck in an aquarium, where many ova of 
 fresh-water shells were hatching; and I found that numbers 
 of the extremely minute and just-hatched shells crawled 
 on the feet, 'and clung to them so firmly that when taken 
 out of the water they could not be jarred off, though at a 
 somewhat more advanced age they would voluntarily drop 
 off. These just-hatched molluscs, though aquatic in their 
 nature, survived on the duck's feet, in damp air, from 
 twelve to twenty hours; and in this length of time a duck 
 or heron might fiy at least six or seven hundred miles, and 
 if blown across the sea to an oceanic island, or to any other 
 distant point, would be sure to alight on a pool or rivulet. 
 Sir Charles Lyell informs me that a dytiscus has been 
 caught with an ancylus (a fresh-water shell like a limpet) 
 firmly adhering to it; and a water-beetle of the same family, 
 a colymbetes, once flew on board the “ Beagle;" when forty- 
 five miles distant from the nearest land: how much farther 
 it might have been blown by a favoring gale no one can 
 tell. 
 
 With respect to plants, it has long been known what 
 enormous ranges many fresh-water, and even marsh species, 
 have, both over continents and to the most remote oceanic 
 islands. This is strikingly illustrated, according to Alph. 
 de Candolle, in those large groups of terrestrial plants, 
 which have very few aquatic members; for the latter seem 
 
408 FRESH-WAT^Tt PRODtC~tlDff& 
 
 immediately to acquire, as if in consequence, a wido 
 range. I think favorable means of dispersal explain 
 this fact. I have before mentioned that earth occa- 
 tionally adheres in some quantity to the feet and beaks 
 of birds. Wading birds, which frequent the muddy edges 
 of ponds, if suddenly flushed, would be the most likely to 
 have muddy feet. Birds of this order wander more than 
 those of any other; and they are occasionally found on the 
 most remote and barren islands of the open ocean; they 
 would not he likely to alight _ on the surface of the 
 sea, so that any dirt on their feet would not be 
 washed off; and when gaining the land, they would be sure 
 to fly to their natural fresh-water haunts. I do not believe 
 that botanists are aware how charged the mud of ponds is 
 with seeds; I have tried several little experiments, but will 
 here o-ive only the most striking case: I took in February 
 three tablespoonfuls of mud from three different points, 
 beneath water, on the edge of a little pond; this mud when 
 dried weighed only six and three-fourth ounces; I kept it 
 covered up in my study for six months, pulling up and 
 counting each plant as it grew; the plants weie of many 
 kinds, and were altogether 537 in number; and yet the 
 viscid mud was all contained in a breakfast cup! Consider¬ 
 ing these facts, I think it would be an inexplicable cir¬ 
 cumstance if water birds did not transport the seeds of 
 fresh-water plants to unstocked ponds and streams, situated 
 at verv distant points. The same agency may have come 
 into play with the eggs of some of the smaller fresh-water 
 
 animals. # . 
 
 Other and unknown agencies probably have also played 
 . a part. I have stated that fresh-water fish eat some kind? 
 of seeds, though they reject many other kinds after having 
 swallowed them; even small fish swallow seeds of moderate 
 size, as of the yellow water-lily and Potamogeton. Herons 
 and other birds, century after century, have gone on daily 
 devouring fish; they then take flight and go to other 
 waters, or are blown across the sea; and we have seen that 
 seeds retain their power of germination, when rejected 
 many hours afterward in pellets or in the excrement. 
 When I saw the great size of the seeds of that fine water- 
 lily, the Nelumbium, and remembered Alph.de Candolle's 
 remarks on the distribution of this plant, I thought that 
 
INHABITANTS OF OCEANIC ISLANDS. 
 
 409 
 
 the means of its dispersal must remain inexplicable; but 
 Audubon statesthat he found the seeds of the great southern 
 water-lily (probably according to Dr. Hooker, the Nelumt 
 bium luteum) in a heron's stomach. Now this bird mus- 
 often have flown with its stomach thus well stocked to dis¬ 
 tant ponds, and, then getting a hearty meal of fish, \ 
 analogy makes me believe that it would have rejected the 
 seeds in the pellet in a fit state for germination. 
 
 In considering these several means of distribution, it 
 should be remembered that when a pond or stream is first 
 formed, for instance on a rising islet, it will be unoccupied; 
 and a single seed or egg will have a good chance of succeed¬ 
 ing. Although there will always be a struggle for life be¬ 
 tween the inhabitants of the same pond, however few in 
 kind, yet as the number even in a well-stocked pond is small 
 in comparison with the number of sj)ecies inhabiting an 
 equal area of land, the competition between them will proba¬ 
 bly be less severe than between terrestrial species; conse¬ 
 quently an intruder from the waters of a foreign country 
 would have a better chance of seizing on a new place, than 
 in the case of terrestrial colonists. We should also re¬ 
 member that many fresh-water productions are low in the 
 scale of nature, and we have reason to believe that such 
 beings become modified more slowly than the high; 
 and this will give time for the migration of aquatic species. 
 We should not forget the probability of many fresh-water 
 forms having formerly ranged continuously over immense 
 areas, and then having become extinct at intermediate 
 points. But the wide distribution of fresh-water plants, 
 and of the lower animals, whether retaining the same 
 identical form, or in some degree modified, apparently 
 depends in main part on the wide dispersal of their seeds 
 and eggs by animals, more especially by fresh-water birds, / 
 which have great powers of flight, and naturally travel 
 from one piece of water to another. 
 
 ON" THE INHABITANTS OF OCEANIC ISLANDS. 
 
 We now come to the last of the three classes of facts, 
 which I have selected as presenting the greatest amount 
 of difficulty with respect to distribution, on the view that 
 not only all the individuals of the same species have 
 
410 
 
 INHABITANTS OF OCEANIC ISLANDS. 
 
 migrated from some one area, but that allied species, 
 although now inhabiting the most distant points, have pro¬ 
 ceeded from a single area, the birthplace of their early pro¬ 
 genitors. I have already given my reasons for disbeliev¬ 
 ing in continental extensions within the period of existing 
 species on so enormous a scale that all the many islands 
 of the several oceans were thus stocked with their present 
 terrestrial inhabitants. This view removes many difficul¬ 
 ties, but it does not accord with all the facts in regard to 
 the productions of islands. In the following remarks I 
 shall not confine myself to the mere question of dispersal, 
 but shall consider some other cases bearing on the truth of 
 the two theories of independent creation and of descent 
 with modification. 
 
 The species of all kinds which inhabit oceanic islands 
 are few in number compared with those on equal continen¬ 
 tal areas: Alph. de Candolle admits this for plants, and 
 Wollaston for insects, blew Zealand, for instance, with 
 its lofty mountains and diversified stations, extending over 
 780 miles of latitude, together with the outlying islands of 
 Auckland, Campbell and Chatham, contain altogether 
 only 960 kinds of flowering plants; if we compare this moder¬ 
 ate number with the species which swarm over equal areas 
 in Southwestern Australia or at the Cape of Good Hope, 
 we must admit that some cause, independently of different 
 physical conditions, has given rise to so great a difference 
 in number. Even the uniform county of Cambridge has 
 847 plants, and the little island of Anglesea 764, but a 
 few ferns and a few introduced plants are included in 
 these numbers, and the comparison in some other respects 
 is not quite fair. We have evidence that the barren island 
 of Ascension aboriginally possessed less than half a dozen 
 flowering plants; yet many species have now become 
 naturalized on it, as they have in New Zealand and on 
 every other oceanic island which can be named. In St. 
 Helena there is reason to believe that the naturalized plants 
 and animals have nearly or quite exterminated many native 
 productions. He who admits the doctrine of the creation 
 of each separate species, will have to admit that a sufficient 
 number of the best adapted plants and animals were not 
 created for oceanic islands; for man has unintentionally 
 stocked them far more fully and perfectly than did nature. 
 
INHABITANTS OF OCEANIC ISLANDS. 
 
 411 
 
 Although in oceanic islands the species are few in 
 number, the proportion of endemic kinds (i. e. those 
 found nowhere else in the world) is often extremely large. 
 If we compare, for instance, the number of endemic land- 
 shells in Madeira, or of endemic birds in the Galapagos 
 Archipelago, with the number found on any continent, 
 and then compare the area of the island with that of the 
 continent, we shall see that this is true. This fact might 
 have been theoretically expected, for, as already explained, 
 species occasionally arriving, after long intervals of time in 
 the new and isolated district, and having to compete with 
 new associates, would be eminently liable to modification, 
 and would often produce groups of modified descendants. 
 But it by no means follows that, because in an islaud 
 nearly all the species of one class are peculiar, those of 
 another class, or of another section of the same class, are 
 peculiar; and this difference seems to depend partly on the 
 species which are not modified having immigrated in a 
 body, so that their mutual relations have not been much 
 disturbed; and partly on the frequent arrival of unmodified 
 immigrants from the mother-country, with which the 
 insular forms have intercrossed. It should be borne in 
 mind that the offspring of such crosses would certainly 
 gain in vigor; so that even an occasional cross would pro¬ 
 duce more effect than might have been anticipated. I will 
 give a few illustrations of the foregoing remarks: in the 
 Galapagos Islands there are twenty-six land birds; of these, 
 twenty-one (or perhaps twenty-three) are peculiar, whereas 
 of the eleven marine birds only two are peculiar; and it is 
 obvious that marine birds could arrive at these islands 
 much more easily and frequently than land birds. Ber¬ 
 muda, on the other hand, which lies at about the same 
 distance from North America as the Galapagos Islands do 
 from South America, and which has a very peculiar soil, 
 does not possess a single endemic land bird; and we know 
 from Mr. J. M. Jones’ admirable account of Bermuda, 
 that very many North American birds occasionally or even 
 frequently visit this island. Almost every year, as I 
 am informed by Mr. E. V. Harcourt, many European and 
 African birds are blown to Madeira; this island is inhabited 
 by ninety-nine kinds, of which one alone is peculiar, though 
 very closely related to a European form; and three or four 
 
412 
 
 INIIA BIT A NTS OF OCEANIC ISLANDS. 
 
 other species are confined to this island and to the Canaries. 
 So that the Islands of Bermuda and Madeira have been 
 stocked from the neighboring continents with birds, which 
 for long ages have there struggled together, and have 
 become mutually co-adapted. Hence, when settled in their 
 new homes, each kind will have been kept by the others to 
 its proper place and habits, and will consequently have 
 been but little liable to modification. Any tendency to 
 modification will also have been checked by intercrossing 
 with the unmodified immigrants, often arriving from the 
 mother-country. Madeira again is inhabited by a wonder¬ 
 ful number of peculiar land-shells, whereas not one species 
 of sea-shell is peculiar to its shores: now, though we do 
 not know how sea-shells are dispersed, yet we can see that 
 their eggs or larvae, perhaps attached to sea-weed or float¬ 
 ing timber, or to the feet of wading birds, might be trans¬ 
 ported across three or four hundred miles of open sea far 
 more easily than land-shells. The different orders of 
 insects inhabiting Madeira present nearly parallel cases. 
 
 Oceanic islands are sometimes deficient in animals of 
 certain whole classes, and their places are occupied by 
 other classes; thus in the Galapagos Islands reptiles, and 
 in New Zealand gigantic wingless birds, take, or recently 
 took, the place of mammals. Although New Zealand is here 
 spoken of as an oceanic island, it is in some degree doubtful 
 whether it should be so ranked; it is of large size, and is 
 not separated from Australia by a profoundly. deep sea; 
 from its geological character and the direction of its mount¬ 
 ain ranges, the Rev. W. B. Clarke has lately maintained 
 that this island, as well as New Caledonia, should be con¬ 
 sidered as appurtenances of Australia. Turning to plants, 
 Dr. Hooker has shown that in the Galapagos Islands the 
 proportional numbers of the different orders are very dif¬ 
 ferent from what they are elsewhere. All such differences 
 in number, and the absence of certain whole groups of 
 animals and plants, are generally accounted for by sup¬ 
 posed differences in the physical conditions of the islands; 
 but this explanation is not a little doubtful. Facility of 
 immigration seems to have been fully as important as the 
 nature of the conditions. 
 
 Many remarkable little facts could he given with respect 
 to the inhabitants 3 f oceanic islands. For instance,, in 
 
INHABITANTS OF OCEANIC ISLANDS. 413 
 
 certain islands not tenanted by a single mammal, some of 
 the endemic plants have beautifully hooked seeds; yet few 
 relations are more manifest than that hooks serve for the 
 transportal of seeds in the wool or fur of quadrupeds. 
 But a hooked seed might be carried to an island by other 
 means; and the plant then becoming modified would form 
 an endemic species, still retaining its hooks, which would 
 form a useless appendage, like the shrivelled wings under 
 the soldered wing-covers of many insular beetles. Again, 
 islands often possess trees or bushes belonging to orders 
 which elsewhere include only herbaceous species; now 
 trees, as Alph. de Candolle has shown, generally have, 
 whatever the cause may be, confined ranges. Hence trees 
 would be little likely to reach distant oceanic islands; and 
 an herbaceous plant, which had no chance of successfully 
 competing with the many fully developed trees growing on 
 a continent, might, when established on an island, gain an 
 advantage over other herbaceous plants by growing taller 
 and taller and overtopping them. In this case, natural 
 selection would tend to add to the stature of the plant, to 
 whatever order it belonged, and thus first convert it into a 
 bush and then into a tree. 
 
 ABSENCE OF BATRACHIANS AND TERRESTRIAL Tn A.MMALS 
 
 ON OCEANIC ISLANDS. 
 
 With respect to the absence of whole orders of animals 
 on oceanic islands, Bory St. Vincent long ago remarked 
 that Batrachians (frogs, toads, newts) are never found on 
 any of the many islands with which the great oceans are 
 ' studded. I have taken pains to verify this assertion, and 
 have found it true, with the exception of New Zealand, 
 New Caledonia, the Andaman Islands, and perhaps the 
 Solomon Islands and the Seychelles. But I have already 
 remarked that it is doubtful whether New Zealand and 
 New Caledonia ought to be classed as oceanic islands; and 
 this is still more doubtful with respect to the Andaman and 
 Solomon groups and the Seychelles. This general absence 
 of frogs, toads and newts on so many true oceanic islands 
 can not be accounted for by their physical conditions: in¬ 
 deed it seems that islands are peculiarly fitted for these 
 animals; for frogs have been introduced into Madeira, the 
 
414 
 
 ABSENCE CF TERRESTRIAL 
 
 Azores and Mauritius, and have multiplied so as to become 
 a nuisance. But as these animals and their spawn are im¬ 
 mediately killed (with the exception, as far as known, of 
 one Indian species) by sea-water, there would be great 
 difficulty in their transportal across the sea, and therefore 
 we can see why they do not exist on strictly oceanic 
 islands. But why, on the theory of creation, they should 
 not have been created there, it would be very difficult to 
 explain. 
 
 Mammals offer another and similar case. I have care¬ 
 fully searched the oldest voyages, and have not found a 
 single instance, free from doubt, of a terrestrial mammal 
 (excluding domesticated animals kept by the natives) in¬ 
 habiting an island situated about 300 miles from a conti¬ 
 nent or great continental island; and many islands situated 
 at a much less distance are equally barren. The Falkland 
 Islands, which are inhabited by a wolf-like fox, come near¬ 
 est to an exception; but this group cannot be considered 
 as oceanic, as it lies on a bank in connection with the 
 mainland at a distance of about 280 miles; moreover, ice¬ 
 bergs formerly brought bowlders to its western shores, and 
 they may have formerly transported foxes, as now fre¬ 
 quently happens in the arctic regions. Yet it cannot be 
 said that small islands will not support at least small mam¬ 
 mals, for they occur in many parts of the world on very 
 small islands, when lying close to a continent; and hardly 
 an island can be named on which our smaller quadrupeds 
 have not become naturalized and greatly multiplied. It 
 cannot be said, on the ordinary view of creation, that there 
 has not been time for the creation of mammals; many vol¬ 
 canic islands are sufficiently ancient, as shown by the 
 stupendous degradation which they have suffered, and by 
 their tertiary strata: there has also been time for the pro¬ 
 duction of endemic species belonging to other classes; and 
 on continents it is known that new species of mammals ap¬ 
 pear and disappear at a quicker rate than other and lower 
 animals.. Although terrestrial mammals do not occur on 
 oceanic islands, aerial mammals do occur on almost every 
 island. New Zealand possesses two bats found nowhere 
 else in the world: Norfolk Island, the Viti Archipelago, 
 the Bonin Islands, the Caroline and Marianne Archi¬ 
 pelagoes, and Mauritius, all possess their peculiar bats. 
 
MAMMALS ON OCEANIC ISLANDS. 
 
 415 
 
 Why, it may be asked, has the supposed creative force 
 produced bats and no other mammals on remote islands? 
 On my view this question can easily be answered; for no 
 terrestrial mammal can be transported across a wide space 
 of sea, but bats can fly across. Bats have been seen wan¬ 
 dering by day far over the Atlantic Ocean; and two North 
 American species, either regularly or occasionally, visit Ber¬ 
 muda, at the distance of 600 miles from the mainland. I 
 hear from Mr. Tomes, who has specially studied this 
 family, that many species have enormous ranges, and are 
 found on continents and on far distant islands. Hence, we 
 have only to suppose that such wandering species have 
 been modified in their new homes in relation to their new 
 position, and we can understand the presence of endemic 
 bats on oceanic islands, with the absence of all other ter¬ 
 restrial mammals. 
 
 Another interesting relation exists, namely, between 
 the depth of the sea separating islands from each other, 
 or from the nearest continent, and the degree of affinity 
 of their mammalian inhabitants. Mr. Windsor Earl has 
 made some striking observations on this head, since greatly 
 extended by Mr. Wallace's admirable researches, in regard 
 to the great Malay Archipelago, which is traversed near 
 Celebes by a space of deep ocean, and this separates two 
 widely distinct mammalian faunas. On either side, the 
 islands stand on a moderately shallow submarine bank, 
 and these islands are inhabited by the same or by closely 
 allied quadrupeds. I have not as yet had time to follow 
 up this subject in all quarters of the world; but as far as I 
 have gone, the relation holds good. For instance, Britain 
 is separated by a shallow channel from Europe, and the 
 mammals are the same on both sides; and so it is with all 
 the islands near the shores of Australia. The West Indian 
 Islands, on the other hand, stand on a deeply submerged 
 bank, nearly one thousand fathoms in depth, and here we 
 find American forms, but the species and even the genera 
 are quite distinct. As the amount of modification which 
 animals of all kinds undergo partly depends on the lapse 
 of time, and as the islands which are separated from each 
 other, or from the mainland, by shallow channels, are more 
 likely to have been continuously united within a recent 
 period than the islands separated by deeper channels, we 
 
416 
 
 ABSENCE OF TERRESTRIAL 
 
 can understand how it is that a relation exists between the 
 depth of the sea separating two mammalian faunas, and 
 the degree of their affinity, a relation which is quite inex¬ 
 plicable on the theory of independent acts of creation. 
 
 The foregoing statements in regard to the inhabitants of 
 oceanic islands, namely, the fewness of the species, with a 
 large proportion consisting of endemic forms—the mem¬ 
 bers of certain groups, but not those of other groups in the 
 same class, having been modified—the absence of certain 
 Afhole orders, as of batrachians and of terrestrial mammals, 
 notwithstanding the presence of aerial bats, the singular 
 proportions of certain orders of plants, herbaceous forms 
 having been developed into trees, etc., seem to me to accord 
 better with the belief in the efficiency of occasional means 
 of transport, carried on during a long course of time, than 
 with the belief in the former connection of all oceanic 
 islands with the nearest continent; for on this latter view 
 it is probable that the various classes would have immi¬ 
 grated more uniformly, and from the species having 
 entered in a body, their mutual relations would not have 
 been much disturbed, and consequently, they would either 
 have not been modified, or all the species in a more equa¬ 
 ble manner. 
 
 I do not deny that there are many and serious difficul¬ 
 ties in understanding how many of the inhabitants of the 
 more remote islands, whether still retaining the same spe¬ 
 cific form or subsequently modified, have reached their 
 present homes. But the probability of other islands having 
 once existed as halting-places, of which not a wreck now 
 remains, must not be overlooked. I will specify one diffi¬ 
 cult case. Almost all oceanic islands, even the most 
 isolated and smallest, are inhabited by land-shells, gener¬ 
 ally by endemic species, but sometimes by species found 
 elsewhere, striking instances of which have been given 
 by Dr. A. A. Gould in relation to the Pacific. Now it 
 is notorious that land-shells are easily killed by sea¬ 
 water; their eggs, at least such as I have tried, sink in 
 it and are killed. Yet there must be some unknown, 
 but occasionally efficient means for their transportal. 
 Would the just-hatched young sometimes adhere to the 
 feet of birds roosting on the ground and thus get trans¬ 
 ported? It occurred to me that land-shells, when hyber- 
 
MAMMALS ON OCEANIC ISLANDS. 
 
 41? 
 
 Bating and having a membranous diaphragm over the 
 mouth of the shell, might be floated in chinks of drifted 
 timber across moderately wide arms of the sea. And I find 
 that several species in this state withstand uninjured an im¬ 
 mersion in sea-water during seven days. One shell, the Helix 
 pomatia, after having been thus treated, and again hyber- 
 nating, was put into sea-water for twenty days and perfectly 
 recovered. During this length of time the shell might 
 have been carried by a marine current of average swiftness 
 to a distance of 660 geographical miles. As this Helix has 
 a thick calcareous operculum I removed it, and when it 
 had formed a new membranous one, I again immersed it 
 for fourteen days in sea-water, and again it recovered and 
 crawled away. Baron Aucapitaine has since tried similar 
 experiments. He placed 100 land-shells, belonging to ten 
 species, in a box pierced with holes, and immersed it for a 
 fortnight in the sea. Out of the hundred shells twenty- 
 seven recovered. The presence of an operculum seems to 
 have been of importance, as out of twelve specimens of 
 Cyclostoma elegans, which is thus furnished, eleven re¬ 
 vived. It is remarkable, seeing how well the Helix pomatia 
 resisted with me the salt-water, that not one of fifty-four 
 specimens belonging to four other species of Helix tried by 
 Aucapitaine recovered. It is, however, not at all probable 
 that land-shells have often been thus transported; the 
 feet of birds offer a more probable method. 
 
 ON THE RELATIONS OF THE INHABITANTS OF ISLANDS TO 
 THOSE OF THE NEAREST MAINLAND. 
 
 The most striking and important fact for us is the 
 affinity of the species which inhabit islands to those of the 
 nearest mainland, without being actually the same. 
 Numerous instances could be given. The Galapagos Arch¬ 
 ipelago, situated under the equator, lies at the distance of 
 between 500 and 600 miles from the shores of South 
 America. Here almost every product of the land and 
 of the water bears the unmistakable stamp of the Amer¬ 
 ican continent. There are twenty-six land birds. Of 
 these twenty-one, or perhaps twenty-three, are ranked as 
 distinct species, and would commonly be assumed to have 
 been here created; yet the close affinity of most of these 
 
 i 
 
418 
 
 RELATIONS OF THE INHABITANTS OF 
 
 birds to American species is manifest in every character in 
 their habits, gestures and tones of voice. So it is with the 
 other animals, and with a large proportion of the plants, 
 as shown by Dr. Hooker in his admirable Flora of this 
 archipelago. The naturalist, looking at the inhabitants of 
 these volcanic islands in the Pacific, distant several hun¬ 
 dred miles from the continent, feels that he is standing on 
 American land. Why should this be so? Why should the 
 species which are supposed to have been created in the 
 Galapagos Archipelago, and nowhere else, bear so plainly 
 the stamp of affinity to those created in America? 
 There is nothing in the conditions of life, in the 
 geological nature of the islands, in their height or 
 climate, or in the proportions in which the several classes 
 aie associated together, which closely resembles the 
 conditions of the South American coast. In fact, 
 there is a considerable dissimilarity in all these respects. 
 On the other hand, there is a considerable degree of resem¬ 
 blance in the volcanic nature of the soil, in the climate, 
 height, and size of the islands, between the Galapagos and 
 Cape Verde Archipelagos: but what an entire and abso¬ 
 lute difference in their inhabitants! The inhabitants of 
 the Cape Verde Islands are related to those of Africa, like 
 those of the Galapagos to America. Facts, such as these, 
 admit of no sort of explanation on the ordinary view of in¬ 
 dependent creation; whereas, on the view here maintained, 
 it is obvious that the Galapagos Islands would be likely to 
 receive colonists from America, whether by occasional 
 means of transport or (though I do not believe in this doc¬ 
 trine) by formerly continuous land, and the Cape Verde 
 Islands from Africa; such colonists would be liable to 
 modification—the principle of inheritance still betraying 
 their original birthplace. 
 
 Many analogous facts could be given: indeed it is an 
 almost universal rule that the endemic productions of 
 islands are related to those of the nearest continent, or of 
 the nearest large island. The exceptions are few, and 
 most of them can be explained. Thus, although Kergue¬ 
 len Land stands nearer to Africa than to America, the 
 plants are related, and that very closely, as we know from 
 Dr. Hooker’s account, to those of America: but on the 
 view that this island has been mainly stocked by seeds 
 
ISLANDS TO THOSE OF THE MAINLAND. 419 
 
 brought with earth and stones on icebergs, drifted by the 
 prevailing currents, this anomaly disappears. New Zealand 
 in its endemic planes is much more closely related to Aus¬ 
 tralia, the nearest mainland, than to any other region: and 
 this is what might have been expected; but it is also 
 plainly related to South America, which, although the 
 next nearest continent, is so enormously remote, that the 
 fact becomes an anomaly. But this difficulty partially dis¬ 
 appears on the view that New Zealand, South America, 
 and the other southern lands, have been stocked in part 
 from a nearly intermediate though distant point, namely, 
 from the antarctic islands, when they were clothed with 
 vegetation, during a warmer tertiary period, before the 
 commencement of the last Glacial period. The affinity, 
 which, though feeble, I am assured by Dr. Hooker is real, 
 between the flora of the south-western corner of Australia 
 and of the Cape of Good Hope, is a far more remarkable 
 case; but this affinity is confined to the plants, and will, 
 no doubt, some day be explained. 
 
 The same law which has determined the relationship be¬ 
 tween the inhabitants of islands and the nearest mainland, 
 is sometimes displayed on a small scale, but in a most in¬ 
 teresting manner, within the limits of the same archi¬ 
 pelago. Thus each separate island of the Galapagos 
 Archipelago is tenanted, and the fact is a marvelous 
 one, by many distinct species; but these species are 
 related to each other in a very much closer manner 
 than to the inhabitants of the American continent, or of 
 any other quarter of the world. This is what might 
 have been expected, for islands situated so near to each 
 other would almost necessarily receive immigrants from the 
 some original source, and from each other. But how is it 
 that many of the immigrants have been differently modi¬ 
 fied, though only in a small degree, in islands situated 
 within sight of each other, having the same geolog¬ 
 ical nature, the same height, climate, etc. ? This long 
 appeared to me a great difficulty: but it arises in chief 
 part from the deeply-seated error of considering the phys¬ 
 ical conditions of a country as the most important; 
 whereas it cannot be disputed that the nature of the 
 other species with which each has to compete, is at 
 least as important, and generally a far more import- 
 
420 
 
 RELATIONS OF THE INHABITANTS 01 
 
 ant element of success. Now, if we look to the species 
 which inhabit the Galapagos Archipelago, and are likewise 
 found in other parts of the world, we find that they differ 
 considerably in the several islands. This difference might 
 indeed have been expected if the islands have been stocked 
 by occasional means of transport—a seed, for instance, of 
 one plant having been brought to one island, and that of 
 another plant to another island, though all proceeding 
 from the same general source. Hence, when in former 
 times an immigrant first settled on one of the islands, or 
 when it subsequently spread from one to another, it would 
 undoubtedly be exposed to different conditions in the dif¬ 
 ferent islands, for it would have to compete with a differ¬ 
 ent set of organisms; a plant, for instance, would find the 
 ground best fitted for it occupied by somewhat different 
 species in the different islands, and would be exposed to 
 the attacks of somewhat different enemies. If, then, it 
 varied, natural selection would probably favor different 
 varieties in the different islands. Some species, however, 
 might spread and yet retain the same character throughout 
 the" group, just as we see some species spreading widely 
 throughout a continent and remaining the same. 
 
 The really surprising fact in this case of the Galapagos 
 Archipelago, and in a lesser degree in some analogous 
 cases, is that each new species after being formed in any 
 one island, did not spread quickly to the other islands. 
 But the islands, though in sight of each other, are sepa¬ 
 rated by deep arms of the sea, in most cases wider than the 
 British Channel, and there is no reason to suppose that 
 they have at any former period been continuously united. 
 The currents of the sea are rapid and deep between the 
 islands, and gales of wind are extraordinarily rare; so that 
 the islands are far more effectually separated from each other 
 than they appear on a map. Nevertheless, some of the 
 species, both of those found in other parts of the world 
 and of those confined to the archipelago, are common to 
 the several islands; and we may infer from the present 
 manner of distribution that they have spread from one 
 island to the others. But we often take, I think, an 
 erroneous view of the probability of closely allied species 
 invading each other's territory, when put into free inter¬ 
 communication, Undoubtedly, if one species has any 
 
islands to Those of the mainland. 421 
 
 advantage over another, it will in a very brief time 
 wholly or in part supplant it; but if both are equally well 
 fitted for their own places, both will probably hold their 
 separate places for almost any length of time. Being 
 familiar with the fact that many species, naturalized 
 through man's agency, have spread with astonishing 
 rapidity over wide areas, we are apt to infer that most 
 species would thus spread; but we should remember that 
 the species which become naturalized in new countries 
 are not generally closely allied to the aboriginal inhabi¬ 
 tants, but are very distinct forms, belonging in a large 
 proportion of cases, as shown by Alph. de Candolle, 
 to distinct genera. In the Galapagos Archipelago, many 
 even of the birds, though so well adapted for flying 
 from island to island, differ on the different islands; 
 thus there are three closely allied species of mocking- 
 thrush, each confined to its own island. Now let us 
 suppose the mocking-thrush of Chatham Island to be 
 blown to Charles Island, which has its own mocking- 
 thrush; why should it succeed in establishing itself there? 
 We may safely infer that Charles Island is well stocked with 
 its own species, for annually more eggs are laid and young 
 birds hatched than can possibly be reared; and we may 
 infer that the mocking-thrush peculiar to Charles Island is 
 at least as well fitted for its home as is the species peculiar 
 to Chatham Island. Sir C. Lyell and Mr. Wollaston 
 have communicated to me a remarkable fact bearing on 
 this subject; namely, that Madeira and the adjoining islet 
 of Porto Santo possesses many distinct but representative 
 species of land-shells, some of which live in crevices of 
 stone; and although large quantities of stone are annually 
 transported from Porto Santo to Madeira, yet this latter 
 island has not become colonized by the Porto Santo 
 species; nevertheless, both islands have been colonized by 
 European land-shells, which no doubt had some advantage 
 over the indigenous species. From these considerations I 
 think we need not greatly marvel at the endemic species 
 which inhabit the several islands of the Galapagos Archi¬ 
 pelago not having all spread from island to island. On 
 the same continent, also, preoccupation has probably 
 played an important part in checking the commingling of 
 the species which inhabit different districts with nearly the 
 
422 RELATIONS OF THE INHABITANTS OF 
 
 same physical conditions. Thus, the south-east and south¬ 
 west corners of Australia have nearly the same physical 
 conditions, and are united by continuous land, yet they are 
 inhabited by a vast number of distinct mammals, birds 
 and plants; so it is, according to Mr. Bates, with the 
 butterflies and other animals inhabiting the great, open, 
 and continuous valley of the Amazons. 
 
 The same principle which governs the general character 
 of the inhabitants of oceanic islands, namely, the relation 
 to the source whence colonists could have been most 
 easily derived, together with their subsequent modifica¬ 
 tion, is of the widest application throughout nature. We 
 see this on every mountain-summit, in every lake and 
 marsh. For Alpine species, excepting in as far as the 
 same species have become widely spread during the Glacial 
 epoch, are related to those of the surrounding lowlands; 
 thus we have in South America, Alpine humming-birds, 
 Alpine rodents, Alpine plants, etc., all strictly belonging 
 to American forms; and it is obvious that a mountain, as 
 it became slowly upheaved, would be colonized from the 
 surrounding lowlands. So it. is with the inhabitants of 
 lakes and marshes, excepting in so far as great facility of 
 transport has allowed the same forms to prevail through¬ 
 out large portions of the world. We see the same princi¬ 
 ple in the character of most of the blind animals inhabiting 
 the caves of America and of Europe. Other analogous 
 facts could be given. It will, I believe, be found uni¬ 
 versally true, that wherever in two regions, let them be 
 ever, so distant, many closely allied or representative' 
 species occur, there will likewise be found some identical 
 species; and wherever many closely-allied species occur, 
 there will be found. many forms which some naturalists 
 rank as distinct species, and others as mere varieties; these 
 doubtful forms showing us the steps in the progress of 
 modification. 
 
 . The relation between the power and extent of migra¬ 
 tion in certain species, either at the present or 
 at. some former period, and the existence at remote 
 points of the world of closely allied species, is shown 
 in another and more general way. Mr. Gould remarked 
 to me long ago, that in those genera of birds which range 
 over the world, many of the species have very wide ranges. 
 
ISLANDS TO THOSE OF THE MAINLAND . 423 
 
 I can hardly doubt that this rule is generally true, though 
 difficult of proof. Among mammals, we see it strikingly 
 displayed in bats, and in a lesser degree in the Felidae and 
 Canidae. We see the same rule in the distribution of butter¬ 
 flies and beetles. So it is with most of the inhabitants of 
 fresh water, for many of the genera in the most distinct 
 classes range over the world, and many of the species have 
 enormous ranges. It is not meant that all, but that some 
 of the species have very wide ranges in the genera which 
 range very widely. Nor is it meant that the species in 
 such genera have, on an average, a very wide range; for 
 this will largely depend on how far the process of modifica¬ 
 tion has gone; for instance, two varieties of the same 
 species inhabit America and Europe, and thus the species 
 has an immense range; but, if variation were to be carried 
 a little further, the two varieties would be ranked as dis¬ 
 tinct species, and their range would be greatly reduced. 
 Still less is it meant, that species which have the capacity 
 of crossing barriers and ranging widely, as in the case of 
 certain powerfully-winged birds, will necessarily range 
 widely; for we should never forget that to range widely 
 implies not only the power of crossing barriers, but the 
 more important power of being victorious in distant lands 
 in the struggle for life with foreign associates. But accord¬ 
 ing to the view that all the species of a genus, though dis¬ 
 tributed to the most remote points of the world, are 
 descended from a single progenitor, we ought to find, and 
 I believe as a general rule we do find, that some at least of 
 the species range very widely. 
 
 We should bear in mind that many genera in all classes 
 are of ancient origin, and the species in this case will 
 have had ample time for dispersal and subsequent modifi¬ 
 cation. There is also reason to believe, from geological 
 evidence, that within each great class the lower organisms 
 change at a slower rate than the higher; consequently they 
 will have had a better chance of ranging widely and of still 
 retaining the same specific character. This fact, together 
 with that of the seeds and eggs of most lowly organized 
 forms being very minute and better fitted for distant trans- 
 portal, probably accounts for a law which has long been 
 observed, and which has lately been discussed by Alph. de 
 Candolle in regard to plants, namely, that the lower any 
 group of organisms stands the more widely it ranges. 
 
424 
 
 SUMMARY. 
 
 The relations just discussed—namely, lower organisms 
 ranging more widely than the higher—some of the species 
 of widely-ranging genera themselves ranging widely — 
 such facts, as alpine, lacustrine, and marsh productions 
 being generally related to those which live on the surround¬ 
 ing low lands and dry lands—the striking relationship 
 between the inhabitants of islands and those of the nearest 
 mainland—the still closer relationship of the distinct in¬ 
 habitants of the islands in the same archipelago—are inex¬ 
 plicable on the ordinary view of the independent creation 
 of each species, but are explicable if we admit colonization 
 from the nearest or readiest source, together with the sub¬ 
 sequent adaptation of the colonists to their new homes. 
 
 SUMMARY OF THE LAST AND PRESENT CHAPTERS. 
 
 In these chapters I have endeavored to show that if we 
 make due allowance for our ignorance of the full effects of 
 changes of climate and of the level of the land, which 
 have certainly occurred within the recent period, and of 
 other changes which have probably occurred—if we re¬ 
 member how ignorant we are with respect to the many 
 curious means of occasional transport—if we bear in mind, 
 and this is a very important consideration, how often a 
 species may have ranged continuously over a wide area, 
 and then have become extinct in the intermediate tracts— 
 the difficulty is not insuperable in believing that all the 
 individuals of the same species, wherever found, are 
 descended from common parents. And we are led to this 
 conclusion, which has been arrived at by many naturalists 
 under the designation of single centers of creation, by 
 various general considerations, more especially from the 
 importance of barriers of all kinds, and from the ana¬ 
 logical distribution of subgenera, genera and families. 
 
 With respect to distinct species belonging to the same 
 genus, which on our theory have spread from one parent- 
 source; if we make the same allowances as before for our 
 ignorance, and remember that some forms of life have 
 changed very slowly, enormous periods of time having been 
 thus granted for their migration, the difficulties are far 
 from insuperable; though in this case, as in that of the 
 individuals of the same species, they are often great. 
 
SUMMARY. 
 
 425 
 
 I .£ s exemplifying the effects of climatical changes on dis¬ 
 tribution, I have attempted to show how important a part 
 the last Glacial period has played, which affected even the 
 equatorial regions, and which, during the alternations of; 
 the cold in the north and the south, allowed the produc¬ 
 tions of opposite hemispheres to mingle, and left some of 
 them stranded on the mountain-summits in all parts of the 
 world. As showing how diversified are the means of oc¬ 
 casional transport, I have discussed at some little length 
 the means of dispersal of fresh-water productions. 
 
 . tlie difficulties be not insuperable in admitting that 
 m the long course of time all the individuals of the 
 same species, and likewise of the several species belonging 
 
 < to the same genus, have proceeded from some one source*; 
 then all the grand leading facts of geographical distribution 
 are explicable on the theory of migration, together with 
 subsequent modification and the multiplication of new 
 forms. We can thus understand the high importance of 
 barriers, whether of land or water, in not only separating 
 but in apparently forming the several zoological and 
 botanical provinces. We can thus understand the con¬ 
 centration of related species within the same areas; and 
 how it is that under different latitudes, for instance, in 
 South Ameiica, the inhabitants of the plains and mount¬ 
 ains, of the forests, marshes and deserts, are linked 
 together in so mysterious a manner, and are likewise 
 linked to the extinct beings which formerly inhabited 
 the same continent. Bearing in mind that the mutual 
 relation of organism to organism is of the highest im¬ 
 portance, we can see why two areas, having nearly the 
 same physical conditions, should often be inhabited by 
 very different forms of life; for according to the length 
 of time which has elapsed since the colonists entered one 
 of the regions, or both; according to the nature of the 
 communication which allowed certain forms and not others 
 to enter, either in greater or lesser numbers; according or 
 not as those which entered happened to come into more 
 or less direct competition with each other and with the 
 aborigines; and according as the immigrants were capable 
 of varying more or less rapidlv, there would ensue in the 
 two or more regions, independently of their physical con¬ 
 ditions, infinitely diversified conditions of life; there would 
 
426 
 
 SUMMARY. 
 
 \ 
 
 be an almost endless amount of organic action and reaction, 
 and we should find some groups of beings greatly, and 
 some only slightly modified; some developed in great force, 
 some existing in scanty numbers—and this we do find in 
 the several great geographical provinces of the world. 
 
 On these same principles we can understand, as I have 
 endeavored to show, why oceanic islands should have few 
 inhabitants, but that of these, a large proportion should be 
 endemic or peculiar; and why, in relation to the means of 
 migration, one group of beings should have all its species 
 peculiar, and another group, even within the same class, 
 should have all its species the same with those in an 
 adjoining quarter of the world. We can see why whole 
 groups of organisms, as batrachians and terrestrial mam¬ 
 mals, should be absent from oceanic islands, while the 
 most isolated islands should possess their own peculiar 
 species of aerial mammals or bats. We can see why, in 
 islands, there should be some relation between the presence 
 of mammals, in a more or less modified condition, and the 
 depth of the sea between such islands and the mainland. 
 We can clearly see why all the inhabitants of an archipelago, 
 though specifically distinct on the several islets, should be 
 closely related to each other; and should likewise be 
 related, but less closely, to those of the nearest continent, 
 or other source whence immigrants might have been 
 derived. We can see why, if there exist very closely allied 
 or representative species in two areas, however distant from 
 each other, some identical species will almost always there 
 be found. 
 
 As the late Edward Forbes often insisted, there is a 
 striking parallelism in the laws of life throughout time 
 and space; the laws governing the succession of forms in 
 past times being nearly the same with those governing at 
 the present time the differences in different areas. We 
 see this in many facts. The endurance of each species 
 and group of species is continuous in time; for the appar¬ 
 ent exceptions to the rule are so few that they may fairly 
 be attributed to our not having as yet discovered in an 
 intermediate deposit certain forms which are absent in it, 
 but which occur both above and below: so in space, it cer¬ 
 tainly is the general rule that the area inhabited by a 
 single species, or by a group of species, is continuous, and 
 
SUMMARY. 
 
 42? 
 
 the exceptions, which are not rare, may, as I have 
 attempted to show, be accounted for by former migrations 
 under ditferent circumstances, or through occasional means 
 of transport, or by the species having become extinct in 
 the intermediate tracts. Both in time and space species 
 and groups of species have their points of maximum 
 development. Groups of species, living during the same 
 period of time, or living within the same area, are often 
 characterized by trifling features in common, as of sculpt¬ 
 ure or color. In looking to the long succession of past 
 ages, as in looking to distant provinces throughout the 
 world, we find that, species in certain classes differ little 
 from each other, while those in another class, or only in a 
 different section of the same order, differ greatly from 
 each other. In both time and space the lowly organized 
 members of each class generally change less than the 
 highly organized; but there are in both cases marked 
 exceptions to the rule. According to our theory, these 
 several relations throughout time and space are intelligible; 
 for whether we look to the allied forms of life which have 
 changed during successive ages, or to those which have 
 changed after having migrated into distant quarters, in 
 both cases they are connected by the same bond of ordinary 
 generation; in both cases the laws of variation have been 
 the same, and modifications have been accumulated by the 
 same means of natural selection. 
 
m 
 
 CLASSIFICATION. 
 
 CHAPTER XIV. 
 
 MUTUAL AFFINITIES OF ORGANIC BEINGS: MORPHOLOGY— 
 EMBRYOLOGY—RUDIMENTARY ORGANS. 
 
 Classification, groups subordinate to groups—Natural system—Rules 
 and difficulties in classification, explained on tbe theory of 
 descent with modification—Classification of varieties—Descent 
 always used in classification—Analogical or adaptive characters— 
 Affinities, general, complex and radiating—Extinction separates 
 and defines groups—Morphology, between members of the same 
 class, between parts of the same individual—Embryology, laws 
 of, explained by variations not supervening at an early age, and 
 being inherited at a corresponding age—Rudimentary organs, 
 their origin explained—Summary. 
 
 CLASSIFICATION. 
 
 From the most remote period in the history of the world 
 organic beings have been found to resemble each other in 
 descending degrees, so that they can be classed in groups 
 under groups. This classification is not arbitrary like the 
 grouping of the stars in constellations. The existence of 
 groups would have been of simple significance, if one group 
 had been exclusively fitted to inhabit the land, and another 
 the water; one to feed on flesh, another on vegetable 
 matter, and so on; but the case is widely different, for it is 
 notorious how commonly members of even the same sub¬ 
 group have different habits. In the second and fourth 
 chapters, on Variation and on Natural Selection, I have 
 attempted to show that within each country it is the widely 
 ranging, the much diffused and common, that is the 
 dominant species, belonging to the larger genera in each 
 class, which vary most. The varieties, or incipient species, 
 thus produced, ultimately become converted into new and 
 distinct species; and these, on the principle of inheritance, 
 tend to produce other new and dominant species. Conse- 
 
CLASSIFICA TIOFT. 
 
 429 
 
 quently the groups which are now large, and which gen¬ 
 erally include many dominant species, tend to go on in¬ 
 creasing in size. I further attempted to show that from 
 the varying descendants of each species trying to occupy 
 as many and as different places as possible in the economy 
 of natuie, they constantly tend to diverge in character. 
 This latter conclusion is supported by observing the great 
 diversity of forms, which, in any small area, come into the 
 closest competition, and by certain facts in naturalization. 
 
 . attempted also to show that there is a steady tendency 
 in the forms which are increasing in number and diverging 
 in character, to supplant and exterminate the preceding, 
 less divergent and less improved forms. I request the 
 reader to turn to the diagram illustrating the action, as 
 formerly explained, of these several principles; and he will 
 see that the inevitable result is, that the modified descend¬ 
 ants proceeding from one progenitor become broken up into 
 groups subordinate to groups. In the diagram each letter 
 on the uppermost line may represent a genus including 
 several species; and the whole of the genera along this 
 upper line form together one class, for all are descended 
 from one ancient parent, and, consequently, have inherited 
 something in common. But the three genera on the left 
 hand have, on this same principle, much in common, and 
 form a subfamily, distinct from that containing the next 
 two genera on the right hand, which diverged from a com¬ 
 mon parent at the fifth stage of descent. These five genera 
 have also much in common, though less than when grouped 
 in subfamilies; and they form a family distinct from that 
 containing the three genera still further to the right hand, 
 which diverged at an earlier period. And all these genera' 
 descended from (A), form an order distinct from the genera 
 descended from (I). So that we here have many species 
 descended from a single progenitor grouped into genera; 
 and the genera into subfamilies, families and orders, all 
 under one great class. The grand fact of the natural sub¬ 
 ordination of organic beings in groups under groups, 
 which, from its familiarity, does not always sufficiently 
 strike us, is in my judgment thus explained. No doubt 
 organic beings, like all other objects, can be classed in many 
 ways, either artificially by single characters, or more natu¬ 
 rally by a number of characters. We know, for instance, 
 
430 CLASSIFICATION. 
 
 that minerals and the elemental substances can be thus 
 arranged. In this case there is of course no relation to 
 o-enealogical succession, and no cause can at present be 
 assigned for their falling into groups. But with organic 
 beings the case is different, and the view above given 
 accords with their natural arrangement m group under 
 group; and no other explanation has ever been attempted. 
 
 Naturalists, as we have seen, try to arrange the species, 
 genera and families in each class, on what is called the 
 Natural System. But what is meant by this system. 
 Some authors look at it merely as a scheme foi arranging 
 together those living objects which are most alike, and 
 for separating those which are most unlike; or as an 
 artificial method of enunciating, as briefly as possible, gen¬ 
 eral propositions—that is, by one sentence to give the chai- 
 acters common, for instance, to all mammals, by another 
 those common to all carnivora, by another those common 
 to the dog-genus, and then, by adding a single sentence, a 
 full description is given of each kind of dog. I he in¬ 
 
 genuity and utility of this system are indisputable. But 
 many naturalists think that something more is meant by 
 the Natural System; they believe that it reveals the plan 
 of the Creator; but unless it be specified whether order m 
 time or space, or both, or what else is meant by the Pj a ^ 
 of the Creator, it seems to me that nothing is thus added 
 to our knowledge. Expressions such as that famous ono 
 by Linn sens, which we often meet with in a moie or less 
 concealed form, namely, that the characters do not make 
 the genus, but that the genus gives the characters, seem to 
 imply that some deeper bond is included in our classifica¬ 
 tions than mere resemblance. I believe that this is the 
 case, and that community of descent—the one known 
 cause of close similarity in organic beings is the bond, 
 which, though observed^by various degrees of modification, 
 is partially revealed to us by our classifications. 
 
 Let us now consider the rules followed in classification, 
 and the difficulties which are encountered on the view that 
 classification either gives some unknown plan of creation, 
 or is simply a scheme for enunciating general propositions 
 and of placing together the forms most like each other. 
 It might have been thought (and was in ancient times 
 thought) that those parts of the structure which deter- 
 
CLASSIFICA TIOJST. 
 
 431 
 
 mined. the habits of life, and the general place of each 
 being in the economy of nature, would be of very high im¬ 
 portance in classification. Nothing can be more false. 
 No one regards the external similarity of a mouse to a 
 shrew, of a dugong to a whale, of a whale to a fish, as of 
 any importance. These resemblances, though so inti¬ 
 mately connected with the whole life of the being, are 
 ranked as merely “adaptive or analogical characters;” but 
 to the consideration of these resemblances we shall recur. 
 It may even be given as a general rule, that the less any 
 part of the organization is concerned with special habits, 
 the more important it becomes for classification. As an 
 instance: Owen, in speaking of the dugong, says, “The 
 generative organs, being those which are most remotely 
 related to the habits and food of an animal, I have always 
 regarded as affording very clear indications of its true affin¬ 
 ities. We are least likely in the modifications of these 
 organs to mistake a merely adaptive for an essential char¬ 
 acter.” With plants how remarkable it is that the organs 
 of vegetation, on which their nutrition and life depend, 
 are of little signification; whereas the organs of reproduc¬ 
 tion, with their product the seed and embryo, are of para¬ 
 mount importance! So again, in formerly discussing cer¬ 
 tain morphological characters which are not functionally 
 important, we have seen that they are often of the highest 
 service in classification. This depends on their constancy 
 throughout many allied groups; and their constancy 
 chiefly depends on any slight deviations not having been 
 preserved and accumulated by natural selection, which 
 acts only on serviceable characters. 
 
 That the mere physiological importance of an organ 
 does not determine its classificatory value, is almost 
 proved by the fact, that in allied groups, in which the 
 same organ, as we have every reason to suppose, has nearly 
 the same physiological value, its classificatory value is 
 widely different. No naturalist can have worked long at 
 any group without being struck with this fact; and it has 
 been fully acknowledged in the writings of almost every 
 author. It will suffice to quote the highest authority, 
 Robert Brown, who, in speaking of certain organs in the 
 Proteaceae, says their generic importance, “ like that of all 
 their parts, not only in this, but, as I apprehend in every 
 
432 
 
 CLASSIFICATION. 
 
 natural family, is very unequal, and in some? cases seems to 
 be entirely lost.” Again, in another work he says, the 
 genera of the Connaracese “ differ in having one or more 
 ovaria, in the existence or absence of albumen, in the im¬ 
 bricate or valvular aestivation. Any one of these charac¬ 
 ters singly is frequently of more than generic importance, 
 
 , though here even, when all taken together, they appear in- 
 i sufficient to separate Onestis from Oonnarus.” To give ail 
 example among insects: in one great division of the Hy- 
 menoptera, the antennae, as Westwood has remarked, are 
 most constant in structure; in another division they differ 
 much, and the differences are of quite subordinate value 
 in classification; yet no one will say that the antennae in 
 these two divisions of the same order are of unequal physi¬ 
 ological importance. Any number of instances could be 
 given of the varying importance for classification of the 
 same important organ within the same group of beings. 
 
 Again, no one will say that rudimentary or atrophied 
 organs are of high physiological or vital importance; yet, 
 undoubtedly, organs in this condition are often of much 
 value in classification. No one will dispute that the rudi¬ 
 mentary teeth in the upper jaws of young ruminants, and 
 certain rudimentary bones of the leg, are highly serviceable 
 in exhibiting the close affinity between ruminants and 
 pachyderms. Robert Brown has strongly insisted on the 
 fact that the position of the rudimentary florets is of the 
 highest importance in the classification of the grasses. 
 
 Numerous instances could be given of characters derived 
 from parts which must be considered of very trifling physi¬ 
 ological importance, but which are universally admitted as 
 highly serviceable in the definition of whole groups. For 
 instance, whether or not there is an open passage from the 
 nostrils to the mouth, the only character, according to 
 Owen, which absolutely distinguishes fishes and reptiles—- 
 the inflection of the angle of the lower jaw in Marsupials— 
 the manner in which the wings of insects are folded—mere 
 color in certain Algae—mere pubescence on parts of the 
 flower in grasses—the nature of the dermal covering, as 
 hair or feathers, in the Yertebrata. If the Ornithorhyn- 
 chus had been covered with feathers instead of hair, this 
 external and trifling character would have been considered 
 by naturalists as an important aid in determining the de¬ 
 gree of affinity of this strange creature to birds. 
 
CLASSIFICATION. 
 
 433 
 
 The importance, for classification, of trifling characters, 
 mainly depends on their being correlated with many other 
 characters of more or less importance. The value indeed 
 of an aggregate of characters is very evident in natural his¬ 
 tory. Hence, as has often been remarked, a species may 
 depart from its allies in several characters, both of high 
 physiological importance, and of almost universal preva¬ 
 lence, and yet leave us in no doubt where it should 
 be ranked. Hence, also, it has been found that a 
 classification founded on any single character, however 
 important that may be, has always failed; for no part of 
 the organization is invariably constant. The importance 
 of an aggregate of characters, even when none are impor¬ 
 tant, alone explains the aphorism enunciated by Linnaeus, 
 namely, that the characters do not give the genus, but the 
 genus gives the character; for this seems founded on the 
 appreciation of many trifling points of resemblance, too 
 slight to be defined. Certain plants, belonging to the 
 Malpighiaceae, bear perfect and degraded flowers; in the 
 latter, as A. de Jussieu has remarked, “ The greater num¬ 
 ber of the characters proper to the species, to the genus, 
 to the family, to the class, disappear, and thus laugh at 
 our classification.” When Aspicarpa produced in France, 
 during several years, only these degraded flowers, depart¬ 
 ing so wonderfully in a number of the most important 
 points of structure from the proper type of the order, yet 
 M. Richard sagaciously saw, as Jussieu observes, that this 
 genus should still be retained among the Malpighiaceae. 
 This case well illustrates the spirit of our classifications. 
 
 Practically, when naturalists are at work, they do not 
 trouble themselves about the physiological value of the 
 characters which they use in defining a group or in allo¬ 
 cating any particular species. If they find a character 
 nearly uniform, and common to a great number of forms, 
 and not common to others, they use it as one of high 
 value; if common to some lesser number, they use it as of 
 subordinate value. This principle has been broadly con¬ 
 fessed by some naturalists to be the true one; and by none 
 more clearly than by that excellent botanist, Aug. !3L 
 Hilaire. If several trifling characters are always found in 
 combination, though no apparent bond of connection can 
 be discovered between them, especial value is set on them 
 
434 
 
 CLASSIFICA TIOtf. 
 
 As in most groups of animals, important organs, such as 
 those for propelling the blood, or for aerating it, or those 
 for propagating the race, are found nearly uniform, they 
 are considered as highly serviceable in classification; but in 
 some groups all these, the most important vital organs, are 
 found to offer characters of quite subordinate value. Thus, 
 as Fritz Muller has lately remarked, in the same group of 
 crustaceans, Cypridina is furnished with a heart, while in 
 two closely allied genera, namely Cypris and Cytherea, 
 there is no such organ; one species of Cypridina has well- 
 developed branchiae, while another species is destitute of 
 them. 
 
 We can see why characters derived from the embryo 
 should be of equal importance with those derived from the 
 adult, for a natural classification of course includes all 
 ages. But it is by no means obvious, on the ordinary 
 view, why the structure of the embryo should be more im¬ 
 portant for this purpose than that of the adult, which 
 alone plays its full part in the economy of nature. Yet it 
 has been strongly urged by those great naturalists, Milne 
 Edwards and Agassiz, that embryological characters are 
 the most important of all; and this doctrine has very gen¬ 
 erally been admitted as true. Nevertheless, their impor¬ 
 tance has sometimes been exaggerated, owing to the adap¬ 
 tive characters of larvae not having been excluded; in order 
 to show this, Fritz Muller arranged, by the aid of such 
 characters alone, the great class of crustaceans, and the ar¬ 
 rangement did not prove a natural one. But there can be 
 no doubt that embryonic, excluding larval characters, are 
 of the highest value for classification, not only with animals 
 but with plants. Thus the main divisions of flowering 
 plants are founded on differences in the embryo—on the 
 number and position of the cotyledons, and on the mode of 
 development of the plumule and radicle. We shall im¬ 
 mediately see why these characters possess so high a value 
 in classification, namely, from the natural system being 
 genealogical in its arrangement. 
 
 Our classifications are often plainly influenced by chains 
 of affinities. Nothing can be easier than to define a 
 number of characters common to all birds; but with 
 crustaceans, any such definition has hitherto been found 
 impossible. There are crustaceans at the opposite ends of 
 
CLASSIFICATION. 
 
 435 
 
 the series, which have hardly a character in common; yet 
 the species at both ends, from being plainly allied to others, 
 and these to others, and so onward, can be recognized as 
 unequivocally belonging to this, and to no other class of 
 the Articulata. 
 
 Geographical distribution has often been used, though 
 perhaps not quite logically, in classification, more espec¬ 
 ially in very large groups of closely allied forms. Tem- 
 minck insists on the utility or even necessity of this 
 practice in certain groups of birds; and it has been fol¬ 
 lowed by several entomologists and botanists. 
 
 Finally, with respect to the comparative value of the 
 various groups of species, such as orders, suborders, fam¬ 
 ilies, subfamilies, and genera, they seem to be, at least at 
 present, almost arbitrary. Several of the best botanists, 
 such as Mr. Bentham and others, have strongly insisted on 
 their arbitrary value. Instances could be given among 
 plants and insects, of a group first ranked by practiced 
 naturalists as only a genus, and then raised to the rank of 
 a subfamily or family; and this has been done, not be¬ 
 cause further research has detected important structural 
 differences, at first overlooked, but because numerous allied 
 species, with slightly different grades of deference, hav<j 
 been subsequently discovered. 
 
 . All the foregoing rules and aids and difficulties in clas^ 
 sification may be explained, if I do not greatly deceive 
 myself, on the view that the Natural System is founded on 
 descent with .modification—that the characters which 
 naturalists consider as showing true affinity between any 
 two or more species, are those which have 'been inherited 
 from a common parent, all true classification being genea. 
 logical—that community of descent is the hidden bond 
 which naturalists have been unconsciously seeking, and not 
 some unknown plan of creation, or the enunciation of 
 general, propositions, and the mere putting together and 
 separating objects more or less alike. 
 
 But I must explain my meaning more fully. I believe 
 that the arrangement of the groups within each class, in 
 due subordination and relation to each other, must be 
 strictly genealogical in order to be natural; but that the 
 amount of difference in the several branches or groups, 
 though allied in the same degree in blood to their 
 
 
436 
 
 CLASSIFIGA TION. 
 
 common progenitor, may differ greatly, being due to 
 the different degrees of modification which they have 
 undergone; and this is expressed by the forms being 
 ranked under different genera, families, sections or 
 orders. The reader will best understand what is meant, 
 if he will take the trouble to refer to the diagram in 
 the fourth chapter. We will suppose the letters A to 
 L to represent allied genera existing during the Silurian 
 epoch, and descended from some still earlier form. In 
 three of these genera (A, F and I), a species has trans¬ 
 mitted modified descendants to the present day, repre¬ 
 sented by the fifteen genera (a 14 to z 14 ) on the uppermost 
 horizontal line. Now, all these modified descendants from 
 a single species are related in blood or descent in the same 
 degree. They may metaphorically be called cousins to the 
 same millionth degree, yet they differ widely and in dif¬ 
 ferent degrees from each other. The forms descended 
 from A, now broken up into two or three families, consti¬ 
 tute a distinct order from those descended from I, also 
 broken up into two families. Nor can the existing species 
 descended from A be ranked in the same genus with the 
 parent A, or those from I with parent I. But the existing 
 genus f 14 may be supposed to have been but slightly mod¬ 
 ified, and it will then rank with the parent genus F, just 
 as some few still living organisms belong to Silurian genera. 
 So that the comparative value of the differences between 
 these organic beings, which are all related to each other in 
 the same degree in blood, has come to be widely different. 
 Nevertheless, their genealogical arrangement remains 
 strictly true, not only at the present time, but at each suc¬ 
 cessive period of descent. All the modified descendants 
 from A will have inherited something in common from 
 their common parent, as will all the descendants from I; 
 s© will it be with each subordinate branch of descendants 
 at each successive stage. If, however, we suppose any de¬ 
 scendant of A or of I to have become so much modified as 
 to have lost all traces of its parentage in this case, its place 
 in the natural system will be lost, as seems to have 
 occurred with some few existing organisms. All the 
 descendants of the genus F, along its whole line of 
 descent, are supposed to have been but little modi¬ 
 fied, and they form a single genus. But this genus, 
 
CLASSIFICA TION. 
 
 437 
 
 though much isolated, will still occupy its proper interme¬ 
 diate position. The representation of the groups, as here 
 given in the diagram on a flat surface, is much too simple. 
 The branches ought to have diverged in all directions. If 
 the names of the groups had been simply written down in 
 a linear series the representation would have been still less 
 natural; and it is notoriously not possible to represent in a 
 series, on a flat surface, the affinities which we discover in 
 nature among the beings of the same group. Thus, the 
 natural system is genealogical in its arrangement, like a 
 pedigree. But the amount of modification which the dif- 
 erent groups have undergone has to be expressed by rank¬ 
 ing them under different so-called genera, subfamilies, 
 families, sections, orders and classes. 
 
 It may be worth while to illustrate this view of classifi¬ 
 cation, by taking the case of languages. If we possessed 
 a perfect pedigree of mankind, a genealogical arrangement 
 of the races of man would afford the best classification of 
 the various languages now spoken throughout the world; 
 and if all extinct languages, and all intermediate and 
 slowly changing dialects, were to be included, such an 
 arrangement would be the only possible one. Yet it might 
 be that some ancient languages had altered very little and 
 had given rise to few new languages, while others had 
 altered much owing to the spreading, isolation and state of 
 civilization of the several co-descended races, and had thus 
 given rise to many new dialects and languages. The 
 various degrees of difference between the languages of the 
 same stock would have to be expressed by groups sub¬ 
 ordinate to groups; but the proper or even the only possi¬ 
 ble arrangement would still be genealogical; and this 
 would be strictly natural, as it would connect together all 
 languages, extinct and recent, by the closest affinities, 
 and would give the filiation and origin of each tongue. 
 
 In confirmation of this view, let us glance at the classifi¬ 
 cation of varieties, which are known or believed to be des¬ 
 cended from a single species. These are grouped under 
 the species, with the subvarieties under the varieties; and 
 in some cases, as with the domestic pigeon, with several 
 other grades of difference. Nearly the same rules are fol¬ 
 lowed as in classifying species. Authors have insisted on 
 the necessity of arranging varieties on a natural instead of 
 
438 
 
 CLASSIFICATION. 
 
 an artificial system; we are cautioned, for instance, not to 
 class two varieties of the pine-apple together, merely be¬ 
 cause their fruit, though the most important part, happens 
 to be nearly identical; no one puts the Swedish and com¬ 
 mon turnip together, though the esculent and thickened 
 stems are so similar. Whatever part is found to be most 
 constant, is used in classing varieties: thus the great agri¬ 
 culturist Marshall says the horns are very useful for this 
 purpose with cattle, because they are less variable than the 
 shape or color of the body, etc.; whereas with sheep the 
 horns are much less serviceable, because less constant. In 
 classing varieties, I apprehend that if we had a real pedi¬ 
 gree, a genealogical classification would be universally pre¬ 
 ferred; and it has been attempted in some cases. For we 
 might feel sure, whether there had been more or less modi¬ 
 fication, that the principle of inheritance would keep the 
 forms together which were allied in the greatest number of 
 points. In tumbler pigeons, though some of the sub- 
 varieties differ in the important character of the length of 
 the beak, yet all are kept together from having the common 
 habit of tumbling: but the short-faced breed has nearly or 
 quite lost this habit: nevertheless, without any thought on 
 the subject, these tumblers are kept in the same group, 
 because allied in blood and alike in some other respects. . 
 
 With species in a state of nature, every naturalist has in 
 fact brought descent into his classification; for he includes 
 in his lowest grade, that of species, the two sexes; and how 
 enormously these sometimes differ in the most important 
 characters is known to every naturalist: scarcely a single 
 fact can be predicated in common of the adult males and 
 hermaphrodites of certain cirripedes, and yet no one 
 dreams of separating them. As soon as the three Orchi- 
 dean forms, Monachanthus, Myanthus, and Catasetum, 
 which had previously been ranked as three distinct genera ; 
 were known to be sometimes produced on the same plant, 
 they were immediately considered as varieties; and now I 
 have been able to show that they are the male, female, and 
 hermaphrodite forms of the same species. The naturalist 
 includes as one species the various larval stages of the same 
 individual, however much they may differ from each other 
 and from the adult, as well as the so-called alternate gen¬ 
 erations of Steenstrup, which can only in a technical sense 
 
CLASSIFIGA TION. 
 
 439 
 
 be considered as the same individual. He includes mon¬ 
 sters and varieties, not from their partial resemblance to 
 the parent-form, but because they are descended from it. 
 
 As descent has universally been used in classing to¬ 
 gether the individuals of the same species, though the 
 males and females and lame are sometimes extremely 
 different; and as it has been used in classing varieties 
 which have undergone a certain, and sometimes a consid¬ 
 erable amount of modification, may not this same element 
 of descent have been unconsciously used in grouping 
 species under genera, and genera under higher groups, all 
 under the so-called natural system? I believe it has been 
 unconsciously used; and thus only can I understand the 
 several rules and guides which have been followed by our 
 best systematists. As we have no written pedigrees, we 
 are forced to trace community of descent by resemblances 
 of any kind. Therefore, we choose those characters which 
 are the least likely to have been modified, in relation to 
 the conditions of life to which each species has been recently 
 exposed. Rudimentary structures on this view are as good, 
 as, or even sometimes better than other parts of the organ¬ 
 ization. We care not how trifling a character may be—let 
 it be the mere inflection of the angle of the jaw, the manner 
 in which an insect’s wing is folded, whether the skin be 
 covered by hair or feathers—if it prevail throughout many 
 and different species, especially those having very different 
 habits of life, it assumes high value; for we can account for 
 its presence in so many forms with such different habits, 
 only by inheritance from a common parent. We may err 
 in this respect in regard to single points of structure, but 
 when several characters, let them be ever so trifling, 
 concur throughout a large group of beings having different 
 habits, we may feel almost sure, on the theory of descent, 
 that these characters have been inherited from a common 
 ancestor; and we know that such aggregated characters 
 have especial value in classification. 
 
 We can understand why a species or a group of species 
 may depart from its allie j, in several of its most important 
 characteristics, and yet be safely classed with them. This 
 may be safely done, and is often done, as long as a suffi¬ 
 cient number of characters, let them be ever so unimpor¬ 
 tant, betrays the hidden bond of community of descent. 
 
440 
 
 ANALOGICAL RESEMBLANCES. 
 
 Let two forms have not a single character in common, yet, 
 if these extreme forms are connected together by a chain 
 of intermediate groups, we may at once infer their com¬ 
 munity of descent, and we put them all into the same 
 class. " As we find organs of high physiological impor¬ 
 tance—those which serve to preserve life under the most 
 diverse conditions of existence—are generally the most 
 constant, we attach especial value to them; but if these 
 same organs, in another group or section of a group, are 
 found to differ much, we at once value them less in our 
 classification. We shall presently see why embryological 
 characters are of such high classificatory importance. 
 Geographical distribution may sometimes be brought use¬ 
 fully into play in classing large genera, because all the 
 species of the same genus, inhabiting any distinct and 
 isolated region, are in all probability descended from the 
 same parents. 
 
 ANALOGICAL RESEMBLANCES. 
 
 We can understand, on the above views, the very impor¬ 
 tant distinction between real affinities and analogical or 
 adaptive resemblances. Lamarck first called attention to 
 this subject, and he has been ably followed by Macleayand 
 others. The resemblance in the shape of the body and in 
 the fin-like anterior limbs between dugongs and whales, and 
 between these two orders of mammals and fishes, are ana¬ 
 logical. So is the resemblance between a mouse and a 
 shrew-mouse (Sorex), which belong to different orders' 
 and the still closer resemblance, insisted on by Mr. Mivart. 
 between the mouse and a small marsupial animal (Antech* 
 in us) of Australia. These latter resemblances may be 
 accounted for, as it seems to me, by adaptation for similarly 
 active movements through thickets and herbage, togethei 
 with concealment from enemies. 
 
 Among insects there are innumerable similar instances; 
 thus Linnaeus, misled by external appearances, actually 
 classed an homopterous insect as a moth. We see some¬ 
 thing of the same kind even with our domestic varieties, 
 as in the strikingly similar shape of the body in the im¬ 
 proved breeds of the Chinese and common pig, which are 
 descended from distinct species; and in the similarly thick- 
 
ANALOGICAL RESEMBLANCES. 
 
 441 
 
 ened stems of the common and specifically distinct Swedish 
 turnip. The resemblance between the greyhound and the 
 race-horse is hardly more fanciful than the analogies which 
 have been drawn by some authors between widely different 
 animals. 
 
 On the view of characters being of real importance for 
 classification, only in so far as they reveal descent, we can 
 clearly understand why analogical or adaptive characters, 
 although of the utmost importance to the welfare of the 
 being, are almost valueless to the systematist. For animals, 
 belonging to two most distinct lines of descent, may have 
 become adapted to similar conditions, and thus have as¬ 
 sumed a close externa] resemblance; but such resemblances 
 will not reveal—will rather tend to conceal their blood- 
 relationship. We can thus also understand the apparent 
 paradox, that the very same characters are analogical when 
 one group is compared with another, but give true affinities 
 when the members of the same group are compared to¬ 
 gether: thus, the shape of the body and fin-like limbs are 
 only analogical when whales are compared with fishes, 
 being adaptations in both classes for swimming through 
 the water; but between the several members of the whale 
 family, the shape of the body and the fin-like limbs offer 
 characters exhibiting true affinity; for as these parts are 
 so nearly similar throughout the whole family, we cannot 
 doubt that they have been inherited from a common ances¬ 
 tor. So it is with fishes. 
 
 Numerous cases could be given of striking resemblances 
 in quite distinct beings between single parts or organs, 
 which have been adapted for the same functions. A good 
 instance is afforded by the close resemblance of the jaws of 
 the dog and Tasmanian wolf or Thylacinus—animals 
 which are widely sundered in the natural system. But 
 this resemblance is confined to general appearance, 
 as in the prominence of the canines, and in the cut¬ 
 ting shape of the molar teeth. For the teeth really 
 differ much: thus the dog has on each side of the 
 upper jaw four pre-molars and only two molars; while 
 the Thylacinus has three pre-molars and four molars. The 
 molars also differ much in the two animals in relative size 
 and structure. The adult dentition is preceded by a widely 
 different milk dentition. Any one may, of course, deny 
 
ANALOGICAL RESEMBLANCES. 
 
 i42 
 
 that the teeth in either case have been adapted for tearing 
 flesh, through the natural selection of successive variations; 
 but if this be admitted in the one case, it is unintelligible 
 to me that it should be denied in the other. I am glad to 
 find that so high an authority as Professor Flower has come 
 to this same conclusion. 
 
 The extraordinary cases given in a former chapter, of 
 widely different fishes possessing electric organs—of widely 
 different insects possessing luminous organs — and of 
 orchids and asclepiads having pollen-masses with viscid 
 discs, come under this same head of analogical resem¬ 
 blances. But these cases are so wonderful that they were 
 introduced as difficulties or objections to our theory. In 
 all such cases some fundamental difference in the growth 
 or development of the parts, and generally in their matured 
 structure, can be detected. The end gained is the same, 
 but the means, though appearing superficially to be the 
 same, are essentially different. The principle formerly 
 alluded to under the term of analogical variation has prob¬ 
 ably in these cases often come into play; that is, the mem¬ 
 bers of the same class, although only distantly allied, have 
 inherited so much in common in their constitution, that 
 they are apt to vary under similar exciting causes in a 
 similar manner; and this would obviously aid in the ac¬ 
 quirement through natural selection of parts or organs, 
 strikingly like each other, independently of their direct 
 inheritance from a common progenitor. 
 
 As species belonging to distinct classes have often been 
 adapted by successive slight modifications to live under 
 nearly similar circumstances—to inhabit, for instance, the 
 three elements of land, air and water—we can perhaps 
 understand how it is that a numerical parallelism has 
 s< metimes been observed between the subgroups of distinct 
 classes. A naturalist, struck with a parallelism of this 
 nature, by arbitrarily raising or sinking the value of the 
 groups in several classes (and all our experience shows that 
 their valuation is as yet arbitrary), could easily extend the 
 parallelism over a wide range; and thus the septenary, 
 quinary, quaternary and ternary classifications have prob¬ 
 ably arisen. 
 
 "there is another and curious class of cases in which 
 close external resemblance does not depend on adaptation 
 
ANALOGICAL RESEMBLANCES. 
 
 443 
 
 to similar habits of life, but lias been gained for the sake 
 of protection. I allude to the wonderful manner in which 
 certain butterflies imitate, as first described by Mr. Bates, 
 other and quite distinct species. This excellent observer 
 has shown that in some districts of South America, where, 
 for instance, an Ithomia abounds in gaudy swarms, an¬ 
 other butterfly, namely, a Leptalis, is often found mingled 
 in the same flock; and the latter so closely resembles the 
 Ithomia in every shade and stripe of color, and even in the 
 shape of its wings, that Mr. Bates, with his eyes sharpened 
 by collecting during eleven years, was, though always on 
 his guard, continually deceived. When the mockers and 
 the mocked are caught and compared, they are found to 
 be very different in essential structure, and to belong not 
 only to distinct genera, but often to distinct families. 
 Had this mimicry occurred in only one or two instances, 
 it might have been passed over as a strange coincidence. 
 But, if we proceed from a district where one Leptalis imi¬ 
 tates an Ithomia, another mocking and mocked species, be¬ 
 longing to the same two genera, equally close in their 
 resemblance, may be found. Altogether no less than ten 
 genera are enumerated, which include species that imitate 
 other butterflies. The mockers and mocked always in¬ 
 habit the same region; we never find an imitator living 
 remote from the form which it imitates. The mockers are 
 almost invariably rare insects; the mocked in almost every 
 case abounds in swarms. In the same district in which a 
 species of Leptalis closely imitates an Ithomia, there are 
 sometimes other Lepidoptera mimicking the same Ithomia: 
 so that in the same place, species of three genera of butter¬ 
 flies and even a moth are found all closely resembling a 
 butterfly belonging to a fourth genus. It deserves especial 
 notice that many of the mimicking forms of the 
 Leptalis, as well as of the mimicked forms, can be shown 
 by a graduated series to be merely varieties of the same 
 species; while others are undoubtedly distinct species. 
 But why, it may be asked, are certain forms treated as the 
 mimicked and others as the mimickers? Mr. Bates satis¬ 
 factorily answer this question by showing that the form 
 which is imitated keeps the usual dress of the group to 
 which it belongs, while the counterfeiters have changed 
 their dress and do not resemble their nearest allies. 
 
444 
 
 ANALOGICAL RESEMBLANCES. 
 
 We are next led to inquire what reason can be assigned 
 for certain butterflies and moths so often assuming tne 
 dress of another and quite distinct form; why, to the per¬ 
 plexity of naturalists, has nature condescended to the 
 tricks of the stage? Mr. Bates has, no doubt, hit on the 
 true explanation. The mocked forms, which always 
 abound in numbers, must habitually escape destruction to 
 a large extent, otherwise they could not exist in such 
 swarms; and a large amount of evidence has now been 
 collected, showing that they are distasteful to birds and 
 other insect-devouring animals. The mocking forms, on 
 the other hand, that inhabit the same district, are com¬ 
 paratively rare, and belong to rare groups; hence, they 
 must suffer habitually from some danger, for otherwise, 
 from the number of eggs laid by all butterflies, they would 
 in three or four generations swarm over the whole country. 
 Now if a member of one of these persecuted and rare groups 
 were to assume a dress so like that of a well-protected 
 species that it continually deceived the practiced eyes of an 
 entomologist, it would often deceive predaceous birds and 
 insects, and thus often escape destruction. Mr. Bates 
 may almost be said to have actually witnessed the process 
 by which the mimickers have come so closely to resemble 
 the mimicked; for he found that some of the forms of 
 Leptalis which mimic so many other butterflies, varied in 
 an extreme degree. In one district several varieties oc¬ 
 curred, and of these one alone resembled, to a certain 
 extent, the common Ithomia of the same district. In 
 another district there were two or three varieties, one of 
 which was much commoner than the others, and this 
 closely mocked another form of Ithomia. From facts of 
 this nature, Mr. Bates concludes that the Leptalis first 
 varies; and when a variety happens to resemble in some 
 degree any common butterfly inhabiting the same district, 
 this variety, from its resemblance to a flourishing and little 
 persecuted kind, has a better chance of escaping destruc¬ 
 tion from predaceous birds and insects, and is consequently 
 oftener preserved; “ the less perfect degrees of resemblance 
 being generation after generation eliminated, and only the 
 others left to propagate their kind.” So that here we have 
 an excellent illustration of natural selection. 
 
 Messrs. Wallace and Trimen have likewise described 
 
ANALOGICAL RESEMBLANCES. 
 
 445 
 
 several equally striking cases of imitation in the Lepidop- 
 tera of the Malay Archipelago and Africa, and with some 
 other insects. Mr. Wallace has also detected one such case 
 with birds, but we have none with the larger quadrupeds. 
 The much greater frequency of imitation with insects than 
 with other animals, is probably the consequence of their 
 small size; insects cannot defend themselves, excepting in¬ 
 deed the kinds furnished with a sting, and I have never 
 heard of an instance of such kinds mocking other insects, 
 though they are mocked; insects cannot easily escape by 
 flight from the larger animals which prey on them; there¬ 
 fore, speaking metaphorically, they are reduced, like most 
 weak creatures, to trickery and dissimulation. 
 
 It should be observed that the process of imitation prob¬ 
 ably never commenced between forms widely dissimilar in 
 color. But, starting with species already somewhat like each 
 other, the closest resemblance, if beneficial, could readily be 
 gained by the above means, and if the imitated form was 
 subsequently and gradually modified through any agency, 
 the imitating form would be led along the same track, and 
 thus be altered to almost any extent, so that it might ulti¬ 
 mately assume an appearance or coloring wholly unlike 
 that of the other members of the family to w 7 hich it be¬ 
 longed. There is, however, some difficulty on this head, 
 for it is necessary to suppose in some cases that ancient 
 members belonging to several distinct groups, before they 
 had diverged to their present extent, accidentally resem¬ 
 bled a member of another and protected group in a suffi¬ 
 cient degree to afford some slight protection, this having 
 given the basis for the subsequent acquisition of the most 
 perfect resemblance. 
 
 OK THE NATURE OF THE AFFINITIES CONNECTING 
 
 ORGANIC BEINGS. 
 
 As the modified descendants of dominant species, belong¬ 
 ing to the larger genera, tend to inherit the advantages 
 which made the groups to which they belong large and 
 their parents dominant, they are almost sure to spread 
 widely, and to seize on more and more places in the 
 economy of nature. The larger and more dominant 
 groups within each class thus tend to go on increasing in 
 
AFFINITIES CONNECTING 
 
 446 
 
 size, and they consequently supplant many smaller and 
 feebler groups. Thus, we can account for the fact that 
 all organisms, recent and extinct, are included under a few 
 great orders and under still fewer classes. As showing 
 how few the higher groups are in number, and how widely 
 they are spread throughout the world, the fact is striking 
 that the discovery of Australia has not added an insect 
 belonging to a new class, and that in the vegetable king¬ 
 dom, as I learn from Dr. Hooker, it has added only two or 
 three families of small size. 
 
 In the chapter on geological succession I attempted to 
 show, on the principle of each group having generally 
 diverged much in character during the long-continued 
 process of modification, how it is that the more ancient 
 forms of life often present characters in some degree inter¬ 
 mediate between existing groups. As some few of the 
 old and intermediate forms have transmitted to the present 
 day descendants but little modified, these constitute our so- 
 called osculant or aberrant species. The more aberrant 
 any form is, the greater must be the number of connecting 
 forms which have been exterminated and utterly lost. 
 And we have evidence of aberrant groups having suffered 
 severely from extinction, for they are almost always repre¬ 
 sented by extremely few species, and such species as do 
 occur are generally very distinct from each other, which 
 again implies extinction. The genera Ornithorhynchus 
 and Lepidosiren, for example, would not have been less 
 aberrant had each been represented by a dozen species, in¬ 
 stead of as at present by a single one, or by two or three. 
 We can, I think, account for this fact only by looking at 
 aberrant groups as forms which have been conquered by 
 more successful competitors, with a few members still 
 preserved under unusually favorable conditions. 
 
 Mr. Waterhouse has remarked that when a member 
 belonging to one group of animals exhibits an affinity to a 
 quite distinct group, this affinity in most cases is general 
 and not special; thus, according to Mr. Waterhouse, of all 
 Rodents, the bizcacha is most nearly related to Marsupials; 
 but in the joints in which it approaches this order, its 
 relations are general, that is, not to any one Marsupial 
 species more than to another. As these points of affinity 
 are believed to be real and not merely adaptive, they must 
 
ORGANIC BEINGS. 
 
 4-47 
 
 be due in accordance with our view to inheritance from a 
 common progenitor. Therefore, we must suppose either 
 that all Rodents, including the bizcacha, branched off from 
 some ancient Marsupial, which will naturally have been 
 more or less intermediate in character with respect to all 
 existing Marsupials; or that both Rodents and Marsupials 
 branched off from a common progenitor, and that both 
 groups have since undergone much modification in divergent 
 directions. On either view we must suppose that the 
 bizcacha has retained, by inheritance, more of the char¬ 
 acters of its ancient progenitor than have other Rodents; 
 and therefore it will not be specially related to any one 
 existing Marsupial, but indirectly to all or nearly all Mar¬ 
 supials, from having partially retained the character of 
 their common progenitor, or of some early member of the 
 grou23. On the other hand, of all Marsupials, as Mr. 
 Waterhouse has remarked, the Phascolomys resembles 
 most nearly, not any one species, but the general order of 
 Rodents. In this case, however, it may be strongly sus¬ 
 pected that the resemblance is only analogical, owing to 
 the Phascolomys having become adapted to habits like 
 those of a Rodent. The elder De Candolle has made 
 nearly similar observations on the general nature of the 
 affinities of distinct families of plants. 
 
 On the principle of the multiplication and gradual diver¬ 
 gence in character of the species descended from a com¬ 
 mon progenitor, together with their retention by inherit¬ 
 ance of some characters in common, we can understand 
 the excessively complex and radiating affinities by which 
 all the members of the same family or higher group are 
 connected together. For the common progenitor of a 
 whole family, now broken up by extinction into distinct 
 groups and subgroups, will have transmitted some of its 
 characters, modified in various ways and degrees, to all the 
 species; and they will consequently be related to each 
 other by circuitous lines of affinity of various lengths (as 
 may be seen in the diagram so often referred to), mounting 
 up through many predecessors. As it is difficult to show 
 the blood relationship between the numerous kindred of 
 any ancient and noble family, even by the aid of a genea¬ 
 logical tree, and almost impossible to do so without this 
 aid, we can understand the extraordinary difficulty which 
 
448 
 
 AFFINITIES CONNECTING 
 
 naturalists have experienced in describing, without the aid 
 of a diagram, the various affinities which they perceive 
 between the many living and extinct members of the same 
 great natural class. 
 
 Extinction, as we have seen in the fourth chapter, has 
 played an important part in defining and widening the 
 intervals between the several groups in each class. We 
 mav thus account for the distinctness of whole classes from, 
 each other—for instance, of birds from all other vertebrate 
 animals—by the belief that many ancient forms of 
 life have been utterly lost, through which the early pro¬ 
 genitors of birds were formerly connected with the early 
 progenitors of the other and at that time less differentiated 
 vertebrate classes. There has been much less extinction 
 of the forms of life which once connected fishes with 
 Batrachians. There has been still less within some whole 
 classes, for instance the Crustacea, for here the most won¬ 
 derfully diverse forms are still linked together by a Iona* 
 and only partially broken chain of affinities. Extinction 
 has only defined the groups: it had by no means made 
 them; for if every form which has ever lived on this earth 
 were suddenly to reappear, though it would be quite im¬ 
 possible to give definitions by which each group could be 
 distinguished, still a natural classification, or at least a 
 natural arrangement, would be possible. We shall see this 
 by turning to the diagram; the letters, A to L, may repre¬ 
 sent eleven Silurian genera, some of which have produced 
 large groups of modified descendants, with every link in 
 each branch and sub-branch still alive; and the links not 
 greater than those between existing varieties. In this case 
 it would be quite impossible to give definitions by which 
 the several members of the several groups could be distin¬ 
 guished from their more immediate parents and descend¬ 
 ants. Yet the arrangement in the diagram would still 
 hold good and would be natural; for, on the principle of 
 inheritance, all the forms descended, for instance, from A, 
 would have something in common. In a tree we can dis¬ 
 tinguish this or that branch, though at the actual fork the 
 two unite and blend together. We could not, as I have 
 said, define the several groups; but we could pick out types, 
 or forms, representing most of the characters of each group, 
 whether large or small, and thus give a general idea of the 
 
ORGANIC BEINGS. 
 
 449 
 
 value of the differences between them. This is what we 
 should be driven to, if we were ever to succeed in collecting 
 all the forms in any one class which have lived throughout 
 all time and space. Assuredly we shall never succeed in 
 making so perfect a collection: nevertheless, in certain 
 classes, we are tending toward this end; and Milne Ed¬ 
 wards has lately insisted, in an able paper, on the high 
 importance of looking to types, whether or not we can 
 separate and define the groups to which such types belong. 
 
 Finally, we have seen that natural selection, which fol¬ 
 lows from the struggle for existence, and which almost 
 inevitably leads to extinction and divergence of character 
 in the descendants from any one parent-species, explains 
 that great and universal feature in the affinities of all or¬ 
 ganic beings, namely, their subordination in group under 
 group. We use the element of descent in classing the 
 individuals of both sexes and of all ages under one species, 
 although they may have but few characters in common; we 
 use descent in classing acknowledged varieties, however 
 different they may be from their parents; and I believe 
 that this element of descent is the hidden bond of con¬ 
 nection which naturalists have sought under the term of 
 the Natural System. On this idea of the natural system 
 being, in so far as it has been perfected, genealogical in its 
 arrangement, with the grades of difference expressed by 
 the terms genera, families, orders, etc., we can under¬ 
 stand the rules which we are compelled to follow in 
 our classification. We can understand why we value 
 certain resemblances far more than others; why we 
 use rudimentary and useless organs, or others of trifling 
 physiological importance; why, in finding the relations 
 between one group and another, we summarily reject ana¬ 
 logical or adaptive characters, and yet use these same char¬ 
 acters within the limits of the same group. We can 
 clearly see how it is that all living and extinct forms can 
 be grouped together within a few great classes; and how 
 the several members of each class are connected together 
 by the most complex and radiating lines of affinities. We 
 shall never, probably, disentangle the inextricable web of 
 the affinities between the members of any one class; but 
 when we have a distinct object in view, and do not look 
 to some unknown plan of creation, we may hope to make 
 sure but slow progress* — 
 
450 
 
 MORPHOLOGY. 
 
 Professor Hackel in liis “Generelle Morphologic” and 
 in other works, has recently brought his great knowledge 
 and abilities to bear on what he calls phylogeny, or the 
 lines of descent of all organic beings. In drawing up the 
 several series he trusts chiefly to embryological characters, 
 but receives aid from homologous and rudimentary organs, 
 as well as from the successive periods at which the various 
 forms of life are believed to have first appeared in our 
 geological formations. He has thus boldly made a great 
 beginning, and shows us how classification will in the 
 
 future be treated. 
 
 * 
 
 MORPHOLOGY. 
 
 We have seen that the members of the same class, in¬ 
 dependently of their habits of life, resemble each other in 
 the generafplan of their organization. This resemblance 
 is often expressed by the term “ unity of type;” or by say¬ 
 ing that the several parts and organs in the different 
 species of the class are homologous. The whole subject is 
 included under the general term of Morphology. This is 
 one of the most interesting departments of natural history, 
 and may almost be said to be its very soul. What can be 
 more curious than that the hand of a man, formed for 
 giasping, that of a mole for digging, the leg of the horse, 
 the paddle of the porpoise, and the wing of the bat, should 
 all be constructed on the same pattern, and should include 
 similar bones, in the same relative positions? How curious 
 it is, to give a subordinate though striking instance, that 
 the hind feet of the kangaroo, which are so well fitted for 
 bounding over the open plains—those of the climbing, leaf¬ 
 eating koala, equally well fitted for grasping the branches 
 of trees—those of the ground-dwelling, insect or poot-eat- 
 ing, bandicoots—and those of some other Australian mar¬ 
 supials—should all be constructed on the same extraor¬ 
 dinary type, namely with the bones of the second and 
 third digits extremely slender and enveloped within the 
 same skin, so that they appear like a single toe furnished 
 with two claws. Notwithstanding this similarity of pat¬ 
 tern, it is obvious that the hind feet of these several 
 animals are used for as widely different purposes as it is 
 possible to conceive. The case is rendered all the more 
 
MORPHOLOGY. 
 
 451 
 
 striking by the American opossums, which follow nearly 
 the same habits of life as some of their Australian relatives, 
 having feet constructed on the o .‘dinary plan. Professor 
 Flower, from whom these statements are taken, remarks 
 in conclusion: “We may call this conformity to type, 
 without getting much nearer to an explanation of the 
 phenomenon;” and he then adds “but is it not powerfully 
 suggestive of true relationship, of inheritance from a 
 common ancestor?” 
 
 Geoffroy St. Hilaire has strongly insisted on the high 
 importance of relative position or connection in homolo¬ 
 gous parts; they may differ to almost any extent in form 
 and size, and yet remain connected together in the 
 same invariable order. We never find, for instance, the 
 bones of the arm and forearm, or of the thigh and leg, 
 transposed. Hence, the same names can be given to the 
 homologous bones in widely different animals. We see the 
 same great law in the construction of the mouths of insects: 
 what can be more different than the immensely long 
 spiral proboscis of a sphinx-moth, the curious folded one 
 of a bee or bug, and the great jaws of a beetle? Yet 
 all these organs, serving for such widely different purposes, 
 are formed by infinitely numerous modifications of an upper 
 lip, mandibles, and two pairs of maxillae. The same law 
 governs the construction of the mouths and limbs of 
 crustaceans. So it is with the flowers of plants. 
 
 Nothing can be more hopeless than to attempt to ex¬ 
 plain this similarity of pattern in members of the same 
 class, by utility or by the doctrine of final causes. The 
 hopelessness of the attempt has been expressly admitted by 
 Owen in his most interesting work on the “ Nature of 
 Limbs.” On the ordinary view of the independent creation 
 of each being, we can only say that so it is; that it has 
 pleased the Creator to construct all the animals and plants 
 in each gretff class on a uniform plan; but this is not a 
 scientific explanation. 
 
 The explanation is to a large extent simple, on the theory 
 of the selection of successive slight modifications, each 
 being profitabxo in some way to the modified form, but 
 often affecting by correlation other parts of the organiza¬ 
 tion. In changes of this nature, there will be little or no 
 tendency to alter the original pattern, or to transpose the 
 
452 
 
 MORPr^LOG r. 
 
 parts. The bones of a limb might be shortened and flat¬ 
 tened to any extent, becoming at tjie same time enveloped 
 in thick membrane, so as to serve as a fin; or a webbed 
 hand might have all its bones, or certain bones, lengthened 
 to any extent, with the membrane connecting them 
 increased, so as to serve as a wing; yet all these modifica¬ 
 tions would not tend to alter the framework of the bones 
 or the relative connection of the parts. If we suppose 
 that an early progenitor—the archetype, as it may be 
 called—of all mammals, birds and reptiles, had its limbs 
 constructed on the existing general pattern, for whatever 
 purpose they served, we can at once perceive the plain 
 signification of the homologous construction of the limbs 
 throughout the class. So with the mouths of insects, we 
 have only to suppose that their common progenitor had an 
 upper lip, mandibles, and two pairs of maxillae, these parts 
 being perhaps very simple in form; and then natural selec¬ 
 tion will account for the definite diversity in the structure 
 and functions of the mouths of insects. Nevertheless, it is 
 conceivable that the general pattern of an organ might 
 become so much obscured as to be finally lost, by the 
 reduction and ultimately by the complete abortion of cer¬ 
 tain parts, by the fusion of other parts, and by the doubling 
 or multiplication of others, variations which we know to be 
 within the limits of possibility. In the paddles of the 
 gigantic extinct ,:ea-lizards, and in the mouths of certain 
 suctorial crustaceans, the general pattern seems thus to 
 have become partially obscured. 
 
 There is another and equally curious branch of our sub¬ 
 ject; namely, serial homologies, or the comparison of the 
 different parts or organs in the same individual, and not 
 of the same parts or organs in different members of the 
 same class. Most physiologists believe that the bones of 
 the skull are homologous—that is, correspond in number 
 and in relative connection—with the elemental parts of a 
 certain number of vertebras. The anterior and posterior 
 limbs in all the higher vertebrate classes are plainly homo¬ 
 logous. So it is with the wonderfully complex jaws and 
 legs of crustaceans. It is familiar to almost every one, 
 that in a flower the relative position of the sepals, petals, 
 stamens and pistils, as well as their intimate structure, are 
 intelligible on the view that they consist of metamorphosed 
 
MORPHOLOGY. 
 
 453 
 
 ]«IY0S, arranged in a spire. In monstrous plants, we often 
 get direct evidence of the possibility of one organ being 
 transformed into another; and we can actually see, during 
 the early or embryonic stages of development in flowers, as 
 well as in crustaceans and many other animals, that organs 
 which when mature become extremely different are at first 
 exactly alike. 
 
 How inexplicable are the cases of serial homologies on 
 the ordinary view of creation! Why should the brain be 
 inclosed in a box composed of such numerous and such ex¬ 
 traordinarily shaped pieces of bone, apparently represent¬ 
 ing vertebrae? As Owen has remarked, the benefit derived 
 from the yielding of the separate pieces in the act of par¬ 
 turition by mammals, will by no means explain the same 
 construction in the skulls of birds and reptiles. Why 
 should similar bones have been created to form the wing 
 and the leg of a bat, used as they are for such totally differ¬ 
 ent purposes, namely, flying and walking? Why should 
 one crustacean, which has an extremely complex mouth 
 formed of many parts, consequently always have fewer 
 legs; or conversely, those with many legs have simpler 
 mouths? Why should the sepals, petals, stamens and 
 pistils, in each flower, though fitted for such distinct pur¬ 
 poses, be all constructed on the same pattern? 
 
 On the theory of natural selection, we can, to a certain 
 extent, answer these questions. We need not here con¬ 
 sider how the bodies of some animals first became divided 
 into a series of segments, or how they became divided into 
 right and left sides, with corresponding organs, for such 
 questions are almost beyond investigation. It is, however, 
 probable that some serial structures are the result of cells 
 multiplying by division, entailing the multiplication of the 
 parts developed from such cells. It must suffice for our 
 purpose to bear in mind that an indefinite repetition of the 
 same part or organ is the common characteristic, as Owen 
 has remarked, of all low or little specialized forms; there¬ 
 fore the unknown progenitor of the Yertebrata probably 
 possessed many vertebrae; the unknown progenitor of the 
 Articulata, many segments; and the unknown progenitor 
 of flowering plants, many leaves arranged in one or more 
 spires. We have also formerly seen that parts many times 
 repeated are eminently liable to vary, not only in number. 
 
454 
 
 MORPHOLOGY. 
 
 but in form. Consequently sucli parts, being already pres¬ 
 ent in considerable numbers, and being highly variable, 
 would naturally afford the materials for adaptation to the 
 most different purposes; yet they would generally retain, 
 through the force of inheritance, plain traces of their orig¬ 
 inal or fundamental resemblance. They would retain this 
 resemblance all the more, as the variations, which afforded 
 the basis for their subsequent modification through natural 
 selection, would tend from the first to be similar; tlm parts 
 being at an early stage of growth alike, and being subjected 
 to nearly the same conditions. Such parts, whether more 
 or less modified, unless their common origin became wholly 
 obscured, would be serially homologous. 
 
 In the great class of molluscs, though the parts in dis¬ 
 tinct species can be shown to be homologous, only a few 
 serial homologies, such as the valves of Chitons, can be 
 indicated; that is, we are seldom enabled to say that one 
 part is homologous with another part in the same indi¬ 
 vidual. And we can understand this fact; for in molluscs, 
 even in the lowest members of the class, we do not find 
 nearly so much indefinite repetition of any one part as we 
 find in the other great classes of the animal and vegetable 
 kingdoms. 
 
 But morphology is a much more complex subject than 
 it at first appears, as has lately been well shown in 
 a remarkable paper by Mr. E. Ray Lankester, who has 
 drawn an important distinction between certain classes 
 of cases which have all been equally ranked by naturalists 
 as homologous. He proposes to call the structures which 
 resemble each other in distinct animals, owing to their de¬ 
 scent from a common progenitor with subsequent modifica¬ 
 tion, homogenous ; and the resemblances which cannot thus 
 be accounted for, he proposes to call homoplastic. For 
 instance, he believes that the hearts of birds and mammals 
 are as a whole homogenous—that is, have been derived 
 from a common progenitor; but that the four cavities of the 
 heart in the two classes are homoplastic—that is, have been 
 independently developed. Mr. Lankester also adduces the 
 close resemblance of the parts on the right and left sides of 
 the body, and in the successive segments of the same indi¬ 
 vidual animal; and here we have parts commonly called 
 homologous which bear no relation to the descent of dis- 
 
DEVELOPMENT AND EMBRYOLOGY. 
 
 455 
 
 tinct species from a common progenitor. Homoplastic 
 structures are the same with those which I have classed, 
 though in a very imperfect manner, as analogous modifica¬ 
 tions or resemblances. Their formation may be attributed 
 in part to distinct organisms, or to distinct parts of the 
 same organism, having varied in an analogous manner; 
 and in part to similar modifications, having been preserved 
 for the same general purpose or function, of which many 
 instances have been given. 
 
 Naturalists frequently speak of the skull as formed of 
 metamorphosed vertebrae; the jaws of crabs as metamor¬ 
 phosed legs; the stamens and pistils in flowers as metamor¬ 
 phosed leaves; but it would in most cases be more correct, 
 as Professor Huxley has remarked, to speak of both skull 
 and vertebrae, jaws and legs, etc., as having been metamor¬ 
 phosed, not one from the other, as they now exist, but 
 from some common and simpler element. Most natural¬ 
 ists, however, use such language only in a metaphorical 
 sense; they are far from meaning that during a long course 
 of descent, primordial organs of any kind—vertebrae in the 
 one case and legs in the other—-have actually been con¬ 
 verted into skulls or jaws. Yet so strong is the appearance 
 of this having occurred that naturalists can hardly avoid 
 employing language having this plain signification. Ac¬ 
 cording to the views here maintained, such language may 
 be used literally; and the wonderful fact of the jaws, for 
 instance, of a crab retaining numerous characters, which 
 they probably would have retained through inheritance, if 
 they had really been metamorphosed from true though ex¬ 
 tremely simple legs, is in part explained. 
 
 DEVELOPMENT AND EMBRYOLOGY. 
 
 This is one of the most important subjects in the whole 
 round of natural history. The metamorphoses of insects, 
 with which every one is familiar, are generally effected 
 abruptly by a few stages; but the transformations are in 
 reality numerous and gradual, though concealed. A cer¬ 
 tain ephemerous insect (Chloeon) during its development, 
 moults, as shown by Sir J. Lubbock, above twenty times, 
 and each time undergoes a certain amount of change; and 
 in this case we see the act of metamorphosis performed in 
 
456 DEVELOPMENT AND EMBR TO LOO T. 
 
 a primary and gradual manner. Many insects, and espec¬ 
 ially certain crustaceans, show us what wonderful changes 
 of structure can be effected during development. Such 
 changes, however, reach their acme in the so-called alternate 
 generations of some of the lower animals. It is, for instance 
 an astonishing fact that a delicate branching coralline, stud¬ 
 ded with polypi, and attached to a submarine rock, should 
 produce, first by budding and then by transverse division 
 a host of huge floating jelly-fishes; and that these should 
 produce eggs, from which are hatched swimming animal¬ 
 cules, which attach themselves to rocks and become devel¬ 
 oped into branching corallines; and so on in an endless 
 cycle. The belief in the essential identity of the process 
 of alternate generation and of ordinary metamorphosis has 
 been greatly strengthened by Wagner's discovery of the 
 larva or maggot of a fly, namely the Cecidomyia, produc¬ 
 ing asexually other larvae, and these others, which finally 
 aie developed into mature males and females, propagating 
 their kind in the ordinary manner by eggs. 
 
 It may be worth notice that when Wagner's remarkable 
 discovery was first announced, I was asked how was it pos¬ 
 sible to account for the larvae of this fly having acquired 
 the power of asexual reproduction. As long as the case 
 remained unique no answer could be given. But already 
 Cxi inim has shown that another fly, a Ohironomus, repro- 
 duces itself in nearly the same manner, and he believes 
 that this occurs frequently in the order. It is the pupa 
 and not the larva, of the Ohironomus which has this 
 power; and Grimm further shows that this case, to a cer¬ 
 tain extent, “unites that of the Cecidomyia with the 
 pai thenogenesis of the Coccidas;" the term parthenogen- 
 esis implying that the mature females of the Coccid® are 
 capable of producing fertile eggs without the concourse of 
 the male. Certain animals belonging to several classes are 
 now Known to have the power of ordinary reproduction at 
 an unusually early age; and we have only to accelerate 
 parthenogenetic reproduction by gradual steps to an earlier 
 ana earlier age—Ohironomus showing us an almost exactly 
 intermediate stage, viz., that of the pupa—and we can 
 perhaps account for the marvelous case of the Cecidomyia. 
 
 It has already been stated that various parts in the same 
 individual, which are exactly alike during an early embry- 
 
1)E VELOPMENT AND EMBlt TO LOO Y. 457 
 
 onic period, become widely different and serve for widely 
 different purposes in the adult state. So again it has 
 been shown that generally the embryos of the most 
 distinct species belonging to the same class are closely 
 similar, but become, when fully developed, widely 
 dissimilar. A better proof of this latter fact can not be 
 given than the statement by Von Baer that “ the embryos 
 of mammalia, of birds, lizards and snakes, probably also 
 of chelonia, are in the earliest states exceedingly like one 
 another, both as a whole and in the mode of development 
 of their parts; so much so, in fact, that we can often dis¬ 
 tinguish the embryos only by their size. In my possession 
 are two little embryos in spirit, whose names I have 
 omitted to attach, — 1 at present I am quite unable to say 
 to what class they belong. They* may be lizards or small 
 birds, or very ycuii" mammalia, .:o complete is the similar¬ 
 ity in the mode of formation of the head and trunk in these 
 animals. The extremities, however, are still absent in 
 these embryos. But even if they had existed in the earliest 
 stage of their development we should learn nothing, for 
 the feet of lizards and mammals, the wings and feet of 
 birds, no less than the hands and feet of man, all arise 
 from the same fundamental form.” The larvae of most 
 crustaceans, at corresponding stages of development, 
 closely resemble each other, however different the adults 
 may become; and so it is with very many other animals. 
 A trace of the law of embryonic resemblance occasionally 
 lasts till a rather late age: thus birds of the same genus, 
 and of allied genera, often resemble each other in their 
 immature plumage; as we see in the spotted feathers in the 
 young of the thrush group. In the cat tribe, most of the 
 species when adult are striped or spotted in lines; and 
 stripes or spots can be plainly distinguished in the whelp 
 of the lion and the puma. We occasionally, though rarely, 
 see something of the same kind in plants; thus the first 
 leaves of the ulex or furze,, and the first leaves of the 
 phyllodineous acacias, are pinnate or divided like the 
 ordinary leaves of the leguminosse. 
 
 I.he points of structure, in which the embryos of widely 
 different animals within the same class resemble each other, 
 often have no direct relation to their conditions of exist¬ 
 ence. We can not, for instance, suppose that in the era* 
 
m 
 
 DEVELOPMENT AND EMBRYOLOGY. 
 
 bryos of the vertebrata the peculiar loop-like courses of th& 
 arteries near the branchial slits are related to similar con¬ 
 ditions—in the young mammal which is nourished in the 
 womb of its mother, in the egg of the bird which is hatched 
 in a nest, and in the spawn of a frog under water. We 
 have no more reason to believe in such a relation than we 
 have to believe that the similar bones in the hand of a 
 man, wing of a bat, and fin of porpoise, are related to 
 similar conditions of life. No one supposes that the stripes 
 on the whelp of a lion, or the spots on the young black¬ 
 bird, are of any use to these animals. 
 
 The case, however, is different when an animal, during 
 any part of its embryonic career, is active, and has to pro¬ 
 vide for itself. The period of activity may come on 
 earlier or later in life; but whenever it comes on, the 
 adaptation of the larva to its conditions of life is just as per¬ 
 fect and as beautiful as in the adult animal. In how im¬ 
 portant a manner this has acted, has recently been 
 well shown by Sir J. Lubbock in his remarks on the 
 close similarity of the larv® of some insects belonging 
 to very different orders, and on the dissimilarity of the 
 larvae of other insects within the same order, according 
 to their habits of life. Owing to such adaptations the 
 similarity of the larvae of allied animals is sometimes 
 greatly obscured; especially when there is a division of 
 labor during the different stages of development, as 
 when the same larva has during one stage to search for 
 food, and during another stage has to search for a place of 
 attachment. Cases can even be given of the larvse of allied 
 species, or groups of species, differing more from each 
 other than do the adults. In most cases, however, the 
 larvae, though active, still obey, more or less closely, the 
 law of common embryonic resemblance. Cirripedes afford 
 a good instance of this; even the illustrious Cuvier did not 
 perceive that a barnacle was a crustacean: but a glance at 
 the larva shows this in an unmistakable manner. So again 
 the two main divisions of cirripedes, the pedunculated and 
 sessile, though differing widely in external appearance, 
 have larvag in all their stages barely distinguishable. 
 
 The embryo in the course of development generally rises 
 in organization. I use this expression, though I am aware 
 that it is hardly possible to define clearly what is meant by 
 
Development and embryology. 459 
 
 organization being higher or lower. But no one probably 
 will dispute that the butterfly is higher than the cater¬ 
 pillar. . In some cases, however, the mature animal must 
 De considered as lower in the scale than the larva, as with 
 certain parasitic crustaceans. To refer once again to cirri- 
 pedes: the larvae in the first stage have three pairs of loco¬ 
 motive organs, a simple single eye, and a probosciformed 
 mouth,, with which they feed largely, for they increase 
 much in size. In the second stage, answering to the 
 chiysalis stage of butterflies, they have six pairs of beauti¬ 
 fully constructed natatory legs, a pair of magnificent com¬ 
 pound eyes, and extremely complex antenna;; but they 
 nave a closed and imperfect mouth, and cannot feed: their 
 function at this stage is, to search out by their well-devel¬ 
 oped organs of sense, and to reach by their active powers 
 of swimming, a proper place on which to become attached 
 and to undergo their final metamorphosis. When this is 
 completed they are fixed for life: their legs are now con¬ 
 verted into prehensile organs; they again obtain a well- 
 constructed mouth; but they have no antennae, and their 
 two eyes are now reconverted into a minute, single, simple 
 eye-spot. I11 this, last and complete state, cirripedes may 
 be considered as either more highly or more lowly organized 
 than they were in the larval condition. But in some genera 
 the laryas become developed into hermaphodites having 
 the ordinary structure, and into what I have called com- 
 plemental males; and in the latter the development has 
 assuredly been retrograde, for the male is a mere sack, 
 which lives for a short time and is destitute of mouth, 
 stomach, and every other organ of importance, excepting 
 those for reproduction. 
 
 We are so much accustomed to see a difference in struc¬ 
 ture between the embryo and the adult, that we are tempted 
 to look at this difference as in some necessary manner 
 contingent on growth. But there is no reason why, for 
 instance, the wing of a bat, or the fin of a porpoise, should 
 not have been sketched out with all their parts in proper 
 proportion, as soon as any part became visible. In some 
 whole groups of animals and in certain members of other 
 groups this is the case, and the embryo does not at any 
 period differ widely from the adult: thus Owen has re¬ 
 marked in regard to cuttle-fish, “ there is no metamor- 
 
460 
 
 DEVELOPMENT AND EMBRYOLOGY. 
 
 phosis; the cephalopodic character is manifested long be¬ 
 fore the parts of the embryo are completed." Land-shells 
 and fresh-water crustaceans are born having their proper 
 forms, while the marine members of the same two great 
 classes pass through considerable and often great changes 
 during their development. Spiders, again, barely undergo 
 any metamorphosis. The larvae of most insects pass through 
 a worm-like stage, whether they are active and adapted to 
 diversified habits, or are inactive from being placed in the 
 midst of proper nutriment, or from being fed by their 
 parents; but in some few cases, as in that of Aphis, if we 
 look to the admirable drawings of the development of this 
 insect, by Professor Huxley, we see hardly any trace of tiie 
 vermiform stage. 
 
 Sometimes it is only the earlier developmental stages 
 which fail. Thus, Fritz Muller has made the remarkable 
 discovery that certain shrimp-like crustaceans (allied to 
 Penceus) first appear under the simple nauplius-form, and 
 after passing through two or more zoea-stages, and then 
 through the mysis-stage, finally acquire their mature 
 structure: now in the whole great malacostracan order, to 
 which these crustaceans belong, no other member is as yet 
 known to be first developed under the nauplius-form, 
 though many appear as zoeas; nevertheless Muller assigns 
 reasons for his belief, that if there had been no suppression 
 of development, all these crustaceans would have appeared 
 as nauplii. 
 
 How, then, can we explain these several facts in embry¬ 
 ology—namely, the very general, though not universal, 
 difference in structure between the embryo and the adult; 
 the various parts in the same individual embryo, which 
 ultimately become very unlike, and serve for diverse pur¬ 
 poses, being at an early period of growth alike; the com¬ 
 mon, but not invariable, resemblance between the embryos 
 or larvae of the most distinct species in the same class; the 
 embryo often retaining, while within the egg or womb, 
 structures which are of no service to it, either at that or at 
 a later period of life; on the other hand, larvae which have 
 to provide for their own wants, being perfectly adapted to 
 the surrounding conditions; and lastly, the fact of certain 
 larvae standing higher in the scale of organization than the 
 mature animal into which they are developed? I believe 
 that all these facts can be_explained as follows. 
 
DEVELOPMENT AND EMBRYOLOGY. 
 
 461 
 
 It is commonly assumed, perhaps from monstrosities 
 affecting the embryo at a very early period, that slight 
 variations or individual differences necessarily appear at an 
 equally early period. We have little evidence on this 
 head, but what we have certainly points the other wav; for 
 it is notorious that breeders of cattle, horses and various 
 fancy animals, can not positively tell, until some time after 
 birth, what will be the merits and demerits of their young 
 animals. We see this plainly in our own children; we 
 can not tell whether a child will be tall or short, or what 
 its precise features will be. The question is not, at what 
 period of life each variation may have been caused, but at 
 what period the effects are displayed. The cause may have 
 acted, and I believe often has acted, on one or both par¬ 
 ents before the act of generation. It deserves notice that 
 it is of no importance to a very young animal, as long as it 
 remains in its mothers womb or in the egsr, or as long as 
 it is nourished and protected by its parent, whether most 
 of its characters are acquired a little earlier or later in life. 
 It would not signify, for instance, to a bird which obtained 
 its. food by having a much-curved beak whether or not 
 while young it possessed a beak of this shape, as long as it 
 was fed by its parents. 
 
 I have stated in the first chapter, that at whatever age a 
 \aiiation first appears in the parent, it tends to reappear 
 at a corresponding age in the offspring. Certain vari¬ 
 ations can only appear at corresponding ages; for instance, 
 peculiarities in the caterpillar, cocoon, or imago states of 
 the silk-moth; or, again, in the full-grown horns of cattle. 
 But variations which, for all that we can see might have 
 first appeared either earlier or later in life, likewise tend to 
 reappear at a corresponding age in the offspring and 
 parent. I am far from meaning that this is invariably the 
 case, and I could give several exceptional cases of varia¬ 
 tions (taking the word in the largest sense) which 
 have supervened at an earlier age in the child than in the 
 parent. 
 
 These two principles, namely, that slight variations gen¬ 
 erally appear at a not very early period of life, and are in¬ 
 herited at a corresponding not early period, explain, as I 
 believe, all the above specified leading facts in embryology. 
 But first let us look to a few analogous cases in our domes- 
 
462 
 
 DEVELOPMENT aNO EMBRYOLOGY. 
 
 tic varieties. Some authors who have written on dogs 
 maintain that the greyhound and bull-dog, though so dif¬ 
 ferent, are really closely allied varieties, descended from 
 the same wild stock, hence I was curious to see how far 
 their puppies differed from each other. I was told by 
 breeders that they differed just as much as their parents, 
 and this, judging by the eye, seemed almost to be the case; 
 but on actually measuring the old dogs and their six-days- 
 old puppies, I found that the puppies had not acquired 
 nearly their full amount of proportional difference. So, 
 again, I was told that the foals of cart and race horses—• 
 breeds which have been almost wholly formed by selection 
 under domestication—differed as much as the full-grown 
 animals; but having had careful measurements made of 
 the dams and of three-days-old colts of race and heavy 
 cart-horses, I find that this is by no means the case. 
 
 As we have conclusive evidence that the breeds of the 
 pigeon are descended from a single wild species, I com¬ 
 pared the young within twelve hours after being hatched. 
 I carefully measured the proportions (but will not here 
 give the details) of the beak, width of mouth, length of 
 nostril and of eyelid, size of feet and length of leg, in the 
 wild parent species, in pouters, fantails, runts, barbs, 
 dragons, carriers and tumblers. Now, some of.these birds, 
 when mature, differ in so extraordinary a manner in the 
 length and form of beak, and in other P^aracters, that they 
 would certainly have been ranked ^'"distinct genera if 
 found in a state of nature. But when the nestling birds 
 of these several breeds were placed in a row, though most 
 of them could just be distinguished, the proportional dif¬ 
 ferences in the above specified points were incomparably 
 less than in the full-grown birds. Some characteristic 
 points of difference—for instance, that of the width of 
 mouth—could hardly be detected in the young. But there 
 was one remarkable exception to this rule, for the young of 
 the short-faced tumbler differed from the young of the 
 wild rock-pigeon, and of the other breeds, in almost exactly 
 the same proportions as in the adult stage. 
 
 These facts are explained by the above two principles. 
 Fanciers select their dogs, horses, pigeons, etc., for breed¬ 
 ing, when nearly grown up. They are indifferent whether 
 the desired qualities are acquired earlier or later in life, if 
 
DEVELOPMENT AND EMBRYOLOGY. 
 
 463 
 
 the full-grown animal possesses them. And the cases just 
 given, more especially that of the pigeons, show that the 
 characteristic differences which have been accumulated 
 by man’s selection, and which give value to his breeds, 
 do not generally appear at a very early period of life, and 
 are inherited at a corresponding not early period. But the 
 case of the short-faced tumbler, which when twelve hours 
 old possessed its proper characters, proves that this is not 
 the universal rule; for here the characteristic differences 
 must either have appeared at an earlier period than usual, 
 or, if not so, the differences must have been inherited, not 
 at a corresponding, but at an earlier age. 
 
 Now, let us apply these two principles to species in a 
 state of nature. Let us take a group of birds, descended 
 from some ancient form and modified through natural 
 selection for different habits. Then, from the many slight 
 successive variations having supervened in the several 
 species at a not early age, and having been inherited at a 
 corresponding age, the young will have been but little 
 modified, and they will still resemble each other much more 
 closely than do the adults, just as we have seen with the 
 breeds of the pigeon. We may extend this view to widely 
 distinct structures and to whole classes. The fore limbs, 
 for instance, which once served as legs to a remote progen¬ 
 itor, may have become, through a long course of modifica¬ 
 tion, adapted in one descendant to act as hands, in another 
 as paddles, in another as wings; but on the above two 
 principles the fore limbs will not have been much modified 
 in the embryos of these several forms; although in each 
 form the fore limb will differ greatly in the adult state. 
 Whatever influence long continued use or disuse may have 
 had in modifying the limbs or other parts of any species, 
 this will chiefly or solely have affected it when nearly 
 mature, when it was compelled to use its full powers to 
 gain its own living; and the effects thus produced will have 
 been transmitted to the offspring at a corresponding nearly 
 mature age. Thus the young will not be modified, or will 
 be modified only in a slight degree, through the effects of 
 the increased use or disuse of parts. 
 
 With some animals the successive variations may have 
 supervened at a very early period of life, or the steps may 
 have been inherited at an earlier age than that at which 
 
464 
 
 DEVELOPMENT AND EMBRYOLOGY. 
 
 they first occurred. In either of these cases, the young or 
 embryo will closely resemble the mature parent-form, as 
 we have seen with the short-faced tumbler. And this is 
 the rule of development in certain whole groups, or in 
 certain sub-groups alone, as with cuttle-fish, land-shells, 
 fresh-water crustaceans, spiders, and some members of 
 the great class of insects. With respect to the final 
 cause of the young in such groups not passing through 
 any metamorphosis, we can see that this would follow 
 from the following contingencies: namely, from the 
 young having to provide at a very early age for their 
 own wants, and from their following the same habits of 
 life with their parents; for in this case it would be in¬ 
 dispensable for their existence that they should be modified 
 in the same manner as their parents. Again, with respect 
 to the singular fact that many terrestrial and fresh-water 
 animals do not undergo any metamorphosis, while marine 
 members of the same groups pass through various trans¬ 
 formations, Fritz Muller has suggested that the process of 
 slowly modifying and adapting an animal to live on the 
 land or in fresh water, instead of in the sea, would be 
 greatly simplified by its not passing through any larval 
 stage; for it is not probable that places well adapted for 
 both the larval and mature stages, under such new and 
 greatly changed habits of life, would commonly be found 
 unoccupied or ill-occupied by other organisms. In this 
 case the gradual acquirement at an earlier and earlier age 
 of the adult structure would be favored by natural selec¬ 
 tion; and all traces of former metamorphoses would finally 
 be lost. 
 
 If, on the other hand, it profited the young of an ani¬ 
 mal to follow habits of life slightly different from those of 
 the parent-form, and consequently to be constructed on a 
 slightly different plan, or if it profited a larva already dif¬ 
 ferent from its parent to change still further, then, on the 
 principle of inheritance at corresponding ages, the young 
 or the larva? might be rendered by natural selection more 
 and more different from their parents to any conceivable 
 extent. Differences in the larva might, also, become corre¬ 
 lated with successive stages of its development; so that the 
 larva, in the first stage, might come to differ greatly from 
 the larva in the second stage, as is the case with many ani* 
 
DEVELOPMENT AND EMBRYOLOGY . 
 
 465 
 
 mals. The adult might also become fitted for sites or 
 habits, in which organs of locomotion or of the senses, etc., 
 would be useless; and in this case the metamorphosis 
 would be retrograde. 
 
 From the remarks just made we can see how by changes 
 of structure in the young, in conformity with changed 
 habits of life, together with inheritance at corresponding 
 ages, animals might come to pass through stages of devel¬ 
 opment, perfectly distinct from the primordial condition 
 of their adult progenitors. Most of our best authorities 
 are now convinced that the various larval and pupal stages 
 of insects have thus been acquired through adaptation, and 
 not through inheritance from some ancient form. The 
 curious case of Sitaris—a beetle which passes through cer¬ 
 tain unusual stages of development—will illustrate how 
 this might occur. The first larval form is described by M. 
 Fabre, as an active, minute insect, furnished with six legs, 
 two long antennae, and four .eyes. These larvae are 
 hatched in the nests of bees; and when the male bees 
 emerge from their burrows, in the spring, which they do 
 before the females, the larvae spring on them, and after¬ 
 ward crawl on to the females while paired with the males. 
 As soon as the female bee deposits her eggs on the surface 
 of the honey stored in the cells, the larvae of the Sitaris 
 leap on the eggs and devour them. Afterward they 
 undergo a complete change; their eyes disappear; theirlegs 
 and antennae become rudimentary, and they feed on honey; 
 so that they now more closely resemble the ordinary larvae 
 of insects; ultimately they undergo a further transforma¬ 
 tion, and finally emerge as the perfect beetle. Now, if an 
 insect, undergoing transformations like those of the 
 Sitaris, were to become the progenitor of a whole new class 
 of insects, the course of development of the new class 
 would be widely different from that of our existing insects; 
 and the first larval stage certainly would not represent the 
 former condition of any adult and ancient form. 
 
 On the other hand it is highly probable that with many 
 animals the embryonic or larval stages show us, more or 
 less completely, the condition of the progenitor of the whole 
 group in its adult state. In the great class of the Crus¬ 
 tacea, forms wonderfully distinct from each other, namely, 
 suctorial parasites, cirripedes, entomostraca, and even the 
 
466 DEVELOPMENT AND EMBRYOLOGY. 
 
 malacostraca, appear at first as larvae under the nauplius- 
 form; and as these larvae live and feed in the open 
 sea, and are not adapted for any peculiar habits of 
 life, and from other reasons assigned by Fritz Muller, it 
 is probable that at some very remote period an independ¬ 
 ent adult animal, resembling the Nauplius, existed, and 
 subsequently produced, along several divergent lines of 
 descent, the above-named great Crustacean groups. So 
 again, it is probable, from what we know of the embryos 
 of mammals, birds, fishes and reptiles, that these animals 
 are the modified descendants of some ancient progenitor, 
 which was furnished in its adult state with branchke, a 
 swim-bladder, four fin-like limbs, and a long tail, all fitted 
 for an aquatic life. 
 
 As all the organic beings, extinct and recent, which 
 have ever lived, can be arranged within a few great classes; 
 and as all within each class have, according to our theorv, 
 been connected together by fine gradations, the best, and* 
 if our collections were nearly perfect, the only possible 
 arrangement would be genealogical; descent "being the 
 hidden bond of connection which naturalists have been 
 seeking under the term of the Natural System. On this 
 view we can understand how it is that, in the eyes of most 
 naturalists, the structure of the embryo is even more 
 important for classification than that of the adult. In 
 two or more groups of animals, however much they may 
 differ from each other in structure and habits in their 
 adult condition, if they pass through closely similar 
 embryonic stages, we may feel assured that they all are 
 descended from one parent-form, and are therefore closely 
 related. Thus, community in embryonic structure reveals 
 community of descent; but dissimilarity in embryonic 
 development does not prove discommunity of descent, for 
 in one of two groups the developmental stages may have 
 been suppressed, or may have been so greatly modified 
 through adaptation to new habits of life as to be no longer 
 recognizable. Even in groups, in which the adults have 
 been modified to an extreme degree, community of origin 
 is often revealed by the structure of the larvae; we have 
 seen, for instance, that cirripedes, though externally so like 
 shell-fish, are at once known by their larvas to belong to 
 the great class of crustaceans. As the embryo often shows 
 
DEVELOPMENT AND EMBHYOLOG T. 467 
 
 ns more or less plainly the structure of the less modified 
 d.nd ancient progenitor of the group, we can see why ancient 
 and extinct forms so often resemble in their adult state the 
 embryos of existing species of the same class. Agassiz 
 believes this to be a universal law of nature; and we mav 
 hope hereafter to see the law proved true. It can, how¬ 
 ever, be proved true only in those cases in which the 
 ancient state of the progenitor of the group has not been 
 wholly obliterated, either by successive variations having 
 supervened at_a very early period of growth, or by such 
 variations having been inherited at an earlier age than that 
 at which they first appeared. It should also be borne in 
 mind, that the law may be true, but yet, owing to the 
 geological record not extending far enough back in time, 
 may remain for a long period, or for ever, incapable of 
 demonstration. The law will not strictly hold good in 
 those cases in which an ancient form became adapted in 
 its larvae state to some special line of life, and transmitted 
 the same larval state to a whole group of descendants; for 
 such larval will not resemble any still more ancient form 
 in its adult state. 
 
 Thus, as it seems to me, the leading facts in embryology, 
 which are second to none in importance, are explained on 
 the principle of variations in the many descendants from 
 some one ancient progenitor, having appeared at a not 
 very early period of life, and having been inherited at a 
 corresponding period. Embryology rises greatly in inter¬ 
 est, when we look at the embryo as a picture, more or less 
 obscured, of the progenitor, either in its adult or larval 
 state, of all the members of the same great class. 
 
 RUDIMENTARY, ATROPHIED, AND ABORTED ORGANS. 
 
 Organs or parts in this strange condition, bearing the 
 plain stamp of inutility, are extremely common, or even 
 general, throughout nature. It would be impossible to 
 name one of the higher animals in which some part or 
 other is not in a rudimentary condition. In the mamma¬ 
 lia, for instance, the males possess rudimentary mammas; 
 in snakes one lobe of the lungs is rudimentary; in birds 
 the ii bastard-wing ” may safely be considered as a rudir 
 mentary digit, and in some species the whole wing is so fa- 
 
46S 
 
 RUDIMENTARY , ATROPHIED , 
 
 rudimentary that it cannot be used for flight. What can 
 be more curious than the presence of teeth in foetal whales, 
 which when grown up have not a tooth in their heads; or 
 the teeth, which never cut through the gums, in the upper 
 jaws of unborn calves? 
 
 Rudimentary organs plainly declare their origin and 
 meaning in various ways. There are beetles belonging to 
 closely allied species, or even to the same identical species, 
 which have either full-sized and perfect wings, or mere 
 rudiments of membrane, which not rarely lie under wing- 
 covers firmly soldered together; and in these cases it is im¬ 
 possible to doubt, that the rudiments represent wings. 
 Rudimentary organs sometimes retain their potentiality: 
 this occasionally occurs with the mammae of male mammals, 
 which have been known to become well developed and to 
 secrete milk. So again in the udders in the genus Bos, 
 there are normally four developed and two rudimentary 
 teats; but the latter in our domestic cows sometimes be¬ 
 come well developed and yield milk. In regard to plants, 
 the petals are sometimes rudimentary, and sometimes well 
 developed in the individuals of the same species. In cer¬ 
 tain plants having separated sexes Kolreuter found that by 
 crossing a species, in which the male flowers included 
 a rudiment of a pistil, with an hermaphrodite species, 
 having of course a well-developed pistil, the rudiment in 
 the hybrid offspring was much increased in size; and this 
 clearly shows that the rudimentary and perfect pistils are 
 essentially alike in nature. An animal may possess vari¬ 
 ous parts in a perfect state, and yet they may in one sense 
 be rudimentary, for they are useless: thus the tadpole of 
 the common salamander or water-newt, as Mr. G. H. 
 Lewes remarks, “ has gills, and passes its existence in the 
 water; but the Salamandra atra, which lives high up 
 among the mountains, brings forth its young full-formed. 
 This animal never lives in the water. Yet if we open a 
 gravid female, we find tadpoles inside her with exquisitely 
 feathered gills; and when placed in water they swim about 
 like the tadpoles of the water-newt. Obviously this aquatic 
 organization has no reference to the future life of the 
 animal, nor has it any adaptation to its embryonic con¬ 
 dition; it has solely reference to ancestral adaptations, it 
 repeats a phase in the development of its progenitors.” 
 
AND ABORTED ORGANS. 
 
 469 
 
 An organ, serving for two purposes, may become rudi¬ 
 mentary or utterly aborted for one, even the more impor¬ 
 tant purpose, and remain perfectly efficient for the other. 
 Thus, in plants, the office of the pistil is to allow the pollen- 
 tubes to reach the ovules within the ovarium. The pistil 
 consists of a stigma supported on a style; but in some Com¬ 
 posite, the male florets, which of course cannot be fecun¬ 
 dated, have a rudimentary pistil, for it is not crowned with 
 a stigma; but the style remains well developed and is 
 clothed in the usual manner with hairs, which serve to 
 brush the pollen out of the surrounding and conjoined 
 anthers. Again, an organ may become rudimentary for 
 its proper purpose, and be used for a distinct one: in cer¬ 
 tain fishes the swim-bladder seems to be rudimentary for 
 its proper function of giving buoyancy, but has become 
 converted into a nascent breathing organ or lung. Many 
 similar instances could be given. 
 
 Useful organs, however little they may be developed, 
 unless we have reason to suppose that they were formerly 
 more highly developed, ought not to be considered as 
 rudimentary. They may be in a nascent condition, and in 
 progress toward further development. Rudimentary 
 organs, on the other hand, are either quite useless, such as 
 teeth which never cut through the gums, or almost useless, 
 such as the wings of an ostrich, which serve merely as 
 sails. As organs in this condition would formerly, when still 
 less developed, have been of even less use than at present, 
 they cannot formerly have been produced through varia¬ 
 tion and natural selection, which acts solely by the preser¬ 
 vation of useful modifications. They have been partially 
 retained by the power of inheritance, and relate to a 
 former state of things. It is, however, often difficult to 
 distinguish between rudimentary and nascent organs; for 
 we can judge only by analogy whether a part is capable of 
 further development, in which case alone it deserves to be 
 called nascent. Organs in this condition will always be 
 somewhat rare; for beings thus provided will commonly 
 have been supplanted by their successors with the same 
 organ in a more perfect state, and consequently will have 
 become long ago extinct. The wing of the penguin is of 
 high service, acting as a fin; it may, therefore, represent 
 the nascent state of the wing: not that I believe this to be 
 
470 
 
 RUDIMENTARY , ATROPHIED , 
 
 the case; it is more probably a reduced organ, modified 
 for a new function: the wing of the Apteryx, on the other 
 hand, is quite useless, and is truly rudimentary. Owen 
 considers the simple filamentary limbs of the Lepidosiren 
 as the “beginnings of organs which attain full functional 
 development in higher vertebrates; ” but, according to the 
 view lately advocated by Dr. Gunther, they are probably 
 remnants, consisting of the persistent axis of a fin, with 
 the lateral rays or branches aborted. The mammary glands 
 of the Ornithorhynchus may be considered, in comparison 
 with the udders of a cow, as in a nascent condition. The 
 ovigerous frena of certain cirripedes, which have ceased to 
 give attachment to the ova and are feebly developed, are 
 nascent branchiae. 
 
 Rudimentary organs in the individuals of the same 
 species are very liable to vary in the degree of their devel- ' 
 opment and in other respects. In closely allied species, 
 also, the extent to which the same organ has been reduced 
 occasionally differs much. This latter fact is well exem¬ 
 plified in the state of the wings of female moths belonging 
 to the same family. Rudimentary organs may be utterly 
 aborted; and this implies, that in certain animals or 
 plants, parts are entirely absent which analogy would 
 lead us to expect to find in them, and which are occasion¬ 
 ally found in monstrous individuals. Thus in most of the 
 Scrophulariacese the fifth stamen is utterly aborted; yet we 
 may conclude that a fifth stamen once existed, for a rudi¬ 
 ment of it is found in many species of the family, and this 
 rudiment occasionally becomes perfectly developed, as may 
 sometimes be seen in the common snap-dragon. In tracing 
 the homologies of any part in different members of the 
 same class, nothing is more common, or, in order fully to 
 understand the relations of the parts, more useful than the 
 discovery of rudiments. This is well shown in the draw¬ 
 ings given by Owen of the leg bones of the horse, ox and 
 rhinoceros. 
 
 It is an important fact that rudimentary organs, such as 
 teeth in the upper jaws of whales and ruminants, can often 
 be detected in the embryo, but afterward wholly disappear. 
 It is also, I believe, a universal rule, that a rudimentary 
 part is of greater size in the embryo relatively to the ad¬ 
 joining parts, than in the adult; so that the organ at this 
 
AND ABORTED ORGANS. 
 
 471 
 
 early age is less rudimentary, or even cannot be said to be 
 in any degree rudimentary. Hence rudimentary organs in 
 the adult are often said to have retained their embryonic 
 condition. 
 
 I have now given the leading facts with respect to rudi¬ 
 mentary organs. In reflecting on them, every one must be 
 struck with astonishment; for the same reasoning power 
 which tells us that most parts and organs are exquisitely 
 adapted for certain purposes, tells us with equal plainness 
 that these rudimentary or atrophied organs are imperfect 
 and useless. In works on natural history, rudimentary 
 organs are generally said to have been created “for the 
 sake of symmetry,” or in order “ to complete the scheme 
 of nature.” But this is not an explanation, merely 
 a re-statement of the fact. Nor is it consistent with itself: 
 thus the boa-constrictor has rudiments of hind limbs and 
 of a pelvis, and if it be said that these bones have been re¬ 
 tained “to complete the scheme of nature,” why, as Pro¬ 
 fessor Weismann asks, have they not been retained by other 
 snakes, which do not possess even a vestige of these same 
 bones? What would be thought of an astronomer who 
 maintained that the satellites revolve in elliptic courses 
 round their planets “for the sake of symmetry,” because 
 the planets thus revolve round the sum? An eminent 
 physiologist accounts for the presence of rudimentary 
 organs, by supposing that they serve to excrete matter in 
 excess, or matter injurious to the system; but can we sup¬ 
 pose that the minute papilla, which often represents the 
 pistil in male flowers, and which is formed of mere cellular 
 tissue, can thus act? (Jan we suppose that rudimentary 
 teeth, which are subsequently absorbed, are beneficial to 
 the rapidly growing embryonic calf by removing matter so 
 precious as phosphate of lime? When a man’s fingers have 
 been amputated, imperfect nails have been known to ap¬ 
 pear on the stumps, and I could as soon believe that these 
 vestiges of nails are developed in order to excrete horny 
 matter, as that the rudimentary nails on the fin of the 
 manatee have been developed for this same purpose. 
 
 On the view of descent with modification, the origin of 
 rudimentary organs is comparatively simple; and we can 
 understand to a large extent the laws governing tlieit 
 imperfect development. We have plenty of cases of rudi- 
 
473 
 
 RUDIMENTARY\ ATROPHIED , 
 
 mentary organs in our domestic productions, as the stump 
 of a tail in tailless breeds, the vestige of an ear in 
 earless breeds of sheep—the reappearance of minute dang¬ 
 ling horns in hornless breeds of cattle, more especially, 
 according to Youatt, in young animals—and the state of 
 the whole flower in the cauliflower. We often see rudi¬ 
 ments of various parts in monsters; but I doubt whether 
 any of these cases throw light on the origin of rudimentary 
 organs in a state of nature, further than by showing that 
 rudiments can be produced; for the balance of evidence 
 clearly indicates that species under Jiature do not undergo 
 great and abrupt changes. But we learn from the study 
 of our domestic productions that the disuse of parts leads 
 to their reduced size; and that the result is inherited. 
 
 It appears probable that disuse has been the main agent 
 in rendering organs rudimentary. It would at first lead 
 by slow steps to the more and more complete reduction of 
 a part, until at last it became rudimentary—as in the case 
 of the eyes of animals inhabiting dark caverns, and of the 
 wings of birds inhabiting oceanic islands, which have 
 seldom been forced by beasts of prey to take flight, and 
 have ultimately lost the power of flying. Again, an organ, 
 useful under certain conditions, might become, injurious 
 under others, as with the wings of beetles living on small 
 and exposed islands; and in this case natural selection will 
 have aided in reducing the organ, until it was rendered 
 harmless and rudimentary. 
 
 Any change in structure and function, which can be 
 effected by small stages, is within the power of natural 
 selection; so that an organ rendered, through changed 
 habits of life, useless or injurious for one purpose, might 
 be modified and used for another purpose. An organ 
 might, also, be retained for one alone of its former func¬ 
 tions. Organs, originally formed by the aid of natural 
 selection, when rendered useless may well be variable, for 
 their variations can no longer be checked by natural selec¬ 
 tion. All this agrees well with what we see under nature. 
 Moreover, at whatever period of life either disuse or selection 
 reduces an organ, and this will generally be when the being 
 has come to maturity and has to exert its full powers of 
 action, the principle of inheritance at corresponding ages 
 will tend to reproduce the organ in its reduced state at the 
 
AND ABORTED ORGANS. 
 
 473 
 
 same mature age, but will seldom affect it in the embryo. 
 Thus we can understand the greater size of rudimentary 
 organs in the embryo relatively to the adjoining parts, and 
 their lesser relative size in the adult. If, for instance, the 
 digit of an adult animal was used less and less during 
 many generations, owing to some change of habits, or if an 
 organ or gland was less and less functionally, exercised, we 
 may infer that it would become reduced in size in the 
 adult descendants of this animal, but would retain nearly 
 its original standard of development in the embryo. 
 
 There remains, however, this difficulty. After an organ 
 has ceased being used, and has become in consequence 
 much reduced, how can it be still further reduced in size 
 until the merest vestige is left; and how can it be finally 
 quite obliterated? It is scarcely possible that disuse can 
 go on producing any further effect after the organ has 
 once been rendered functionless. Some additional ex¬ 
 planation is here requisite which I cannot give. If, for 
 instance, it could be proved that every part of the organ¬ 
 ization tends to vary in a greater degree toward diminution 
 than toward augmentation of size, then we should be able 
 to understand how an organ which has become useless 
 would be rendered, independently of the effects of disuse, 
 rudimentary and would at last be wholly suppressed; for 
 the variations toward diminished size would no longer be 
 checked by natural selection. The principle of the economy 
 of growth, explained in a former chapter, by which the 
 materials forming any part, if not useful to the possessor, 
 are saved as far as is possible, will perhaps come into play 
 in rendering a useless part rudimentary. But this prin¬ 
 ciple will almost necessarially be confined to the earlier stages 
 of the process of reduction; for we cannot suppose that a 
 minute papilla, for instance, representing in a male flowei 
 the pistil of the female flower, and formed merely of cellu- 
 lai tissue, could be further reduced or absorbed for the 
 sake of economizing nutriment. 
 
 Finally, as rudimentary organs, by whatever steps they 
 may have been degraded into their present useless condi¬ 
 tion, are the record of a former state of things, and have 
 been retained solely through the power of inheritance—we 
 can understand, on the genealogical view of classification, 
 how it is that systematists, in placing organisms in their 
 
474 
 
 SUMMARY. 
 
 proper places in the natural system, have often found rudi- 
 mentaiy parts as useful as, or even sometimes more useful 
 than, paits of high physiological importance. Rudimentary 
 organs may be compared with the letters in a word, still 
 retained in the spelling, but become useless in the pro¬ 
 nunciation, but which serve as a clue for its derivation. 
 On the view of descent with modification, we may conclude 
 that the existence of organs in a rudimentary, imperfect, 
 and useless condition, or quite aborted, far from presenting 
 a strange difficulty, as they assuredly do on the old doctrine 
 of creation, might even have been anticipated in accordance 
 with the views here explained. 
 
 SUMMARY. 
 
 In this chapter I have attempted to show that the 
 arrangement of all organic beings throughout all time in 
 groups under groups—that the nature of the relationships 
 by which all living and extinct organisms are united by 
 complex, radiating, and circuituous lines of affinities into 
 a few grand classes—the rules followed and the difficulties 
 encountered by naturalists in their classifications—the 
 value set upon characters, if constant and prevalent, 
 whether of high or of the most trifling importance, or, as 
 with rudimentary organs of no importance—the wide 
 opposition in value between analogical or adaptive charac- 
 teis, and characters of true affinity; and other such rulesj 
 —all naturally follow if we admit the common parentage 
 of allied forms, together with their modification through 
 vanation and natural selection, with the contingencies of 
 extinction and divergence of character. In considering 
 this view of classification, it should be borne in mind that 
 the element of descent has been universally used in rank- 
 ing together the sexes, ages, dimorphic forms, and acknowl¬ 
 edged \ arieties of the same species, however much they 
 may differ from each other in structure If we extend the 
 use of this element of descent—the one certainly known 
 cause of similarity in organic beings—we shall understand 
 what is meant by the Natural System: it is genealogical 
 in its attempted arrangement, with the grades of acquired 
 difference marked by the terms, varieties, species, genera, 
 families, orders, and classes. ° 
 
SUMMARY. 
 
 475 
 
 On this same view of descent with modification, most 
 of the great facts in Morphology become intelligible— 
 whether we look to the same pattern displayed by the 
 different species of the same class in their homologous 
 organs, to whatever purpose applied; or to the serial and 
 lateral homologies in each individual animal and plant. 
 
 On the principle of successive slight variations, not 
 necessarily or generally-supervening at a very early period 
 of life, and being inherited at a corresponding period, we 
 can understand the leading facts in embryology; namely, 
 the close resemblance in the individual embryo of the parts 
 which are homologous, and which when matured become 
 widely different in structure and function; and the resem¬ 
 blance of the homologous parts or organs in allied though 
 distinct species, though fitted in the adult state for habits 
 as different as is possible. Larvae are active embryos, 
 which have been specially modified in a greater or less 
 degree in relation to their habits of life, with their modifi¬ 
 cations inherited at a corresponding early age. On these 
 same principles, and bearing in mind that when organs 
 are reduced in size, either from disuse or through natural 
 selection, it will generally be at that period of life when 
 the being has to provide for its own wants, and bearing in 
 in mind how strong is the force of inheritance—the occur¬ 
 rence of rudimentary organs might even have been antici¬ 
 pated. The importance of embryological characters and 
 of rudimentary organs in classification is intelligible, on 
 the view that a natural arrangement must be genealogical. 
 
 Finally, the several classes of facts which have been con¬ 
 sidered in this chapter, seem to me to nroclaim so plainly, 
 that the innumerable species, genera and families, with 
 which this world is peopled, are all descended, each 
 within its own class or group, from common parents, and 
 have all been modified in the course of descent, that I 
 should without hesitation adopt this view, even if it were 
 unsupported by other facts or arguments. 
 
-176 
 
 RECAPITULA TION. 
 
 CHAPTER XV. 
 
 RECAPITULATION AND CONCLUSION. 
 
 Recapitulation of the objections to the theory of Natural Selection_ 
 
 Recapitulation of the general and special circumstances in its 
 favor—Causes of the general belief in the immutability of 
 species—How far the theory of Natural Selection may he 
 extended—Effects of its adoption on the study of Natural 
 History—Concluding remarks. 
 
 As this whole volume is one long argument, it may be 
 convenient to the reader to have the leading facts and 
 inferences briefly recapitulated. 
 
 ^ That many and serious objections may be advanced 
 against the theory of descent with modification through 
 variation and natural selection, I do not deny. I have en¬ 
 deavored to give to them their full force. Nothing at first 
 can appear more difficult to believe than that the more 
 complex organs and instincts have been perfected, not by 
 means superior to, though analogous with, human reason, 
 but by the accumulation of innumerable slight variations, 
 each good for the individual possessor. Nevertheless, this 
 difficulty, though appearing to our imagination insuper¬ 
 ably great, can not be considered real if we admit the fol¬ 
 lowing propositions, namely, that all parts of tha n rg m,i_ 
 zation and instincts offer. at least, individual differences — 
 that there is a struggle for existence leading to"the nrescr- 
 vation of profitable deviations of structureor instinct^ 
 and, lastly, that gradation s in the stufp. of perfccth^Th f 
 eac h organ may hav e existed, each goo d of it s kind. The 
 truth of these propositions can not, I think, be disputed. 
 
 It is, no doubt, extremely difficult even to conjecture 
 by what gradations many structures have been perfected, 
 more especially among broken and failing groups of 
 organic beings, which have suffered much extinction; but 
 x we see so many strange gradations in nature, that we ought 
 
RECAP ITU LA TION. 
 
 47? 
 
 t ube extremely cautious in saving thft t any: o rgan or in ¬ 
 stinc t, or any whole structure, could not have arrived at 
 its present sta te by maiTy' g i’adu'ateT lffepsT There* arc, it 
 must be admitted, cases of special difficulty opposed to the 
 theory of natural selection: and one of the most curious of 
 these is the existence in the same community of two or 
 three defined castes of workers or sterile female ants; but I 
 have attempted to show how these difficulties can be 
 mastered. 
 
 With respect to the almost universal sterility of species 
 when first crossed, which forms so remarkable a contrast 
 with the almost universal fertility of varieties when crossed, 
 I must refer the reader to the recapitulation of the facts 
 given at the end of the ninth chapter, which seem to me 
 conclusively to show that this sterility is no more a special 
 endowment than is the incapacity of two distinct kinds 
 of trees to be grafted together; but that it is incidental on 
 differences confined to the reproductive systems of the in¬ 
 tercrossed species. We see the truth of this conclusion in 
 the vast difference in the results of crossing, the same two 
 species reciprocally—that is, when one species is first used 
 as the father and then as the mother. Analogy from the 
 consideration of dimorphic and trimorphic plants clearly 
 leads to the same conclusion, for when the forms are 
 illegitimately united, they yield few or no se , ( 
 
 offspring are more or less sterile; and these forms belong 
 to the same undoubted species., and differ from each other 
 in no respect except in their reproductive organs and 
 functions. 
 
 Although the fertility of varieties when intercrossed, and 
 of their mongrel offspring, has been asserted by so many 
 authors to be universal, this cannot be considered as quite 
 correct after the facts given on the high authority of Gart¬ 
 ner and Kolreuter. Most of the varieties which have been 
 experimented on have been produced under domestication; 
 and as domestication (I do not mean mere confinement) 
 almost certainly tends to eliminate that sterility which, 
 judging from analogy, would have affected the parent-spe¬ 
 cies if intercrossed, we ought not to expect that domesti¬ 
 cation would likewise induce sterility in their modified 
 descendants when crossed. This elimination of sterility 
 apparently follows from the same cause which allows ou. y 
 
478 RECAPITULATION, 
 
 domestic animals to breed freely under diversified circum¬ 
 stances; and this again apparently follows from their 
 having been gradually accustomed to frequent changes in 
 their conditions of life. 6 
 
 A double and parallel series of facts seems to throw much 
 light on the sterility of species, when first crossed, and of 
 their hybrid offspring. On the one side, there is good 
 reason to believe that slight changes in the conditions of 
 lite give vigor and fertility to all organic beings. We know 
 also that a cross between the distinct individuals of the 
 same variety and between distinct varieties, increases the 
 number of their offspring, and certainly gives to them in¬ 
 creased size and vigor. This is chiefly owing to the forms 
 winch are crossed having been exposed to somewhat dif¬ 
 ferent conditions of life ; fori have ascertained by a labori¬ 
 ous series of experiments that if all the individuals of the 
 same variety be subjected during several generations to the 
 came conditions, the good derived from crossing is often 
 much diminished or wholly disappears. This is one side of 
 the case. On the other side, we know that species which 
 have long been exposed to nearly uniform conditions, when 
 they are subjected under confinement to new and greatly 
 changed conditions, either perish, or if they survive, are 
 rendered sterile, though retaining perfect health. This 
 does not occur, or only in a very slight degree, with our 
 domesticated productions, which have long been exposed 
 to fluctuating conditions. Hence when we find that hybrids 
 produced by a cross between two distinct species are few in 
 number, owing to their perishing soon after conception or 
 at a very early age, or if surviving that they are rendered 
 more or less sterile, it seems highly probable that this 
 result is due to their having been in fact subjected to a great 
 change in their conditions of life, from being compounded 
 ot two distinct organizations. He who will explain in a 
 definite manner why, for instance, an elephant or a fox will 
 not breed under confinement in its native country, whilst 
 ,. e domestic pig or dog will breed freely under the most 
 diversified conditions, will at the same time be able to give 
 a definite answer to the question why two distinct species, 
 when crossed, as well as their hybrid offspring, are gener¬ 
 ally rendered more or less sterile, while two domesticated 
 
 Cr ° SSed aud tlieir mou S rel offspring are per- 
 
RECAPITULA TION. 
 
 479 
 
 Turning to geograph ical distribution, the difficulties en¬ 
 countered on the theory of descent with modification 
 are serious enough. All the individuals of the same 
 species, and all the species of the same genus, or even 
 higher group, are descended from common parents; and 
 therefore, in however distant and isolated parts of the 
 world they may now be found, they must in the course of 
 successive generations have traveled from some one point 
 to all the others. We are often wholly unable even to con¬ 
 jecture how this could have been effected. Yet. as we have 
 reason to believe that some species have retained the same 
 specific form for very long periods of time, immensely long 
 as measured by years, too innch stress ought not to.be laid 
 on the occasional wide diffusion of the same species; for 
 during very long periods there will always have been a 
 good chance for wide migration by many means. A broken 
 or interrupted range ma y often be accounted for by the e x¬ 
 tinction of the species in the intermediate region s. It can 
 not be denied that we are as yet very ignorant as to the full 
 extent of the various climatical and geographical changes 
 which have affected the earth during modern periods; and 
 such changes will often have facilitated migration. As an 
 example, t have attempted to show how potent has been the 
 influence of the Glacial period on t he distribu tion oJLJhe 
 sfl.rrm~fl.nri of afiiefl snecies'Througho ut the world. We are 
 as yet profoundly ignorant of the many occasional means 
 of transport. With respect to distinct species of the same 
 genus, inhabiting distant and isolated regions, as the pro¬ 
 cess of modification has necessarily been slow, all the 
 means of migration will have been possible during a very 
 long period; and consequently the difficulty of the wide 
 diffusion of the species of the same genus is in some degree 
 
 lessened. 
 
 As according to the t heory of natu ral selection an inter¬ 
 m inable nnmher~ dTTntermediate forms must have existe d", 
 TTp¥rng~to gether all the species in eanh group bv-gradation s 
 as fineas our existing v arieties, it mav he asked. Why do we 
 not~see~these linking forms ail around us? Why are not all 
 organic beings blended together in an inextricable chaos? 
 With respect to existing forms, we should remember that 
 we have no rig ht to expect fexcepting io-dis- 
 
 cover directly connecting links betwe en them..but only be- 
 
480 
 
 RECA PTTULA TTOK. 
 
 tHoeu ° ac]l and SQme ext inct and supplanted form. Evmi 
 on a wide area, winch has during along period remained 
 
 ofhfe p? 118 ' and ° f W Ki ich * the clim atic and other conditions 
 fi i.. .?i l v U A ge msenslbI .y'1 proceeding from a district oc¬ 
 cupied by one species into another district occupied bv a 
 closely allied species, we have no just right to expect often 
 to find intermediate varieties in the intermediate zones For 
 we have reason to believe that only a few species of a genus 
 
 exrincJ lde !?°l Change; th ® 0ther s P ecies becoming utterly 
 extinct and leaving no modified progeny. Of the species 
 
 winch do change, only a few within the same count™ 
 
 effected at T h ““i ‘T 5 and , a11 modifications are slowly 
 effected. I have also shown that the intermediate varieties 
 
 iuld « a \ fil ', St eXi8te , d in the intermediate zones 
 would be liable to be supplanted by the allied forms on 
 
 ei ler hand; for the latter, from existing in greater num¬ 
 bers would generally be modified and improved at a 
 (pucker rate than the intermediate varieties, which existed 
 
 he I*' nUmber ? ; 80 that the intermediate varieties would 
 in the long run, besuppUnted and exterminated. 
 
 On this doctrine of the extermination of an infinitude of 
 r nceung lmks, between the living and extinct inhabi¬ 
 tants of the vvorld, and at each successive period be- 
 ween the extinct and still older species, why is not 
 e'eiy geological formation charged with such links? Whv 
 does not every collection of fossil remains afford plain evi- 
 dence of the gradation and mutation of the forms of life? 
 Although geological research has undoubtedly revealed the 
 m m® 1 exl stence of many links, bringing numerous forms 
 ife much closer together, it does not yield the infinitely 
 many fine gradations between past and present species ri- 
 qmred on the theory, and this is the most obvious of the 
 many objections which may be urged against it Whv 
 again, do whole groups of allied species appear’ though 
 this appearance is often false, to have come in suddenly on 
 t e successive geological stages? Although we now know 
 that organic beings appeared on this globe, at a period in¬ 
 calculably remote, long before the lowest bed of P the Cam¬ 
 brian system was deposited, why do we not find beneath 
 this system great piles of strata stored with the remains of 
 he progenitors of the Cambrian fossils? For on the 
 tlieoiy, such strata must somewhere have been deposited at 
 
REGAPITULA TIOJS. 481 
 
 these ancient and utterly unknown epochs of the world’s 
 history. 
 
 I can answer these questions and objections only on the 
 supposition that the geological record is far more imperfect 
 than most geologists believe. The number of specimens in 
 all our museums is absolutely as nothing compared with 
 the countless generations of countless species which have 
 certainly existed. The parent form of any two or more 
 species would not be in all its characters directly interme¬ 
 diate between its modified offspring, any more than the 
 rock-pigeon is directly intermediate in crop and tail be¬ 
 tween its descendants, the pouter and fantail pigeons. 
 We should not be able to recognize a species as the parent 
 of another and modified species, if we were to examinine 
 the two ever so closely, unless we possessed most of the 
 intermediate links; and owing to the imperfection of the 
 geological record, we have no just right to expect to find 
 so many links. If two or three, or even more linking 
 forms were discovered, they would simply be ranked by 
 many naturalists as so many new species, more especially if 
 found in different geological substages, let their dif¬ 
 ferences be ever so slight. Numerous existing doubtful 
 forms could be named which are probably varieties; but 
 who will pretend that in future ages so many fossil links 
 will be discovered, that naturalists will be able to decide 
 whether or not these doubtful forms ought to be called 
 varieties? Only a small portion of the world has been geo¬ 
 logically explored. Only organic beings of certain classes 
 can be preserved in a fossil condition, at least in any great 
 number. Many species when once formed never undergo 
 any further change but become extinct without leaving 
 modified descendants; and the periods during which spe¬ 
 cies have undergone modification, though long as meas¬ 
 ured by years, have probably been short in comparison 
 with the periods during which they retained the same 
 form. It is the dominant and widely ranging species 
 which vary most frequently and vary most, and varieties 
 are often at first local—both causes rendering the discov¬ 
 ery of intermediate links in any one formation less likely. 
 Local varieties will not spread into other and distant 
 regions until they are considerably modified and improved; 
 and when they hive spread, and are discovered in a geolog- 
 
482 
 
 REG A PI TULA TION. 
 
 ical formation, they appear as if suddenly created there, 
 and will he simply classed as new species. Most forma¬ 
 tions have been intermittent in their accumulation, and 
 their duration has probably been shorter than the average 
 duration of specific forms. Successive formations are Tn 
 most cases separated from each other by blank intervals of 
 time of great length, for fossiliferons formations thick 
 enough to resist future degradation can, as a general rule, 
 be accumulated only where much sediment is deposited on 
 the subsiding bed of the sea. During the alternate periods of 
 elevation and of stationary level the record will generally 
 be blank. During these latter periods there will probably 
 be more variability in the forms of life; during periods of 
 subsidence, more extinction. 
 
 . With res]Dect to the absence of strata rich in fossils be¬ 
 neath the Cambrian formation, I can recur only to the 
 hypothesis given in the tenth chapter; namely, that though 
 our continents and oceans have endured for an enormous 
 period in nearly their present relative positions, we have 
 no reason to assume that this has always been the case; 
 consequently formations much older than any now known 
 may lie buried beneath the great cceans. With respect to 
 the lapse of time not having been sufficient since our planet 
 was consolidated for the assumed amount of organic change, 
 and this objection, as urged by Sir William Thompson, & is 
 probably one of the gravest as yet advanced, I can only 
 say, firstly, that we do not know at what rate species change, 
 as measured by years, and secondly, that many philoso¬ 
 phers are not as yet willing to admit that we know enough 
 of the constitution of the universe and of the interior of 
 our globe to speculate with safety on its past duration. 
 
 That the geological record is imperfect all will admit; 
 but that it is imperfect to the degree required by our 
 theory, few will be inclined to admit. If we look to long 
 enough intervals of time, geology plainly declares that 
 species have all changed; and they have changed in the 
 manner required by the theory, for they have changed 
 slowly and in a graduated manner. We clearly see this in 
 the fossil remains from consecutive formations invariably 
 being much more closely related to each other than are the 
 fossils from widely separated formations. 
 
 Such is the sum of the several chief objections and 
 
RECAPITULA TION . 
 
 483 
 
 difficulties which may be justly urged against the theory; 
 and I have now briefly recapitulated the answers and ex¬ 
 planations which, as far as I can see, may be given. 
 
 I have felt these difficulties far too heavily during many 
 years to doubt their weight. But it deserves especial notice 
 that the more important objections relate to questions on 
 which we are confessedly ignorant; nor do we know how 
 ignorant we are. We do,not know all the possible transi¬ 
 tional gradations between the simplest and the mosUper- 
 fect organs; it cannot be pretended that we know all the 
 varied means of Distribution during the long lapse of 
 years, or that we know how imperfect is the Geological 
 Record. Serious as these several objections are, in my 
 judgment they are by no means sufficient to overthrow the 
 theory of descent with subsequent modification. 
 
 Now let us turn to the other side of the argument. 
 Under domestication we see much variability, caused, or at 
 least excited, by changed conditions of life; but often in so 
 obscure a manner, that we are tempted to consider the varia¬ 
 tions as spontaneous. Variability is governed by many com- \ 
 plex laws, by correlated growth, compensation, the increased 
 use and disuse of parts, and the definite action of the sur- l 
 rounding conditions. There is much difficulty in ascer¬ 
 taining how largely our domestic productions have been 
 modified; but we may safely infer that the amount has ‘ 
 been large, and that modifications can be inherited for long 
 periods. As long as the conditions of life remain the same, 
 we have reason to believe that a modification, which has 
 already been inherited for many generations, may continue 
 to be inherited for an almost infinite number of generations. 
 On the other hand we have evidence that variability, when 
 it has once come into play, does not cease under domesti¬ 
 cation for a very long period ; nor do we know that it 
 ever ceases, for new varieties are still occasionally pro¬ 
 duced by our oldest domesticated productions. ^ 
 
 Variability is not actually caused by man ; ^ie only 
 unintentionally exposes organic beings to new conditions 
 of life and then nature acts on the organization and causes 
 it to vary. But man can and does select the variations 
 given to him by nature, and thus accumulates them in any 
 desired manner. He thus adapts animals and plants for 
 
484 
 
 RECAPITULA TION. 
 
 his own benefit or pleasure. He may do this methodically, 
 or he may do it unconsciously by preserving the individ¬ 
 uals most useful or pleasing to him without any intention 
 of altering the breed. It is certain that he can largely 
 influence the character of a breed by selecting, in each suc¬ 
 cessive generation, individual differences so slight as to be 
 inappreciable except by an educated eye. This unconscious 
 process of selection has been the great agency in the for¬ 
 mation of the most distinct and useful domestic breeds. 
 That many breeds produced by man have to a large extent 
 the character of natural species, is shown by the inextri¬ 
 cable doubts whether many of them are varieties or aborig¬ 
 inally distinct species. 
 
 There is no reason why the principles which have acted 
 so efficiently under domestication should not have acted 
 under nature. In the survival of favored individuals and 
 races, during the constantly recurrent Struggle for Exist¬ 
 ence, we see a powerful and ever-acting form of Selection. 
 The struggle for existence inevitably follows from the high 
 geometrical ratio of increase which is common to all 
 organic beings. This high rate of increase is proved by 
 calculation—by the rapid increase of many animals and 
 plants during a succession of peculiar seasons, and when 
 naturalized in new countries. More individuals are born 
 than can possibly survive. A grain in the balance may 
 determine which individuals shall live and which shall die 
 —which variety or species shall increase in number, and 
 which shall decrease; or finally become extinct. As the 
 individuals of the same species come in all respects into 
 the closest competition with each other, the struggle will 
 generally be most severe between them ; it will be almost 
 equally severe between the varieties of the same species, 
 and next in severity between the species of the same genus. 
 On the other hand the struggle will often be severe 
 between beings remote in the scale of nature. The 
 slightest advantage in certain individuals, at any age or 
 during any season, over those with which they come into 
 competition, or better adaptation in however slight a 
 degree to the surrounding physical conditions, will, in the 
 long run, turn the balance. 
 
 With animals having separated sexes, there will be in 
 most cases a struggle between the males for the possession 
 
RECAPITULA TION. 
 
 485 
 
 of the females. The most vigorous males, or those which 
 have most successfully struggled with their conditions of 
 life, will generally leave most progeny. But success will 
 often depend on the males having special weapons or means 
 of defense or charms; and a slight advantage will lead 
 to victory. 
 
 As geology plainly proclaims that each land has under¬ 
 gone great physical changes, we might have expected to 
 find that organic beings have varied under nature, in the 
 same way as they have varied under domestication. And 
 if there has been any variability under nature, it would be 
 an unaccountable fact if natural selection had not come 
 into play. It has often been asserted, but the assertion is 
 incapable of proof, that the amount of variation under 
 nature is a strictly limited quantity. Man, though acting 
 on external characters alone and often capriciously, can 
 produce within a short period a great result by adding up 
 mere individual differences in his domestic productions; 
 and every one admits that species present individual differ¬ 
 ences. But, beside such differences, all naturalists admit 
 that natural varieties exist, which are considered 
 sufficiently distinct to be worthy of record in systematic 
 works. No one has drawn any clear distinction between 
 individual differences and slight varieties; or between more 
 plainly marked varieties and subspecies and species. On 
 separate continents, and on different parts of the same con¬ 
 tinent, when divided by barriers of any kind, and on outlying 
 islands, what a multitude of forms exist, which some 
 experienced naturalists rank as varieties, others as geo¬ 
 graphical races or subspecies, and others as distinct, 
 though closely allied species! 
 
 If, then, animals and plants do vary, let it be ever so 
 slightly or slowly, why should not variations or individual 
 differences, which are in any way beneficial, be preserved 
 and accumulated through natural selection, or the survival of 
 the fittest? If man can by patience select variations useful 
 to him, why, under changing and complex conditions of 
 life, should not variations useful to nature's living products 
 often arise, and be preserved or selected? What limit can 
 be put to this power, acting during long ages and rigidly 
 scrutinizing the whole constitution, structure and habits 
 of each creature, favoring the good and rejecting the bad? 
 
486 
 
 RECAPITULA TION. 
 
 I can see no limit to this power, in slowly and beautifully 
 adapting each form to the most complex relations of life. 
 4 he theory of natural selection, even if we look no further 
 than this, seems to be in the highest degree probable. I 
 have already recapitulated, as fairly as I could, the opposed 
 difficulties and objections: now let us turn to the special 
 facts and arguments in favor of the theory. 
 
 On the view that species are only strongly marked and 
 permanent varieties, and that each species first existed as a 
 variety, we can see why it is that no line of demarcation 
 can be drawn between species, commonly supposed to have 
 been produced hy special acts of creation, and varieties 
 which are acknowledged to have been produced by second¬ 
 ary laws. On this same view we can understand how it 
 is that in a region where many species of a genus have been 
 produced, and where they now flourish, these same species 
 should present many varieties; for where the manufactory 
 of species has been active, we might expect, as a general 
 rule, to find it still in action; and this is the case if varie¬ 
 ties be incipient species. Moreover, the species of the 
 larger genera, which afford the greater number of varieties 
 or incipient species, retain to a certain degree the character 
 of varieties;, for they differ from each other by a less 
 amount of difference than do the species of smaller genera. 
 The closely allied species also of a larger genera apparently 
 have restricted ranges, and in their affinities they are 
 clustered in little groups round other species—in both 
 respects resembling varieties. These are strange relations 
 on the view that each species was independently created, 
 but are intelligible if each existed first as a variety. 
 
 As each species tends by its geometrical rate of repro¬ 
 duction to increase inordinately in number; and as the 
 modified descendants of each species will be enabled to 
 increase by as much as they become more diversified in 
 habits and structure, so as to be able to seize on many and 
 widely different places in the economy of nature, there 
 will be a constant tendency in natural selection to preserve 
 the.most divergent offspring of any one species. Hence, 
 during a long-continued course of modification, the 
 slight differences characteristic of varieties of the same 
 species, tend to be augmented into the greater differences 
 
R EC A PTTUL A TION. 
 
 487 
 
 characteristic of the species of the same genus. New and 
 improved varieties will inevitably supplant and exterminate 
 the older, less improved, and intermediate varieties; and 
 thus species are rendered to a large extent defined and dis- 
 ’ tinct objects. Dominant species belonging to the larger 
 groups within each class tend to give birth to new and 
 dominant forms; so that each large group tends to become 
 still larger, and at the same time more divergent in character. 
 But as all groups cannot thus go on increasing in size, for 
 the world would not hold them, the more dominant groups 
 beat the less dominant. This tendency in the large groups 
 to go on increasing in size and diverging in character, 
 together with the inevitable contingency of much extinc¬ 
 tion, explains the arrangement of all the forms of life in 
 groups subordinate to groups, all within a few great classes, 
 which has prevailed throughout all time. This grand fact 
 of the grouping of all organic beings under what is called 
 the Natural System, is utterly inexplicable on the theory 
 of creation. 
 
 As natural selection acts solely by accumulating slight, 
 successive, favorable variations, it can produce no great or 
 sudden modifications; it can act only by short and slow 
 steps. Hence, the canon of “ Natura non facit saltum,” 
 which every fresh addition to our knowledge tends to con¬ 
 firm, is on this theory intelligible. We can see why 
 throughout nature the same general end is gained by an 
 almost infinite diversity of means, for every peculiarity 
 when once acquired is long inherited, and structures 
 already modified in many different ways have to be adapted 
 for the same general purpose. We can, in short, see wh}^ 
 nature is prodigal in variety, though niggard in innovation. 
 But why this should be a law of nature if each species has 
 been independently created no man can explain. 
 
 Many other facts are, as it seems to me, explicable on 
 this theory. How strange it is that a bird, under the form 
 of a woodpecker, should prey on insects on the ground; 
 that upland geese, which rarely or never swim, would 
 possess webbed feet; that a thrush-like bird should dive 
 and feed on sub-aquatic insects; and that a petrel should 
 have the habits and structure fitting it for the life of an 
 qjiIrT and so in endless other cases. But on the view of 
 each species constantly trying to increase in number, with 
 
488 
 
 RECA PITITLA TION. 
 
 natural selection always ready to adapt the slowly varying 
 descendants of each to any unoccupied or ill-occupied place 
 m natuie, these facts cease to be strange, or migfht even 
 have been anticipated. 
 
 We can to a certain extent understand how it is that 
 there is so much beauty throughout nature; for this may 
 be largely attributed to the agency of selection. That 
 beauty, according to our sense of it, is not universal, must 
 be admitted by every one who will look at some venomous 
 snakes, at some fishes, and at certain hideous bats with a 
 distorted resemblance to the human face. Sexual selection 
 has given the most brilliant colors, elegant patterns, and 
 other ornaments to the males, and sometimes to both sexes 
 oi many birds, butterflies and other animals. With birds 
 it has often rendered the voice of the male musical to the 
 temale, as well as to our ears. Flowers and fruit have 
 been rendered conspicuous by brilliant colors in contrast 
 with the green foliage, in order that the flowers may be 
 easily seen, visited and fertilized by insects, and the seeds 
 disseminated by birds. How it comes that certain colors 
 sounds and forms should give pleasure to man and the 
 lower animals, that is, how the sense of beauty in its 
 simplest form was first acquired, we do not know any 
 
 more than how certain odors and flavors were first rendered 
 agreeable. 
 
 . As natu f al selection acts by competition, it adapts and 
 lmpioves the inhabitants of each country only in relation 
 to their co-inhabitants; so that we need feel no surprise at 
 the species of any one country, although on the ordinary 
 view supposed to have been created and specially adapted 
 tor that country, being beaten and supplanted by the 
 naturalized productions from another land. Nor ouo-ht 
 we to marvel if all the contrivances in nature be notfas 
 tar ns we can judge, absolutely perfect, as in the case even 
 ot the human eye; or if some of them be abhorrent to our 
 ideas of fitness. We need not marvel at the sting of the 
 bee when used against an enemy, causing the bee's own 
 death, at drones being produced in such great numbers 
 foi one single act, and being then slaughtered by their 
 sterile sisters; at the astonishing waste of pollen by our 
 fir-trees; at the instinctive hatred of the queen-bee for her 
 own fertile daughters; at ichneumonidse feeding within the 
 
RECAPITULATION. 
 
 489 
 
 living bodies of caterpillars; or at other such cases. The 
 wonder, indeed, is, on the theory of natural selection, that 
 more cases of the want of absolute perfection have not been 
 detect 3d. 
 
 The complex and little known laws governing the pro- 
 duction of varieties are the same, as far as we can judge, 
 with the laws which have governed the production of dis¬ 
 tinct species. In both cases physical conditions seem to 
 have produced some direct and definite effect, but how 
 much we cannot say. Thus, when varieties enter any new 
 station, they occasionally assume some of the characters 
 proper to the species of that station. With both varieties 
 and species, use and disuse seem to have produced a con¬ 
 siderable effect; for it is impossible to resist this conclusion 
 when we look, for instance, at the logger-headed duck, 
 which has wings incapable of flight, in nearly the same 
 condition as in the domestic duck; or when we look at 
 the burrowing tucu-tucu, which is occasionally blind, and 
 then at certain moles, which are habitually blind and have 
 their eyes covered with skin; or when we look at the blind 
 animals inhabiting the dark caves of America and Europe. 
 With varieties and species, correlated variation seems to 
 have played an important part, so that when one part has 
 been modified other parts have been necessarially modified. 
 With both varieties and species, reversions to long-lost 
 characters occasionally occur. How inexplicable on the 
 theory of creation is the occasional appearance of stripes 
 on the shoulders and legs of the several species of the 
 horse-genus and of their hybrids! How simply is this 
 fact explained if we believe that these species are all de¬ 
 scended from a striped progenitor, in the same manner as 
 the several domestic breeds of the pigeon are descended 
 from the blue and barred rock-pigeon! 
 
 On the ordinary view of each species having been inde¬ 
 pendently created, why should specific characters, or those 
 by which the species of the same genus differ from each 
 other, be more variable than generic characters in which 
 they all agree? Why, for instance, should the color of a 
 flower be more likely to vary in any one species of a genus, 
 if the other species possess differently colored flowers, than 
 if all possessed the same colored flowers? If species are 
 only well-marked varieties, of which the characters have 
 
490 
 
 RECAP IT IT LA TlON. 
 
 become in a high degree permanent, we can understand 
 this fact; for they have already varied since they branched 
 off from a common progenitor in certain characters, by 
 which they have come to be specifically distinct from each 
 other; therefore these same characters would be more 
 likely again to vary than the generic characters which have 
 been inherited without change for an immense period. 
 It is inexplicable on the theory of creation why a part de¬ 
 veloped in a very unusual manner in one species alone of a 
 genus, and therefore, as we may naturally infer, of great 
 importance to that species, should be eminently liable to 
 variation; but, on our view, this part has undergone, 
 since the several species branched off from a common pro¬ 
 genitor, an unusual amount of variability and modification, 
 and therefore we might expect the part generally to be 
 still variable. But a part may be developed in the most 
 unusual manner, like the wing of a bat, and yet not be 
 more variable than any other structure, if the part be com¬ 
 mon to many subordinate forms, that is, if it has been in¬ 
 herited for a very long period; for in this case it will have 
 been rendered constant by long-continued natural selection. 
 
 Glancing at instincts, marvelous as some are, they offer 
 no greater difficulty than do corporeal structures on the 
 theory of the natural selection of successive, slight, but 
 profitable modifications. We can thus understand why 
 nature moves by graduated steps in endowing different 
 animals of the same cla ss with their several instincts. I 
 have attempted to show how much light the principle of 
 gradation throws on the admirable architectural powers of 
 the hive-bee. Habit no doubt often comes into play in 
 modifying instincts; but it certainly is not indispensable, 
 as we see in the case of neuter insects, which leave no 
 progeny to inherit the effects of long-continued habit. 
 On the view of all the species of the same genus having 
 descended from a common parent, and having inherited 
 much in common, we can understand how it is that allied 
 species, when placed under widely different conditions of 
 life, yet follow nearly the same instincts; why the thrushes 
 of tropical and temperate South America, for instance, 
 line their nests with mud like our British species. On the 
 view of instincts having been slowly acquired through 
 natural selection, we need not marvel at some instincts 
 
RECAP ITU LA TION, 
 
 491 
 
 being not perfect and liable to mistakes, and at many 
 instincts causing other animals to suffer. 
 
 If species be only well-marked and permanent varieties, 
 we can at once see why their crossed offspring should 
 follow the same complex laws in their degrees and kinds of 
 resemblance to their parents—in being absorbed into each 
 other by successive crosses, and in other such points—as do 
 the crossed offspring of acknowledged varieties. This 
 similarity would be a strange fact, if species had been in¬ 
 dependently created and varieties had been produced 
 through secondary laws. 
 
 If we admit that the geological record is imperfect to an 
 extreme degree, then the facts, which the record does give, 
 strongly support the theory of descent with modification. 
 New species have come on the stage slowly and at succes¬ 
 sive intervals; and the amount of change after equal 
 intervals of time, is widely different in different groups. 
 The extinction of species and of whole groups of species, 
 which has played so conspicuous a part in the history of 
 the organic world, almost inevitably follows from the prin¬ 
 ciple of natural selection; for old forms are -supplanted by 
 new and improved forms. Neither single species nor 
 groups of species reappear when the chain of ordinary 
 generation is once broken. The gradual diffusion of dom¬ 
 inant forms, with the slow modification of their descend¬ 
 ants, causes the forms of life, after long intervals of time, 
 to appear as if they had changed simultaneously through¬ 
 out the world. The fact of the fossil remains of each 
 formation being in some degree intermediate in character 
 between the fossils in the formations above and below, is 
 simply explained by their intermediate position in the 
 chain of descent, the grand fact that all extinct beings 
 can be classed with all recent beings, naturally follows from 
 the living and the extinct being the offspring of common 
 parents. As species have generally diverged in character 
 during their long course of descent and modification, we 
 can understand why it is that the more ancient forms, or 
 early progenitors of each group, so often occupy a position 
 in some degree intermediate between existing groups. 
 Recent forms are generally looked upon as being, on the 
 whole, higher in the scale of organization than ancient 
 forms; and they must be higher, in so far as the later and 
 
m 
 
 RECAriTVLA TION. 
 
 more improved forms have conquered the older and less 
 improved forms in the struggle for life; they have also 
 generally had their organs more specialized for different 
 functions. This fact is perfectly compatible with numer¬ 
 ous beings still retaining simple and but little improved 
 structures, fitted for simple conditions of life; it is likewise 
 compatible with some forms having retrograded in organi¬ 
 zation, by having become at each stage of descent better 
 fitted for new and degraded habits of life. Lastly, the 
 wonderful law of the long endurance of allied forms on the 
 same continent—of marsupials in Australia, of edentata in 
 America, and other such cases—is intelligible, for within 
 the same country the existing and the extinct will be 
 closely allied by descent. 
 
 Looking to geographical distribution, if we admit that 
 there has been during the long course of ages much migra¬ 
 tion from one part of the world to another, owing to 
 former climatical and geographical changes and to the 
 many occasional and unknown means of dispersal, then 
 we can understand, on the theory of descent with modi¬ 
 fication, most of the great leading facts in distribution. 
 We can see why there should be so striking a parallelism 
 in the distribution of organic beings throughout space, and 
 in their geological succession throughout time; for in 
 both cases the beings have been connected by the bond 
 of ordinary generation, and the means of modification 
 have been the same. We see the full meaning of the 
 wonderful fact, which has struck every traveler, namely, 
 that on the same continent, under the most diverse con¬ 
 ditions, under heat and cold, on mountain and lowland, 
 on deserts and marshes, most of the inhabitants within 
 each great class are plainly related; for they are the descend¬ 
 ants of the same progenitors and early colonists. On this 
 same principle of former migration, combined in most 
 cases with modification, we can understand, by the aid of 
 the Glacial period, the identity of some few plants, and the 
 close alliance of many others, on the most distant mount¬ 
 ains, and in the northern and southern temperate zones; 
 and likewise the close alliance of some of the inhabitants 
 of the sea in the northern and southern temperate lati¬ 
 tudes, though separated by the whole intertropical ocean. 
 Although two countries may nresent physical conditions as 
 
RECAPITULA 770N. 
 
 493 
 
 closely similar as the same species ever require, we need 
 feel no surprise at their inhabitants being widely different, 
 if they have been for a long period completely sundered 
 from each other; for as the relation of organic to organ¬ 
 ism is the most important of all relations, an. as the two 
 countries will have received colonists at various periods 
 and in different proportions, from some other country or 
 from each other, the course of modification in the two 
 areas will inevitably have been different. 
 
 # On this view of migration, with subsequent modifica¬ 
 tion, we see why oceanic islands are inhabited by only few 
 species, but of these, why many are peculiar or endemic 
 forms. We clearly see why species belonging to those 
 groups of animals which cannot cross wide spaces of the 
 ocean, as frogs and terrestrial mammals, do not inhabit 
 oceanic islands; and why, on the other hand, new and 
 peculiar species of bats, animals which can traverse the 
 ocean, are often found on islands far distant from any con¬ 
 tinent. Such cases as the presence of peculiar species of 
 bats on oceanic islands and the absence of all other terres¬ 
 trial mammals, are facts utterly inexplicable on the theory 
 of independent acts of creation. 
 
 The existence of closely allied representative species in 
 any two areas, implies, on the theory of descent with 
 modification, that the same parent-forms formerly inhab¬ 
 ited both areas: and we almost invariably find that wher¬ 
 ever many closely allied species inhabit two areas, some 
 identical species are still common to both. Wherever 
 many closely allied yet distinct species occur, doubtful 
 forms and varieties belonging to the same groups likewise 
 occur. It is a rule of high generality that the inhabitants 
 of each area are related to the inhabitants of the nearest 
 source whence immigrants might have been derived. We 
 see this in the striking relation of nearly all the plants and 
 animals of the Galapagos Archipelago, of Juan Fernandez, 
 and of the other American islands, to the plants and 
 animals of the neighboring American mainland; and of 
 those of the Cape de Verde Archipelago, and of the other 
 African islands to the African mainland. It must be ad¬ 
 mitted that these facts receive no explanation on the 
 theory of creation. 
 
 The fact, as we have seen, that all past and present 
 
494 
 
 'RECAP 1TTJLA TION . 
 
 organic beings can be arranged within a few great classes, in 
 groups subordinate to groups, and with the extinct groups 
 often falling in between the recent groups, is intelligible 
 on the the of natural selection with its contingencies of 
 extinction and divergence of character. On these same 
 principles we see how it is that the mutual affinities 
 of the forms within each class are so complex and 
 circuitous. We see why certain characters are far more 
 serviceable than others for classification; why adaptive 
 characters, though of paramount importance to the beings 
 are of hardly any importance in classification; why charac¬ 
 ters derived from rudimentary parts, though of no service 
 to the beings, are often of high classifieatory value; and 
 why embryological characters are often the most valuable 
 of all. The real affinities of all organic beings, in contra¬ 
 distinction to their adaptive resemblances, are due to inher¬ 
 itance or community of descent. The Natural System is a 
 genealogical arrangement, with the acquired grades of dif¬ 
 ference, marked by the terms, varieties, species, genera, 
 families, etc.; and we have to discover the lines of descent 
 by the most permanent characters, whatever they may be, 
 and of however slight vital importance. 
 
 The similar framework of bones in the hand of a man, 
 wing of a bat, fin of the porpoise, and leg of the horse— 
 the same number of vertebrae forming the neck of the 
 giraffe and of the elephant—and innumerable other such 
 facts, at once explain themselves on the theory of descent 
 -with slow and slight successive modifications. The simi¬ 
 larity of pattern in the wing and in the leg of a bat, though 
 used for such different purpose—in the jaws and legs of a 
 crab—in the petals, stamens, and pistils of a flower, is like¬ 
 wise, to a large extent, intelligible on the view of the grad¬ 
 ual modification of parts or organs, which were aboriginally 
 alike in an early progenitor in each of these classes. On 
 the principle of successive variations not always superven¬ 
 ing at an early age, and being inherited at a corresponding 
 not early period of life, we clearly see why the embryos ox 
 mammals, birds, reptiles, and fishes should be so closely 
 similar, and so unlike the adult forms. We may cease 
 marveling at the embryo of an air-breathing mammal or 
 bird having branchial slits and arteries running in loops, 
 like those of a fish which has to breathe the air dissolved 
 in water by the aid of well-developed branchiae. 
 
CONCLUSION. 
 
 495 
 
 Disuse, aided sometimes by natural selection, will often 
 have reduced organs when rendered useless under changed 
 habits or conditions of life; and we can understand on this 
 view the meaning of rudimentary organs. But disuse and 
 selection will generally act on each creature, when it has 
 come to maturity and has to play its full part in the strug¬ 
 gle for existence, and will thus have little power on an 
 organ during early life; hence the organ will not be reduced 
 or rendered rudimentary at this early age. The calf, for 
 instance, has inherited teeth, which never cut through the 
 gums of the upper jaw, from an early procenitor having 
 well-developed teeth; and we may believe, that the teeth in 
 the mature animal were formerly reduced by disuse, owing 
 to the tongue and palate, or lips, having become excellently 
 fitted through natural selection to browse without their aid; 
 whereas in the calf, the teeth have been left unaffected, 
 and on the principle of inheritance at corresponding ages 
 have been inherited from a remote period to the present 
 day. On the view of each organism with all its separate 
 parts having been specially created, how utterly inexplica¬ 
 ble is it that organs bearing the plain stamp of inutility, 
 such as the teeth in the embryonic calf or the shriveled 
 wings under the soldered wing-covers of many beetles, 
 should so frequently occur. Nature may be said to have 
 taken pains to reveal her scheme of modification, by means 
 of rudimentary organs, of embryological and homologous 
 structures, but we are too blind to understand her 
 meaning. 
 
 I have now recapitulated the facts and considerations 
 which have thoroughly convinced me that species have been 
 modified, during a long course of descent. This has been 
 effected chiefly through the natural selection of numerous 
 successive, slight, favorable variations ; aided in an impor¬ 
 tant manner by the inherited effects of the use and disuse 
 of parts; and in an unimportant manner, that is, in relation 
 to adaptive structures, whether past or present, by the 
 direct action of external conditions, and by variations 
 which seem to us in our ignorance to arise spontaneously. 
 It appears that I formerly underrated the frequency and 
 value of these latter forms of variation, as leading to per¬ 
 manent modifications of structure independently of natural 
 selection. But as my conclusions have lately been much 
 
49C 
 
 CONCLUSION. 
 
 misrepresented, and it has been stated that I attribute the 
 modification of species exclusively to natural selection, I 
 may be permitted to remark that in the first edition of this 
 work, and subsequently, I placed in a most conspicuous 
 position—namely, at the close of the Introduction—the 
 following words : “ I am convinced that natural selection 
 has been the main but not the exclusive means of modi- 
 fication. I his has been of no avail. Great is the power 
 of steady misrepresentation ; but the history of science 
 shows that fortunately this power does not long endure. 
 
 It can hardly be supposed that a false theory would 
 explain, in so satisfactory a manner as does the theory 
 of natural selection, the several large classes of facts above 
 specified. It has recently been objected that this is an 
 unsafe method of arguing; but it is a method used in 
 judging of the common events of life, and has often been 
 used by the greatest natural philosophers. The undulatory 
 theory of light has thus been arrived at; and the belief iu 
 the revolution of the earth on its own axis was until lately 
 supported by hardly any direct evidence. It is no valid 
 objection that science as yet throws no light on the far 
 higher problem of the essence or origin of life. Who can 
 explain what is the essence of the attraction of gravity ? 
 No one now objects to following out the results consequent 
 on this unknown element of attraction; notwithstanding 
 that Leibnitz formerly accused Newton of introducing 
 “ occult qualities and miracles into philosophy.” 
 
 I see no good reasons why the views given in this volume 
 should shock the religious feelings of any one. It is satis¬ 
 factory, as showing how transient such impressions are, to 
 remember that the greatest discovery ever made by man, 
 namely, the law of the attraction of gravity, was also 
 attacked by Leibnitz, “as subversive of natural, and infer- 
 entially of revealed, religion.” A celebrated author and 
 divine has written to me that “ he has gradually learned to 
 see that it is just as noble a conception of the Deity to 
 believe that He created a few original forms capable of 
 self-developmerit into other and needful forms, as to 
 believe that He required a fresh act of creation to supply 
 the voids caused by the action of His laws.” 
 
 Why, it may be asked, until recently did nearly all the 
 most eminent living naturalists and geologists disbelieve iu 
 
CON CL US TON. 
 
 49? 
 
 Che mutability of species? It cannot be asserted that 
 organic beings in a state of nature are subject to no varia¬ 
 tion; it cannot be proved that the amount of variation in 
 the course of long ages is a limited quantity; no clear dis¬ 
 tinction has been, or can be, drawn between species and 
 well-marked varieties. It cannot be maintained that^ 
 species when intercrossed are invariably sterile and varieties 
 invariably fertile; or that sterility is a special endowment 
 and sign of creation. The belief that species were immut¬ 
 able productions was almost unavoidable as long as the 
 history of the world was thought to be of short duration; 
 and now that we have acquired some idea of the lapse of 
 time, we are too apt to assume, without proof, that the 
 geological record is so perfect that it would have afforded 
 ns plain evidence of the mutation of species, if they had 
 undergone mutation. 
 
 But the chief cause of our natural unwillingness to admit 
 that one species has given birth to other and distinct species, 
 is that we are always slow in admitting great changes of 
 which we do not see the steps. The difficulty is the same 
 as that felt by so many geologists, when Lyell first insisted 
 that long lines of inland cliffs had been formed, and great 
 valleys excavated, by the agencies which we still see at work. 
 The mind cannot possibly grasp the full meaning of the 
 term of even a million years; it cannot add up and perceive 
 the full effects of many slight variations, accumulated during 
 an almost infinite number of generations. 
 
 Although I am fully convinced of the truth of the views 
 given in this volume under the form of an abstract, I by no 
 means expect to convince experienced naturalists whose 
 minds are stocked with a multitude of facts all viewed, dur¬ 
 ing a long course of years, from a point of view directly op¬ 
 posite to mine. It is so easy to hide our ignorance under 
 such expressions as the “plan of creation,” “unity of de¬ 
 sign,” etc., and to think that we give an explanation when 
 we only restate a fact. Any one whose disposition leads 
 him to attach more weight to unexplained difficulties than 
 to the explanation of a certain number of facts will certainly 
 reject the theory. A few naturalists, endowed with much 
 flexibility of mind, and who have already begun to doubt 
 the immutability of species, may be influenced by this vol¬ 
 ume; but I look with confidence to the future, to young 
 
408 
 
 CON CL USIOff. 
 
 and rising naturalists, who will be able to view both sides 
 of the question with impartiality. Whoever is led to be¬ 
 lieve that species are mutable will do good service by con* 
 scientiously expressing his conviction ; for thus only can the 
 load of prejudice by which this subject is overwhelmed be 
 removed. 
 
 Several eminent naturalists have of late published their 
 belief that a multitude of reputed species in each genus are 
 not real species; but that other species are real, that is, 
 have been independently created. This seems to me a 
 strange conclusion to arrive at. They admit that a multi¬ 
 tude of forms, which till lately they themselves thought 
 were special creations, and which are still thus looked at 
 by the majority of naturalists, and which consequently have 
 all the external characteristic features of true species— 
 they admit that these have been produced by variation, 
 but they refuse to extend the same view to other and 
 slightly different forms. Nevertheless, they do not pretend 
 that they can define, or even conjecture, which are the 
 created forms of life, and which are those produced by 
 secondary laws. They admit variation as a vera causa in 
 one case, they arbitrarily reject it in another, without as¬ 
 signing any distinction in the two cases. The day will 
 come when this will be given as a curious illustration of 
 the blindness of preconceived opinion. These authors seem 
 no more startled at a miraculous act of creation than at an 
 ordinary birth. But do they really believe that at 
 innumerable periods in the earth’s history certain ele¬ 
 mental atoms have been commanded suddenly to flash into 
 living tissues? Do they believe that at each supposed act 
 of creation one individual or many were produced? Were 
 all the infinitely numerous kinds of animals and plants 
 created as eggs or seed, or as full grown? and in the case 
 of mammals, were they created bearing the false marks of 
 nourishment from the mother’s womb? Undoubtedly some 
 of these same questions cannot be answered by those who 
 believe in the appearance or creation of only a few forms 
 of life, or of some one form alone. It has been main¬ 
 tained by several authors that it is as easy to believe in the 
 creation of a million beings as of one; but Maupertuis’ 
 philosophical axiom of least action ” leads the mind more 
 willingly to admit the smaller number; and certainly we 
 
CONCLUSION. 
 
 499 
 
 ought not to believe that innumerable beings within each 
 great class have been created with plain, but deceptive, 
 marks of descent from a single parent. 
 
 As a record of a former state of things, I have retained 
 in the foregoing paragraphs, and elsewhere, several sen¬ 
 tences which imply that naturalists believe in the separate 
 creation of each species; and I have been much censured 
 for having thus expressed myself. But undoubtedly this 
 was the general belief when the first edition of the present 
 work appeared. I formerly spoke to very many natural¬ 
 ists on the subject of evolution, and never once met with 
 any sympathetic agreement. It is probable that some did 
 then believe in evolution, but they were either silent or ex¬ 
 pressed themselves so ambiguously that it was not easy to 
 understand their meaning. Now, things are wholly 
 changed, and almost every naturalist admits the great prim 
 ciple of evolution. There are, however, some who still 
 think that species have suddenly given birth, through quite 
 unexplained means, to new and totally different forms. 
 But, as I have attempted to show, weighty evidence can 
 be opposed to the admission of great and abrupt modifica¬ 
 tions. Under a scientific point of view, and as leading to 
 further investigation, but little advantage is gained by be= 
 lieving that new forms are suddenly developed in an inex¬ 
 plicable manner from old and widely different forms, over 
 the old belief in the creation of species from the dust of 
 the earth. 
 
 It may be asked how far I extend the doctrine of the 
 modification of species. The question is difficult to 
 answer, because the more distinct the forms are which we 
 consider, by so much the arguments in favor of com¬ 
 munity of descent become fewer in number and less ir 
 force. But some arguments of the greatest weight extend 
 very far. All the members of whole classes are connected 
 together by a chain of affinities, and all can be classed on 
 the same principle, in groups subordinate to groups. 
 Fossil remains sometimes tend to fill up very wide inter¬ 
 vals between existing orders. 
 
 Organs in a rudimentary condition plainly show that an 
 early progenitor had the organ in a fully developed condi¬ 
 tion, and this in some cases implies an enormous amount 
 of modification in the descendants. Throughout whole 
 
500 
 
 CONCLUSION. 
 
 classes various structures are formed on the same pattern, 
 and at a very early age the embryos closely resemble each 
 other. Therefore I cannot doubt that the theory of de¬ 
 scent with modification embraces all the members of the 
 same great class or kingdom, I believe that animals are 
 descended from at most only four or five progenitors, and 
 plants from an equal or lesser number. 
 
 Analogy would lead me one step further, namely, to the 
 belief that all animals and plants are descended from some 
 one prototype. But analogy may be a deceitful guide. 
 Nevertheless all living things have much in common, in 
 their chemical composition, their cellular structure, their 
 laws of growth, and. their liability to injurious influences. 
 We see this even in so trifling a fact as that the same 
 poison often similarly alfects plants and animals; or that 
 the poison secreted by the gall-fly produces monstrous 
 giowths on the wild rose or oak tree. With all organic 
 beings, excepting perhaps some of the very lowest, sexual 
 reproduction seems to be essentially similar. With all, as 
 far as is at present known, the germinal vesicle is the 
 same; so that all organisms start from a common origin,: 
 If we look even to the two main divisions—namely, to^the 
 animal and vegetable kingdoms—certain low forms are so 
 far intermediate in character that naturalists have disputed 
 to which kingdom they should be referred. As Professor 
 Asa Gray has remarked, “ the spores and other reproduc¬ 
 tive bodies of many of the lower algae may claim to have 
 flist a characteristically animal, and then an unequivocally 
 vegetable existence.” Therefore, on the principle of 
 natural selection with divergence of character, it does not 
 seem incredible that, from some such low and intermediate 
 foim, both animals and plants may have been developed" 
 and. if we .admit this, we must likewise admit that all the 
 oiganic beings which have ever lived on this earth may be 
 descended from some one primordial form. But this infer¬ 
 ence is chiefly grounded on analogy, and it is immaterial 
 whether or not it be accepted. No doubt it is possible, as 
 Mr. G. H. Lewes has urged, that at the first commence¬ 
 ment of life many different forms were evolved* but if so, 
 we may conclude that only a very few have left modified 
 descendants. Por, as I have recently remarked in regard 
 to the members of each great kingdom, such as the Verte- 
 
CONCLUSION. 
 
 50 J 
 
 brata, Articulata, etc., we have distinct evidence in their 
 embryological, homologous, and rudimentary structures, 
 that within each kingdom all the members are descended 
 from a single progenitor. 
 
 When the views advanced by me in this volume, and by 
 Mr. Wallace or when analogous views on the origin of 
 species are generally admitted, we can dimly foresee that 
 there will be a considerable revolution in natural history. 
 Systematists will be able to pursue their labors as at pres¬ 
 ent; but they will not be incessantly haunted by the 
 shadowy doubt whether this or that form be a true species. 
 This, I feel sure and I speak after experience, will be no 
 slight relief. The endless disputes whether or not some 
 fifty species of British brambles are good species will cease. 
 Systematists will have only to decide (not that this will be 
 easy) whether any form be sufficiently constant and distinct 
 from other forms, to be capable of definition; and if defina¬ 
 ble, whether the differences be sufficiently important to 
 deserve a specific name. This latter point will become a 
 far more essential consideration than it is at present; for 
 differences, however slight, between any two forms, if not 
 blended by intermediate gradations, are looked at by most 
 naturalists as sufficient to raise both forms to the rank of 
 species. 
 
 Hereafter we shall be compelled to acknowledge that 
 the only distinction between species and well-marked varie¬ 
 ties is, that the latter are known, or believed to be con¬ 
 nected at the present day by intermediate gradations, 
 whereas species were formerly thus connected. Hence, 
 without rejecting the consideration of the present existence 
 of intermediate gradations between any two forms, we 
 shall be led to weigh more carefully and to value higher 
 the actual amount of difference between them. It is quite 
 possible that forms now generally acknowledged to be 
 merely varieties may hereafter be thought worthy of 
 specific names; and in this case scientific and common lan¬ 
 guage will come into accordance. In short, we shall have 
 to treat species in the same manner as those naturalists 
 treat genera, who admit that genera are merely artificial 
 combinations made for convenience* This mav not be a 
 cheering prospect; but we shall at least be freed from the 
 vain search for the undiscovered and undjscoverable 
 essence of the term species® 
 
502 
 
 CONCLUSION. 
 
 The other and more general departments of natural his¬ 
 tory will rise greatly in interest. The terms used by nat¬ 
 uralists, of affinity, relationship, community of type, 
 paternity, morphology, adaptive characters, rudimentary 
 and aborted organs, etc., will cease to be metaphorical and 
 will have a plain signification. When we no longer look 
 at an organic being as a savage looks at a ship, as some¬ 
 thing wholly beyond his comprehension; when we regard 
 every production of nature as one which has had a long 
 history; when we contemplate every complex structure and 
 instinct as the summing up of many contrivances, each 
 useful to the possessor, in the same way as any great 
 mechanical invention is the summing up of the labor, the 
 experience, the reason, and even the blunders of numerous 
 workmen; when we thus view each organic being, how far 
 more interesting—I speak from experience—does the study 
 of natural history become! 
 
 A grand and almost untrodden field of inquiry will be 
 opened, on the causes and laws of variation, on correlation, 
 on the effects of use and disuse, on the direct action of 
 external conditions, and so forth. The study of domestic 
 productions will rise immensely in value. A new variety 
 raised by man will be a more important and interesting 
 subject for study than one more species added to the infin¬ 
 itude of already recorded species. Our classifications will 
 come to be, as far as they can be so made, genealogies; 
 and will then truly give what may be called the plan of 
 creation. The rules for classifying will no doubt become 
 simpler when we have a definite object in view. We pos¬ 
 sess no pedigree or armorial bearings; and we have to dis¬ 
 cover and trace the many diverging lines of descent in our 
 natural genealogies, by characters of any kind which have 
 long been inherited. Rudimentary organs will speak 
 infallibly with respect to the nature of long-lost structures. 
 Species and groups of species which are called aberrant, 
 and which may fancifully be called living fossils, will aid 
 us in forming a picture of the ancient forms of life. 
 Embryology will often reveal to us the structure, in some 
 degree obscured, of the prototypes of each great class. 
 
 When we can feel assured that all the individuals of the 
 same species, and all the closely allied species of most genera, 
 have, within a not very remote period descended from one 
 
 N 
 
CONCLUSION. 
 
 503 
 
 parent, and "have migrated from some one birth-place; anu 
 when we better know the many means of migration, then, 
 by the light which geology now throws, and will continue 
 to throw, on former changes of climate and of the level of 
 the land, we shall surely be enabled to trace in an admir¬ 
 able manner the former migrations of the inhabitants of 
 the whole world. Even at present, by comparing the 
 differences between the inhabitants of the sea on the 
 opposite sides of a continent, and the nature of the various 
 inhabitants on that continent in relation to their apparent 
 means of immigration, some light can be thrown on ancient 
 geography. 
 
 The noble science of geology loses glory from the extreme 
 imperfection of the record. The crust of the earth, with 
 its imbedded remains, must not be looked at as a well-filled 
 museum, but as a poor collection made at hazard and at 
 rare intervals. The accumulation of each great fossilifer- 
 ous formation will be recognized as having depended on 
 an unusual occurrence of favorable circumstances, and the 
 blank intervals between the successive stages as having 
 been of vast duration. But we shall be able to gauge with 
 some security the duration of these intervals by a compari¬ 
 son of the preceding and succeeding organic forms. We 
 must be cautious in attempting to correlate as strictly 
 contemporaneous two formations, which do not include 
 many identical species, by the general succession of the 
 forms of life. As species are produced and exterminated 
 by slowly acting and still existing causes, and not by 
 miraculous acts of creation; and as the most important of 
 all causes of organic change is one which is almost inde¬ 
 pendent of altered and perhaps suddenly altered physical 
 conditions, namely, the mutual relation of organism to 
 organism—the improvement of one organism entailing the 
 improvement or the extermination of others; it follows, 
 that the amount of organic change in the fossils of con¬ 
 secutive formations probably serves as a fair measure of 
 the relative, though not actual lapse of time. A number 
 of species, however, keeping in a body might remain for a 
 long period unchanged, while within the same period, 
 several of these species, by migrating into new countries 
 and coming into competition with foreign associates, might 
 become modified; so that we must not overrate the accuracy 
 of organic change as a measure of time. 
 
504 
 
 CONGL US ION. 
 
 In the future I see open fields for far more important 
 researches. Phychology will be securely based on the 
 foundation already well laid by Mr. Herbert Spencer, that 
 of the necessary acquirement of each mental power and 
 capacity by gradation. Much light will be thrown on the 
 origin of man and his history. 
 
 Authors of the highest eminence seem to be fully satisfied 
 with the view that each species has been independently 
 created. To my mind it accords better with what we 
 know of the laws impressed on matter by the Creator, that 
 the production and extinction of the past and present in¬ 
 habitants of the world should have been due to secondary 
 causes, like those determining the birth and death of the 
 individual. When I view all beings not as special creations, 
 but as the lineal descendants of some few beings which lived 
 long before the first bed of the Cambrian system was de¬ 
 posited, they seem to me to become ennobled. Judging from 
 the past, we may safely infer that not one living species will 
 transmit its unaltered likeness "to a distinct futurity. 
 And of the species now living very few will transmit 
 progeny of any kind to a far distant futurity; for the 
 manner in which all organic beings are grouped, shows 
 that the greater number of species in each genus, and all 
 the species in many genera, have left no descendants, 
 but have become utterly extinct. We can so far take a 
 prophetic glance into futurity as to foretell that it will be 
 the common and widely spread species, belonging to the 
 larger and dominant groups within each class, which will 
 ultimately prevail and procreate new and dominant species. 
 As all the living forms of life are the lineal descendants of 
 those which lived long before the Cambrian epoch, we may 
 feel certain that the ordinary succession by generation has 
 never once been broken, and that no cataclysm has deso¬ 
 lated the whole world. Hence, we may look with some 
 confidence to a secure future of great length. And as 
 natural selection works solely by and for the good of each 
 being, all corporeal and mental endowments will tend to 
 progress toward perfection. 
 
 It is interesting to contemplate a tangled bank, clothed 
 with many plants of many kinds, with birds singing on the 
 bushes, with various insects flitting about, and with worms 
 crawling through the damp earth, and to reflect that these 
 
CONCLUSION ; 
 
 505 
 
 elaborately constructed forms, so different from each other, 
 and dependent upon each other in so complex a manner, 
 have all been produced by laws acting around us. These 
 laws, taken in the largest sense, being Growth with repro¬ 
 duction; Inheritance which is almost implied by reproduc¬ 
 tion; Variability from the indirect and direct action of the 
 conditions of life, and from use and disuse: a Ratio of In¬ 
 crease so high as to lead to a Struggle for Life, and as a 
 consequence to Natural Selection, entailing Divergence of 
 Character and the Extinction of less improved forms. 
 Thus, from the war of nature, from famine and death, the 
 most exalted object which we are capable of conceiving, 
 namely, the production of the higher animals, directly fol¬ 
 lows. There is grandeur in this view of life, with its sev¬ 
 eral powers, having been originally breathed by the Creator 
 into a few forms or into one; and that, while this planet 
 has gone circling on according to the fixed law of gravity, 
 from so simple a beginning endless forms most beautiful 
 and most wonderful have been, and are being evolved. 
 
 
 M) /Y^CU^ 
 
 

 
GLOSSARY 
 
 OF THE 
 
 PRINCIPAL SCIENTIFIC TERMS USED IN THE 
 
 PRESENT VOLUME.* 
 
 Aberrant. —Forms or groups of animals or plants which, deviate 
 in important characters from their nearest allies, so as not to 
 be easily included in the same group with them, are said to 
 be aberrant. 
 
 Aberration (in Optics).—In the refraction of light by a convex lens 
 the rays passing through different parts of the lens are brought 
 to a focus at slightly different distances—this is called spherical 
 aberration; at the same time the colored rays are separated by 
 the prismatic action of the lens and likewise brought to a focus 
 at different distances—this is chromatic aberration. 
 
 Abnormal. —Contrary to the general rule. 
 
 Aborted. —An organ is said to be aborted, when its development 
 has been arrested at a very early stage. 
 
 Albinism. —Albinos are animals in which the usual coloring matters 
 characteristic of the species have not been produced in the 
 skin and its appendages. Albinism is the state of being an 
 Albino. 
 
 Alg^e.—A class of plants including the ordinary sea-weeds and the 
 filamentous fresh-water weeds. 
 
 Alternation of Generations. —This term is applied to a peculiar 
 mode of reproduction which prevails among many of the lower 
 animals, in which the egg produces a living form quite different 
 from its parent, but from which the parent-form is reproduced 
 by a process of budding, or by the division of the substance of 
 the first product of the egg. 
 
 Ammonites. — A group of fossil, spiral, chambered shells, allied to 
 the existing pearly Nautilus, but having the partitions between 
 the chambers waved in complicated patterns at their junction 
 with the outer wall of the shell. 
 
 *1 am indebted to the kindness of Mr. W. S. Dallas for this Glossary, 
 
 whieh has been given because several readers have complained to me that 
 
 gome of the terms used were unintelligible to them. Mr. Dallas has 
 
 endeavored to give the explanations of the terms in as popular a form as 
 
 possible. * 
 
508 
 
 GLOSSARY. 
 
 Analogy,— That resemblance of structures which depends upon 
 eimibinty of function, as in the wings of insects and birds 1 
 
 of eachother 168 *** Said t0 b ° be analo 9 OU8 > and to be analogues 
 
 ANmALeuLE — A minute animal: generally applied to those visible 
 only by the microscope. 
 
 Annelids —A class of worms in which the surface of the body 
 exhibits a more or less distinct division into rings or segments, 
 generally provided with appendages for locomotion and with 
 gills. It includes the ordinary marine worms, the earth-worms 
 and the leeches. ’ 
 
 ANT l I l N ±,T^ 0i . nted ) orga “ s a PP ended to the head in Insects, Crusta- 
 cea and Centipedes, and not belonging to the mouth. 
 
 j ie s ummi ts of the stamens of flowers, in which the 
 pollen or fertilizing dust is produced. 
 
 maUa^' Apla °entata or Aplacental Mammals. See Mam- 
 
 Archetypal.— Of or belonging to the Archetype, or ideal primitive 
 izefl 1 UP ° U Wblcb a11 tbe bein £ s of a group seem to be organ- 
 
 AHT ^ LATA ’~n gr r t n division of tbe Anim al Kingdom character- 
 tin^ gen D r ^ Uj by bavmg the surface of the body divided into 
 rings called segments, a greater or less number of which are 
 
 Centipedes) Wlt h Jointed le S s (such as Insects, Crustaceans and 
 
 Asymmetrical. —Having the two sides unlike. 
 
 Atrophied. Arrested in development at a very early stage. 
 
 B alanus. The genus including the common Acorn-shells which 
 li\ e in abundance on the rocks of the sea-coast. 
 
 B atr achians. A class of animals allied to the Reptiles, but under¬ 
 going a peculiar metamorphosis, in which the young animal is 
 
 !“n y d rwTs°) “ d “ es by « illS - 4*.“ 
 
 B °'Tdays7r L g?ave‘r SPOrted W ° CkS ° f 6t0ne generaUy imbedded 
 
 clas . s °i f ma !' in 1 e Mollusca > or soft-bodied animals, 
 
 a stalWvl W n b a blVal + V ; e sbeb ’ atta ched to submarine objects by 
 a stalk which passes through an aperture in one of the valves 
 
 ZriedZte Zuth £ed armS ’ bj ‘ he aCti0 “ ° f Which food ia 
 
 Branchial— Gills or organs for respiration in water 
 Branchial.— Pertaining to gills or branchi®. 
 
 CAMBmAN System.-A series of very ancient Paleozoic rocks 
 txjtween the Laurentian and the Silurian. Until recently thei 
 were regarded as the oldest fossiliferous rocks 
 
 CA ™<f he Dog ' fami1 ^ deluding the Dog, Wolf, Fox, Jackal, 
 Carapace.— The shell enveloping the anterior part of the body in 
 
GLOSSARY: 509 
 
 Crustaceans generally; applied also to tlie hard shelly pieces of 
 the Cirripedes. 
 
 Carboniferous. —This term is applied to the great formation which 
 includes, among other rocks, the coal-measures. It belongs to 
 the oldest, or Palaeozoic, system of formations. 
 
 Caudal —Of or belonging to the tail. 
 
 Cephalopods. —The highest class of the Mollusca, or soft-bodied 
 animals, characterized by having the mouth surrounded by a 
 greater or less number of fleshy arms or tentacles, which, m 
 most living species, are furnished with sucking-cups. ( Exam¬ 
 ples , Cuttle-fish, Nautilus.) 
 
 Cetacea. —An order of Mammalia, including the Whales, Dolphins, 
 etc., having the form of the body fish-like, the skin naked, and 
 only the fore limbs developed. 
 
 Chelonia. —An order of Reptiles including the Turtles, Tortoises, 
 etc. 
 
 Cirripedes. —An order of Crustaceans including the Barnacles and 
 Acorn-shells. Their young resemble those of many other Crus¬ 
 taceans in form; but when mature they are always attached to 
 other objects, either directly or by means of a stalk, and their 
 bodies are enclosed by a calcareous shell composed of several 
 pieces, two of which can open to give issue to a bunch of curled, 
 jointed tentacles, which represent the limbs. 
 
 Coccus.—The genus of Insects including the Cochineal. In these 
 the male is a minute, winged fly, and the female generally a 
 motionless, berry-like mass. 
 
 COCOON.—A case usually of silky material, in which insects are fre¬ 
 quently enveloped during the second or resting-stage (pupa) of 
 their existence. The term “cocoon-stage” is here used as 
 equivalent to “ pupa-stage.” 
 
 Cgelospermous. —A term applied to those fruits of the Umbelliferae 
 which have the seed hollowed on the inner face. 
 
 Coleoptera. —Beetles, an order of Insects, having a biting mouth 
 and the first pair of wings more or less horny, forming sheaths 
 for the second pair, and usually meeting in a straight line down 
 the middle of the back. 
 
 Column. —A peculiar organ in the flowers of Orchids, in winch 
 the stamens, style and stigma (or the reproductive parts) are 
 united. 
 
 Composite or Compositous Plants. —Plants in which the inflores¬ 
 cence consists of numerous small flowers (florets) brought 
 together into a dense head, the base of which is inclosed by a 
 common envelope. {Examples, the Daisy, Dandelions, etc.) 
 
 Conferva. —The filamentous weeds of fresh water. 
 
 Conglomerate. —A rock made up of fragments of rock or pebbles, 
 cemented together by some other material. 
 
 Corolla. — The second envelope of a flower usually composed of 
 colored, leaf-like organs (petals), which may be united by their ' 
 edges either in the basal part or throughout. 
 
 Correlation. —The normal coincidence of one phenomenon, charac¬ 
 ter, etc., with another. 
 
510 
 
 GLOSSARY. 
 
 Corymb.—A bunch of flowers in which those springing from the 
 lower part of the flower-stalks are supported on long stalks so as 
 to be nearly on a level with the upper ones. 
 
 Cotyledons. —The first or seed-leaves of plants. 
 
 Crustaceans. —A class of articulated animals, having the skin of 
 the body generally more or less hardened by the deposition of 
 calcareous matter, breathing by means of gills. (Examples, 
 Crab, Lobster, Shrimp, etc.) 
 
 Curculio. The old generic term for the Beetles known as Weevils, 
 characterized by their four jointed feet, and by the head being 
 produced into a sort of beak, upon the sides of which the 
 antennae are inserted. 
 
 Cutaneous.—O f or belonging to the skin. 
 
 Degradation.— The wearing down of land by the action of the sea 
 or of meteoric agencies. 
 
 Denudation.—T he wearing away of the surface of the land by 
 water. 
 
 Devonian System or Formation.—A series of Palaeozoic rocks, 
 including the Old Red Sandstone. 
 
 Dicotyledons or Dicotyledonous Plants.— A class of plants 
 characterized by having two seed-leaves, by the formation of new 
 wood between the bark and the old wood (exogenous growth) 
 and by the reticulation of the veins of the leaves. The parts of 
 the flowers are generally in multiples of five. 
 
 Differentiation. —The separation or discrimination of parts or 
 organs which in simpler forms of life are more or less united. 
 
 Dimorphic.— Having two distinct forms.—Dimorphism is the condi - 
 dition of the appearance of the same species under two dissimilar 
 forms. 
 
 Dioecious.— Having the organs of the sexes upon distinct indi¬ 
 viduals. 
 
 Diorite. —A peculiar form of Greenstone. 
 
 Dorsal.—O f or belonging to the back. 
 
 Edentata.— A peculiar order of Quadrupeds, characterized by the 
 absence of at least the middle incisor (front) teeth in both jaws. 
 {Examples, the Sloths and Armadillos.) 
 
 Elytra. —The hardened fore-wings of Beetles, serving as sheaths 
 for the membranous hind-wings, which constitute the true 
 organs of flight. 
 
 Embryo.— The young animal undergoing development within the 
 egg or womb. 
 
 Embryology. —The study of the development of the embryo. 
 
 Endemic. —Peculiar to a given locality. 
 
 Entomostraca. A division of the class Crustacea, having all the 
 segments of the body usually distinct, gills attached to the feet 
 or organs of the mouth, and the feet fringed with fine hairs. 
 They are generally of small size. 
 
 Eocene. The earliest of the three divisions of the Tertiarv epoch 
 of geologists. Rocks of this age contain a small proportion of 
 shells identical with species now living. 
 
GLOSSARY. 
 
 511 
 
 Ephemerous Insects. —Insects allied to the May-fly. 
 
 Fauna. —The totality of the animals naturally inhabiting a certain 
 country or region, or which have lived during a given geological 
 period. 
 
 Felidae. —The Cat-family. 
 
 Feral. —Having become wild from a state of cultivation or domesti¬ 
 cation. 
 
 Flora.—T he totality of the plants growing naturally in a country, 
 or during a given geological period. 
 
 Florets. —Flowers imperfectly developed in some respects, and col¬ 
 lected into a dense spike or head, as in the Grasses, the Dande¬ 
 lion, etc. 
 
 Fcetal. —Of or belonging to the foetus, or embryo in course of 
 development. 
 
 Foraminifera.—A class of animals of very low organization and 
 generally of small size, having a jelly-like body, from the sur¬ 
 face of which delicate filaments can be given off and retracted for 
 the prehension of external objects, and having a calcareous or 
 sandy shell, usually divided into chambers and perforated with 
 small apertures. 
 
 Fossiliferous. —Containing fossils. 
 
 Fossorial. —Having a faculty of digging. The Fossorial Hymen- 
 optera are a group of Wasp-like Insects, w r liich burrow in sandy 
 soil to make nests for their young. 
 
 Frenum (pi. Frena).—A small band or fold of skin. 
 
 Fungi (sing. Fungus). —A class of cellular plants, of which Mush¬ 
 rooms, Toadstools and Moulds, are familiar examples. 
 
 Furcula. —The forked bone formed by the union of the collar-bones 
 in many birds, such as the common Fowl. 
 
 Gallinaceous Birds. —An order of Birds of which the common 
 Fowl, Turkey and Pheasant, are well-known examples. 
 
 Gallus. —The genus of birds which includes the common Fowl. 
 
 Ganglion.—A swelling or knot from which nerves are given off as 
 from a center. 
 
 Ganoid Fishes. —Fishes covered with peculiar enameled bony 
 scales. Most of them are extinct. 
 
 Germinal Vesicle. —A minute vesicle in the eggs of animals, from 
 which the development of the embryo proceeds. 
 
 Glacial Period. —A period of great cold and of enormous extension 
 of ice upon the surface of the earth. It is believed that glacial 
 periods have occurred repeatedly during the geological history of 
 the earth, but the term is generally applied to the close of the 
 Tertiary epoch, when nearly the whole of Europe was subjected 
 to an arctic climate. 
 
 Gland. —An organ which secretes or separates some peculiar product 
 from the blood or sap of animals or plants. 
 
 Glottis. —The opening of the windpipe into the oesophagus or 
 gullet. 
 
 Gneiss.— A rock approaching granite in composition, but more or less 
 
512 
 
 GLOSSARY. 
 
 laminated, and really produced by the alteration of a sedimentary 
 deposit after its consolidation. 
 
 Grallatores. —The so-called Wading-birds (Storks, Cranes, Snipes, 
 etc.), which are generally furnished with long legs, bare of 
 feathers above the heel, and have no membranes between the 
 toes. 
 
 Granite.—A rock consisting essentially of crystals of felspar and 
 mica in a mass of quartz. 
 
 Habitat.—T he locality in which a plant or animal naturally lives. 
 
 Hemiptera. —An order or sub-order of Insects, characterized by the 
 possession of a jointed beak or rostrum, and by having the fore¬ 
 wings horny in the basal portion and membranous at the 
 extremity, where they cross each other. This group includes 
 the various species of Bugs. 
 
 Hermaphrodite. —Possessing the organs of both sexes. 
 
 Homology. —That relation between parts which results from their 
 development from corresponding embryonic parts, either in 
 different animals, as in the case of the arm of man. the fore leg 
 of a quadruped, and the wing of a bird; or in the same indi¬ 
 vidual, as in the case of the fore and hind legs in quadrupeds, 
 and the segments or rings and their appendages of which the 
 body of a worm, a centipede, etc., is composed. The latter is 
 called serial homology. The parts which stand in such a relation 
 to each other are said to be homologous, and one such part or organ 
 is called the homologue of the other. In different plants the 
 parts of the flower are homologous, and in general these parts 
 are regarded as homologous with leaves. 
 
 Homoptera.— An order or sub-order of Insects having (like the 
 Hemiptera) a jointed beak, but in which the fore-wings are 
 either wholly membranous or wholly leathery. The Cicada ?, 
 Frog-hoppers, and Aphides, are well-known examples. 
 
 Hybrid.—T he offspring of the union of two distinct species. 
 
 Hymenoptera.— An order of Insects possessing biting jaws and 
 usually four membranous wings in which there are a few veins. 
 Bees and Wasps are familiar examples of this group. 
 Hypertrophied.— Excessively developed. 
 
 Ichneumonid^e.—A family of Hymenopterous insects, the members 
 of which lay their eggs in the bodies or eggs of other insects. 
 
 Imago.— The perfect (generally winged) reproductive state of an 
 insect. 
 
 Indigens.—T he aboriginal animal or vegetable inhabitants of a 
 country or region. 
 
 Inflorescence. —The mode of arrangement of the flowers of plants. 
 
 Infusoria. A class of microscopic Animalcules, so called from their 
 having originally been observed in infusions of vegetable 
 matters. 1 hey consist of a gelatinous material inclosed in & 
 delicate membrane, the whole or part of which is furnished with 
 short vibrating hairs (called cilia), by means of which the 
 animalcules swim through the water or convey the minute parti¬ 
 cles of their food to the orifice of the mouth. 
 
GLOSSARY. 
 
 513 
 
 Insectivorous. —Feeding on Insects. 
 
 Invertebrata, or Invertebrate Animals. —Those animals which 
 do not possess a backbone or spinal column. 
 
 Lacunae. —Spaces left among the tissues in some of the lower 
 animals, and serving in place of vessels for the circulation of the 
 fluids of the body. 
 
 Lamellated. —Furnished with lamellae or little plates. 
 
 Larva (pi. Larvae). —The first condition of an insect at its issuing 
 from the egg, when it is usually in the form of a grub, cater¬ 
 pillar or maggot. 
 
 Larynx. —The upper part of the windpipe opening into the gullet 
 
 Laurentian. —A group of greatly altered and very ancient rocks! 
 which is greatly developed along the course of the St. Lawrence, 
 whence the name. It is in these that the earliest known traces 
 of organic bodies have been found. 
 
 Leguminos^e. —An order of plants represented by the common Peas 
 and Beans, having an irregular flower in which one petal stands 
 up like a wing, and the stamens and pistil are inclosed in a 
 sheath formed by two other petals. The fruit is a pod (or 
 legume). 
 
 Lemurid^e. —A group of four-handed animals, distinct from the 
 Monkeys, and approaching the Insectivorous Quadrupeds in some 
 of their characters and habits. Its members have the nostrils 
 curved or twisted, and a claw instead of a nail upon the first 
 finger of the hind hands. 
 
 Lepidoptera. —An order of Insects, characterized by the possession 
 of a spiral proboscis, and of four large more or less scaly wings. 
 It includes the well-known Butterflies and Moths. 
 
 Littoral. —Inhabiting the sea-shore. 
 
 Loess. —A marly deposit of recent (Post-Tertiary) date, which occu¬ 
 pies a great part of the valley of the Rhine. 
 
 Malacostraca. —The higher division of the Crustacea, including 
 the ordinary Crabs, Lobsters, Shrimps, etc., together with the 
 Wood-lice and Sand-hoppers. 
 
 Mammalia. —The highest class of animals, including the ordinary 
 hairy quadrupeds, the Whales and Man, and characterized by 
 the production of living young which are nourished after birth 
 by milk from the teats (Mamma, Mammary glands) of the 
 mother. A striking difference in embryonic development has 
 led to the division of this class into two great groups; in one of 
 these, when the embryo has attained a certain stage, a vascular 
 connection, called the placenta, is formed between the embryo 
 and the mother; in the other this is wanting, and the young are 
 produced in a very incomplete state. The former, including the 
 greater part of the class, are called Placental mammals; the 
 latter, or Aplacental mammals, include the Marsupials and M0110- 
 tremes ( Ornithorhynchus ). 
 
 Mammiferous. —Having mammae or teats (see Mammalia). 
 Mandibles ia Insects.—T he first or uppermost pair of jaws, which 
 
514 
 
 GLOSSARY, 
 
 are generally solid, liorny, biting organs. In Birds the term is 
 applied to both jaws witb their horny coverings. In Quadrupeds 
 the mandible is properly the lower jaw. 
 
 Marsupials. —An order of Mammalia in which the young are born 
 in a very incomplete state of development and carried by the 
 mother, while sucking, in a ventral pouch (marsupium), such as 
 the Kangaroos, Opossums, etc. (see Mammalia). 
 
 MaxillvE in Insects. —The second or lower pair of jaws, which are 
 composed of several joints and furnished with peculiar jointed 
 appendages called palpi or feelers. 
 
 Melanism. —The opposite of albinism; an undue development of 
 coloring material in the skin and its appendages. 
 
 Metamorphic Rocks. —Sedimentary rocks which have undergone 
 alteration, generally by the action of heat, subsequently to their 
 deposition and consolidation. 
 
 Mollusca. —One of the great divisions of the Animal Kingdom, 
 including those animals which have a soft body, usually furnished 
 with a shell, and in which the nervous ganglia, or centers, pre¬ 
 sent no definite general arrangement. They are generally 
 known under the denomination of “shell-fish;” the cuttle-fish, 
 and the common snails, whelks, oysters, mussels and cockles, 
 may serve as examples of them. 
 
 Monocotyledons, or Monocotyledonous Plants. —Plants in 
 which the seed sends up only a single seed-leaf (or cotyledon); 
 characterized by the absence of consecutive layers of wood in the 
 stem (endogenous growth), by the veins of the leaves being 
 generally straight, and by the parts of the flowers being gener¬ 
 ally in multiples of three. {Examples, Grasses, Lilies, Orchids, 
 Palms, etc.) 
 
 Moraines. —The accumulations of fragments of rock brought down 
 by glaciers. 
 
 Morphology. —The law of form or structure independent of func¬ 
 tion. 
 
 Mysis-stage. —A stage in the development of certain Crustaceans 
 (Prawns), in which they closely resemble the adults of a genus 
 {Mysis) belonging to a slightly lower group. 
 
 Nascent. —Commencing development. 
 
 Natatory. —Adapted for the purpose of swimming. 
 
 Nauplius-form. —The earliest stage in the development of many 
 Crustacea, especially belonging to the lower groups. In this 
 stage the animal has a short body, with indistinct indications ol 
 a division into segments, and three pairs of fringed limbs. This 
 form of the common fresh-water Cyclops was described as a dis¬ 
 tinct genus under the name of Nauplius. 
 
 Neuration.— The arrangement of the veins or nervures in the 
 wings of Insects. 
 
 Nictitating Membrane. —A semi-transparent membrane, which 
 can be drawn across the eye in Birds and Reptiles, either to 
 moderate the effects of a strong light or to sweep particles of 
 dust, etc., from the surface of the eye. 
 
GLOSSARY. 
 
 515 
 
 Neuters.— Imperfectly developed females of certain social insects 
 (such as Ants and Bees), which perform all the labors of the 
 community. Hence they are also called workers. 
 
 Ocelli. —The simple eyes or stemmata of Insects, usually situated 
 on the crown of the head between the great compound eyes. 
 
 (Esophagus.—T he gullet. 
 
 Oolitic.—A great series of secondary rocks, so called from the 
 texture of some of its members, which appear to be made up of 
 a mass of small egg-like calcareous bodies. 
 
 Operculum. —A calcareous plate employed by many Mollusca to 
 close the aperture of their shell. The opercular valves of Cirri- 
 pedes are those which close the aperture of the shell. 
 
 Orbit. —The bony cavity for the reception of the eye. 
 
 Organism.—A n organized being, whether plant or animal. 
 
 Orthospermous. —A term applied to those fruits of the Umbelliferse 
 which have the seed straight. 
 
 Osculant. —Forms or groups apparently intermediate between and 
 connecting other groups are said to be osculant. 
 
 Ova.—E ggs. 
 
 Ovarium or Ovary (in plants).—The lower part of the pistil or 
 female organ of the flower, containing the ovules or incipient 
 seeds; by growth after the other organs of the flower have 
 fallen, it usually becomes converted into the fruit. 
 
 Ovigerous. —Egg-bearing. 
 
 Ovules (of plants).—The seeds in the earliest condition. 
 
 Pachyderms. —A group of Mammalia, so called from their thick 
 skins, and including the Elephant, Rhinocerous, Hippopotamus, 
 etc. 
 
 Palaeozoic. —The oldest system of fossiliferous rocks. 
 
 Palpi. —Jointed appendages to some of the organs of the mouth in 
 Insects and Crustacea. 
 
 Papilionace^e. —Anorder of Plants (see Leguminos^e). —The flowers 
 of these plants are called papilionaceous, or butterfly-like, from 
 the fancied resemblance of the expanded superior petals to the 
 wings of a butterfly. 
 
 Parasite.—A n animal or plant living upon or in, and at the 
 expense of, another organism. 
 
 Parthenogenesis. —The production of living organisms from unim¬ 
 pregnated eggs or seeds. 
 
 Pedunculated. —Supported upon a stem or stalk. The peduncu¬ 
 lated oak has its acorns borne upon a footstool. 
 
 Peloria or Pelorism. —The appearance of regularity of structure 
 in the flowers of plants which normally bear irregular flowers. 
 
 Pelvis. —The bony arch to which the hind limbs of vertebrate 
 animals are articulated. 
 
 Petals. —The leaves of the corolla, or second circle of organs in a 
 flower. They are usually of delicate texture and brightly colored. 
 
 Phyllodineous. —Having flattened, leaf-like twigs or leaf-stalks 
 instead of true leaves. 
 
516 
 
 GLOSSARY. 
 
 1 tgment. I he coloring material produced generally in the super¬ 
 ficial parts of animals. The cells secreting it are called pigment - 
 
 C6LC8• 
 
 Pinnate.— Bearing leaflets on each side of a central stalk. 
 
 Pistils.— The female organs of a flower, which occupy a position in 
 the center of the other floral organs. The pistil is generally 
 divisible into the ovary or germen, the style and the stigma. 
 Placentalia, Placentata, or Placental‘Mammals.— See Mam 
 malia. 
 
 Plantigrades.— Quadrupeds which walk upon the whole sole c< 
 the foot, like the Bears. 
 
 Plastic. —Readily capable of change. 
 
 Pleistocene Period.— Ths latest portion of the Tertiary epoch. 
 
 1 lumule (in plants).—The minute bud between the seed-leaves of 
 newly-germinated plants. 
 
 Plutonic Rocks.—R ocks supposed to have been produced by 
 
 ^ igneous action in the depths of the earth. 
 
 Pollen.— The male element in flowering plants; usually a fine dust 
 produced by the anthers, which, by contact with the stigma 
 effects the fecundation of the seeds. This impregnation is 
 brought about by means of tubes ( pollen-tubes ) which issue from 
 the pollen-grains adhering to the stigma, and penetrate through 
 the tissues until they reach the ovary. 
 
 Polyandrous (flowers).—Flowers having many stamens. 
 
 Polygamous Plants.—P lants in which some flowers are unisexual 
 and others hermaphrodite. The unisexual (male and female) 
 flowers, may be on the same or on different plants. 
 
 Polymorphic. —Presenting many forms. 
 
 Polyzoary.— The common structure formed by the cells of the 
 Polyzoa, such as the well-known Sea-mats. 
 
 Prehensile.—C apable of grasping. 
 
 Prepotent. —Having a superiority of power. 
 
 Primaries.— The feathers forming the tip of the wing of a bird, and 
 inserted upon that part which represents the hand of man 
 
 Processes.— Projecting portions of bones, usually for the attach¬ 
 ment of muscles, ligaments, etc. 
 
 Propolis.— A resinous material collected by the Hive-Bees from the 
 opening buds of various trees. 
 
 Protean. —Exceedingly variable. 
 
 Protozoa.— The lowest great division of the Animal Kingdom, 
 lhese animals are composed of a gelatinous material and show 
 scarcely any trace of distinct organs. The Infusoria, Foramini- 
 fera and Sponges, with some other forms, belong to this division. 
 
 Pupa (pi. Pup^e) —The second stage in the development of an 
 Insect, from which it emerges in the perfect (winged) reproduc¬ 
 tive form. In most insects the pupal stage is passed in perfect 
 repose. The chrysalis is the pupal state of Butterflies. 
 
 Ramus.—O ne half of the lower iaw in the Mammalia. The portion 
 which rises to articulate with the skull is called the ascendina 
 ramus. * 
 
GLOSSARY. 
 
 517 
 
 Radicle. —The minute root of an embryo plant. 
 
 Range. —The extent of country over which a plant or animal is 
 naturally spread. Range in time expresses the distribution of a 
 species or group through the fossiliferous beds of the earth’s 
 crust. 
 
 Retina. —The delicate inner coat of the eye, formed by nervous 
 filaments spreading from the optic nerve and serving for the 
 perception of the impressions produced by light. 
 
 Retrogression. —Backward development. When an animal, as it 
 approaches maturity, becomes less perfectly organized than 
 might be expected from its early stages and known relationships, 
 it is said to undergo a retrograde development or metamorphosis. 
 
 Rhizopods.—A class of lowly organized animals (Protozoa), having a 
 gelatinous body, the surface of which can be protruded in the 
 form of root-like processes or filaments, which serve for locomo¬ 
 tion and the prehension of food. The most important order is 
 that of the Foraminifera. 
 
 Rodents. —The gnawing Mammalia, such as the Rats, Rabbits and 
 Squirrels. They are especially characterized by the possession 
 of a single pair of chisel-like cutting teeth in each jaw, between 
 which and the grinding teeth there is a great gap. 
 
 Rubus.—T he Bramble Genus. 
 
 Rudimentary. —Very imperfectly developed. 
 
 Ruminants. —The group of Quadrupeds which ruminate or chew the 
 cud, such as oxen, sheep and deer. They have divided hoofs, 
 and are destitute of front teeth in the upper jaw. 
 
 Sacral. —Belonging to the sacrum, or the bone composed usually of 
 two or more united vertebrae to which the sides of the pelvis in 
 vertebrate animals are attached. 
 
 Sarcode. —The gelatinous material of which the bodies of the lowest 
 animals (Protozoa) are composed. 
 
 Scutell^e. —The horny plates with which the feet of birds are 
 generally more or less covered, especially in front. 
 
 Sedimentary Formations. —Rocks deposited as sediments from 
 water. 
 
 Segments. —The tranverse rings of which the body of an articulate 
 animal or Annelid is composed. 
 
 Sepals. —The leaves or segments of the calyx, or outermost envelope 
 of an ordinary flower. They are usually green, but sometimes 
 brightly colored. 
 
 Serratures. —Teeth like those of a saw. 
 
 Sessile. —Not supported on a stem or footstalk. 
 
 Silurian System.—A very ancient system of fossiliferous rocks 
 belonging to the earlier part of the Palaeozoic series. 
 
 Specialization. —The setting apart of a particular organ for the 
 performance of a particular function. 
 
 Spinal Chord. —The central portion of the nervous system in the 
 Vertebrata. which descends from the brain through the arches 
 of the vertebrae, and gives off nearly all the nerves to the various 
 organs of the body. 
 
 ( 
 
518 
 
 GLOSSARY. 
 
 Stamens. —The male organs of flowering plants, standing in a circle 
 within the petals. They usually consist of a filament and an 
 anther, the anther being the essential part in which the pollen, 
 or fecundating dust, is formed. 
 
 Sternum.— The breast-bone. 
 
 Stigma. —The apical portion of the pistil in flowering plants. 
 
 Stipules. —Small leafy organs placed at the base of the footstalks of 
 the leaves in many plants. 
 
 Style.— The middle portion of the perfect pistil, which rises like a 
 column from the ovary and supports the stigma at its summit. 
 
 Subcutaneous.— Situated beneath the skin. 
 
 Suctorial.— Adapted for sucking. 
 
 Sutures (in the skull).—The lines of junction of the bones of which 
 the skull is composed. 
 
 Tarsus (pi. Tarsi).— The jointed feet of articulate animals, such as 
 Insects. 
 
 Teleostean Fishes.— Fishes of the kind familiar to us in the 
 present day, having the skeleton usually completely ossified and 
 the scales horny. 
 
 Tentacula or Tentacles.— Delicate fleshy organs of prehension 
 or touch possessed by many of the lower animals. 
 
 Tertiary. —The latest geological epoch, immediately preceeding the 
 establishment of the present order of things. 
 
 Trachea. —The windpipe or passage for the admission of air to the 
 lungs. 
 
 Tridactyle.— Three-fingered, or composed of three movable parts 
 attached to a common base. 
 
 Trilobites. —A peculiar group of extinct Crustaceans, somewhat 
 resembling the Wood-lice in external form, and, like some of 
 them, capable of rolling themselves up into a ball. Their 
 remains are found only in the Palseozoic rocks, and most abund¬ 
 antly in those of Silurian age. 
 
 Trimorphic. —Presenting three distinct forms. 
 
 Umbelliferae. —An order of plants in which the flowers, which 
 contain five stamens and a pistil with two styles, are supported 
 upon footstalks which spring from the top of the flower stem 
 and spread out like the wires of an umbrella, so as to bring all 
 the flowers in the same head (umbel) nearly to the same level. 
 ( Examples , Parsley and Carrot.) 
 
 Ungulata. —Hoofed quadrupeds. 
 
 Unicellular.— Consisting of a single cell. 
 
 Vascular. —Containing blood-vessels. 
 
 Vermiform.— Like a worm. 
 
 Vertebrata; or Vertebrate Animals, — The highest division of 
 the animal kingdom, so called from the presence in most cases of 
 a backbone composed of numerous joints or vertebrce, which con¬ 
 stitutes the center of the skeleton and at the same time supports 
 and protects the central parts of the nervous system. 
 
GLOJSSAHY. 
 
 519 
 
 Whorls.— The circles or spiral lines in which the parts of plants are 
 arranged upon the axis of growth. 
 
 Workers. —See Neuters. 
 
 Zoea-stage. —The earliest stage in the development of many of the 
 higher Crustacea, so called from the name of Zoea applied to 
 these young animals when they were supposed to constitute a 
 peculiar genus. 
 
 Zooids. —In many of the lower animals (such as the Corals, Medusae, 
 etc.) reproduction takes place in two ways, namely, by means of 
 eggs and by a process of budding with or without separation 
 from the parent of the product of the latter, which is often very 
 di fferent from that of the egg. The individuality of the species 
 is represented by the whole of the form produced between two 
 sexual reproductions; and these forms, which are apparently 
 individual animals, have been called zooids. 
 
» ,1 
 
 i 
 
 i 
 
 
INDEX 
 
 Abberant groups, 447. 
 
 Abyssinia, plants of, 401. 
 
 Acclimatization, 133. 
 
 Adoxa, 205. 
 
 Affinities of extinct species, 356. 
 
 -of organic beings, 445. 
 
 Agassiz, on Amblyopsis, 133. 
 
 -, on groups of species sud¬ 
 denly appearing, 342. 
 
 -, on prophetic forms, 357. 
 
 -, on embryological succession, 
 
 366. 
 
 -, on the Glacial period, 389. 
 
 -, on embryological charac¬ 
 ters, 434. 
 
 -, on the latest tertiary forms, 
 
 329. 
 
 •-, on parallelism of embryo- 
 
 logical development and geo¬ 
 logical succession, 466. 
 
 -, Alex., on pedicellariae, 226. 
 
 Algae of New Zealand, 399. 
 
 Alligators, males, fighting, 81. 
 
 Alternate generations, 456. 
 
 Amblyopsis, blind fish, 133. 
 
 America, North, productions al¬ 
 lied to those of Europe, 393. 
 
 —=—,-, bowlders and glaciers 
 
 of, 395. 
 
 .-, South, no modern forma¬ 
 
 tions on west coast, 322. 
 
 Ammonites, sudden extinction of, 
 351. 
 
 Anagallis, sterility of, 279. 
 
 Analogy of variations, 150. 
 
 Andaman Islands inhabited by a 
 toad, 413. 
 
 Ancylus, 407. 
 
 Animals, not domesticated from 
 being variable, 15. 
 
 -, domestic, descended from 
 
 several stocks, 16. 
 
 -,-, acclimatization of, 134. 
 
 Animals of Australia, 106. 
 
 -with thicker fur in cold cli¬ 
 mates, 127.. 
 
 -, blind, in caves, 131. 
 
 -extinct, of Australia, 367. 
 
 Anomma, 273. 
 
 Antarctic islands, ancient flora of, 
 419. 
 
 Antechinus, 440. 
 
 Ants attending aphides, 245. 
 
 -, slave-making instinct, 255. 
 
 -, neuters, structure of, 272. 
 
 Apes, not having acquired intel¬ 
 lectual powers, 214. 
 
 Aphides, attended by ants, 245. 
 Aphis, development of, 460. 
 Apteryx, 166. 
 
 Arab horses, 30. 
 
 Aralo-Caspian Sea, 367. 
 Archeopteryx, 335. 
 
 Archiac, M. de, on the succession 
 of species, 353. 
 
 Artichoke, Jerusalem, 135, 
 Ascension, plants of, 410. 
 Asclepias, pollen of, 180. 
 Asparagus, 383. 
 
 Aspicarpa, 433. 
 
 Asses, striped, 152. 
 
 -, improved by selection, 36. 
 
 Ateuchus, 129. 
 
 Aucapitaine, on land-shells, 417. 
 Audubon, on habits of frigate- 
 bird, 169. 
 
522 
 
 INDEX. 
 
 Audubon, on variation in birds' 
 nests, 246. 
 
 -, on heron eating seeds, 409. 
 
 Australia, animals of, 106. 
 
 «-, dogs of, 249. 
 
 •-, extinct animals of, 367. 
 
 -, European plants in, 398, 
 
 --, glaciers of, 395. 
 
 Azara, on hies destroying cattle, 
 67. 
 
 Azores, flora of, 388. 
 
 Babington, Mr., on British plants, 
 44 
 
 Baer, Von, standard of Highness, 
 116. 
 
 -, comparison of bee and fish, 
 
 364. 
 
 -, embryonic similarity of the 
 
 Vertebrata, 458. 
 
 Baker, Sir S., on the giraffe, 211. 
 Balancement of growth, 139. 
 Baleen, 216. 
 
 Barberry, flowers of, 91. 
 
 Barrande, M., on Silurian colo 
 nies, 344. 
 
 -, on the succession of species, 
 
 354. 
 
 -, on parallelism of palaeozoic 
 
 formations, 356. 
 
 -, on affinities of ancient 
 
 species, 357. 
 
 Barriers, importance of, 373. 
 Bates, Mr., on mimetic butterflies, 
 443, 444. 
 
 Batrachians on islands, 413. 
 
 Bats, how structure acquired, 166. 
 
 -, distribution of, 415. 
 
 Bear, catching water-insects, 168. 
 Beauty, how acquired, 189, 488. 
 Bee, sting of, 194. 
 
 --, queen, killing rivals, 194. 
 
 -, Australian, extermination 
 
 of, 70. 
 
 Bees, fertilizing flowers, 68. 
 
 --, hive, not sucking the red 
 
 clover, 88. 
 
 -, hive, cell making instinct, 
 
 259. 
 
 -, Ligurian, 88. 
 
 -, variation in habits, 246. 
 
 Bees, parasitic, 255. 
 
 -, humble, cells of, 260. 
 
 Beetles, wingless, in Madeira, 130. 
 
 -with deficient tarsi, 129. 
 
 Bentham, Mr., on British plants, 
 44. 
 
 -, on classification, 435. 
 
 Berkeley, Mr., on seeds in salt 
 water, 383. 
 
 Bermuda, birds of, 412. 
 
 Birds acquiring fear, 246. 
 
 -, beauty of, 191. 
 
 -- annually cross the Atlantic, 
 
 389. 
 
 -, color of, on continents, 127. 
 
 -, footsteps, and remains of, 
 
 in secondary rocks, 335. 
 
 -, fossil, in caves of Brazil, 
 
 367. 
 
 -, of Madeira, Burmuda and 
 
 Galapagos, 412, 413. 
 
 -, song of males, 82. 
 
 ■-, transporting seeds, 387. 
 
 -, waders, 408. 
 
 -, wingless, 128, 166. 
 
 Bizcacha, 376. 
 
 -, affinities of, 447. 
 
 Bladder for swimming, in fish, 
 175. 
 
 Blindness of cave animals, 130. 
 Blyth, Mr., on distinctness of 
 Indian cattle, 16. 
 
 -, on striped hemionus, 138. 
 
 -, on crossed geese, 284. 
 
 Borrow, Mr., on the Spanish 
 pointer, 30. 
 
 Borv St. Vincent, on Batrachians, 
 413. 
 
 Bosquet, M., on fossil Chtha- 
 malus, 336. 
 
 Bowlders, erratic, on the Azores, 
 388. 
 
 Branchiae, 176, 177. 
 
 -, of crustaceans, 181. 
 
 -, Braun, Prof., on the seeds 
 
 of Fumariaceae, 206. 
 
 Brent, Mr., on house-tumblers, 
 248. 
 
 Britain, mammals of, 415, 
 
 Broca, Prof., on Natural Selec- 
 I tion, 201. 
 
INDEX. 
 
 Bronn, Prof., on duration of 
 specific forms, 326. 
 
 -, various objections by, 201. 
 
 Brown, Robert, on classification, 
 432. 
 
 -, Sequard, on inherited muti¬ 
 lations, 129. 
 
 Busk, Mr., on the Polyzoa, 228. 
 
 Butterflies, mimetic, 443, 444, 
 445. 
 
 Buzareingues, on sterility of varie¬ 
 ties, 304. 
 
 Cabbage, varieties of, crossed, 9. 
 
 Calceolaria, 282. 
 
 Canary-birds, sterility of hybrids, 
 282. 
 
 Cape de Verde Islands, produc¬ 
 tions of, 418. 
 
 --, plants of, on mountains, 
 
 398. 
 
 Cape of Good Hope, plants of, 
 121, 410. 
 
 Carpenter, Dr., on foraminifera, 
 364. 
 
 Carthamus, 205. 
 
 Catasetum, 184, 438. 
 
 Cats, with blue eyes, deaf, 10. 
 
 -, variation in habits of, 247. 
 
 - curling tail when going to 
 
 spring, 193. 
 
 Cattle destroying fir-trees, 67. 
 
 - destroyed by flies in Para¬ 
 guay, 67. 
 
 -breeds of, locally extinct, 
 
 101 . 
 
 -, fertility of Indian and Euro¬ 
 pean breeds, 283. 
 
 -, Indian, 16, 283. 
 
 Cave, inhabitants of, blind, 130. 
 
 Cecidomyia, 456. 
 
 Celts, proving antiquity of man, 
 16. 
 
 Centers of Creation, 378. 
 
 Cephalopodae, structures of eyes, 
 180. 
 
 -, development of, 460. 
 
 Cercopithecus, tail of, 223. 
 
 Ceroxylus laceratus, 216. 
 
 Cervulus, 283. 
 
 Cetacea, teeth and hair, 137. 
 
 523 
 
 Cetacea, development of the 
 whalebone, 216. 
 
 Cetaceans, 216. 
 
 Ceylon, plants of, 399. 
 
 Chalk formation, 352. 
 
 Characters, divergence of, 101. 
 
 -, sexual, variable, 141, 146. 
 
 -, adaptive or analogical, 440. 
 
 Charlock, 71. 
 
 Checks to increase, 63. 
 
 -, mutual, 65. 
 
 Chelae of Crustaceans, 228. 
 Chickens, instinctive tameness of, 
 
 , 249. 
 
 Chironomus, its asexual reproduc¬ 
 tion, 456. 
 
 Chthamalinae, 320. 
 
 Chthamalus, cretacean species of, 
 336. 
 
 Circumstances favorable to selec¬ 
 tion of domestic products, 35, 
 
 —--to natural selection, 94. 
 
 Cirripedes capable of crossing, 93. 
 
 -, carapace aborted, 140. 
 
 -, their ovigerous frena, 177. 
 
 -, fossil, 336. 
 
 -, larvae of, 458. 
 
 Claparede, Prof., on the hair- 
 claspers of the Acaridae, 182. 
 Clarke, Rev. W. B., on old 
 glaciers in Australia, 396. 
 Classification, 428. 
 
 Clift, Mr., on the succession of 
 types, 367. 
 
 Climate, effects of, in checking 
 increase of beings, 64. 
 
 -, adaptation of, to organisms* 
 
 133. 
 
 Climbing plants, 175. 
 
 -, development of, 231. 
 
 Clover visited by bees, 88. 
 
 Cobites, intestine of, 175, 
 Cockroach, 71. 
 
 Collections, palaeontological, poor, 
 319. 
 
 Color, influenced by climate, 127. 
 
 -, in relation to attack by flies, 
 
 , 189. 
 
 Columba livia, parent of domes¬ 
 tic pigeons, 20. 
 
 Colymbetes, 407. 
 
524 
 
 INDEX. 
 
 Compensation of growth, 139. 
 
 Composite, flowers and seeds of, 
 137. 
 
 — — , outer and inner florets of, 
 205. 
 
 --, male flowers of, 469. 
 
 Conclusion, general, 495. 
 
 Conditions, slight changes in, 
 favorable to fertility, 296. 
 
 Convergence of genera, 120. 
 
 Coot, 169. 
 
 Cope, Prof., on the acceleration 
 or retardation of the period of 
 reproduction, 177. 
 
 Coral-islands, seeds drifted to, 
 385. 
 
 -reefs, indicating movements 
 
 of earth, 385. 
 
 Corn crake, 170. 
 
 Correlated variation in domestic 
 productions, 10. 
 
 Coryanthes, 183. 
 
 Creation, single centers of, 378. 
 
 Crinum, 281. 
 
 Croll, Mr., on subaerial denuda¬ 
 tion, 316, 318. 
 
 -, on the age of our oldest for¬ 
 mations, 338. 
 
 -, on alternate Glacial periods 
 
 in the North and South, 396. 
 
 Crosses, reciprocal, 287. 
 
 Crossing of domestic animals, 
 importance in altering breeds, 
 18. 
 
 -, advantages of, 90. 
 
 -, unfavorable to selection, 94. 
 
 Criiger, Dr., on Coryanthes, 183. 
 
 Crustacea of New Zealand, 399. 
 
 Crustacean, blind, 131. 
 
 -air-breathers, 181. 
 
 Crustaceans, their chelae, 228. 
 
 Cryptocerus, 272. 
 
 Ctenomys, blind, 130. 
 
 Cuckoo, instinct of, 242, 250. 
 
 Cunningham, Mr., on the flight 
 of the logger-headed duck, 128. 
 
 Currants, grafts of, 290. 
 
 Currents of sea, rate of, 384. 
 
 Cuvier, on conditions of existence, 
 242. 
 
 -, Fred., on instinct, 242. 
 
 Cuvier, on fossil monkeys, 335. 
 Cyclostoma, resisting salt water, 
 417. 
 
 Dana, Prof., on blind cave-ani¬ 
 mals, 132. 
 
 -, on relations of crustaceans 
 
 of Japan, 395. 
 
 -, on crustaceans of New 
 
 Zealand, 399. 
 
 Dawson, Dr., on eozoon, 339. 
 
 De Candolle, Aug. Pyr., on strug¬ 
 gle for existence, 58. 
 
 -, on umbelliferae, 138. 
 
 -, on general affinities, 447. 
 
 De Candolle, Alph., on the varia¬ 
 bility of oaks, 47. 
 
 -, on low plants, widely dis¬ 
 persed, 423. 
 
 -, on widely-ranging plants 
 
 being variable, 50. 
 
 -, on naturalization, 105. 
 
 -, on winged seeds, 139. 
 
 -, on Alpine species suddenly 
 
 becoming rare, 160. 
 
 -, on distribution of plants 
 
 with large seeds, 385. 
 
 -, on vegetation of Australia, 
 
 401. 
 
 -, on fresh-water plants, 407. 
 
 -, on insular plants, 410. J 
 
 Degradation of rocks, 315. 
 Denudation, rate of, 316. 
 
 -of oldest rocks, 339. 
 
 -of granite areas, 324. 
 
 Development of ancient forms, 
 363. 
 
 Devonian system, 361. 
 
 Dianthus, fertility of crosses, 285 
 Dimorphism in plants, 42, 297. 
 Dirt on feet of birds, 387. 
 Dispersal, means of, 381. 
 
 -during Glacial period, 389. 
 
 Distribution, geographical, 373. 
 
 -, means of, 381. 
 
 Disuse, effect of, under nature, 
 128. 
 
 Diversification of means for same 
 general purpose, 182. 
 
 Division, physiological, of labor 
 105. 
 
INDEX. 525 
 
 Divergence of character, 101. 
 
 Dog, resemblance of jaw to that 
 of the Thylacinus, 441. 
 
 Dogs, hairless, with imperfect 
 teeth, 11. 
 
 --descended from several wild 
 
 stocks, 17. 
 
 -, domestic instincts of, 248. 
 
 -, inherited civilization of, 
 
 248. 
 
 -, fertility of breeds together, 
 
 283. 
 
 -,-of crosses, 802. 
 
 -, proportions of body in dif¬ 
 ferent breeds, when young, 
 461. 
 
 Domestication, variation under, 6. 
 Double flowers, 271. 
 
 Downing, Mr , on fmit-trees in 
 America, 78. 
 
 Dragon flies, intestines of, 175. 
 Drift-timber, 885. 
 
 Driver-ant, 274. 
 
 Drones killed by other bees, 194. 
 Duck, domestic, wings of, re¬ 
 duced, 10. 
 
 -, beak of, 217. 
 
 -, logger headed, 166. 
 
 Duckweed, 407. 
 
 Dugong, affinities of, 481. 
 Dung-beetles with deficient tarsi, 
 129. 
 
 Dytiscus, 407. 
 
 Earl, Mr. W., on the Malay 
 Archipelago. 415. 
 
 Ears, drooping, in domestic ani¬ 
 mals, 10. 
 
 -, rudimentary, 472. 
 
 Earth, seeds in roots of trees, 885. 
 
 -charged with seeds, 387. 
 
 Echinodermata,their pedicellari®, 
 225. 
 
 Eciton, 272. 
 
 Economy of organization, 139. 
 Edentata, teeth and hair, 137. 
 
 ——, fossil species of, 492! 
 Edwards, Milne, on physiological 
 division of labor, 105. 
 
 -, on gradations of structure, 
 
 185 
 
 Edwards, on embryological char¬ 
 acters, 434. 
 
 Eggs, young birds escaping from, 
 80. 
 
 Egypt, productions of, not modi¬ 
 fied, 200. 
 
 Electric organs, 178. 
 
 Elephant, rate of increase, 60. 
 
 -, of Glacial period, 135. 
 
 Embryology, 455. 
 
 Eozoon Canadense, 339. 
 
 Epilepsy inherited, 128. 
 
 Existence, struggle for, 57. 
 
 --, condition of, 198. 
 
 Extinction, as bearing on natural 
 selection, 115. 
 
 ——, of domestic varieties, 111 
 -, 347. 
 
 Eye, structure of, 171. 
 
 Eye, correction for aberration, 
 194. 
 
 Eyes, reduced, in moles, 130. 
 
 Fabre, M., on hymenoptera fight¬ 
 ing, 82. 
 
 -, on parasitic sphex, 255. 
 
 -, on Sitaris, 465. 
 
 Falconer, Dr., on naturalization 
 of plants in India, 61. 
 
 —■ - on elephants and mastodons, 
 861. 
 
 -and Cautley, on mammals of 
 
 sub-Himalayan beds, 368. 
 Falkland Islands, wolf of, 414. 
 Faults, 817. 
 
 Faunas, marine, 374. 
 
 Fear, instinctive, in birds, 249. 
 Feet of birds, young molluscs ad¬ 
 hering to, 407. 
 
 Fertilization variously effected, 
 183, 191. 
 
 Fertility of hybrids, 280. 
 
 -, from slight changes in con¬ 
 ditions, 296. 
 
 -of crossed varieties, 301. 
 
 Fir-trees destroyed by cattle, 67, 
 ——, pollen of, 195. 
 
 Fish, flying, 166. 
 
 -, teleostean, sudden appear¬ 
 ance of, 336. 
 
 -eating seeds- 886, 408- 
 
520 
 
 INDEX . 
 
 Fish, fresh-water, distribution of, 
 406. 
 
 Fishes, ganoid, now confined to 
 fresh water, 98. 
 
 -, electric organs of, 178. 
 
 -, ganoid, living in fresh 
 
 water, 351. 
 
 -, of southern hemisphere, 
 
 399. 
 
 Flat-fish, their structure, 220. 
 Flight, powers of, how acquired, 
 166. 
 
 Flint-tools, proving antiquity of 
 
 man, 16. 
 
 Flower, Prof., on the Larnyx, 
 
 225. 
 
 -, on Halitherium, 357. 
 
 •-on the resemblance between 
 
 the jaws of the dog and Tliyla- 
 cinus, 441. 
 
 Flower, Prof., on the homology 
 of the feet of certain mar¬ 
 supials, 451. 
 
 Flowers, structure of, in relation 
 to crossing, 86. 
 
 -, of composite and umbelli- 
 
 ferae, 137, 205. 
 
 -, beauty of, 191. 
 
 ■-, double, 271. 
 
 Flysch formation, destitute of or¬ 
 ganic remains, 320. 
 
 Forbes, Mr. D., on glacial action 
 in the Andes, 396. 
 
 -, E., on colors of shells, 127. 
 
 -, on abrupt range of shells in 
 
 depth, 161. 
 
 --, on poorness of palaeonto¬ 
 logical collections, 319. 
 
 -, on continuous succession of 
 
 genera, 346. 
 
 ——, on continental extensions, 
 382, 383. 
 
 --, on distribution during Gla¬ 
 cial period, 390. 
 
 --, on parallelism in time and 
 
 space, 426. 
 
 Forests, changes in, in America, 
 69. 
 
 Formation, Devonian, 361. 
 
 -, Cambrian, 339. 
 
 ——, intermittent, 328, 
 
 Formations, thickness of, in 
 Britain, 317. 
 
 Formica rufescens, 255. 
 
 -, sanguinea, 256. 
 
 -, tiava, neuter of, 273. j 
 
 Forms, lowly organized, long en 
 during, 118. 
 
 Frena, ovigerous, of cirri pedes, 
 176 
 
 Fresh-water productions, dis¬ 
 persal of, 405. 
 
 Fries, on species in large genera 
 being closely allied to othei 
 species, 54. 
 
 Frigate-bird, 169. 
 
 Frogs on islands, 413. 
 
 Fruit-trees, gradual improvement 
 of, 31. 
 
 -in United States, 48. 
 
 -, varieties of, acclimatized in 
 
 United States, 135. 
 
 Fuci, crossed, 287, 293. 
 
 Fur, thicker in cold climates, 127. 
 
 Furze, 457. 
 
 Galapagos Archipelago, birds of, 
 411. 
 
 -productions of, 417, 419. 
 
 Galaxias, its wide range, 406. 
 
 Galeopithecus, 165. 
 
 Game, increase of, checked by 
 vermin, 65. 
 
 Gartner, on sterility of hybrids, 
 279, 280, 284. 
 
 -, on reciprocal crosses, 286. 
 
 -, on crossed maize and ver- 
 
 bascum, 304. 
 
 -, on comparison of hybrids 
 
 and mongrels, 306, 307. 
 
 Gaudry, Prof., on intermediate 
 genera of fossil mammals in 
 Attica, 357. 
 
 Geese, fertility when crossed, 283. 
 
 -, upland, 169. 
 
 Geikie. Mr., on subaerial denuda¬ 
 tion, 316. 
 
 Genealogy, important in classifi¬ 
 cation, 435. 
 
 Generations, alternate, 456. 
 
 Geographical distribution, 373. 
 
 Geography, ancient, 503. 
 
INDEX. 
 
 52 ? 
 
 Geoffroy St. Hilaire. on balance- 
 ment, 139= 
 
 - ; on homologous organs. 451. 
 
 -. Isidore, on variability of re 
 
 peated parts 140. 
 
 -or correlation, in monstrosi¬ 
 ties, 10 
 
 -, on correlation 137. 
 
 -, on variable parts being 
 
 often monstrous, 145. 
 
 Geology, future progress of, 502. 
 
 -, imperfection of the record, 
 
 503. 
 
 Gervais, Prof., on Typotherium, 
 357. 
 
 Giraffe, tail of, 186. 
 
 -, structure of, 209. 
 
 Glacial period, 389. 
 
 -, affecting the North and 
 
 South, 395. 
 
 Glands, mammary, 224. 
 
 Gmelin, on distribution, 390 
 Godwin-Austen, Mr., on the 
 Malay Archipelago, 331. 
 
 Goethe, on compensation of 
 growth, 139. 
 
 Gomphia, 207. 
 
 Gooseberry, grafts of, 290. 
 
 Gould, Dr. Aug. A., on land- 
 shells, 416. 
 
 -, Mr,, on colors of birds, 127. 
 
 -, on instincts of cuckoo, 253. 
 
 -, on distribution of genera of 
 
 birds, 422. 
 
 Gourds, crossed, 304. 
 
 Graba, on the Uria lacrymas, 85. 
 Grafting, capacity of, 289, 290. 
 Granite, areas of denuded, 324. 
 Grasses, varieties of, 103, 
 
 Gray, Dr. Asa, on the variability 
 of oaks, 47. 
 
 ■-, on man not causing varia¬ 
 
 bility, 73. 
 
 -, on sexes of the holly, 87. 
 
 -, on trees of the United 
 
 States, 93. 
 
 -, on naturalized plants in the 
 
 United States, 105. 
 
 -, on aestivation, 206. 
 
 -, on rarity of intermediate va¬ 
 rieties, 162 
 
 Gray, on Alpine plants, 390. 
 
 -, Dr. J. E., on striped mule^ 
 
 152. 
 
 Grebe, 169 
 
 Grimm, on asexual reproduction, 
 456. 
 
 Groups, aberrant, 446. 
 
 Grouse, colors of, 78. 
 
 ~—> red, a doubtful species, 45. 
 Growth, compensation of, 139. 
 Gunther, Dr., on flat-fish, 222. 
 
 -, on prehensile tails, 223. 
 
 -, on the fishes of Panama, 
 
 374. 
 
 •-> on the range of fresh-water 
 
 fishes, 406. 
 
 -, on the limbs of Lepidosiren, 
 
 470. 
 
 Haast, Dr., on glaciers of New 
 Zealand, 395. 
 
 Habit, effect of, under domes¬ 
 tication, 10. 
 
 - ;, effect, of, under nature, 129. 
 
 Habit, diversified,of same species, 
 167. 
 
 Hackel, Prof., on classification 
 and the lines of descent, 450. 
 Hair and teeth, correlated, 137. 
 Halitherium, 357. 
 
 Harcourt, Mr. E. V., on the birds 
 of Madeira, 411. 
 
 Hartung, M., on bowlders in the 
 Azores, 388. 
 
 Hazel-nuts, 384. 
 
 Hearne, on habits of bears, 168. 
 Heath, changes in vegetation, 66. 
 Hector, Dr., on glaciers of New 
 Zealand, 395. 
 
 Heer, Oswald, on ancient culti¬ 
 vated plants, 16. 
 
 -on plants of Madeira, 98. 
 
 Helianthemum, 207. 
 
 Helix pomatia, 417. 
 
 ——, resisting salt water, 417. 
 Helmholtz, M., on the imperfeo- 
 tion of the human eye, 194. 
 Helosciadium, 384. 
 
 Hemionus, striped, 154. 
 
 Hensen, Dr., on the eyes of 
 Cephalopoda, 180. 
 
52S 
 
 INDEX. 
 
 Herbert W., on straggle for exist¬ 
 ence, 58. 
 
 -, on sterility of hybrids, 281. 
 
 Hermaphrodites crossing, 90. 
 
 Heron eating seed, 409. 
 
 Heron, Sir R., on peacocks, 82. 
 
 Heusinger, on white animals poi¬ 
 soned by certain plants, 11. 
 
 Hewitt, Mr., on sterility of first 
 crosses, 293. 
 
 Hildebrand, Prof., on the self- 
 sterility of Corydalis, 281. 
 
 Hilgendorf, on intermediate varie¬ 
 ties, 325. 
 
 Himalaya, glaciers of, 395. 
 
 -, plants of, 398. 
 
 Hippeastrnm, 281. 
 
 Hippocampus, 224. 
 
 Hofmeister, Prof., on the move¬ 
 ments of plants, 234. 
 
 Holly-trees, sexes of, 87. 
 
 Hooker, Dr., on trees of New 
 Zealand, 93. 
 
 -, on acclimatization of Hima¬ 
 layan trees, 134. 
 
 Hooker, Dr., on flowers of um- 
 belliferae, 138. 
 
 -, on the position of ovules, 
 
 204. 
 
 — — , on glaciers of Himalaya, 
 395. 
 
 -, on algae of New Zealand, 
 
 399. 
 
 -, on vegetation at the base of 
 
 the Hymalaya, 399. 
 
 -, on plants of Tierra del 
 
 Fuego, 397. 
 
 --, on Australian plants, 398, 
 
 '419. 
 
 --, on relations of flora of 
 
 America, 401. 
 
 ■-, on flora of the Antarctic 
 
 lands, 403, 418. 
 
 -, on the plants of the Gala¬ 
 pagos, 412, 417. 
 
 -. on glaciers of the Lebanon, 
 
 395. 
 
 -, on man not causing varia¬ 
 bility, 73, 
 
 -, on plants of mountains of 
 
 Fernando, Po, 398. 
 
 Hooks on palms, 188. 
 
 -on seeds, on islands, 413. 
 
 Hopkins, Mr., on denudation, 
 
 323. 
 
 Hornbill, remarkable instinct of, 
 276. 
 
 Horns, rudimentary, 472. 
 
 Horse, fossil, in La Plata, 348. 
 
 -, proportions of, when young 
 
 462. 
 
 Horses destroyed by flies in Para, 
 guay, 67. 
 
 -, striped, 152. 
 
 Horticulturists, selection applied 
 by, 28. 
 
 Huber, on cells of bees, 264. 
 
 ——, P., on reason blended with 
 instinct, 242. 
 
 -, on habitual nature of in¬ 
 stincts, 243. 
 
 -, on slave-making ants, 255. 
 
 -, on Melipona domestica, 260. 
 
 Hudson, Mr., on the Ground- 
 Woodpecker of La Plata, 168. 
 
 -, on the Molothrus, 253. 
 
 Humble-bees, cells of, 260. 
 Hunter, J., on secondary sexual 
 characters, 142. 
 
 Hutton, Captain, on crossed 
 geese, 283. 
 
 Huxley, Prof., on structure of 
 hermaphrodites, 93. 
 
 -, on the affinities of the 
 
 Sirenia, 357. 
 
 -, on forms connecting birds 
 
 and reptiles, 357. 
 
 -, on homologous organs, 455. 
 
 -, on the development oi 
 
 aphis, 460. 
 
 Hvbrids and mongrels compared, 
 305. 
 
 Hybridism, 277. 
 
 Hydra, structure of, 175. 
 Hymenoptera, fighting, 82. 
 Hymenopterous insect, diving 
 169. 
 
 Hyoseris, 205. 
 
 Ibla, 140. 
 
 Icebergs transporting seeds, 38? 
 Increase, rate of, 60. 
 
INDEX . 529 
 
 Individuals, numbers favorable to 
 selection, 94. 
 
 -, many, whether simulta¬ 
 neously created, 380. 
 Inheritance, laws of, 12. 
 
 -, at corresponding ages, 12. 
 
 Insects, color of, fitted for their 
 stations, 78. 
 
 -, sea side, colors of, 127. 
 
 -, blind, in caves.. 131. 
 
 --, luminous, 180. 
 
 -their resemblance to certain 
 
 objects, 214. 
 
 -, neuter, 272. 
 
 Instinct, 242. 
 
 -. not varying simultaneously 
 
 with structure, 270. 
 
 Instincts, domestic, 247. 
 Intercrossing, advantages of, 90, 
 296. 
 
 Islands, oceanic, 409. 
 
 Isolation favorable to selection, 
 96. 
 
 Japan, productions of, 395. 
 
 Java, plants of, 398. 
 
 Jones, Mr. J. M., on the birds of 
 Bermuda, 411. 
 
 Jourdain, M., on the eye-spots of 
 star fishes, 171. 
 
 Jukes, Prof., on subaerial denu¬ 
 dation, 316. 
 
 Jussieu, on classification, 433. 
 
 Kentucky, caves of, 101. 
 Kerguelen-land, flora of, 403, 418. 
 Kidney-bean, acclimatization of, 
 135. 
 
 Kidneys of birds, 137J 
 Kirby, on tarsi deficient in bee¬ 
 tles, 129. 
 
 Knight, Andrew, on cause of 
 variation, 6. 
 
 Kolreuter, on intercrossing, 89. 
 
 -, on the barberry, 91. 
 
 -, on sterility of hybrids, 278, 
 
 281. 
 
 --, on crossed varieties of nico 
 
 tiana, 305. 
 
 •-, on crossing male and herma¬ 
 
 phrodite flowers, 468. 
 
 Kolreuter, on reciprocal crosses, 
 287 
 
 Lamarck, on adaptive characters, 
 440. 
 
 Lancelet, 118. 
 
 -, eyes of, 173. 
 
 Landois, on the development of 
 the wings of insects, 176. 
 Land-shells, distribution of. 416. 
 
 -, of Madeira, naturalized, 421. 
 
 -, resisting salt water, 417. 
 
 Languages, classification of, 437. 
 Lankester, Mr. E. Ray, on Longe¬ 
 vity, 200. 
 
 -, on homologies, 454. 
 
 Lapse, great, of time, 314. 
 
 Larvae, 457, 458, 459. 
 
 Laurel, nectar secreted by the 
 leaves, 86. 
 
 Laurentian formation, 339. 
 
 Laws of variation, 126. 
 
 Leech, varieties of, 70. 
 Leguminosae, nectar secreted by 
 glands, 86, 
 
 Leibnitz’ attack on Newton, 496. 
 Lepidosiren, 98, 358. 
 
 -, limbs in a nascent condition, 
 
 470. 
 
 Lewes, Mr. G. H., on species not 
 having changed in Egypt, 200. 
 
 -, on the Salamandra atra, 
 
 468. 
 
 -, on many forms of life hav¬ 
 ing been at first evolved, 500. 
 Life, struggle for, 58. 
 
 Lingula, Silurian, 338. 
 
 Linnaeus, aphorism of, 430, 
 
 Lion, mane of, 82. 
 
 -, young of, striped, 457. 
 
 Lobelia fulgens, 68, 91. 
 
 -, sterility of crosses, 281. 
 
 Lockwood, Mr., on the ova of the 
 Hippocampus, 224. 
 
 Locusts transporting seeds, 386. 
 Logan, Sir W., on Laurentian 
 formation, 339. 
 
 Lowness of structure connected 
 with variability, 140. 
 
 -, related to wide distribution, 
 
 423. 
 
530 
 
 INDEX. 
 
 Lowe, Rev. R. T., on locusts 
 visiting Madeira, 386, 
 
 Lubbock, Sir J., on tbe nerves of 
 coccus, 41. 
 
 -, on secondary sexual charac¬ 
 ters, 147. 
 
 -, on a diving kymenopterous 
 
 insect, 169. 
 
 -—on affinities, 331. 
 
 --; on metamorphoses, 455, 458. 
 
 Lucas, Dr. P., on inheritance, 11. 
 
 -, on resemblance of child to 
 
 parent, 308. 
 
 Lund and Clausen, on fossils of 
 Brazil, 367. 
 
 Lyell, Sir C., on the struggle for 
 existence, 58. 
 
 -, on modern changes of the 
 
 earth, 89. 
 
 -, on terrestrial animals not 
 
 having been developed on isl¬ 
 ands, 213. 
 
 -,on a carboniferous land-shell, 
 
 320. 
 
 -, on strata beneath Silurian 
 
 system, 386. 
 
 -, on the imperfection of the 
 
 geological record, 342. 
 
 -, on the appearance of 
 
 species, 342. 
 
 --, on Barrande’s colonies, 344. 
 
 -, on tertiary formations of 
 
 Europe and North America, 352. 
 
 --, on parallelism of tertiary 
 
 formations, 356. 
 
 ——, on transport of seeds by 
 icebergs, 388. 
 
 -——, on great alterations of cli¬ 
 mate, 404. 
 
 --, on the distribution of fresh¬ 
 water shells, 407. 
 
 ——, on land-shells of Madeira, 
 421. 
 
 Lyell and Dawson, on fossilized 
 trees in Nova Scotia, 328. 
 Lythrum salicaria, trimorphic, 
 300. 
 
 Macleay, on analogical characters, 
 440. 
 
 Macrauchenia 357. 
 
 M’Donnell, Dr., on electric organs, 
 178. 
 
 Madeira, plants of, 98. 
 
 -, beetles of, wingless, 129. 
 
 -, fossil land-shells of, 367 
 
 -, birds of, 411. 
 
 Magpie tame in Norway, 246. 
 Males fighting, 81. 
 
 Maize, crossed, 304. 
 
 Malay Archipelago compared with 
 Europe, 331. 
 
 -, mammals of, 415. 
 
 Malm, on flat-fish, 221. 
 Malpighiaceae, small imperfect 
 flowers of, 204. 
 
 -, 433. 
 
 Mammae, their development, 224. 
 
 -, rudimentary, 467. 
 
 Mammals, fossil, in secondary 
 formation, 335. 
 
 -, insular, 414. 
 
 Man, origin of, 504. 
 
 Manatee, rudimentary nails of, 
 471. 
 
 Marsupials of Australia, 106. 
 
 -, structure of their feet, 450. 
 
 Marsupials, fossil species of, 367 
 Martens, M., experiment on seeds, 
 384. 
 
 Martin, Mr. W. C., on striped 
 mules, 153. 
 
 Masters, Dr., on Saponaria, 207. 
 Matteucci, on the electric organs 
 of rays, 178. 
 
 Matthiola, reciprocal crosses of, 
 287. 
 
 Maurandia, 232. 
 
 Means of dispersal, 381. 
 
 Melipona domestica, 260. 
 
 Merrill, Dr., on the American 
 cuckoo, 251. 
 
 Metamorphism of oldest rocks. 
 339. 
 
 Mice destroying bees, 68. 
 
 -, acclimatization of, 134. 
 
 -, tails of, 223. 
 
 Miller, Prof., on the cells of bees, 
 261, 265. 
 
 Mirabilis, crosses of, 287. 
 
 Missel-thrush, 70 
 
 Mistletoe, complex relations of, 3 
 
INDEX, 
 
 Mivart, Mr., on tlie relation of 
 hair and teeth, 137, 
 
 -, on the eyes of cephalopoas. 
 
 180. 
 
 -, various objections to Natu 
 
 ral Selection, 209. 
 
 -, on abrupt modifications, 
 
 237. 
 
 -, on the resemblance of the 
 
 mouse and antechinus, 440. 
 Mocking-thrush of the Galapagos, 
 421. 
 
 Modification of species not abrupt, 
 499. 
 
 Moles, blind, 130. 
 
 Molothrus, habits of, 253. 
 Mongrels, fertility and sterility of, 
 301. 
 
 -and hybrids compared, 305. 
 
 Monkeys, fossil, 355. 
 Monachanthus, 438. 
 
 Mons, Van, on the origin of fruit 
 trees, 25. 
 
 Monstrosities, 39. 
 
 Moquin - Tandon, on sea - side 
 plants, 127. 
 
 Morphology, 450. 
 
 Morren, on the leaves of Oxalis, 
 233 
 
 Moths, hybrid, 283. 
 
 Mozart, musical powers of, 243. 
 Mud. seeds in, 408. 
 
 Mules, striped, 153. 
 
 Muller, Adolph, on the instincts 
 of the cuckoo, 251. 
 
 Muller, Dr. Ferdinand, on Alpine 
 Australian plants, 398. 
 
 Muller, Fritz, on dimorphic crus¬ 
 taceans, 42, 274. 
 
 --, on the lancelet, 119. 
 
 -, on air-breathing crusta¬ 
 ceans, 181. 
 
 --, on the self-sterility of 
 
 orchids, 281. 
 
 -, on embryology in relation 
 
 to classification, 434. 
 
 -, on the metamorphoses of 
 
 crustaceans, 460, 466. 
 
 -, on terrestrial and fresh¬ 
 water organisms not under¬ 
 going any metamorphosis, 464. | 
 
 531 
 
 MiiIIei>, Fritz, on climbing plants, 
 233. 
 
 Multiplication of species not in¬ 
 definite, 121. 
 
 Murchison, Sir R., on the forma 
 tions of Russia, 321. 
 
 --, on azoic formations, 339. 
 
 -, on extinction, 347. 
 
 Murie, Dr., on the modification of 
 the skull in old age, 177. 
 Murray, Mr. A., on cave-insects, 
 132. 
 
 Mustela, vision, 164. 
 
 Myanthus, 438. 
 
 Myrmecocystus, 272. 
 
 Myrmica, eyes of, 273. 
 
 Nageli, on morphological charac' 
 ters, 202. 
 
 Nails, rudimentary. 471. 
 Nathusius, Von, on pigs, 189. 
 Natural history, future progress 
 of, 502. 
 
 -, selection, 73. 
 
 -, system, 430. 
 
 Naturalization of forms distinct 
 from the indigenous species, 
 105. 
 
 Naturalization in New Zealand, 
 193. 
 
 Naudin, on analogous variations 
 in gourds, 149. 
 
 --, on hybrid gourds, 304. 
 
 Naudin, on reversion, 307. 
 Nautilus, Silurian, 338. 
 
 Nectar of plants, 86. 
 
 Nectaries, how formed, 86. 
 Nelumbium luteum, 409. 
 
 Nests, variations in, 246, 269, 275 
 Neuter insects, 272, 273. 
 
 Newman, Col., on humble-bees, 
 
 68 . 
 
 New Zealand, productions of, not 
 perfect, 193. 
 
 -, naturalized products of, 366. 
 
 -, fossil birds of, 367. 
 
 -, glaciers of, 395. 
 
 -, crustaceans of, 399. 
 
 -, algae of 399. 
 
 -, number of plants of, 410. 
 
 -, flora of, 419. 
 
532 
 
 INDEX. 
 
 Newton, Sir I., attacked for irre- 
 ligion, 496. 
 
 -, Prof., on eartli attached to 
 
 a partridge’s foot, 387. 
 Nicotiana, crossed varieties of, 
 305. 
 
 •-, certain species very sterile, 
 
 286. 
 
 Nitsche, Dr., on the Polyzoa, 
 228. 
 
 Noble, Mr., on fertility of Rhodo¬ 
 dendron, 282. 
 
 Nodules, phosphatic, in azoic 
 rocks, 339. 
 
 Oaks, variability of, 47. 
 
 Onites, appelles, 129, 
 
 Ononis, small imperfect flowers 
 of, 204. 
 
 Orchids, fertilization of, 183. 
 
 -, the development of their 
 
 flowers, 230. 
 
 -, forms of, 438. 
 
 Orchis, pollen of, 180. 
 Organization, tendency to ad¬ 
 vance, 116. 
 
 Organs of extreme perfection, 170, 
 
 -, electric, of fishes, 178. 
 
 -, of little importance, 186. 
 
 -, homologous, 451. 
 
 -, rudiments of, and nascent, 
 
 467. 
 
 Ornithorhynchus, 98, 432. 
 
 -, mammae of, 224. 
 
 Ostrich not capable of flight, 213. 
 -, habit of laying eggs to¬ 
 gether, 255. 
 
 -, American, two species of, 
 
 375. 
 
 Otter, habits of, how acquired, 
 164. 
 
 Ouzel, water, 169. 
 
 Owen, Prof., on birds not flying, 
 128. 
 
 -, on vegetative repetition, 
 
 141. 
 
 -, on variability of unusually 
 
 developed parts, 141. 
 
 -, on the eyes of fishes. 173 
 
 -, on the swim-bladder of 
 
 fishes, 176. 
 
 Owen, Prof., on fossil horse of La 
 Plata, 348. 
 
 -, on generalized form, 357. 
 
 -, on relation of ruminants 
 
 and pachyderms, 357. 
 
 -, on fossil birds of New Zea¬ 
 land, 367. 
 
 -, on succession of types, 367 
 
 -, on affinities of the dugong, 
 
 431. 
 
 -, on homologous organs, 451. 
 
 -, on the metamorphosis of ce- 
 
 phalopods, 459. 
 
 Pacific Ocean, faunas of, 375. 
 Pacini, on electic organs, 179. 
 Paley, on no organ formed to give 
 pain, 193. 
 
 Pallas, on the fertility of the 
 domesticated descendants of 
 wild stocks, 284. 
 
 Palm with hooks, 188. 
 
 Papaper bracteatum, 206. 
 Paraguay, cattle destroyed by 
 flies, 67. 
 
 Parasites, 253. 
 
 Partridge, with ball of earth at¬ 
 tached to foot, 287. 
 
 Parts greatly developed, variable, 
 141. 
 
 Parus major, 168. 
 
 Passiflora, 281. 
 
 Peaches in United States, 78. 
 Pear, grafts of, 290. 
 
 Pedicellarise, 226. 
 
 Pelagornium, flowers of, 138. 
 
 -, sterility of, 282. 
 
 Pelvis of women, 137. 
 
 Peloria, 138. 
 
 Period, glacial, 389. 
 
 Petrels, habits of, 169. 
 
 Phasianus, fertility of hybrids, 
 283. 
 
 Pheasant, young, wild, 249. 
 
 Pictet, Prof., on groups of spe¬ 
 cies suddenly appearing, 333. 
 
 -, on rate of organic change, 
 
 344. 
 
 -•. on continuous succession of 
 
 genera, 346. 
 
INDEX. 533 
 
 Pictet. Prof., on close alliance of 
 fossils in consecutivet'ormations, 
 362. 
 
 -, on change in latest tertiary 
 
 forms, 329. 
 
 -, on early transitional links, 
 
 334. 
 
 Pierce, Mr., on varieties of wolves, 
 83. 
 
 Pigeons with feathered feet and 
 skin between toes, 11. 
 
 -, breeds described, and origin 
 
 of, 18. 
 
 -, breeds of, how produced, 
 
 33, 35. 
 
 -, tumbler, not being able to 
 
 get out of egg. 80. 
 
 -, reverting to blue color, 151. 
 
 -, instinct of tumbling, 248. 
 
 -, young of, 462. 
 
 Pigs, black, not affected by the 
 paint-root, 11. 
 
 -, modified by want of exer¬ 
 cise, 189. 
 
 Pistil, rudimentary, 468. 
 
 Plants, poisonous, not affecting 
 certain colored animals, 11. 
 
 -, selection, applied to, 31. 
 
 -, gradual improvement of, 31. 
 
 -, not improved in barbarous 
 
 countries, 32. 
 
 -, dimorphic, 42, 297. 
 
 -, destroyed by insects, 63. 
 
 -, in midst of range, have to 
 
 struggle with other plants, 71. 
 
 -, nectar of, 86. 
 
 -, fleshy, on sea-shores, 127. 
 
 -, climbing, 175, 232. 
 
 -, fresh-water, distribution of, 
 
 407. 
 
 -, low in scale, widely dis¬ 
 tributed, 423. 
 
 Pleuronectidae, their structure, 
 220. 
 
 Plumage, laws of changes in 
 sexes of birds, 82. 
 
 Plums in the United States. 78. 
 Pointer dog, origin of, 3C. 
 
 -, habits of, 248. 
 
 Poison not affecting certain 
 colored animals, 11. 
 
 Poison, similar effect of, on ani¬ 
 mals and plants, 500. 
 
 Pollen of fir-trees, 195. 
 
 - transported by various 
 
 means, 183, 191. 
 
 Pollinia, their development, 230. 
 
 Polyzoa, their avicularia, 228. 
 
 Poole, Col., on striped hemionus, 
 154. 
 
 Potemogeton, 408. 
 
 Pouchet, on the colors of flat-fish, 
 
 222 . 
 
 Prestwich, Mr., on English and 
 French eocene formations, 355. 
 
 Proctotrupes, 169. 
 
 Proteolepas, 140. 
 
 Proteus, 133. 
 
 Psychologv, future progress of, 
 504. 
 
 Pyrgoma, found in the chalk, 
 336. 
 
 Quagga, striped, 154. 
 
 Quatrefages, M., on hybrid moths, 
 283. 
 
 Quercus, variability of, 48. 
 
 Quince, grafts of, 290. 
 
 Rabbits, disposition of young, 
 249. 
 
 Races, domestic, characters of, 14. 
 
 Race-horses, Arab, 30. 
 
 -, English, 381. 
 
 Radcliffe, Dr., the electrical or¬ 
 gans of the torpedo, 178. 
 
 Ramond, on plants of Pyrenees, 
 391. 
 
 Ramsay, Prof., on subaerial denu¬ 
 dation, 316. 
 
 -, on thickness of the British 
 
 formations, 317. 
 
 -, on faults, 317. 
 
 Ramsay, Mr., on instincts of 
 cuckoo, 252. 
 
 Ratio of increase, 60. 
 
 Rats supplanting each other, 70. 
 
 -, acclimatization of, 134. 
 
 -, blind, in cave, 131. 
 
 Rattle-snake, 192. 
 
 Reason and instinct. 242. 
 Recapitulation, general, 476. 
 
534 
 
 INDEX. 
 
 Reciprocity of crosses, 287. 
 
 Record, geological, imperfect, 312. 
 
 Rengger, on dies destroying cat¬ 
 tle, 6-7. 
 
 Reproduction, rate of, 60. 
 
 Resemblance, protective, of in¬ 
 sects, 215. 
 
 -to parents in mongrels and 
 
 hybrids, 306. 
 
 Reversion, law of inheritance, 13. 
 
 -, in pigeons, to blue color, 
 
 151. 
 
 Rhododendron, sterility of, 282. 
 
 Richard, Prof., on Aspicarps, 433. 
 
 Richardson, Sir J., on structure 
 of squirrels, 165. 
 
 -, on fishes of the southern 
 
 hemisphere, 399. 
 
 Robinia, grafts of, 290. 
 
 Rodents, blind, 130. 
 
 Rogers, Prof., Map of N, America, 
 324. 
 
 Rudimentary organs, 467. 
 
 Rudiments important for classi¬ 
 fication, 432. 
 
 Riitimeyer, on Indian cattle, 16, 
 284. 
 
 Salamandre atra, 468. 
 
 Saliva used in nests, 269. 
 
 Salvin, Mr., on the beaks of 
 ducks, 218. 
 
 Sageret, on grafts, 290. 
 
 Salmons, males fighting, and 
 hooked jaws of, 81. 
 
 Salt water, how far injurious to 
 seeds, 383. 
 
 -not destructive to land-shells, 
 
 ^ 417. 
 
 Salter, Mr., on early death of 
 hybrid embryos, 293. 
 
 Saurophagus sulphuratus, 168. 
 
 Schacht, Prof., on Phyllotaxy, 
 205. 
 
 Schiodte, on blind insects, 131. 
 
 -, on flat-fish, 220. 
 
 Schlegel, on snakes, 137. 
 
 Schobl, Dr., on the ears of mice, 
 203. 
 
 Scott, J., Mr., on the self-sterility 
 of orchids, 281. 
 
 Scott, J., Mr., on the crossing of 
 varieties of verbascum, 304. 
 Sea-water, how far injurious to 
 seeds, 383. 
 
 -not destructive to land-shells, 
 
 , 41 7. 
 
 Seabright, Sir J., on crossed ani¬ 
 mals, 18. 
 
 Sedgwick, Prof., on groups of 
 species suddenly appearing, 333. 
 Seedlings destroyed by insects, 63. 
 Seeds, nutriment in, 71. 
 
 -, winged, 139. 
 
 -, means of dissemination, 183, 
 
 191, 385. 
 
 ——, power of resisting salt 
 water, 383. 
 
 -, in crops and intestines of 
 
 birds, 386. 
 
 -, eaten by fish, 386, 408. 
 
 -, in mud, 408. 
 
 -, hooked, on islands, 413. 
 
 Selection of domestic products, 
 25. 
 
 -, principle not of recent ori¬ 
 gin, 29. 
 
 -, unconscious, 29. 
 
 -, natural, 73. 
 
 -, sexual, 81. 
 
 -, objections to term, 74. 
 
 -natural, has not induced 
 
 sterility, 291. 
 
 Sexes, relations of, 81. 
 
 Sexual characters variable, 146. 
 
 -, selection, 81. 
 
 Sheep, Merino, their selection, 27. 
 -, two sub-breeds, uninten¬ 
 tionally produced, 31. 
 
 -, mountain varieties of, 70. 
 
 Shells, colors of, 127. 
 
 -, hinges of, 182. 
 
 -, littoral, seldom embedded, 
 
 , 319- 
 
 Shells, fresh-water, long retain 
 the same forms, 364. 
 
 -, fresh-water, dispersal of, 
 
 406. 
 
 -, of Madeira, 412. 
 
 -, land, distribution of, 412. 
 
 -, land, resisting salt water, 
 
 417. 
 
INDEX. 
 
 535 
 
 Shrew-mouse, 440. 
 
 Silene, infertility of crosses, 286. 
 Silliman, Prof., on blind rat, 
 181. 
 
 Sirenia, tlieir affinities, 857. 
 Sitaris, metamorphosis of, 465. 
 Skulls of young mammals, 188, 
 453. 
 
 Slave-making instinct, 255. 
 
 Smith, Col. Hamilton, on striped 
 horses, 153. 
 
 ■-, Mr. Fred., on slave-making 
 
 ants, 256. 
 
 --, on neuter ants, 273. 
 
 Smith, Dr., on the Polyzoa, 228. 
 Snake with tooth for cutting 
 through egg-shell, 253. 
 Somerville, Lord, on selection of 
 sheep, 27. 
 
 Sorbus, grafts of, 290. 
 
 Sorex, 440. 
 
 Spaniel, King Charles’ breed, 30. 
 Specialization of organs, 117. 
 Species, polymorphic, 41. 
 
 -, dominant, 51. 
 
 -, common, variable, 50. 
 
 -in large genera variable, 52. 
 
 -, groups of, suddenly appear¬ 
 ing, 333, 337. 
 
 -beneath Silurian formations, 
 
 339. 
 
 -successively appearing, 343. 
 
 - changing simultaneously 
 
 throughout the world, 352. 
 Spencer, Lord, on increase in size 
 of cattle, 30. 
 
 -, Herbert, Mr., on the first 
 
 steps in diffentiation, 120. 
 
 -, on the tendency to an 
 
 equilibrium in all forces, 297. 
 Sphex, parasitic, 255. 
 
 Spiders, development of, 460. 
 Sports in plants, 9. 
 
 Sprengel, C. C., on crossing, 89. 
 
 -, on ray-florets, 138. 
 
 Squalodon, 357. 
 
 Squirrels, gradations in structure, 
 165. 
 
 Staffordshire, heath, changes in, 
 
 66 . 
 
 Stag-beetles, fighting, 81. 
 
 Star fishes, eyes of, 171. 
 
 -, their pedicellariae, 227. 
 
 Sterility from changed conditions 
 of life, 8. 
 
 -of hybrids, 279. 
 
 -, laws of, 284. 
 
 -, causes of, 291. 
 
 -, from unfavorable condi¬ 
 tions, 295. 
 
 -not induced through natural 
 
 selection, 292. 
 
 St. Helena, productions of, 410. 
 
 St. Hilaire, Aug., on variability 
 of certain plants, 206. 
 
 -, on classification, 433. 
 
 St. John, Mr., on habits of cats, 
 247. 
 
 Sting of bee, 194. 
 
 Stocks, aboriginal, of domestic 
 animals, 17. 
 
 Strata, thickness of, in Britain, 
 317. 
 
 Stripes on horses, 152. 
 
 Structure, degrees of utility of, 
 
 , 189. 
 
 Struggle for existence, 57. 
 Succession, geological, 343. 
 
 -of types in same areas, 367. 
 
 Swallow, one species supplanting 
 another, 70. 
 
 Swaysland, Mr., on earth adher¬ 
 ing to the feet of migratory 
 birds, 387. 
 
 Swifts, nests of, 269. 
 Swim-bladder, 175. 
 
 Switzerland, lake inhabitations 
 of, 16. 
 
 System, natural, 430. 
 
 Tail of giraffe, 186. 
 
 -of aquatic animals, 187. 
 
 -, prehensible, 223. 
 
 -, rudimentary, 571. 
 
 Tanais, dimorphic, 42. 
 
 Tarsi, deficient, 129. 
 
 Tauscli, Dr., on umbelliferas, 205. 
 Teeth and hair correlated, 137. 
 
 -, rudimentary, in embryonic 
 
 calf, 467, 495. 
 
 Tegetmeier, Mr., on cells of bees, 
 262, 267. 
 
536 
 
 INDEX. 
 
 Temminck, on distribution aiding 
 classification, 435. 
 
 Tendrils, their development, 282. 
 Thompson, Sir W., on the age of 
 the habitable wurld, 338 
 
 -, on the consolidation of the 
 
 crust of the earth, 482. 
 
 Thouin, on grafts, 290. 
 
 Thrush, aquatic species of, 169. 
 
 -, mocking, of the Galapagos, 
 
 421. 
 
 -, young of, spotted, 457. 
 
 -, nest of, 276. 
 
 Thuret, M., on crossed fuci, 287. 
 Th waites, Mr., on acclimatization, 
 134. 
 
 Thylacinus, 441. 
 
 Tierra del Fuego, dogs of, 249. 
 
 -, plants of, 403. 
 
 Timber-drift, 385. 
 
 Time, lapse of, 314. 
 
 -, by itself not causing modi- 
 
 cation, 95. 
 
 Titmouse, 168. 
 
 Toads on islands, 413. 
 
 Tobacco, crossed varieties of, 305. 
 Tomes, Mr., on the distribution 
 of bats, 415. 
 
 Transitions in varieties rare, 159. 
 Traquair, Dr., on flat-fish, 222. 
 Trautschold, on intermediate 
 varieties, 325. 
 
 Trees on islands belong to pecul¬ 
 iar orders, 413. 
 
 -with separated sexes, 92. 
 
 Trifolium pratense, 68, 88. 
 
 -incarnatum, 88. 
 
 Trigonia, 351. 
 
 Trilobites, 338. 
 
 -, sudden extinction of, 351. 
 
 Trimen, Mr., on imitating-insects, 
 444. 
 
 Trimorphism in plants, 42, 297. 
 Troglodytes, 276. 
 
 Tuco-tuco-blind, 130. 
 
 Tumbler pigeons, habits of, he¬ 
 reditary, 248. 
 
 Tumbler, young of, 462. 
 Turkey-cock, tuft of hair on 
 breast, 83. 
 
 c -, naked skin on head, 188. 
 
 Turkey-cock, young of, instinct¬ 
 ively wild, 249. 
 
 Turnip and cabbage, analogous 
 variations of, 149. 
 
 Type, unity of, 197, 198. 
 
 Types, succession of, in same 
 areas, 367. 
 
 Typotherium, 357. 
 
 Udders enlarged by use, 10. 
 
 -, rudimentary, 468. 
 
 Ulex, young leaves of, 457. 
 Umbelliferse, flowers and seeds 
 of, 138. 
 
 -, outer and inner florets of, 
 
 205. 
 
 Unity of type, 197, 198. 
 
 Uria lacrymans, 85. 
 
 Use, effects of, under domestica¬ 
 tion, 10. 
 
 -, effects of, in a state of 
 
 nature, 128. 
 
 Utility, how far important in the 
 construction of each part, 189. 
 
 Valenciennes, on fresh-water fish, 
 406. 
 
 Variability of mongrels and 
 hybrids, 305. 
 
 Variation, under domestication, 7. 
 
 -caused by reproductive sys 
 
 tern being affected by conditions 
 of life, 8. 
 
 -under nature, 39. 
 
 -, laws of, 126. 
 
 -, correlated, 10, 186, 189. 
 
 Variations appear at correspond¬ 
 ing ages, 12, 79. 
 
 - analogous in distinct spe¬ 
 cies, 148. 
 
 Varieties, natural, 37. 
 
 -, struggle between, 70. 
 
 -, domestic, extinction of, 101. 
 
 -, transitional, rarity of, 159. 
 
 -, when crossed, fertile, 301. 
 
 Varieties, when crossed, sterile, 
 303. 
 
 -, classification of, 437. 
 
 Verbascum, sterility of, 281. 
 
 -, varieties of, crossed, 304. 
 
 Verlot, M., on doubt** stocks, 271. 
 
INDEX. 537 
 
 Verneuil, M. de, on the succes¬ 
 sion of species. 353. 
 
 Vibracula of the Polyzoa, 229. 
 
 Viola, small imperfect flowers of, 
 204. 
 
 -, tricolor, 68. 
 
 Virchow, on the structure of the 
 crystalline lens, 173. 
 
 Virginia, pigs of, 78. 
 
 Volcanic islands, denudation of, 
 316. 
 
 Vulture, naked skin on head, 188. 
 
 Wading-birds, 408. 
 
 Wagner, Dr., on Cecidomyia, 456. 
 
 Wagner, Moritz, on the import¬ 
 ance of isolation, 96. 
 
 Wallace, Mr., on origin of spe¬ 
 cies, 1. 
 
 -, on the limit of variation 
 
 under domestication, 36. 
 
 -, on dimorphic lepidoptera, 
 
 42, 274. 
 
 -, on races in the Malay Archi¬ 
 pelago, 44. 
 
 -, on the improvement of the 
 
 eye, 173. 
 
 -, on the walking-stick insect, 
 
 216. 
 
 -, on laws of geographical dis¬ 
 tribution, 380. 
 
 -, on the Malay Archipelago, 
 
 415. 
 
 -, on mimetic animals, 444. 
 
 Walsh, Mr. B. D., on phytopha- 
 gic forms, 45. 
 
 -, on equal variability, 149. 
 
 Water, fresh, productions of, 405. 
 
 Water-hen, 169. 
 
 Waterhouse, Mr., on Australian 
 marsupials, 106. 
 
 -, on greatly developed parts 
 
 being variable, 141. 
 
 -, on the cells of bees, 260. 
 
 -, on general affinities, 446. 
 
 Water-ouzel, 169. 
 
 Watson, Mr. H. C., on range of 
 varieties of British plants, 44, 
 55. 
 
 -, on acclimatization, 134. 
 
 -—, on flora of Azores, 388. 
 
 Watson, Mr. H. C., on rarity of 
 intermediate varieties, 162 
 
 -, on Alpine plants, 391. 
 
 -, on convergence, 120. 
 
 -, on the indefinite multipli 
 
 cation of species, 121. 
 
 Weale, Mr., on locusts transport¬ 
 ing seeds, 387. 
 
 Web of feet in water-birds, 170. 
 Weismann, Prof., on the causes 
 of variability, 7. 
 
 -, on rudimentary organs, 471 
 
 West Indian Islands, mammals of. 
 415. 
 
 Westwood, on species in large 
 genera being closely allied to 
 others, 54* 
 
 -on the tarsi of Engidae, 147. 
 
 -, on the antennae of hymenop- 
 
 terous insects, 432. 
 
 Whales, 216. 
 
 Wheat, varieties of, 103. 
 
 White Mountains, flora of, 390. 
 Whittaker, Mr., on lined of es¬ 
 carpment, 316. 
 
 Wichura, Max, on hybrids, 294, 
 296, 307. 
 
 Wings, reduction of size, 130. 
 
 -of insects homologous with 
 
 branchiae, 176. 
 
 -, rudimentary, in insects, 
 
 467. 
 
 Wolf, crossed with dog, 248. 
 
 -of Falkland Isles, 414. 
 
 Wollaston, Mr., on varieties of 
 insects, 45. 
 
 -, on fossil varieties of shells 
 
 in Madeira, 49. 
 
 Wollaston, Mr., on colors of in¬ 
 sects on sea-shore, 127. 
 
 -, on wingless beetles, 129. 
 
 -, on rarity of intermediate 
 
 varieties, 162. 
 
 -, on insular insects, 410. 
 
 -, on land-shells of Madeira 
 
 naturalized, 42l. 
 
 Wolves, varieties of, 83. 
 Woodcock with earth attached to 
 leg, 387. 
 
 Woodpecker habits of, 108. 
 
 -, green color of, 187. 
 
538 
 
 INDEX. 
 
 Woodward, Mr., on the duration 
 of specific forms, 326. 
 
 -, on Pyrgoma, 336. 
 
 -, on the continuous succession 
 
 of genera, 346. 
 
 *-. on the succession of types, 
 
 367. 
 
 VY orld, species changing simul¬ 
 taneously throughout, 352. 
 
 Wright, Mr. Chauncey, on the 
 giraffe, 211. 
 
 --, on abrupt modifications, 
 
 240. 
 
 Wrens, nest of, 276. 
 
 Wyman, Prof., on correlation of 
 color and effects of poison, 11. 
 -, on the cells of the bee, 262. 
 
 Youatt, Mr., on selection, 27. 
 
 -, on sub breeds of sheep, 31. 
 
 -, on rudimentary horns in 
 
 young cattle, 472. 
 
 Zanthoxylon, 206. 
 
 Zebra, stripes on, 152. 
 
 Zeuglodon, 357. 
 
 TOE END. 
 
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