eA tt K " ‘ Ny it a rh uh YS i, MY ehh vk) hy Way Shh ms ay ; ; * ‘a's PN , 4 ag ayy a ‘ So ah ha fy naar i ; \ see i e 7 ie Cj es vi 4, ye J i ¢ . y eA hh » ae Bern) ate b ey Pent 1 Pe) SOE AN iM i an ee gba at! My a4 4 ‘ Hy) une y 4, ‘ve Lay AY hh Aan mite Wiener roak a eh eK: - Pee | ‘ rfp Pili i t pene f Afsetne Rea Hilal set ida tana ae potest! M: hf ie . ng on et pease ae Seccati eon ttas Kr Rt - " Se aide anny a % pean Beis ent RAM ae, ms ERM ante Uy Wri eas Of eet ta OD TAO om ut pee on eee hee tee oe . ae ee F a or Lt ae eee ieee 566 Ov! CORNELL UNDTYVERSIAY LIBRARY BOUGHT WITH THE INCOME OF THE SAGE ENDOWMENT FUND GIVEN IN I89I BY HENRY WILLIAMS SAGE DATE DUE UI ty H 366. a “Tiina I ao 85 THE ORIGIN AND EVOLUTION OF LIFE ON THE THEORY OF ACTION REACTION AND INTERACTION OF ENERGY HALE LECRERES OF THE NATIONAL ACADEMY OF SCIENCES, WASHINGTON, APRIL, 1916 BY THE SAME AUTHOR MEN OF THE OLD STONE AGE. Illus- trated. 8vo net $5.00 “The book is the ripe fruit of the author's life study, served tn a ‘popular’ form that can be en- joved by any educated reader; in another sense it is the first authoritative summary of the wonderful series of arch@ological discoveries made in recent years."'—New York Times. Charles Scribner’s Sons Tyrannosaurus rex, THE KING OF THE TYRANT SAURIANS. The climax among carnivorous reptiles of a complex mechanism for the capture, storage, and release of energy. Contemporary with and de- stroyer of the large herbivorous dinosaurs. Compare p. 224. THE ORIGIN AND EVOLUTION OF LIFE ON THE THEORY OF ACTION REACTION AND INTERACTION OF ENERGY BY HENRY FAIRFIELD OSBORN SC.D. PRINCETON, HON. LL.D. TRINITY, PRINCETON, COLUMBIA, HON. D.SC. CAMBRIDGE HON. PH.D. CHRISTIANIA RESEARCH PROFESSOR OF ZOOLOGY, COLUMBIA UNIVERSITY VERTEBRATE PALZONTOLOGIST U. S. GEOLOGICAL SURVEY, CURATOR EMERITUS OF VERTEBRATE PALZONTOLOGY IN THE AMERICAN MUSEUM OF NATURAL HISTORY AUTHOR OF ‘‘FROM THE GREEKS TO DARWIN” “THE AGE OF MAMMALS,” “‘MEN OF THE OLD STONE AGE WITH 136 ILLUSTRATIONS NEW YORK CHARLES SCRIBNER’S SONS 1917 7 A373700 CopyRIGHT, 1916, BY THE SCIENCE PRESS COPYRIGHT, 1917, BY CHARLES SCRIBNER’S SONS Published September, 1917 DEDICATED TO MY COLLEAGUE AND FRIEND GEORGE ELLERY HALE HEAD OF THE MOUNT WILSON OBSERVATORY OF THE CARNEGIE INSTITUTION; ARDENT ADVOCATE OF THE SYNTHESIS OF THE SCIENCES IN RESEARCH PREFACE In these lectures we may take some of the initial steps toward an energy conception of Evolution and an energy conception of Heredity and away from the matter and form conceptions which have prevailed for over a century. The first half of this volume is therefore devoted to what we know of the capture, storage, release, and reproduction of energy in its simplest and most elementary living phases; the second half is devoted to the evolution of matter and form in plants and animals, also interpreted largely in terms of energy and mechanics. Lest the reader imagine that through the energy conception I am at present even pretend- ing to offer an explanation of the miracles of adaptation and of heredity, some of these miracles are recited in the second part of this volume to show that the germ evolution is the most incomprehensible phenomenon which has yet been dis- covered in the universe, for the greater part of what we see in animal and plant forms is only the visible expression of the in- visible evolution of the heredity-germ. We are not ready for a clearly developed energy conception of the origin of life, still less of evolution and of heredity; yet we believe our theory of the actions, reactions, and interactions of living energy will prove’ to be a step in the right direction. It is true that in the organism itself, apart from the heredity-germ, we have made great advances’ in the energy 1Some of the reasons for this assertion are presented in the successive chapters of this volume and summarized in the Conclusion. 2 One of the most influential works in this direction is Jacques Loeb’s Dynamics of Living Matter, a synthesis of many years of physicochemical research on the actions and reactions of living organisms. See also Loeb’s more recent work, The Organism as a Whole, published since these lectures were written. vii vill PREFACE conception. We observe many of the means by which energy is stored, and some of the complicated methods by which it is captured, protected, and released. We shall see that highly evolved organisms, such as the large reptiles and mammals and man, present to the eye of the anatomist and physiologist an inconceivable complexity of energy and form; but this we may in part resolve by reading the pages of this volume back- ward, Chinese fashion, from the mammal! to the monad, in which we reach a stage of relative simplicity. Thus the or- ganism as an arena for energy and matter, as a complex of in- tricate actions, becomes in a measure conceivable. The heredity-germ, on the contrary, remains inconceivable in each of its three powers, namely, in the Organism which it produces, in the succession of germs to which it gives rise, and in its own evolution in course of time. Having now stated the main object of these lectures, I invite the reader to study the following pages with care, be- cause they review some of the past history and introduce some of the new spirit and purpose of the search for causes in the domain of energy. I begin with matters which are well known to all biologists and proceed to matters which are somewhat more difficult to understand and more novel in purpose. In this review we need not devote any time or space to fresh arguments for the truth of evolution. The demonstra- ' ticn of evolution as a universal law of living nature is the great intellectual achievement of the nineteenth century. Evolution has outgrown the rank of a theory, for it has won a place in natural law beside Newton’s law of gravitation, and in one sense holds a still higher rank, because evolution is the universal master, while gravitation is one among its many 1Man is not treated at all in this volume, the subject being reserved for the final lectures in the Hale Series. PREFACE ix agents. Nor is the law of evolution any longer to be associ- ated with any single name, not even with that of Darwin, who was its greatest exponent.! It is natural that evolution and Darwinism should be closely connected in many minds, but we must keep clear the distinction that evolution is a law, while Darwinism is merely one of the several ways of inter- preting the workings of this law. In contrast to the unity of opinion on the Jaw of evolution | is the wide diversity of opinion on the causes of evolution. In fact, the causes of the evolution of life are as mysterious as the law of evolution is certain. Some contend that we already know the chief causes of evolution, others contend that we know little or nothing of them. In this open court of con- jecture, of hypothesis, of more or less heated controversy, the great names of Lamarck, of Darwin, of Weismann figure promi- nently as leaders of different schools of opinion; while there are others, like myself,? who for various reasons belong to no school, and are as agnostic about Lamarckism as they are about Darwinism or Weismannism, or the more recent form of Darwinism, termed Mutation by de Vries. In truth, from the period of the earliest stages of Greek thought man has been eager to discover some natural cause of evolution, and to abandon the idea of supernatural interven- tion in the order of nature. Between the appearance of The Origin of Species, in 1859, and the present time there have been great waves of faith in one explanation and then in an- other: each of these waves of confidence has ended in disap- pointment, until finally we have reached a stage of very general 1See From the Greeks to Darwin (Macmillan & Co., 1894), by the present author, in which the whole history of the evolution idea is traced from its first conception down to the time of Darwin. 2 Osborn, H. F., “The Hereditary Mechanism and the Search for the Unknown Factors of Evolution,” The Amer. Naturalist, May, 1895, pp. 418-439. x PREFACE scepticism. Thus the long period of observation, experiment, and reasoning which began with the French natural philosopher Buffon, one hundred and fifty years ago, ends in 1916 with the general feeling that our search for causes, far from being near completion, has only just begun. Our present state of opinion is this: we know to some extent ow plants and animals and man evolve; we do not know why they evolve. We know, for example, that there has existed a more or less complete chain of beings from monad to man, that the one-toed horse had a four-toed ancestor, that man has descended from an unknown ape-like form somewhere in the Tertiary. We know not only those larger chains of descent, but many of the minute details of these transforma- tions. We do not know their internal causes, for none of the explanations which have in turn been offered during the last hundred years satisfies the demands of observation, of experi- ment, of reason. It is best frankly to acknowledge that the chief causes of the orderly evolution of the germ are still en- tirely unknown, and that our search must take an entirely fresh start. As regards the continuous adaptability and fitness of liv- ing things, we have a reasonable interpretation of the causes of some of the phenomena of adaptation, but they are the smaller part of the whole. Especially mysterious are the chief phenomena of adaptation in the germ; the marvellous and continuous fitness and beauty of form and function remain largely unaccounted for. We have no scientific explana- tion for those processes of development from within, which Bergson! has termed “‘l’évolution créatrice,”’ and for which Driesch? has abandoned a natural explanation and assumed ' Bergson, Henri, 1907, L’ Evolution Créatrice. * Driesch, Hans, 1908, The Science and Philosophy of the Organism. PREFACE xl the existence of an entelechy, that is, an internal perfecting influence. This confession of failure is part of the essential honesty of scientific thought. We recall the fact that our baffled state of mind is by no means new, for in Kant’s work of 1790, his Methodical System of the Telcological Faculty of Judgment, he divides all things in nature into the “inorganic,” in which natural causes prevail, and the ‘‘organic,” in which the active teleological (i. ¢., purposive) principle of adaptation is sup- posed to prevail. There was in Kant’s mind a cleft between the domain of primeval matter and the domain of life, for in the latter he assumes the presence of a supernatural principle, of final causes acting toward definite ends. This view is ex- pressed in his Teleological Faculty of Judgment as follows: “But he” (the archeologist of Nature) ‘‘must for this end ascribe to the common mother an organization ordained pur- posely with a view to the needs of all her offspring, otherwise the possibility of suitability of form in the products of the animal and vegetable kingdoms cannot be conceived at all.’’? “Tt is quite certain that we cannot become sufficiently acquainted with organized creatures and their hidden poten- tialities by aid of purely mechanical natural principles; much less can we explain them; and this is so certain, that we may boldly assert that it is absurd for man even to conceive such an idea, or to hope that a Newton may one day arise able to make the production of a blade of grass comprehensible, ac- cording to natural laws ordained by no intention; such an insight we must absolutely deny to man.’’? For a long period after The Origin of Species appeared, Haeckel and many others believed that Darwin had arisen as the Newton for whom Kant did not dare to hope; but no 1 Kant, Emmanuel, 1790, § 70. 2 Tbid., § 74. xi PREFACE one now claims for Darwin’s law of natural selection a rank equal to that of Newton’s law of gravitation. If we admit the possibility that Kant was right, and that we can never become sufficiently acquainted with organized creatures and their hidden potentialities by aid of purely natural principles, we may be compelled to regard the origin and evolution of life as an ultimate law like the law of gravita- tion, which may be mathematically and physically defined, but cannot be resolved into any causes. We are not willing, however, to make such an admission at the present time and to abandon the search for causes. The question then arises, why has our long and arduous search after the causes of evolution so far been unsuccessful ? One reason why our search may have failed appears to be that the chief explorers have been trained in one school of thought, namely, the school of the naturalist. They all began their studies with observations on the external form and color of animals and plants; they have all observed the end results of long processes of evolution. Buffon derived his ideas of the causes of evolution from the comparison of the wild and domestic animals of the Old and New Worlds; Goethe observed the com- parative anatomy of man and of the higher animals; Lamarck observed the higher phases of the vertebrate and invertebrate animals; Darwin observed the form of most of the domestic animals and cultivated plants and, finally, of man, and noted the adaptive significance of the colors of flowers and birds, and the relations of flowers with birds and insects; de Vries compared the wild and cultivated species of plants. Thus all the great naturalists in turn—Buffon, Goethe, Lamarck, Dar- win, and de Vries—have attempted to reason backward, as it were, from the highly organized appearances of form and color to their causes. The same is true of the paleontologists: PREFACE xill Cope turned from the form of the teeth and skeleton backward to considerations of cause and energy, Osborn! reached a con- ception of evolution as of the relations of fourfold form, and hence proposed the word tetraplasy. The Heredity theories of Darwin, of de Vries, of Weis- mann have also been largely in the material conceptions of fine particles of matter such as ‘“‘pangens” and ‘‘ determinants.” There has been some consideration of function and of the internal phenomena of organisms, but there has been little or no serious attempt to reverse the mental processes of the naturalist and substitute those of the physicist in considering the causes of evolution.’ Moreover, all the explanations of evolution which have been offered by three generations of naturalists align themselves under two main ideas only. The first is the idea that the causes of evolution are chiefly from without inward, namely, beginning in the environment of the body and extending into the germ: this idea is centripetal. The second idea is just the reverse: it is centrifugal, namely, that the causes begin in the germ and extend outward into the body and into the environ- ment. The pioneer of the first order of ideas is Buffon, who early reached the opinion that favorable or unfavorable changes of environment directly alter the hereditary form of succeed- ing generations. Lamarck,’ the founder of a broader and more modern conception of evolution, concluded that the changes of form and function in the body and nervous system induced by habit and environment accumulate in the germ, 1 Osborn, H. F., “Tetraplasy, the Law of the Four Inseparable Factors of Evolution,” Jour. Acad. Nat. Sci. Phila., special anniversary volume issued September 14, 1912, pp. 275309. x . 2 See fuller exposition on pp. 10-23 of this volume. 3 For a fuller exposition of the theory of Lamarck, see pp. 143, 144. xiv PREFACE and are handed on by heredity to succeeding generations. This essential idea of LAMARCKISM was refined and extended by Herbert Spencer, by Darwin himself, by Cope and many others; but it has thus far failed of the crucial test of observa- tion and experiment, and has far fewer adherents to-day than it had forty years ago. We now perceive that Darwin’s original thought turned to the opposite idea, namely, to sudden changes in the heredity- germ itself! as giving rise spontaneously to more or less adap- tive changes of body form and function which, if favorable to survival, might be preserved and accumulated through natural selection. This pure DARwrnism has been refined and extended by Wallace, Weismann, and especially of late by de Vries, whose ‘‘mutation theory” is pure Darwinism in a new guise. Weismann’s great contribution to thought has been to point out the very sharp distinction which undoubtedly exists between the hereditary forces and predispositions in the hered- ity-germ and the visible expression of these forces in the or- * as Weismann terms it— ganism. It is in the ‘‘germ-plasm,’ in this volume termed the “ heredity-chromatin”—that the real evolution of all predispositions to form and function is taking place, and the problem of causes of evolution has become an infinitely more difficult one since Weismann has compelled us to realize that the essential question is the causes of germinal evolution rather than the causes of bodily evolution or of en- vironmental evolution. Again, despite the powerful advocacy of pure Darwinism by Weismann and de Vries in the new turn that has been given to our search for causes by the rediscovery of the law of Mendel and the heredity doctrines which group under Men- Osborn, H. F., ““Darwin’s Theory of Evolution by the Selection of Minor Saltations,”’ The Amer. Naturalist, February, 1912, pp. 76-82. PREFACE XV DELISM,' it may be said that Darwin’s law of selection as a natural explanation of the origin of all fitness in form and func- tion has also lost its prestige at the present time, and all of © Darwinism which now meets with universal acceptance is the law of the survival of the fittest, a limited application of Darwin’s: great idea as expressed by Herbert Spencer. Few biologists to-day question the simple principle that the fittest tend to survive, that the unfit tend to be eliminated, and that the present aspect of the entire living world is due to this great pruning-knife which is constantly sparing those which are best fitted or adapted to any conditions of environment and cutting out those which are less adaptive. But as Cope pointed out, the survival of fitness and the origin of fitness are two very different phenomena. If the naturalists have failed to make progress in the search for causes, I believe it is chiefly because they have attempted to reason backward from highly complex plant and animal forms to causes. The cart has always been placed before the horse; or, to express it in another way, thought has turned from the forms of living matter toward a problem which involves the phenomena of living energy; or, still more briefly, we have been thinking from matter backward into energy rather than from energy forward into matter and form. All speculation on the origin of life, fruitless as it may at first appear, has the advantage that it compels a sudden re- versal of the naturalist’s point of view, for we are forced to work from energy upward into form, because, at the begin- ning, form is nothing, energy is everything. Energy appears to be the chief end of life—the first efforts of life work toward the capture of energy, the storage of energy, the release of 1 Mendelism chiefly refers to the distinction and laws of distribution of separable or unit characters in the germ and in the individual in course of its development. Xvi PREFACE energy. The earliest adaptations we know of are designed for the capture and storage of energy. Matter in the state of relative rest known as plant and animal form is present, but, in the simplest and lowliest types of life, form does not conceal and mask the processes of energy as it does in the higher types. Similarly, the earliest fitness we discover in the bacteria or monads is the fitness of group- ing and organizing different kinds of energy—the energy of molecules, of atoms, of electrons as displayed in the twenty- six or more chemical elements which enter into life. In searching among these early episodes of life in its origin we discover that four complexes of energy are successively added and combined. The Inorganic Environment of the sun, of the earth, of the water, of the atmosphere is exploited thor- oughly in search of energy by the Organism: the organism itself becomes an organism only by utilizing the energy of the environment and by coordinating its own internal energies. Whether the Germ as the special centre of heredity and repro- duction of energy is as ancient as the organism we do not know; but we do know that it becomes a distinct and highly complex ‘centre of potential energy which directs the way to the entire energy complex of the newly developing organism. Finally, as organisms multiply and acquire various kinds of energy, the Life Environment arises as a new factor in the energy complex. Thus in the process of the origin and early evolution of life, complexes of four greater and lesser energy groups arise, namely: INORGANIC ENVIRONMENT: the energy content in the sun, the earth, the water, and the air; ORGANISM: the energy of the individual, developing and changing the cells and tissues of the body, including that part of the germ which enters every cell; HEREDITY-GERM: the energies of thé heredity substance (heredity-chromatin) concentrated in the reproduc- PREFACE xvii tive cells of continuous and successive generations, as well as in all the cells and tissues of the organism; and LIFE ENVIRON- MENT: beginning with the monads and alge and ascending in a developing scale of plants and animals. There are here four evolutions of energy rather than one, and the problem of causes is how the four evolutions are ad- justed to each other; and especially how the evolution of the germ adjusts itself to that of the inorganic environment and of the life environment, and to the temporary evolution of the organism itself. I do not propose to evade the difficulties of the problem of the origin and evolution of life by minimizing any of them. Whether our approach through energy will lead to the dis- covery of some at least of the unknown causes of evolution remains to be determined by many years of observation and experiment. Whereas our increasing knowledge of energy in matter reveals an infinity of energized particles even in the in- finitely minute aggregations known as molecules—an infinity which we observe but do not comprehend—we find in our search for causes of the origin and evolution of life that we have reached an entirely new point of departure, namely, that of the physicist and chemist rather than the old point-of departure of the naturalist. We have obtained a starting-point for new and untried paths of exploration which may be followed dur- ing the present century—paths which have long been trodden with a different purpose by physicists and chemists, and by physiologists and biochemists in the study of the organism it- self. The reader may thus follow, step by step, my own experi- ence and development of thought in preparing these lectures. The reason why I happened to begin this volume with the prob- xviii PREFACE lem of energy and end with that of the evolution of form is that these lectures were prepared and delivered midway in a cosmic-evolution series which opened with Sir Ernest Ruther- ford’s! discourse on ‘‘The Constitution of Matter and the Evolution of the Elements,’ and continued with ‘The Evolu- tion of the Stars and the Formation of the Earth,’ by Doctor William Wallace Campbell,’ and ‘‘ The Evolution of the Earth,” by Professor Thomas Chrowder Chamberlin. My friend George Ellery Hale placed upon me the responsibility of weaving the partly known and still more largely unknown narrative which connects the forms of energy and matter ob- served in the sun and stars with the forms of energy and matter which we observe in the bodies of our own mammalian ances- tors. Certainly we appear to inherit some, if not all, of our physicochemical characters from the sun; and to this degree we may claim kinship with the stellar universe. Some of our distinctive characters and functions are actually properties of our ancestral star. Physically and chemically we are the off- spring of our great luminary, which certainly contributes to us all our chemical elements and all the physical properties which bind them together. Some day a constellation of genius will unite in one labora- tory on the life problem. This not being possible at present, I have endeavored during the past two years‘ for the purposes 1 Rutherford, Sir Ernest, ‘The Constitution of Matter and the Evolution of the Elements,” first series of lectures on the William Ellery Hale foundation, delivered in April, 1914; Pop. Sci. Mon., August, 1915, pp. 105-142. . * Campbell, William Wallace, “The Evolution of the Stars and the Formation of the Earth,” second series of lectures on the William Ellery Hale foundation, delivered De- cember 7 and 8, 1914; Pop. Sci. Mon., September, 1915, pp. 209-235; Scientific Monthly, October, 915, pp. 1-17; November, 1915, pp. 177-194; December, IQI5, pp. 238-255. ’ Chamberlin, Thomas Chrowder, ‘The Evolution of the Earth,” third series of lec- tures on the William Ellery Hale foundation, delivered April 19-21, 1915; Scientific Afonthly, May, 1916, pp. 417-437; June, 1916, pp. 536-556. ‘I first opened a note-book on this subject in the month of April, 1915, when I was invited by Doctor George Ellery Hale to undertake the preparation of these lectures. PREFACE X1x of my own task to draw a large number of specialists together in correspondence and in a series of personal conferences and discussions; and whatever merits this volume may possess are partly due to their generous response in time and thought to my invitation. Their suggestions are duly acknowledged in footnotes throughout the text. I have myself approached the problem through a synthesis of astronomy, geology, physics, chemistry, and biology. In consulting authorities on this subject I have made one exception, namely, the problem of the origin of life itself with its vast literature going back to the ancients—I have read none of it and quoted none of it. In order to consider the problem from a fresh and unbiassed point of view, I have also purposely refrained from reading any of the recent and authoritative treatises of Schafer,! Moore,? and others on the origin of life. It will be interesting for the reader to compare the conclusions previously reached by these distinguished chemists with those presented in the following pages. For invaluable guidance in the phenomena of physics I am deeply indebted to my colleague Professor Michael I. Pupin, of Columbia University, who has given me his views as to the fundamental relation of Newton’s laws of motion to the modern laws of heat and energy (thermodynamics), and has clarified the laws of action, reaction, and interaction from the physical standpoint. Without this aid I could never have developed what I believe to be the new biological principle set forth in this work. I owe to him the confirmation of the use of the word interaction as a physical term, which had occurred to me first as a biological term. 1 Schafer, Sir Edward A., Life, Its Nature, Origin, and Maintenance, Longmans, Green & Co., New York, 1912. 2 Moore, Benjamin, The Origin and Nature of Life, Henry Holt & Co., New York; Williams & Norgate, London, 1913. XX PREFACE As to the physicochemical actions and reactions of the living organism I have drawn especially from Loeb’s Dynamics of Living Matter. In the physicochemical section I am also greatly indebted to the very suggestive work of Henderson entitled The Fitness of the Environment, from which I have especially derived the notion that fitness long antedates the origin of life. Professor Hans Zinsser, of Columbia University, has aided in a review of Ehrlich’s theory of antibodies and the results of later research concerning them. Professor Ulric Dahlgren, of Princeton University, has aided the preparation of this work with valuable notes and suggestions on the light, heat, and chemical rays of the sun, and on phosphorescence and electric phenomena in the higher organisms. In the geochemical and geophysical section I am indebted to my colleagues in the National Academy, F. W. Clarke and George F. Becker, not only for the revision of parts of the text, but for many valuable suggestions and criticisms. For suggestions as to the chemical conditions which may have prevailed in the earth during the earliest period in the origin of life, as well as for criticisms and careful revision of the chemical text I am especially indebted to my colleague in Columbia University, Professor William J. Gies. In the astronomic section I desire to express my indebted- ness to George Ellery Hale, of the Mount Wilson Observatory, for the use of photographs, and to Henry Norris Russell, of Princeton University, for notes upon the heat of the primordial earth’s surface. In the early narrative of the earth’s history and in the subsequent geographic and physiographic charts and maps Professor Charles Schuchert and Professor Joseph Barrell, of Yale University, kindly cooperated with the loan of illustrations and otherwise. In the section on the evolution of bacteria, which is a part pertaining to the idea of the early PREFACE xxi evolution of energy in living matter, I enjoyed the cooperation of Doctor I. J. Kligler, formerly of the American Museum of Natural History, and now at the Rockefeller Institute for Medical Research. In the botanical section I am especially indebted to Pro- fessor T. H. Goodspeed, of the University of California, and to Doctor Marshall Avery Howe, of the Botanical Gardens, for many valuable notes and suggestions, as well as for certain illustrations. In the early zoological section I am indebted to my colleagues at Columbia University, Professor Edmund B. Wilson and Professor Gary N. Calkins. Especial thanks are due to Mr. Roy W. Miner, of the American Museum, for his careful comparisons of recent forms of marine life with the Cam- brian forms discovered by Doctor Charles Walcott, who sup- plied me with the beautiful photographs shown in Chapter IV. In preparing the chapters on the evolution of the verte- brates, I have turned to my colleague Professor W. K. Gregory, of the American Museum and Columbia University, who has aided both with notes and suggestions, and in the supervision of various illustrations relating to the evolution of vertebrate form. The illustrations are chiefly from the collections of the American Museum of Natural History, as portrayed in original drawings by Charles R. Knight, Erwin S. Christman, and Richard Deckert. The entire work has been faithfully collated and put through the press by my research assistant, Miss Christina D. Matthew. It affords me great pleasure to dedicate this work to the astronomer friend whose enthusiasm for my own field of work in biology and paleontology has always been a source of en- couragement and inspiration. HENRY FAIRFIELD OSBORN. AMERICAN Museum oF NatTurAL HIstory, February 26, 1917. CONTENTS INTRODUCTION FOUR QUESTIONS REGARDING LIFE THE ENERGY CONCEPT OF LIFE THE FOUR COMPLEXES OF ENERGY PART I. THE ADAPTATION OF ENERGY CHAPTER I PREPARATION OF THE EarTH FOR LIFE THE LIFELESS EARTH THE LIFELESS WATER THE ATMOSPHERE CHAPTER II THE SUN AND THE PHYSICOCHEMICAL ORIGINS OF LIFE HEAT AND LIGHT LIFE ELEMENTS IN THE SUN HEAT AND ELECTRIC ENERGY THE CAPTURE OF SUNLIGHT JONIZATION—THE ELECTRIC ENERGY OF ATOMS COORDINATION OF ACTIVITIES BY MEANS OF INTERACTION FUNCTIONS OF THE CHEMICAL LIFE ELEMENTS . PRIMARY STAGES OF LIFE xxiii PAGE Io 18 24 34 39 43 45 48 51 53 56 59 67 XXIV CONTENTS NEW ORGANIC COMPOUNDS . INTERACTIONS—ENZYMES, ANTIBODIES, HORMONES, AND CHALONES CHEMICAL MESSENGERS PHYSICOCHEMICAL DIFFERENTIATION CHAPTER III ENERGY EvoLuTION oF BACTERIA, ALG, AND PLANTS EVOLUTION OF BACTERIA PROTOPLASM AND HEREDITY-CHROMATIN CHLOROPHYLL—THE SUNLIGHT CONVERTER OF PLANTS EvoLUTION OF ALGE—THE MOST PRIMITIVE PLANTS PLANT AND ANIMAL EVOLUTION CONTRASTED PART II. THE EVOLUTION OF ANIMAL FORM CHAPTER IV THE ORIGINS OF ANIMAL LIFE AND EVOLUTION OF THE INVERTEBRATES EvoLutTion OF PROTOZOA EvoLuTION OF METAzOA . i Hl ey SS CAMBRIAN INVERTEBRATES . . ee ee ENVIRONMENTAL CHANGES ‘ e ache 2s MUTATIONS OF WAAGEN ‘ eo CHAPTER V VISIBLE AND INVISIBLE EVOLUTION OF THE EVOLUTION OF THE GERM CHARACTER EVOLUTION . THE LAWS OF ADAPTATION VERTEBRATES PAGE 69 71 72 78 OI 99 IOI 105 IIO 117 118 134 138 141 146 152 CONTENTS CHAPTER VI EvoLtuTion oF Bopy Form IN THE FISHES AND AMPHIBIANS EARLIEST KNOWN FISHES EARLY ARMORED FISHES PRIMORDIAL SHARKS RISE OF MODERN FISHES EVOLUTION OF THE AMPHIBIANS CHAPTER VII Form EVoLuTION OF THE REPTILES AND BIRDS EARLIEST REPTILES MAMMAL-LIKE REPTILES ADAPTIVE RADIATION OF REPTILES AQUATIC REPTILES CARNIVOROUS DINOSAURS HERBIVOROUS DINOSAURS FLYING REPTILES ORIGIN OF BIRDS ARRESTED REPTILIAN EVOLUTION CHAPTER VIII EVOLUTION OF THE MAMMALS ORIGIN OF MAMMALS CHARACTER EVOLUTION . CAUSES OF EVOLUTION. . . . + «| - MoDES OF EVOLUTION . . . + © 8 ee XXV PAGE 160 165 167 169 177 234 245 251 XXV1 CONTENTS PAGE ADAPTATION TO ENVIRONMENT . . . . ... eg pl oe O28 GEOGRAPHIC DISTRIBUTION. ; y 4 4 He» & % 4 = 4 BRO CHANGES OF PROPORTION fo ae UG ea ae ee ee, oe E28 RETROSPECT AND PROSPECT . . . . eee ee 275 CONCLUSION f 4. ee So. Bi Bike ok 4 281 APPENDIX NOTE I. DIFFERENT MODES OF STORAGE AND RELEASE OF ENERGY IN LIVING ORGANISMS ; 285 II. BLurE-GREEN ALG POSSIBLY AMONG THE FIRST SETTLERS OF OUR PLANET ; 285 III. ONE SECRET OF LIFE—SYNTHETIC TRANSFORMATION OF IN- DIFFERENT MATERIAL 286 IV. INTERACTION THROUGH CATALYSIS—THE ACCELERATION OF CHEMICAL REACTIONS THROUGH THE PRESENCE OF ANOTHER SUBSTANCE WHICH IS NOT CONSUMED BY THE REACTION 286 V. THE CAUSES OR AGENTS OF SPEED AND ORDER IN THE REAC- TIONS OF LIVING BODIES—ENZYMES, COLLOIDS; ETC. 287 VI. INTERACTIONS OF THE ORGANS OF INTERNAL SECRETION AND HEREDITY . . 289 VII. TaBLE—RELATIONS OF THE PRINCIPAL GROUPS OF ANIMALS REFERRED TO IN THE TEXT ae Sy ty. oh 290 BIBLIOGRAPHY: 2 2 08 « @o@ 4 @ we » w x = & 263 INDEX Sy Ge Se AY GOAT a> Bie 4: a2 3307 ILLUSTRATIONS Plate. Tyrannosaurus rex, the “‘king of the tyrant saurians”’ Frontispiece FIG. PAGE 1. The moon’s surface . ; » 36 2. Deep-sea ooze, the foraminifera . eh 32 3. Light, heat, and chemical influence of the sun ‘ 44 4. Chemical life elements in the sun. ; 46 5. The earliest phyla of plant and animal life a 3 50 6. Hydrogen vapor in the solar atmosphere. 60 7. Hydrogen flocculi surrounding sun-spots s 61 8. The sun, showing sun-spots and calcium vapor . 64 9. Chemical life elements in the sun i 65 to. Hand form, determined by heredity and secretions 76 11. Fossil and living bacteria compared 85 12. Protoplasm and chromatin of Ameba 93 13. The two structural components of the living world 94 14. Chromatin in Sequoia and Trillium compared ‘ 96 15. Fossil and living alge compared . 102 16. Typical forms of Protozoa : : . 112 17. Light, heat, and chemical influence of the sun : ‘ 113 18. Skeletons of typical Protozoa . IIS 19. Map—Late Lower Cambrian world environment . 119 2. A Mid-Cambrian trilobite . ; 121 21. Brachiopods, Cambrian and recent ‘ 123 22. Horseshoe crab and shrimp, Cambrian and recent . 124 23. Map—Middle Cambrian world environment 6 a oak Oy 125 24. Sea-cucumbers, Cambrian and recent bo 8 %. Mb, 0 2s 127 xxvii XXVIli ILLUSTRATIONS FIG. 25. 206. 27. 28. 29. 30. a0 32. 33- 34- 35- 36. 37- 38. 39- 40. Worms, Middle Cambrian and recent Chetognaths, Cambrian and recent . Jellyfish, Cambrian and recent The twelve chief habitat zones Life zones of Cambrian and recent invertebrates Map—North America in Cambrian times Sea-scorpions of Silurian times Map—North America in Middle Devonian times Changing environment during fifty million years Fossil starfishes Mutations of Waagen in ammonites Mutations of Spirifer mucronatus Shell pattern and tooth pattern of Glyptodon Teeth of Euprotogonia and Meniscotherium Adaptation of the fingers in a lemur Total geologic time scale Adaptation of form in three marine vertebrates—shark, ichthyosaur, and dolphin Chronologic chart of vertebrate succession The existing lancelets (Amphioxus) Five types of body form in fishes Map—North America in Upper Silurian time . The Ostracoderm Paleaspis The Antiarchi. Bothriolepis The Arthrodira. Dinichthys intermedius A primitive Devonian shark, Cladoselache Adaptive radiation of the fishes Fish types from the Old Red Sandstone Map—the world in Early Lower Devonian times Change of adaptation in the limbs of vertebrates PAGE 128 129 130 131 I31 132 133 134 135 136 139 140 148 149 150 153 155 161 162 163 164 165 166 167 168 170 171 172 FIG. 54. 55+ 56. 57- 58. 59. 60. 62. 63. 64. 65. 66. 67. 68. 60. 70. FE. 72 73- 74. 75: 76. 77- 78. 79. So. 81. 82. ILLUSTRATIONS Deep-sea fishes—extremes of adaptation in locomotion and illumina- tion Phosphorescent illuminating organs of deep-sea fishes . Map—North America in Upper Devonian time The earliest known limbed animal A primitive amphibian Descent of the Amphibia . Chief amphibian types of the Carboniferous Skull and vertebral column of Diplocaulus Map—the world in Earliest Permian time Amphibia of the American Permo-Carboniferous Skeleton of Eryops Map—the world in Earliest Permian time Ancestral reptilian types Reptiles with skulls transitional from the amphibian Map—the world in Middle Permian time The fin-back Permian reptiles Mammal-like reptiles of South Africa A South African “‘dog-toothed”’ reptile Adaptive radiation of the Reptilia Geologic records of reptilian evolution Dinosaur mummy—a relic of flood-plain conditions Reptiles leaving a terrestrial for an aquatic habitat Convergent adaptation of amphibians and reptiles Adaptation of reptiles to the aquatic habitat zones Alternating adaptation of the “‘leatherback”’ turtles The existing ‘‘leatherback”’ turtle Marine adaptation of terrestrial Chelonia Marine pelagic adaptation of the ichthyosaurs . Restorations of two ichthyosaurs XxIX PAGE 173 174 175 176 177 178 179 180 181 182 183 185 186 187 188 189 190 192 193 195 197 199 200 201 202 202 203 204 205 XXX FIG. 83. 84. 86. 87. 88. 89. go. gl. Q2. 93- 04. 95- 96. 97- 98. 99. 100. IOl. 102. 103. Io4. 105. 106. 107. 108. 109. 110. Til. ILLUSTRATIONS Map—North America in Upper Cretaceous time Convergent forms of aquatic reptiles A plesiosaur from the Jurassic of England Types of marine pelagic plesiosaurs Tylosaurus, a sea lizard Upper Triassic life of the Connecticut River Terrestrial evolution of the dinosaurs Map—North America in Upper Triassic time A carnivorous dinosaur preying upon a sauropod Extreme adaptation in the “‘tyrant”’ and ‘‘ostrich”’ dinosaurs Four restorations of the ‘‘ostrich’”’ dinosaur Anchisaurus and Plateosaurus compared Map—the world in Lower Cretaceous time Map—North America in Lower Cretaceous time Three principal types of sauropods Terrestrio-fluviatile theory of the habits of A patosaurus Primitive iguanodont Camptosaurus Upper Cretaceous iguanodonts from Montana Adaptive radiation of the iguanodont dinosaurs Tyrannosaurus and Ceratopsia—offensive and defensive energy complexes Restoration of the Pterodactyl Ancestral tree of the birds Skeletons of Archeopteryx and pigeon compared Silhouettes of Archaeopteryx and pheasant Four evolutionary stages in the four-winged bird Parachute flight of the primitive bird Restoration of Archaeopteryx Reversed aquatic evolution of wing and body form The sei whale, Balenoptera borealis PAGE 206 207 207 208 209 211 217 218 210 220 221 222 224 226 227 228 228 228 220 220 234 FIG. 112. II3. II4. IIS. 116. 117. 118. IIQ. 120. 12. 122. 123. 124. 125. 126. 127. 128. 129. 130. 131. 132. 133. 134. T3153 II. ILLUSTRATIONS The tree shrew, Tupaia Primitive types of monotreme and marsupial . Ancestral tree of the mammals Adaptive radiation of the mammals Alternating adaptation in the kangaroo marsupials Evolution of proportion. Okapi and giraffe Brachydactyly and dolichodactyly Result of removing the thyroid and parathyroid glands Result of removing the pituitary body Main subdivisions of geologic time Map—North Polar theory of the distribution of mammals . Scene in western Wyoming in Middle Eocene times Two stages in the early evolution of the ungulates A primitive whale from the Eocene of Alabama Map—North America in Upper Oligocene time Two stages in the evolution of the titanotheres Evolution of the horn in the titanotheres Horses of Oligocene time Stages in the evolution of the horse Epitome of proportion evolution in the Proboscidea Map—the ice-fields of the fourth glaciation Groups of reindeer and woolly mammoth . Glacial environment of the woolly rhinoceros . Pygmies and plainsmen of New Guinea TABLES . Distribution of the chemical elements . Functions of the life elements . . . . . . . . . to face XXX1 PAGE 33 67 “ THE ORIGIN AND EVOLUTION OF LIFE INTRODUCTION Four questions as to the origin of life. Vitalism or mechanism? Creation or evolution? Law or chance? The energy concept of life. Newton’s laws of motion. Action and reaction. Interaction. The four complexes of energy. Darwin’s law of Natural Selection. WE may introduce this great subject by putting to ourselves four leading questions: First, Is life upon the earth something new? Second, Does life evolution externally resemble stel- lar evolution? Third, Is there evidence that similar internal physicochemical laws prevail in life evolution and in lifeless evolution? Fourth, Are life forms the result of law or of chance? Four QUESTIONS AS TO THE ORIGIN oF LIFE Our first question is one which has not yet been answered by science,! although there are two opinions regarding it. Does the origin of life represent the beginning of something new in the cosmos, or does it represent the continuation and evolu- tion of forms of matter and energy already found in the earth, in the sun, and in the other stars? The traditional opinion is that something new entered this and possibly other planets with the appearance of life; this view is also involved in all the older and newer hypotheses 1 Science consists of the body of well-ascertained and verified facts and laws of nature. It is clearly to be distinguished from the mass of theories, hypotheses, and opinions which are of value in the progress of science. T 2 THE ORIGIN AND EVOLUTION OF LIFE which group around the idea of vitalism or the existence of specific, distinctive, and adaptive energies in living matter— energies which do not occur in lifeless matter. The more modern scientific opinion is that life arose from a recombination of forces pre-existing in the cosmos. To hold to this opinion, that life does not represent the entrance either of a new form of energy or of a new series of laws, but is sim- ply another step in the general evolutionary process, is cer- tainly consistent with the development of mechanics, physics, and chemistry since the time of Newton and of evolutionary thought since Buffon, Lamarck, and Darwin. Descartes (1644) led all the modern natural philosophers in perceiving that the explanation of life should be sought in the physical terms of motion and matter. Kant at first (1755-1775) adopted and later (1790) receded from this opinion. These contrasting opinions, which are certainly as old as Greek philosophy and probably much older, are respectively known as the vitalistic and the mechanistic. We may express as our own opinion, based upon the appli- cation of uniformitarian evolutionary principles, that when life appeared on the earth some energies pre-existing in the cosmos were brought into relation with the chemical elements already existing. In other words, since every advance thus far in the quest as to the nature of life has been in the direc- tion of a physicochemical rather than of a vitalistic explanation, from the time when Lavoisier (1743-1794) put the life of plants on a solar-chemical basis, if we logically follow the same direc- tion we arrive at the belief that the last step into the unknown —one which possibly may never be taken by man—will also be physicochemical in all its measurable and observable proper- ties, and that the origin of life, as well as its development, will ultimately prove to be a true evolution within the pre-existing FOUR QUESTIONS REGARDING LIFE 3 cosmos. Without being either a mechanist or a materialist, one may hold the opinion that life is a continuation of the evolu- tionary process rather than an exception to the rest of the cosmos, because both mechanism and materialism are words borrowed from other sources which do not in the least con- vey the impression which the activities of the cosmos make upon us. This impression is that of limitless and ordered energy. Our second great question relates to the exact significancef of the term evolution when applied to lifeless and to living matter. Is the development of life evolutionary in the same sense or is it essentially different from that of the inorganic world? Let us critically examine this question by comparing the evolution of life with what is known of the evolution of the stars, of the formation of the earth; in brief, of the com- parative anatomy and physiology of the universe as developed by the physicist Rutherford,! by the astronomer Campbell, and by the geologist Chamberlin.? Or we may compare the evolution of life to the possible evolution of the chemical ele- ments themselves from simpler forms, in passing from primitive nebule through the hotter stars to the planets, as first pointed out by Clarke! in 1873, and by Lockyer in 1874. In such comparisons do we find a correspondence between the orderly development of the stars and the orderly develop- ment of life? Do we observe in life a continuation of processes which in general present a picture of the universe slowly cool- ing off and running down? Or, after hundreds of millions of years of more or less monotonous repetition of purely physico- chemical and mechanical reaction, do we find that electrons, 1 Rutherford, Sir Ernest, 1915. 2 Campbell, William Wallace, 1915. 3 Chamberlin, Thomas Chrowder, 1916. 4 Clarke, F. W., 1873, p. 323. 4 THE ORIGIN AND EVOLUTION OF LIFE atoms, and molecules break forth into new forms and mani- festations of energy which appear to be “creative,” convey- ing to our eyes at least the impression of incessant genesis of new combinations of energy, of matter, of form, of function, of character ? To our senses it appears as if the latter view were the cor- rect one, as if something new is breathed into the aging dust, as if the first appearance of life on this planet marks an actual reversal of the previous order of things. Certainly the cosmic processes cease to run down and begin to build up, abandoning old forms and constructing new ones. Through these activities within matter in the living state the dying earth, itself a mere cinder from the sun, develops new chemical compounds; the chemical elements of the ocean are enriched from new sources of supply, as additional amounts of chemical compounds, pro- duced by organisms from the soil or by elements in the earth that were not previously dissolved, are liberated by life proc- esses and ultimately carried out to sea; the very composition of the rocks is changed; a new life crust begins to cover the earth and to spread over the bottom of the sea. Our old in- organic planet is reorganized, and we see in living matter a reversal of the melancholy conclusion reached by Campbell! that ‘Everything in nature is growing older and changing in condition; slowly or rapidly, depending upon circumstances; the meteorological elements and gravitation are tearing down the high places of the earth; the eroded materials are trans- ported to the bottoms of valleys, lakes, and seas; and these results beget further consequences.”’ Thus it certainly appears, in answer to our second ques- tion, that living matter does not follow the old evolutionary or- der, but represents a new assemblage of energies and new types ‘Campbell, William Wallace, 1915, p. 209. FOUR QUESTIONS REGARDING LIFE 5 of action, reaction, and interaction—to use the terms of ther- modynamics—between those chemical elements which may be as old as the cosmos itself, unless they prove to represent an evolution from still simpler elements. Such evolution, we repeat with emphasis, is not like that of the chemical elements or of the stars; the evolutionary proc- ess now takes an entirely new and different direction. Al- though it may arise through combinations of pre-existing ener- gies, it is essentially constructive and apparently though not actually creative;! it is continually giving birth to an infinite variety of new forms and functions which never appeared in the universe before. It is a continuous creation or creative evolution. Although this creative power is something new derived from the old, it presents the first of the numerous con- trasts between the living and the lifeless world. Our third great question, however, relates to the continua- tion of the same physicochemical laws in living as in lifeless — matter, and puts the second question in another aspect. Is there a creation in the strict sense of the term, namely, that some new form of energy arises? No, so far as we observe, the process is still evolutionary rather than creative, because all the new characters and forms of life appear to arise out of new combinations of pre-existing matter. In other words, the old forms of energy transformations appear to be taking a new direction. I shall attempt to show that since in their simple forms living processes are known to be physicochemical and are 1 Creation (L. creatio, creare, pp. creatus; akin to Gr. xpalvey, complete; Sanskrit, V kar, make), in contradistinction to evolution, is the production of something new out of nothing, the act-of producing both the material and the form of that which is made. Evolution is the production of something new out of the building-up and recombination of something which already exists. 7 6 THE ORIGIN AND EVOLUTION OF LIFE more or less clearly interpretable in terms of action, reaction, and interaction, we are compelled to believe that complex forms will also prove to be interpretable in the same terms. None the less, if we affirm that the entire trend of our observation is in the direction of physicochemical explanations rather than of vitalism and vitalistic hypotheses, this is very far from affirming that the explanation of life is purely materialistic, or purely mechanistic, or that any of the present physico- chemical explanations are final or satisfying to our reason. Chemists and biological chemists have very much more to discover. May there not be in the assemblage of cosmic chem- ical elements necessary to life, which we shall distinguish as ” the ‘‘life elements,’ some known element which thus far has not betrayed itself in chemical analysis? This is not impossi- ble, because a known element like radium, for example, might well be wrapped up in living matter but remain as yet unde- tected, owing to its suffusion or presence in excessively small quantities or to its possession of properties that have escaped notice. Or, again, some unknown chemical element, to which the hypothetical term bion might be given, may lie awaiting discovery within this complex of known elements. Or an unknown source of energy may be active here. It is, however, far more probable from our present state of knowledge that unknown principles of action, reaction, and interaction between living forms await discovery; such prin- ciples are indeed adumbrated in the as yet partially explored activities of various chemical messengers in the bodies of plants and animals. We are now prepared for the fourth of our leading questions. If it be determined that the evolution of non-living matter follows certain physical laws, and that the living world con- FOUR QUESTIONS REGARDING LIFE 7 forms to many if not to all of these laws, the final question which arises is: Does the living world also conform to law in its most important aspect, namely, that of fitness or adapta- tion, or does law emerge from chance? In other words, in the origin Gad evolution of living things, does nature make a departure from its previous orderly procedure and substitute chance for law? This is perhaps the very oldest biologic question that has entered the human mind, and it is one on which the widest difference of opinion exists even to-day. Let us first make clear what we mean by the distinction between law and chance. Astronomers have described the orderly development of the stars, and geologists the orderly development of the earth: is there also an orderly development of life? Are life forms, like celestial forms, the result of law or are they the result of chance? That life forms have reached their present stage through the operations of chance has been the opinion held by a great line of natural philosophers from Democritus and Empedocles to Darwin, and including Poulton, de Vries, Bateson, Morgan, Loeb, and many others of our own day. Chance is the very essence of the original Darwinian selec- tion hypothesis of evolution. William James! and many other eminent philosophers have adopted the “chance” view as if it had been actually demonstrated. Thus James observes: ‘Absolutely impersonal reasons would be in duty bound to show more general convincingness. Causation is indeed too obscure a principle to bear the weight of the whole structure of theology. As for the argument from design, see how Dar- winian ideas have revolutionized it. Conceived as we now conceive them, as so many fortunate escapes from almost lim- 1 James, William, 1902, pp. 437-439. 8 THE ORIGIN AND EVOLUTION OF LIFE itless processes of destruction, the benevolent adaptations which we find in nature suggest a deity very different from the one who figured in the earlier versions of the argument. The fact is that these arguments do but follow the combined sug- gestions of the facts and of our feeling. They prove nothing rigorously. They only corroborate our pre-existent partiali- ties.’ Again, to quote the opinion of a recent biological writer: “And why not? Nature has always preferred to work by the hit-or-miss methods of chance. In biological evolution mil- lions of variations have been produced that one useful one might occur.’’! I have long maintained that this opinion is a biological dogma;? it is one of the string of hypotheses upon which Dar- win hung his theory of the origin of adaptations and of species, a hypothesis which has gained credence through constant re- iteration, for I do not know that it has ever been demon- strated through the actual observation of any evolutionary series. That life forms have arisen through /aw has been the opinion of another school of natural philosophers, headed by Aristotle, the opponent of Democritus and Empedocles. This opinion has fewer scientific and philosophical adherents; yet Eucken,'’ following Schopenhauer, has recently expressed it as follows: “From the very beginning the predominant philosophical ten- dency has been against the idea that all the forms we see around us have come into existence solely through an accumulation of accidental individual variations, by the mere blind concurrence of these variations and their actual survival, without the op- ’ Davies, G. R., 1916, p. 583. ? Biology, like theology, has its dogmas. Leaders have their disciples and blind fol- lowers. All great truths, like Darwin’s law of selection, acquire a momentum which sustains half-truths and pure dogmas. 3 Eucken, Rudolf, 1912, p. 257. FOUR QUESTIONS REGARDING LIFE 9 eration of any inner law. Natural science, too, has more and more demonstrated its inadequacy.” A modern chemist also questions the probability of the en- vironmental fitness of the earth for life being a mere chance process, for Henderson remarks: ‘There is, in truth, not one chance in countless millions of millions that the many unique properties of carbon, hydrogen, and oxygen, and especially of their stable compounds, water and carbonic acid, which chiefly make up the atmosphere of a new planet, should simultaneously occur in the three elements otherwise than through the opera- tion of a natural law which somehow connects them together. There is no greater probability that these unique properties should be without due cause uniquely favorable to the organic mechanism. These are no mere accidents; an explanation is to seek. It must be admitted, however, that no explanation is at hand.’’! Unlike our first question as to whether the principle of life introduced something new in the cosmos, a question which is still in the stage of pure speculation, this fourth question of law versus chance in the evolution of life is no longer a matter of opinion, but of direct observation. So far as law is con- cerned, we observe that the evolution of life forms is like that of the stars: their origin and evolution as revealed through paleontology go to prove that Aristotle was essentially right when he said that “Nature produces those things which, being continually moved by a certain principle contained in them- selves, arrive at a certain end.”? What this internal moving principle is remains to be discovered. We may first exclude the possibility that it acts either through supernatural or teleo-— logic interposition through an externally creative power. Al- though its visible results are in a high degree purposeful, we 1 Henderson, Lawrence J., 1913, p. 276. 2 Osborn, H. F., 1894, p. 56. Io THE ORIGIN AND EVOLUTION OF LIFE may also exclude as unscientific the vitalistic theory of an entelechy or any other form of internal perfecting agency dis- tinct from known or unknown physicochemical energies. Since certain forms of adaptation which were formerly mysterious can now be explained without the assumption of an entelechy we are encouraged to hope that all forms may be thus explained. The fact that the causes underlying the origin of many forms of adaptation are still unknown, uncon- ceived, and perhaps inconceivable, does not inhibit our opinion that adaptation will prove to be a continuation of the previous cosmic order rather than the introduction of a new order of things. If, however, we reject the vitalistic hypotheses of the ancient Greeks, and the modern vitalism of Driesch, of Bergson, and of others, we are driven back to the necessity of further experiment, observation, and research, guided by the imagina- tion and checked by verification. As indicated in our Pref- ace, the old paths of research have led nowhere, and the question arises: What lines shall new researches and experi- ments follow? THE ENERGY CONCEPT oF LIFE While we owe to matter and form the revelation of the existence of the great Jaw of evolution, we must reverse our thought in the search for causes and take steps toward an energy conception of the origin of life and an energy conception of the nature of heredity. So far as the creative power of energy is concerned, we are on sure ground: in physics energy controls matter and form; in physiology function controls the organ; in animal mechanics motion controls and, in a sense, creates the form of muscles and bones. In every instance some kind of energy THE ENERGY CONCEPT OF LIFE Il or work precedes some kind of form, rendering it probable that energy also precedes and controls the evolution of life. The total disparity between invisible energy and visible form is the second point which strikes us as in favor of such a conception, because the most phenomenal thing about the heredity-germ is its microscopic size as contrasted with the titanic beings which may rise out of it. The electric energy transmitted through a small copper wire is yet capable of mov- ing a long and heavy train of cars. The discovery by Bec- querel and Curie of radiant energy and of the properties of radium helps us in the same way to understand an energy conception of the heredity-germ, for in radium the energy per unit of mass is enormously greater than the energy quanta which we were accustomed to associate with units of mass; whereas, in most man-made machines with metallic wheels and levers, and in certain parts of the animal machine con- structed of muscle and bone, the work done is proportionate to the size and form. The slow dissipation or degradation of energy in radium has been shown by Curie to be concomitant with the giving off of an enormous amount of heat, while Rutherford and Strutt declare that in a very minute amount of active radium the energy of degradation would entirely dominate and mask all other cosmic modes of transformation of energy; for example, it far outweighs that arising from the gravitational energy which is an ample supply for our cosmic system, the explanation being that the minutest energy ele- ments of which radium is composed are moving at incredible velocities, approaching often the velocity of light, 7. e., 180,000 miles per second. The energy of radium differs from the supposed energy of life in being constantly dissipated and de- graded; its apparently unlimited power is being lost and scat- tered. 12 THE ORIGIN AND EVOLUTION OF LIFE We may imagine that the energy which lies in the life-germ of heredity is very great per unit of mass of the matter which contains it, but that the life-germ energy, unlike that of radium, is in process of accumulation, construction, conservation, rather than of dissipation and destruction. Following the time (1620) when Francis Bacon divined that heat consists of a kind of motion or brisk agitation of the par- ticles of matter, it has step by step been demonstrated that the energy of heat, of light, of electricity, the electric energy of chemical configurations, the energy of gravitation, are all utilized in living as well as in lifeless substances. Moreover, as remarked above (p. 5), no form of energy has thus far been discovered in living substances which is peculiar to them and not derived from the inorganic world. In a broad sense all these manifestations of energy are subject to Newton’s dy- namical laws! which were formulated in connection with the motions of the heavenly bodies, but are found to apply equally to all motions great or little. These three fundamental laws are as follows: I I Corpus omne perseverare in statu Every body perseveres in its suo quiescendi vel movendi uni- | state of rest, or of uniform motion formiter in directum, nisi quatenus | in a right line, unless it is compelled illud a viribus impressis cogitur | to change that state by forces im- statum suum mutare. pressed thereon. 17 am indebted to my colleague M. J. Pupin for valuable suggestions in formulating the physical aspect of the principles of action and reaction. He interprets Newton’s third law of motion as the foundation not only of modern dynamics in the Newtonian sense but in the most general sense, including biological phenomena. With regard to the first law of thermodynamics, it is a particular form of the principle of conservation of en- ergy as applied to heat energy; Helmholtz, who first stated the principle of conservation of energy, derived it from Newtonian dynamics. The second law of thermodynamics started from a new principle, that of Carnot, which apparently had no direct connection with Newton’s third law of motion; this second law, however, in its most general form cannot be fully interpreted except by statistical dynamics, which are a modern offshoot of Newtonian dynamics. 2 Newton’s three laws of motion, first published in Newton’s Principia in 1687. THE ENERGY CONCEPT OF LIFE 13 IT Mutationem motus proportio- nalem esse vi motrici impress, et fieri secundum lineam rectam qua vis illa imprimitur. Il Actioni contrariam semper et zqualem esse reactionem: sive cor- porum duorum actiones in se mutuo semper esse equales et in partes contrarias dirigi. II The alteration of motion is ever proportional to the motive force impressed; and is made in the direc- tion of the right line in which that force is impressed. Til To every action there is always opposed an equal reaction: or the mutual actions of two bodies upon each other are always equal, and directed to contrary parts. Newton’s third law of the equality of action and reaction is the foundation of the modern doctrine of energy,! not only in the Newtonian sense but in the most general sense.2 Newton divined the principle of the conservation of energy in mechanics; Rumford (1798) maintained the universality of the laws of energy; Joule (1843) established the particular principle of the conservation of energy, namely of the exact equivalence be- tween the amount of heat produced and the amount of mechan- ical energy destroyed; and Helmholtz in his great memoir Uber die Erhaltung der Kraft extended this system of conser- vation of energy throughout the whole range of natural phe- nomena. A familiar instance of the so-called transformation of energy is where the sudden arrest of a cool but rapidly moving body produces heat. This was developed as the first law of thermodynamics. At the same time there arose the distinction between po- tential energy, which is stored away in some latent form or manner so that it can be drawn upon for work—such energy 1The term Energy (Gr. évépyetx; év in; goyov, work) in physical science denotes an accumulated capacity for doing mechanical work, and may be either kinetic (energy of heat or motion) or potential (latent or stored energy). 2M. I. Pupin, see note above. 14 THE ORIGIN AND EVOLUTION OF LIFE being exemplified mechanically by the bent spring, chemi- cally by gunpowder, and electrically by a Leyden jar—and kinetic energy, the active energy of motion and of heat. While all active mechanical energy or work may be con- verted into an equivalent amount of heat, the opposite process of turning heat into work involves more or less loss, dissipa- tion, or degradation of energy. This is known as the second law of thermodynamics and is the outgrowth of a principle dis- covered by Sadi Carnot (1824), and developed by Kelvin (1852, 1853). The far-reaching conception of cyclic processes in en- ergy enunciated in Kelvin’s principle of the dissipation of available energy puts a diminishing limit upon the amount of heat energy available for mechanical purposes. The available kinetic energy of motion and of heat which we can turn into work or mechanical effect is possessed by any system of two or more bodies in virtue of the relative rates of motion of their parts, velocity being essentially relative. These two great dynamical principles that the energy of motion can be converted into an equivalent amount of heat, and that a certain amount of heat can be converted into a more limited amount of power were discovered through obser- vations on the motions of larger masses of matter, but they are believed to apply equally to such motions as are involved in the smallest electrically charged atoms (ions) of the chem- ical elements and the particles flying off in radiant energy as phosphorescence. Such movements of infinitesimal particles underlie all the physicochemical laws of action and reaction which have been observed to occur within living things. In all physicochemical processes within and without the organism by which energy is captured, stored, transformed, or released the actions and reactions are equal, as expressed in Newton’s third law. THE ENERGY CONCEPT OF LIFE 15 Actions and reactions refer chiefly to what is going on be- tween the parts of the organism in chemical or physical con- tact, and are subject to the two dynamical principles referred to above. Interactions, on the other hand, refer to what is going on between material parts which are connected with each other by other parts, and cannot be analyzed at all by the two great dynamical principles alone without a knowledge of the structure which connects the interacting parts. For ex- ample, in interaction between distant bodies the cause may be very feeble, yet the potential or stored energy which may be liberated at a distant point may be tremendous. Action and reaction are chiefly simultaneous, whereas interaction connects actions and reactions which are not simultaneous; to use a simple illustration: when one pulls at the reins the horse feels it a little later than the moment at which the reins are pulled —there is interaction between the hand and the horse’s mouth, the reins being the interacting part. An interacting nerve- impulse starting from a microscopic cell in the brain may give rise to a powerful muscular action and reaction at some distant point. An interacting enzyme, hormone, or other chemical messenger circulating in the blood may profoundly modify the growth of a great organism. Out of these physicochemical principles has arisen the con- ception of a living organism as composed of an incessant series of actions and reactions operating under the dynamical laws which govern the transfer and transformation of energy. The central theory which is developed in our speculation on the Origin of Life is that every physicochemical action and reaction concerned in the transformation, conservation, and dissipation of energy, produces also, either as a direct result or as a by-product, a physicochemical agent of interaction which permeates and affects the organism as a whole or affects only some 10 THE ORIGIN AND EVOLUTION OF LIFE special part. Through such interaction the organism is made a unit and acts as one, because the activities of all its parts are correlated. This idea may be expressed in the following simplified scheme of the functions or p/ysiology of the organism: ACTION | | ACTION AND | ————————_ INTERACTION o> AND REACTION | | REACTION Functions of the Functions of the Functions of the Capture, Storage, Coordination, Balance, Capture, Storage, and Release of Cooperation, Compensation, and Release of Energy. Acceleration, Retardation, Energy. of Actions and Reactions. Since it is known that many actions and reactions of the organism—such as those of general and localized growth, of nutrition, of respiration—are coordinated with other actions and reactions through interaction, it is but a step to extend the principle and suppose that all actions and reactions are sim- ilarly coordinated; and that while there was an evolution of action and reaction there was also a corresponding evolution of interaction, for without this the organism would not evolve harmoniously. Evidence for such universality of the interaction principle has been accumulating rapidly of late, especially in experi- mental medicine! and in experimental biology.? It is a further step in our theory to suppose that the directing power of he+ redity which regulates the initial and all the subsequent steps of development in action and reaction, gives the orders, hastens development at one point, retards it at another, is an elab- oration of the principle of interaction. In lowly organisms 1 See the works of Cushing and Crile cited below. “2 See the recent experiments of Morgan and Goodale. THE ENERGY CONCEPT OF LIFE 17 like the monads these interactions are very simple; in higher organisms like man these interactions are elaborated through physicochemical and other agents, some of which have already been discovered although doubtless many more await discovery. Thus we conceive of the origin and development of the or- ganism as a concomitant evolution of the action, reaction, and interaction of energy. Actions and reactions are borrowed from the inorganic world, and elaborated through the produc- tion of the new organic chemical compounds; it is the peculiar evolution and elaboration of the physical principle of inter- action which distinguishes the living organism. Thus the evolution of life may be rewritten in terms of in- visible energy, as it has long since been written in terms of visible form. All visible tissues, organs, and structures are seen to be the more or less simple or elaborate agents of the different modes of energy. One after another special groups of tissues and organs are created and coordinated—organs for the capture of energy from the inorganic environment and from the life environment, organs for .the storage of energy, organs for the transformation of energy from the potential state into the states of motion and heat. Other agents of control are evolved to bring about a harmonious balance between the various or- gans and tissues in which energy is released, hastened or ac- celerated, slowed down or retarded, or actually arrested or inhibited. In the simplest organisms energy may be captured while the organism as a whole is in a state of rest; but at an early stage of life special organs of locomotion are evolved by which energy is sought out, and organs of prehension by which it may be seized. Along with these motor organs are developed organs of offense and defense of many kinds, by means of which stored energy is 18 THE ORIGIN AND EVOLUTION OF LIFE protected from capture or invasion by other organisms. Finally, there is the most mysterious and ‘comprehensive process of all, by which all these manifold modes of energy are reproduced in another organism. The evolution of these complex modes of action, reaction, and interaction is traced through all the early chapters of this volume and is summed up in Chapter V (p. 152) as a physicochemical introduction to the evolution of ver- tebrate form. Tue Four COMPLEXES OF ENERGY The theoretic evolution of the four complexes is somewhat as follows: (x) In the order of time the Inorganic Environment comes first; energy and matter are first seen in the sun, in the earth, in the air, and in the water—each a very wonderful complex of energies in itself. They form, nevertheless, an entirely orderly system, held together by gravitation, moving under Newton’s laws of motion, subject to the more newly discovered laws of thermodynamics. In this complex we observe actions and reactions, the sum of the taking in and the giving out of energy, the conservation of energy. We also observe inter- actions wherein the energy released at certain points may be greater than the energy received, which is merely a stimulus for the beginning of the local energy transformations. This energy is distributed among the eighty or more chemical elements of the sun and other stars. These elements are combined in plants into complex substances, generally with a storage of energy. Such substances are disintegrated into simple substances in ani- mals, generally with a release of energy. All these processes are termed by us physicochemical. THE FOUR COMPLEXES OF ENERGY 19 (2) With life something new appears in the universe, namely, a union of the internal and external adjustment of energy which we appropriately call an Organism. In the course of the evolution of life every law and property in the physico- chemical world is turned to advantage; every chemical ele- ment is assembled in which inorganic properties may serve organic functions. There is an immediate or gradual separa- tion of the organism into two complexes of energy, namely, first, the energy complex of the organism, which is perishable with the term of the life of the individual, and second, the germ or heredity substance, which is perpetual. (3) The idea that the germ is an energy complex is an as yet unproved hypothesis; it has not been demonstrated. The Heredity-germ in some respects bears a likeness to latent or potential interacting energy, while in other respects it is en- tirely unique. The supposed germ energy is not only cumula- tive but is in a sense imperishable, self-perpetuating, and con- tinuous during the whole period of the evolution of life upon the earth, a conception which we owe chiefly to the law of the continuity of the germ-plasm formulated by Weismann. Some of the observed phenomena of the germ in Heredity are chiefly analogous to those of interaction in the Organism, namely, directive of a series of actions and reactions, but in general we know no complete physical or inorganic analogy to the phe- nomena of heredity; they are unique in nature. (4) With the multiplication and diversification of individual organisms there enters a new factor in the environment, namely, the energy complex of the Life Environment. Thus there are combined certainly three, and possibly four, complexes of energy, of which each has its own actions, reac- tions, and interactions. The evolution of life proceeds by sus- 20 THE ORIGIN AND EVOLUTION OF LIFE taining these actions, reactions, and interactions and con- stantly building up new ones: at the same time the potentiality of reproducing these actions, reactions, and interactions in the course of the development of each new organism is gradually being accumulated and perpetuated in the germ. From the very beginning every individual organism is competing with other organisms of its own kind and of other kinds, and the law of the survival of the fittest is ‘operating between the forms and functions of organisms as a whole and between their separate actions, reactions, and interactions. This, as Weismann pointed out, while apparently a selection of the individual organism itself, is actually a selection of the heredity-germ complex, of its potentialities, powers, and pre- dispositions. Thus Selection is not a form of energy nor a part of the energy complex; it is an arbiter between different com- plexes and forms of energy; it antedates the origin of life just as adaptation or fitness antedates the origin of life, as re- marked by Henderson. Thus we arrive at a conception of the relations of organisms to each other and to their environment as of an enormous and always increasing complexity, sustained through the interchange of energy. Darwin’s principle of the survival or elimination of various forms of living energy is, in fact, adumbrated in the survival or elimination of various forms of lifeless energy as witnessed among the stars and planets. In other words, Dar- win’s principle operates as one of the causes of evolution in mak- ing the lifeless and living worlds what they now appear to be, but not as one of the energies of evolution. Selection merely determines which one of a combination of energies shall survive and which shall perish. The complex of four interrelated sets of physicochemical energies which I have previously set forth (p. xvi) as the most THE FOUR COMPLEXES OF ENERGY 21 fundamental biologic scheme or principle of development may now be restated as follows: In each organism the phenomena of life represent the action, reaction, and interaction of four complexes of physicochemical © energy, namely, those of (1) the Inorganic Environment, (2) the developing Organism (protoplasm and body-chromatin), (3) the germ or Heredity-chromatin, (4) the Life Environment. Upon the resultant actions, reactions, and interactions of potential and kinetic energy in each organism Selection is constantly operating wherever there is competition with the corresponding actions, re- actions, and interactions of other organisms. This principle I shall put forth in different aspects as the central thought of these lectures, stating at the outset and often recurring to the admission that it involves several unknown principles and especially the largely hypothetical question whether there is a relation between the action, reaction, and interaction of the internal energies of the germ or heredity- chromatin with the external energies of the inorganic environ- ment, of the developing organism, and of its life environment. In other words, while this is a principle which largely governs the Organism, it remains to be discovered whether it also governs the causes of the Evolution of the Germ. As observed in the Preface (p. xvii) we are studying not one but four simultaneous evolutions. Each of these evolutions appears to be almost infinite in itself as soon as we examine it in detail, but of the four that of the germ or heredity- chromatin so far surpasses all the others in complexity that it appears to us infinite. The physicochemical relations between these four evolu- tions, including the activities of the single. and of the multiply- ing organisms of the Life Environment, may be expressed in 1 Compare Osborn, H. F., 1917, p. 8. 22 THE ORIGIN AND EVOLUTION OF LIFE diagrammatic form, and somewhat more technically than in the Preface, as follows: OrcGaANIsmM A Under Newton’s Laws of Motion and Modern Thermodynamics Actions, Reactions, and Interactions of the 1. Inorganic Environment: physicochemical en- ergies of space, of the sun, earth, air, and water. 2. Organism: physicochemical en- ergies of the devel- oping individual in the tissues, cells, protoplasm, and cell-chromatin. 3. Heredity-Germ: physicochemical en- ergies of the hered- ity-chromatin, in- cluded in the re- productive cells and tissues. 4. Life Environment: physicochemical en- ergies of other or- ganisms. Under Darwin's Law of Natural Selection Survival of the fittest: com- petition, selec- tion, and elim- ination of the energies and forms. ORGANISMS B-Z Under Newton’s Laws of Motion and Modern Thermodynamics Actions, Reactions, and Interactions of the 1. Inorganic Environment: physicochemical en- ergies of space, of the sun, earth, air, and water. 2. Organism: physicochemical en- ergies of the devel- oping individual in the tissues, cells, protoplasm, and cell-chromatin. 3. Heredity-Germ: physicochemical en- ergies of the hered- ity-chromatin in- cluded in the re- productive cells and tissues. 4. Life Environment: physicochemical en- ergies of other or- ganisms, If a single name is demanded for this conception of evolu- tion it might be termed the fetrakinetic theory in reference to THE FOUR COMPLEXES OF ENERGY 23 the four sets of internal and external energies which play upon and within every individual and every race. In respect to form it is a fetraplastic' theory in the sense that every living plant and animal form is plastically moulded by four sets of energies. The derivation of this conception of life and of the possible causes of evolution from the laws which have been developed out of the Newtonian system, and from those of the other great Cambridge philosopher, Charles Darwin, are clearly shown in the above diagram. In these lectures we shall consider in order, first, the evo- lution of the inorganic environment necessary to life; second, theories of the origin of life in regard to the time when it oc- curred and the accumulation of various kinds of energy through which it probably originated; and, third, the orderly develop- ment of the differentiation and adaptation of the most primi- tive forms. Throughout we shall point out some of the more notable examples of the apparent operation of our fundamental biologic principle of the action, reaction, and interaction be- tween the inorganic environment, the organism, the germ, and the life environment. The apparently insuperable difficulties of the problem of the causes of evolution in the germ or heredity-chromatin— causes which are at present almost entirely beyond the realm of observation and experiment—will be made more evident through the development of the second part of our subject, namely, the evolution of the higher living forms of energy upon the earth so far as they have been followed from the stage of monads or bacteria up to that of the higher mammals. 1 Osborn, H. F., 1912.2. -PART I. THE ADAPTATION OF ENERGY CHAPTER I PREPARATION OF THE EARTH FOR LIFE Primordial environment—the lifeless earth. Age of the earth and beginning of the life period. Primordial environment—the lifeless water. Salt as a measure of the age of the ocean. Primordial chemical environment. Primordial environment—the atmosphere. In the spirit of the preparatory work of the great pioneers of geology, such as Hutton, Scrope, and Lyell, and of the his- tory of the evolution of the working mechanism of organic evolution, as developed by Darwin and Wallace,’ our infer- ences as to past processes are founded upon the observation of present processes. In general, our narrative will therefore follow the ‘‘uniformitarian’”? method of interpretation first presented in 1788 by Hutton,? who may be termed the Newton oof geology, and elaborated in 1830 by Lyell,? the master of Charles Darwin. The uniformitarian doctrine is this: present continuity implies the improbability of past catastrophism and violence of change, either in the lifeless or in the living world; moreover, we seek to interpret the changes and laws of past time through those which we observe at the present time. This was Darwin’s secret, learned from Lyell. Cosmic PRIMORDIAL ENVIRONMENT—THE LIFELESS EARTH Let us first look at the cosmic environment, the inorganic world before the entrance of life. Since 1825, when Cuvier! 1 Judd, John W., 1910. ? Hutton, James, 1795. 3 Lyell, Charles, 1830. * Cuvier, Baron Georges L. C. F. D., 1825. 24 THE LIFELESS EARTH 25 published his famous Discours sur les Révolutions de la Surface du Globe, the past history of the earth, of its waters, of the atmosphere, and of the sun—the four great complexes of in- organic environment—has been written with some approach to precision. Astronomy, physics, chemistry, geology, and pa- leontology have each pursued their respective lines of obser- vation, resulting in some concordance and much discordance of opinion and theory. In general we shall find that opinion founded upon life data has not agreed with opinion founded upon physical or chemical data, arousing discord, especially in connection with the problems of the age of the earth and the stability of the earth’s surface. In our review of these matters we may glance at opinions, whatever their source, but our narrative of the chemical origin. and history of life on the earth will be followed by observations on living matter mainly as it is revealed in paleontology and as it exists to-day, rather than on hypotheses and speculations upon pre-existing states. The formation of the earth’s surface is a prelude to our considering the first stage of the environment of life. Accord- ing to the planetesimal theory, as set forth by Chamberlin,! the earth, instead of consisting of a primitive molten globe as pos- tulated by the old nebular hypothesis of Laplace, originated in a nebulous knot of solid matter as a nucleus of growth which was fed by the infall or accretion of scattered nebulous matter (planetesimals) coming within the sphere of control of this knot. The temperature of these accretions to the early earth could scarcely have been high, and the mode of addition of these planetesimals one by one explains the very heterogeneous matter and differentiated specific gravity of the continents and oceanic basins. The present form of the earth’s surface is the 1 Chamberlin, Thomas Chrowder, 1916. 20 THE ORIGIN AND EVOLUTION OF LIFE result of the combined action of the lithosphere (the rocks), hydrosphere (the water), and atmosphere (the air). Liquefac- tion of the rocks occurred locally and occasionally as the result of heat generated by increased pressure and by radioactivity; but the planetesimal hypothesis assumes that the present elastic rigid condition of the earth prevailed—at least in its outer half—throughout the history of its growth from the small original nebular knot to its present proportions and caused the permanence of its continents and of its oceanic basins. We are thus brought to conditions that are fundamental to the evolution of life on the earth. According to the opinion of Chamberlin, cited by Pirsson and Schuchert,! life on the earth may have been possible when it attained the present size of Mars. According to Becker,? who follows the traditional theory of a primitive molten globe, the earth first presented a nearly smooth, equipotential surface, determined not by its mineral composition, but by its density. As the surface cooled down a temperature was reached at which the waters of the gaseous envelope united with the superficial rocks and led to an aqueo- igneous state. After further cooling the second and final con- solidation followed, dating the origin of the granites and grani- tary rocks. The areas which cooled most rapidly and best conducted heat formed shallow oceanic basins, whereas the areas of poor conductivity which cooled more slowly stood out as low continents. The internal heat of the cooling globe still continues to do its work, and the cyclic history of its surface is completed by the erosion of rocks, by the accumulation of sediments, and by the following subsidence of the areas loaded 1 Pirsson, Louis V., and Schuchert, Charles, 1915, p. 535. ? George F. Becker, letter of October 15, 1915. THE LIFELESS EARTH ay down by these sediments. It appears that the internal heat engine is far more active in the slowly cooling continental areas than in the rapidly cooling areas underlying the oceans, as manifested in the continuous outflows of igneous rocks, which, especially in the early history of the earth—at or before the time when life appeared—covered the greater part of the earth’s surface. The ocean beds, being less subject to the work of the internal heat engine, have always been relatively plane; except near the shores, no erosion has taken place. The Age of the Earth and Beginning of the Life Period The age of the earth as a solid body affords our first in- stance of the very wide discordance between physical and biological opinion. Among the chief physical computations are those of Lord Kelvin, Sir George Darwin, Clarence King, and Carl Barus.! In 1879 Sir George Darwin allowed 56,000,- 000 years as a probable lapse of time since the earth parted company with the moon, and this birthtime of the moon was naturally long prior to that stage when the earth, as a cool, crusted body, became the environment of living matter. Far more elastic than this estimate was that of Kelvin, who, in 1862, placed the age of the earth as a cooling body between 20,000,000 and 400,000,000 years, with a probability of 98,000,- ooo years. -Later, in 1897, accepting the conclusions of King and Barus calculated from data for the period of tidal stability, Kelvin placed the age limit between 20,000,000 and 40,000,000 years, a conclusion very unwelcome ‘to evolutionists. As early as 1859 Charles Darwin led the biologists in de- manding an enormous period of time for the processes of evo- 1 Becker, George F., 1910, p. 5. 28 THE ORIGIN AND EVOLUTION OF LIFE lution, being the first to point out that the high degree of evo- lution and specialization seen in the invertebrate fossils at the very base of the Paleozoic was in itself a proof that pre-Palzo- zoic evolution occupied a period as long as or even longer than the post-Paleozoic. In 1869 Huxley renewed this demand for an enormous stretch of pre-Palzozoic or pre-Cambrian time; and as recently as 1896 Poulton! found that 400,000,000 years, the greater limit of Kelvin’s original estimate, was none too much. Later physical computations greatly exceeded this biological demand, for in 1908 Rutherford? estimated the time required for the accumulation of the radium content of a uranium min- eral found in the Glastonbury granitic gneiss of the Early Cambrian as no less than 500,000,000 years. This physical estimate of the age of the Early Cambrian is eighteen times as great as that attained by Walcott? in 1893 from his purely geologic computation of the time rates of deposition and max- imum thickness of strata from the base of the Cambrian up- ward; but recent advances in our knowledge of the radioactive elements preclude the possibility of any trustworthy deter- mination of the age of the elements through the methods sug- gested by Joly and Rutherford. We thus return to the estimates based upon the time required for the deposition of sediments as by far the most reliable, especially for our quest of the beginning of the life period, because erosion and sedimentation imply conditions of the earth, of the water, and of the atmosphere more or less comparable to those under which life is known to exist. These geologic estimates, which begin with that of John Phillips in 1860, may be tabulated as follows: 1 Poulton, Edward B., 1896, p. 808. ? Rutherford, Sir Ernest, 1906, p. 189. 3 Walcott, Charles D., 1893, p. 675. THE LIFELESS EARTH 29 EsTIMATES OF TIME REQUIRED FOR THE Processes oF Past DEPOSITION AND SEDIMENTATION AT RATES SIMILAR TO THOSE OBSERVED AT THE PRESENT Day! T8600, John Phillips: 2954 secd poadle ae awn eases 38- 96 million years. 1890. De Lapparent...............0..00.0.0 ccc eee 67— 90 million years. ESOS UO WalOblacvs. ula tncseeaoaeeniadi sean 55- 70 million years. (27,640,000 years since the base of the Cam- brian Paleozoic; 17,500,000 years or up- ward for the pre-Paleozoic.) TS00: GEikie 005s iis nbaia ca daar eae a nas 100-400 million years. (Minimum too million years; maximum— slowest known rates of deposition— 400 million years.) TOO; Solldsgsi saves ava ees eevee ora eres Bs 34- 80 million years. (The larger estimate of 80 million years on the theory that pre-Paleozoic sediments took as much time as those from the base of the Cambrian upward, allowing for gaps in the stratigraphic column.) These estimates give a maximum of sixty-four miles as the total accumulation of sedimentary rocks, which is equivalent to a layer 2,300 féet thick over the entire face of the earth.’ From these purely geologic data the time ratio of the entire life period is now calculated in terms of millions of years, assuming the approximate reliability of the geologic time scale. The actual amount of rock weathered and deposited was prob- ably far greater than that which has been preserved. In general, these estimates are broadly concordant with those reached by an entirely different method, namely, the amount of sodium chloride (common salt) contained in the ocean,’ to understand which we must first take another glance at the geography and chemistry of the primordial earth. The lifeless primordial earth can best be imagined by look- ing at the lifeless surface of the moon, featured by volcanic 1 Becker, George F., 1910, pp. 2, 3, 5- 2 Clarke, F. W., 1916, p. 30. 3See Salt as a Measure of the Age of the Ocean, p. 35. 30 THE ORIGIN AND EVOLUTION OF LIFE action with little erosion or sedimentation because of the lack of water. The surface of the earth, then, was chiefly spread with granitic masses known as batholiths and with the more super- ficial volcanic outpourings. ‘There were volcanic ashes; there Tic. 1. THE Moon’s SuRFACE. “The lifeless primordial earth can best be imagined by looking at the lifeless surface of the moon.” A portion of the moon’s surface, many miles in diameter, illuminated by the rising or setting sun and showing the craters and areas of lava outflow. The Meteor Crater of Arizona, formerly known as Coon Butte—a huge hole, 4,500 feet in diameter and 600 feet in depth, made by a falling meteorite—is strikingly similar to these lunar craters and suggests the possibility that, instead of being the result of volcanic action, the craters of the moon may have been formed by terrific impacts of meteoric masses. Photograph from the Mt. Wilson Observatory. were gravels, sands, and micas derived from the granites; there were clays from the dissolution of granitic feldspars; there were loam mixtures of clay and sand; there was gypsum from min- eral springs. Bare rocks and soils were inhospitable ingredients for any but the most rudimentary forms of life such as were adapted to feed directly upon the chemical elements and their simplest THE LIFELESS EARTH 31 compounds, or to transform their energy without the friendly aid of sunshine. The only forms of life to-day which can exist in such an inhospitable environment as that of the lifeless earth are certain of the simplest bacteria, which, as we shall see, feed directly upon the chemical elements. It is interesting to note that, in the period when the sun’s light was partly shut off by watery and gaseous vapors, the early volcanic condition of the earth’s surface may have supplied life with fundamentally important chemical elements, as well as with the heat-energy of the waters or of the soils. Volcanic emanations contain! free hydrogen, both oxides of carbon, and frequently hydrocarbons such as methane (CH.) and ammo- nium chloride: the last compound is often very abundant. Volcanic waters sometimes contain ammonium (NH,) salts, from which life may have derived its first nitrogen supply. For example, in the Devil’s Inkpot, Yellowstone Park, ammo- nium sulphate forms 83 per cent of the dissolved saline matter: it is also the principal constituent of the mother liquor of the boric fumaroles of Tuscany, after the boric acid has crystallized out. A hot spring on the margin of Clear Lake, California, contains 107.76 grains per gallon of ammonium bicarbonate. There were absent from the primordial earth the greater part of the fine sediments and detrital material which now cover three-fourths of its surface, and from which a large part of the sodium content has been leached. The original surface of the earth was thus composed of granitic and other igneous rocks to the exclusion of all others,? the essential constituents of these rocks being the lime-soda feldspars from which the sodium of the ocean has since been leached. Waters issuing from such rocks are, as a rule, relatively richer in silica than 1 Clarke, F. W., 1916, chap. VIIT., also pp. 197, 199, 243, 244. 2 Becker, George F., 1910, p. 12. 32 THE ORIGIN AND EVOLUTION OF LIFE They thus furnish a favorable environment for the development of such waters issuing from modern sedimentary areas. low organisms (or their ancestors) as the existing diatoms, radiolarians, and sponges, which have skeletons composed of hydrated silica, cally of opal. The decomposition and mineralogi- therefore the erosion of the massive rocks was slower then than at present, for none of the life agencies of bacteria, of algze, of lichens, and of the higher plants, which are now at work on granites and vol- canic rocks in all the humid DEEP-SEA O0zE, THE FORAMI- NIFERA. Fic, 2. portions of the earth, had yet appeared. On the other hand, Photograph of a small portion of a cal- careous deposit on the sea bottom formed by the dropping down from the sea sur- face of the dead shells of foraminifera, chiefly Globigerina, greatly magnified. Such calcareous deposits extend over large areas of the sea bottom. Repro- duced from The Depths of the Ocean, by Sir John Murray and Doctor Johan much larger areas of these rocks were exposed than at present. In brief, to imagine the primal lifeless earth we must Hjort by permission of the Macmillan subtract all those portions of Company. mineral deposits which as they exist to-day are mainly of organic origin, such as the organic car- bonates and phosphates of lime,! the carbonaceous shales as well as the carbonaceous limestones, the graphites derived from car- bon, the silicates derived from diatoms, the iron deposits made 1TIt seems improbable that organisms originally began to use carbon or phosphorus in elementary form: carbonates and phosphates were probably available at the very be- ginning and resulted from oxidations or decompositions.—W. J. Gies. Phosphate of lime, apatite, is an almost ubiquitous component of igneous rocks, but in very small amount. In more than a thousand analyses of such rocks, the average percentage of P.O; is 0.25 per cent.—F. W. Clarke. THE LIFELESS EARTH ee by bacteria, the humus of the soil containing organic acids, the soil derived from rocks which are broken up by bacteria, and even the ooze from the ocean floor, both calcareous and TABLE I AVERAGE DISTRIBUTION OF THE CHEMICAL ELEMENTS IN EARTH, AIR, AND WATER AT THE PRESENT TIME?! (Life Elements in Italics) The Rocks, The Waters, Average, Lithosphere, | Hydrosphere, The Atmosphere Including 93 per cent 7 per cent Atmosphere ORV ECW scan ens oe enes 47-33 85.79 20.8 50.02 (variable to some extent) SUICOT on. nee eR hee BAS \\\i iii eiaie ll) —dtidadonedas 25.80 Aluminum........... GeOG. LN taatkeeoG ssvesiwedaalans 7.30 LP OW ino eps wee die A teeen diene AiO lt dees. i eee 4.18 Galewm.. ohccieveex: 3-47 wos. | 1a Sees B99 Magnesium.......... 2.24 ye) We seve eer s 2.08 SOD TUT aia, stn mihi siti tea 2.46 ida, $)) -estewed 2.36 Potassium........... 2.46 SOAs) (1j)| -aaviharted 2.28 Hydrogen............ 22 10.67 variable -95 Titanium ........... BAO | eeecde) ||) see deeaceonalines 43 CORD OI cds pices ee ae .19 .002 variable .18 Chlorine......... ceteris 06 BOW. dh! exaipardgoa .20 BrOMIN EG sissee-s nies agate |) Gnaats 2 ie CoS |) ded veges va Phosfhorus.......... Sta Uk” aeheete- | dasareeoies .II Sulphur... ccc eee .12 YOO: hy bankaysenans .II Bari: isos ee-aeees JOSt ll SSenad) IW cadetiaan .08 Manganese........... BOS ill saeneet WIP saitavssometa .08 Strontium........... S02 || sovevazar | aatesadins .02 NUPOGER ccccennvrees| aecax |) strange 78.0 .03 (variable to some extent) Fluorine..........645 BIO!) {I} menace || ~qezeneivenn’s .10 All other elements... . GO NW -nvtate,s || 1 damian, AG silicious, formed from the shells of foraminifera and the skele- tons of diatoms. Thus, before the appearance of bacteria, of alge, of foraminifera, and of the lower plants and lowly inver- tebrates, the surface of the earth was totally different from 1 Clarke, F. W., 1916, p. 34. 34 THE ORIGIN AND EVOLUTION OF LIFE what it is at present; and thus the present chemical composi- tion of terrestrial matter, of the sea, and of the air, as indi- cated by Table I, is by no means the same as its primordial composition 80.000,000 years ago. In Table I all the chemical “life elements”? which enter more or less freely into organic compounds are indicated by italics, showing that life has taken up and made use of practically all the chemical elements of frequent occurrence in the rocks, waters, and air, with the exception of aluminum, barium, and strontium, which are extremely rare in life compounds, and of titanium, which thus far has not been found in any. But even these elements appear in artificial organic compounds, showing combining capacity without biological “‘inclination”’ thereto. In the life compounds, as in the lithosphere and hydrosphere, it is noteworthy that the elements of least atomic weight (Table II) predominate over the heavier elements. PRIMORDIAL ENVIRONMENT—THE LIFELESS WATER According to the nebular theory of Laplace the waters originated in the primordial atmosphere; according to the planetesimal theory of Chamberlin! and Moulton,’ the greater volume of water has been gradually added from the interior of the earth through the vaporous discharges of hot springs. As Suess observes: ‘‘The body of the earth has given forth its ocean.” From the beginning of Archeozoic time, namely, back to a period of 80,000,000 years, we have little biologic or geologic evidence as to the stability of the earth. From the beginning of the Paleozoic, namely, for the period of the last 30,000,000 years, the earth has been in a condition of such stability that 1 Chamberlin, Thomas Chrowder, 1916. * Moulton, F. R., 1912, p. 244. THE LIFELESS WATER 35 the oceanic tides and tidal currents were similar to those of the present day; for the early strata are full of such evidences as ripple marks, beach footprints, and other proofs of regularly recurrent tides.1 As in the case of the earth, the chemistry of the lifeless primordial seas is a matter of inference, 7. ¢., of subtraction of those chemical elements which have been added as the infant earth has grown older. The relatively simple chemical con- tent of the primordial seas must be inferred by deducting the mineral and organic products which have been sweeping into the ocean from the earth during the last 80,000,000 to 90,000,000 years; and also by deducting those that have been precipitated as a result of chemical reactions, calcium chloride reacting with sodium phosphate, for example, to yield precipitated calcium phosphate and dissolved sodium chloride.? The present waters of the ocean are rich in salts which have been derived by solu- tion from the rocks of the continents. Thus we reach our first conclusion as to the origin of life, namely: it is probable that life originated on the continents, either in the moist crevices of rocks or soils, in the fresh waters of continental pools, or in the slightly saline waters of the bordering primordial seas. Salt as a Measure of the Age of the Ocean As long ago as 1715 Edmund Halley suggested that the amount of salt in the ocean might afford a means of computing its age. Assuming a primitive fresh-water ocean, Becker’ in 1gto0 estimated its age as between 50,000,000 and 70,000,000 years, probably closer to the upper limit. The accumulation of sodium was probably more rapid in the early geologic periods 1 Becker, George F., 1910, p. 18. 2W. J. Gies. 3 Becker, George F., 1910, pp. 16, 17. 36 THE ORIGIN AND EVOLUTION OF LIFE than at the present time, because the greater part of the earth’s surface was covered with the granitic and igneous rocks which have since been largely covered or replaced by sedimentary rocks, a diminution causing the sodium content from the earth to be constantly decreasing. This is on the assumption that the primitive ocean had no continents in its basins and that the continental areas were not much greater than at the present time, namely, 20.6 per cent to 25 per cent of the surface of the globe. AGE OF THE OCEAN CALCULATED FROM ITS SODIUM CONTENT ? 1876. T. Mellard Reade. TOG. Ve DOW scs decane Seaehan asa wae 80— 90 million years. 4900... fs JOY ss teccusd degen eee eS go-Ioo million years. TO00:.. SOMASS 2, Aaa wan cacee eden Bele 80-150 million years. Tore: | Beckétisssuvedvedeeckesandeaee 50- 70 million years. tort. F. W. Clarke and Becker...... 94,712,000 years. TOPS<-| Becket ose-as cache oteltiicn es 60-100 million years. TOO. Clarkes. oi sais aihaseeenoncewe somewhat less than too million years. From the mean of the foregoing computations it is inferred that the age of the ocean since the earth assumed its present form is somewhat less than 100,000,000 years. The 63,000,000 tons of sodium which the sea has received yearly by solution from the rocks has been continually uniting with its equivalent of chlorine to form the salt (NaCl) of the existing seas.? So with the entire present content of the sea, its sulphates as well as its chlorides of sodium and of magnesium, its potassium, its calcium as well as those rare chemical elements which occasion- ally enter into the life compounds, such as copper, fluorine, boron, barium—all these earth-derived elements were much 1 Becker, George F., 1915, p. 201; 1910, p. 12. 2 After Becker, George F., 1910, pp. 3-5; and Clarke, F. W., 1916, pp. 150, 152. 3 Becker, George F., 1910, pp. 7, 8, 10, 12. THE LIFELESS WATER 37 rarer in the primordial seas than at the present time. Yet from the first the air in sea-water was much richer in oxygen than the atmosphere.' As compared with primordial sea-water, which was relatively fresh and free from salts and from nitrogen, existing sea-water is an ideal chemical medium for life. As a proof of the special adaptability of existing sea-water to present biochemical con- ditions, a very interesting comparison is that between the chemical composition of the chief body fluid of the highest animals, namely, the blood serum, and the chemical composi- tion of sea-water, as given by Henderson.’ CHEMICAL COMPOSITION OF PRESENT SEA-WATER AND OF BLoop SERUM “Life Elements” In Sea-Water In Blood Serum IS OUI 35 se: Glebe sesec oles RAL een et te ple usc gn 30.59. 39.0 MGRNESTUM: 62 rsa gcen ca Ree Ea OTS 3.79 0.4 COLUMN. Jccaca se ecletne MESS EE 1.20 I.0 POSSUM: weniger tak oun eee se oa wees Tat a4 GCHLOHING. bac ha cae nee ee ARE RE TEE RS 55.27 45.0 SO, (sulphur tetroxide)................. 7.66 sos COs (carbon trioxide)...............20-. 0.21 12.0 “BrOMiNe 2s cacs8 ya jeedoce ose ee eas 0.19 eet P.O; (phosphorous pentoxide)........... Hades 0.4 Primordial Chemical Environment Since the primal sea was devoid of those earth-borne nitro- gen compounds which are indirectly derived first from the atmosphere and then from the earth through the agency of the nitrifying bacteria, those who hold to the hypothesis of the marine origin of protoplasm fail to account for the necessary proportion of nitrogenous matter there to begin with. 1 Pirsson, Louis V., and Schuchert, Charles, 1915, p. 84. 2 Henderson, Lawrence J., 1913, p. 187. 38 THE ORIGIN AND EVOLUTION OF LIFE When we consider that those chemical “life elements” which are most essential to living matter were for a great period of time either absent or present in a highly dilute condition in the ocean, it appears that we must abandon the ancient Greek conception of the origin of life in the sea, and reaffirm our conclusion that the lowliest organisms originated either in moist earths or in those terrestrial waters which contained nitrogen. Nitrate and nitrite occasionally arise from the union of nitrogen and oxygen in electrical discharges during thunder- storms, and were presumably thus produced before life began. These and related nitrogen compounds, so essential for the development of protoplasm, may have been specially concen- trated in pools of water to degrees particularly favorable for the origin of protoplasm: It appears, too, that every great subsequent higher life phase—the bacterial phase, the chlorophyllic algal phase, the protozoan phase—was also primarily of fresh-water and sec- ondarily of marine habitat. From terrestrial waters or soils life may have gradually extended into the sea. It is probable that the succession of marine forms was itself determined to some extent by adaptation to the increasing concentration of saline constituents in sea-water. That the invasion of the sea upon the continental areas occurred at a very early period is demonstrated by the extreme richness and profusion of marine life at the base of the Cambrian. That life originated in water (H2O) there can be little doubt, hydrogen and oxygen ranking as primary elements with nitro- gen. The fitness of water to life is maximal? both as a solvent in all the bodily fluids, and as a vehicle for most of the other chemical compounds. Further, since water itself is a solvent 1 Suggested by Professor W. J. Gies. * These notes upon water are chiefly from the very suggestive treatise, ‘The Fitness of the Environment,” by Henderson, Lawrence J., 1913. THE ATMOSPHERE 39 that fails to react with many substances (with nearly all bio- logical substances) it serves also as a factor of biochemical stability. In relation to the application of our theory of action, re- action, and interaction to the processes of life, the most im- portant property of water is its electric property, known as the dielectric constant. Although itself only to a slight degree dissociated into ions, it is the bearer of dissolved electrolytic substances and thus possesses a high power of electric conduc- tivity, properties of great importance in the development of the electric energy of the molecules and atoms in ionization. Thus water is the very best medium of electric ionization in solution, and was probably essential to the mechanism of life from its very origin.! Through all the electric changes of its contained solvents water itself remains very stable, because the molecules of hydrogen and oxygen are not easily dissociated; their union in water contributes to the living organism a series of proper- ties which are the prime conditions of all physiological and functional activity. The great surface tension of water as manifested in capillary action is of the highest importance to plant growth; it is also an important force acting within the formed colloids, the protoplasmic substance of life. PRIMORDIAL ENVIRONMENT—-THE ATMOSPHERE It is significant that the simplest known living forms derive their chemical “life elements” partly from the, earth, partly from the water, and partly from the atmosphere. This was not improbably true also of the earliest living forms. One of the mooted questions concerning the primordial 1 Henderson, Lawrence J., 1913, p. 256. 40 THE ORIGIN AND EVOLUTION OF LIFE atmosphere! is whether or no it contained free oxygen. The earliest forms of life were probably dependent on atmospheric oxygen, although certain existing bacterial organisms, known as ‘‘anaérobic,” are now capable of existing without it. The primordial atmosphere was heavily charged with water vapor (HO) which has since been largely condensed by cooling. In the early period of the earth’s history volcanoes’ were also pouring into the atmosphere much greater amounts of car- bon dioxide (CO) than at the present time. At present the amount of carbon dioxide in the atmosphere averages about three parts in 10,000, but there is little doubt that the primor- dial atmosphere was richer in this compound, which next to water and nitrogen is by far the most important both in the origin and in the development of living matter. The atmos- pheric carbon dioxide is at present continually being withdrawn by the absorption of carbon in living plants and the release of free oxygen; it is also washed out of the air by rains. On the other hand, the respiration of animals, the combustion of car- bonaceous matter, and the discharges from volcanoes are con- tinually returning it to the air in large quantities. As to carbon, from our present knowledge we cannot con- ceive of organisms that did not consist, from the instant of initial development, of protoplasm containing hydrogen, oxygen, nitrogen, and carbon. Probably carbon dioxide, the most likely source of carbon from the beginning, was reduced in the pri- mordial environment by other than chlorophyllic agencies, by simple chemical influences. Since carbon is a less dominant element’ than nitrogen in the life processes of the simplest bacteria, we cannot agree with the theory that carbon dioxide was coequal with water 1 Becker, George F., letter of October 15, 1915. ? Henderson, Lawrence J., 1913, p. 134. 3 Jordan, Edwin O., 1908, p. 66. THE ATMOSPHERE 41 as a primary compound in the origin of life; it probably was more widely utilized after the chlorophyllic stage of plant evolution, for not until chlorophyll appeared was life equipped with the best means of extracting large quantities of carbon dioxide from the atmosphere. The stable elements of the present atmosphere, for which alone estimates can be given, are essentially as follows:! By Weight | By Volume ORV BON sas aad daathochs Meee ota rae eee 23.024 20.941 INDENO PCT A ae he Ma eanes hawt n 75-539 78.122 ATCO es ocsd oad ates eee Rees 1.437 .937 100.000 100.000 Atmospheric carbon dioxide (CO2), which averages about three parts in every 10,000, and water (H,O) are always present in varying amounts; besides argon, the rare gases helium, xenon, neon, and krypton are present in traces. None of the rare gases which have been discovered in the atmosphere, such as helium, argon, xenon, neon, krypton, and niton—the latter a radium emanation—are at present known to have any rela- tion to the life processes. Carbon dioxide? exists in the atmos- phere as an inexhaustible reservoir of carbon, only slightly depleted by the drafts made upon it by the action of chloro- phyllic plants or by its solution in the waters of the conti nents and oceans. Soluble in water and thus equally mobile, of high absorption coefficient, and of universal occurrence, it constitutes a reservoir of carbon for the development of plants and animals, radiant energy being required to make this carbon available for biological use. Carbon dioxide in water 1 Clarke, F. W., letter of March 7, 1916. 2 Henderson, Lawrence J., 1913, pp. 136-1309. 42 THE ORIGIN AND EVOLUTION OF LIFE forms carbonic acid, one of the few instances of biological decomposition of water. This compound is so unstable that it has never been obtained. Carbon dioxide is derived not only through chlorophyllic agencies by means of free oxygen, but also by the action of certain anaérobic bacteria and moulds without the presence of free oxygen, as, for example, through the catalytic action of zymase, the enzyme of yeast, which is soluble in water. Loeb! dwells upon the importance of the bicarbonates as regulators in the development of the marine organisms by keeping neutral the water and the solutions in which marine animals live. Similarly the life of fresh-water animals is also prolonged by the addition of bicarbonates. 1 Loeb, Jacques, 1906, pp. 96, 97- CHAPTER II THE SUN AND THE PHYSICOCHEMICAL ORIGINS OF LIFE Heat and light. Chemical “ life elements” as they exist in the sun. Primor- dial environment—electric energy and the sun’s heat. Capture of the energy of sunlight. Action and reaction as adaptive properties of the life elements. Interaction or coordination of the properties of the life elements. Adaptation in the colloidal state. Cosmic properties and life functions of the chief chemical life elements. Pure speculation as to the primary physicochemical stages of life. Evolution of actions and reac- tions. Evolution of interactions. New organic compounds. ‘We will now consider the sun as the source of heat, light, and other forms of energy which conditioned the origin of life. HEAT AND LIGHT Tt is possible that in the earlier stages of the earth’s history the sun’s light and heat may have been different in amount from what they are at present; so far as can be judged from the available data it seems probable that, if perceptibly different, they were greater then than now. But if they were greater, the atmosphere must have been more full of clouds—as that of Venus apparently is to-day—and have reflected away into space much more than the 45 per cent of the incident radiation which it reflects at present. On the earth’s surface, beneath the cloud layer, the temperature need not have been much higher than the present mean temperature, but was doubtless much more equable, with more moisture, while the amount of sunlight reaching the earth’s surface may have been less intense and continuous than at present. 43 44 THE ORIGIN AND EVOLUTION OF LIFE The following are among the reasons why the primordial solar influences upon the earth may have differed from the present solar influences. It appears probable that the lifeless surface of the primordial earth was like that of the moon— covered not only with igneous rocks but with piles of heat-stor- HEAT “7 CHEMICAL Billion vibraty per seconds SRe & 2 “lee x g INFRA RED ABC D RS G HI ULTRA VIOLET Fic. 3. Licut, HEAT, AND CHEMICAL INFLUENCE OF THE SUN. Diagram showing how the increase, maximum, and decrease of heat, light, and chemical energy derived from the sun correspond to the velocity of the vibrations. After Ulric Dahlgren. ing débris, as recently described by Russell '—and if, like the moon, the earth had had no atmosphere, then the reflecting power of its surface would have represented a loss of only 40 per cent of the sun’s heat. But a large amount of aqueous. vapor and of carbon dioxide in the primordial atmosphere prob- ably served to form an atmospheric blanket which inhibited the radiation from the earth’s surface of such solar heat as pen- etrated to it, and also prevented excessive changes of temper- ature. Thus there was on the primal earth a greater reg- ularity of the sun’s heat-supply, with more moisture. T Russell, H. N., 1916, p. 75. LIFE ELEMENTS IN THE SUN 45 To sum up, if the primordial atmosphere contained more aqueous vapor and carbon dioxide than at present, the greater cloudiness of the atmosphere would have very considerably in- creased the albedo, that is, the reflection of solar heat, as well as light, away into space. If the earth’s surface was covered with loose débris, it would have retained more of the solar heat which reached it directly; but, with such an atmosphere as is postulated, very little of the solar radiation would have reached the surface directly. What is true of the indirect access of the supply of light from the sun would also be true of the supply of heat. On the other hand, the greater blanketing power of the atmosphere would tend to keep the surface as warm as it is now, in spite of the smaller direct supply of heat. It is also possible that, through the agency of thermal springs and the heat of volcanic regions, primordial life forms may have derived their energy from the heat of the earth as well as from that of the sun. This is in general accord with the fact that the most primitive organisms surviving upon the earth to-day, the bacteria, are dependent upon heat rather than upon light for their energy. We have thus far observed that the primal earth, air, and water contained all the chemical elements and three of the most simple but important chemical compounds, namely, water, nitrates, and carbon dioxide, which are known to be essential to the bacterial or prechlorophyllic, and algal and higher chlorophyllic stages of the life process. CHEMICAL “LIFE ELEMENTS” AS THEY EXIST IN THE SUN An initial step in the origin of life was the coordination or bringing together of these elements which, so far as we know, had never been chemically coordinated before and which are 46 THE ORIGIN AND EVOLUTION OF LIFE widely distributed in the solar spectrum. Therefore, before examining the properties of these elements, it is interesting to trace them back from the earth into the sun and thus into the cosmos. It is through these “properties” which in life CARBON niTeoaen CALCIUM MAGNESIUM ENE {RON ~ HYDROGEN ARO Fic. 4. CHEMICAL LIFE ELEMENTS IN THE SUN. Three regions of the solar spectrum with lines showing the presence of such essential life elements as carbon, nitrogen, calcium, iron, magnesium, sodium, and hydrogen. From the Mount Wilson Observatory. subserve “functions” and ‘‘adaptations”’ that all forms of life, from monad to man, are linked with the universe. Excepting hydrogen and oxygen, the principal elements which enter into the formation of living protoplasm are minor constituents of the mass of matter sown throughout space in comparison with the rock-forming elements.1. Again excepting hydrogen, their lines in the solar spectrum are for the most 1 Russell, Henry Norris, letter of March 6, 1916. LIFE ELEMENTS IN THE SUN 47 part weak, and only shown on high dispersion plates, while hydrogen is represented by very strong lines, as shown by spectroheliograms of solar prominences. The lines of oxygen are relatively faint; it appears principally as a compound, titanium oxide (TiO,) in sun-spots, although a triple line in the extreme red seems also to be due to it. In the chromosphere, or higher atmosphere of the sun, hydrogen is not in a state of combustion, and the fine hydrogen prominences show radia- tions comparable to those in a vacuum tube.? Nitrogen, the next most important life element, is displayed in the so-called cyanogen bands of the ultra-violet, made visible by high-dispersion photographs. Carbon is shown in many lines in green, which are relatively bright near the sun’s edge; it is also present in comets, and carbonaceous meteorites (Orgueil, Kold Bokkeveld, etc.) are well known. Graphite occurs in meteoric irons. In the solar spectrum so far as studied no lines of the “‘life elements,” phosphorus, sulphur, and chlorine, have been de- tected. On the other hand, the metallic elements which enter into the life compounds, iron, sodium, and calcium, are all represented by strong lines in the solar spectrum, the excep- tion being potassium in which the lines are faint. Of the eight metallic elements which are most abundant in the earth’s crust, as well as the non-metallic elements carbon and silicon, six are also among the eight strongest in the solar spectrum. In general, however, the important life elements are very widely distributed in the stellar universe, showing most prominently in the hotter stars, and in the case of hydrogen being uni- versal. We have now considered the source of four “‘life elements,”’ namely, HYDROGEN, OXYGEN, NITROGEN, and CARBON, also the 1 Hale, George Ellery, letter of March ro, 1916. 48 THE ORIGIN AND EVOLUTION OF LIFE presence in the sun and stars of the metallic elements. Before passing to the properties of these and other life elements let us consider how lifeless energy is transformed into living energy. PRIMORDIAL ENVIRONMENT—ELECTRIC ENERGY AND THE Sun’s Heat As remarked above, in the change from the lifeless to the life world, the properties of the chemical life elements become known as the functions of living matter. Stored energy becomes known as nutriment or food. The earliest function of living matter appears to have been to capture and transform the electric energy of those chemical elements which throughout we designate as the “‘life elements.” This function appears to have developed only in the presence of heat energy, derived either from the earth or from the sun or from both; this is the first example in the life process of the capture and utilization of energy wherever it may be found. At a later stage of evolution life captured the light energy of the sun through the agency of chlorophyll, the green coloring matter of plants. In the final stage of evolution the intellect of man is capturing and controlling physicochemical energy in many of its forms. The primal dependence of the electric energy of life on the original heat energy of the earth or on solar heat is demon- strated by the universal behavior of the most primitive organ- isms, because when the temperature of protoplasm is lowered to o° C: the velocity of the chemical reactions becomes so small that in most cases all manifestations of life are suspended, that is, life becomes latent. Some bacteria grow at or very near the freezing-point of water (o° C.) and possibly primordial bacteria-like organisms grew below that point. Even now the HEAT AND’ ELECTRIC ENERGY 49 common ‘hay bacillus” grows at 6° C.!_ Rising temperatures increase the velocity of the biochemical reactions of proto- plasm up to an optimum temperature, beyond which they are in- creasingly injurious and finally fatal to all organisms. In hot springs some of the Cyanophycee (blue-green alg), primitive plants intermediate in evolution between bacteria and alge, sustain temperatures as high as 63° C. and, as a rule, are killed by a temperature of 73° C., which is probably the coagulation point of their proteins. Setchell found bacteria living in water of hot springs at 89° C.?. In the next higher order of the Chlo- rophycee (green alge) the temperature fatal to life is lower, being 43° C.2. Very much higher temperatures are endured by the spores of certain bacilli which survive until temperatures of from 105° C. to 120° C. are reached. There appears to be no known limit to the amount of dry cold which they can withstand.* It is this power of the relatively water-free spores to resist heat and cold which has suggested to Richter (1865), to Kel- vin, and to Arrhenius (1908) that living germs may have per- vaded space and may have reached our planet either in com- pany with meteorites (Kelvin)® or driven by the pressure of light (Arrhenius). The fact that so far as we know life on the earth has only originated once or-during one period, and not repeatedly, does not appear to favor these hypotheses; nor is it courageous to put off the problem of life origin into cosmic 1 Jordan, Edwin O., 1908, pp. 67, 68. 2 Ob. cit., p. 68. 3 Loeb, Jacques, 1906, p. 106. 4 Cultures of bacteria have even been exposed to the temperature of liquid hydrogen (about —250° C.) without destroying their vitality or sensibly impairing their biologic qualities. This temperature is far below that at which any chemical reaction is known to take place, and is only about 23 degrees above the absolute zero point at which, it is believed, molecular movement ceases. On the other hand, when bacteria are frozen in water during the formation of natural ice the death rate is high. See Jordan, Edwin O., 1908, p. 69. 5 Poulton, Edward B., 1896, p. 818. 6 Pirsson, Louis V., and Schuchert, Charles, 1915, pp. 5355 536. 50 THE ORIGIN AND EVOLUTION OF LIFE space instead of resolutely seeking it within the forces and elements of our own humble planet. The thermal conditions of living matter point to the prob- ability that life originated at a time when portions at least —. qT T OBS] DEVONIAN i | =|3 = -L------- i Oz? SILURIAN I ! semeware| bah Se oes Ao Pees ese spose: ° \ ° ' \ ke 6] ORDOVICIAN | VM N <8 t fot ons nn ped @| CAMBRIAN \ 1 eae 1 1 = 4 I T re & | KEWEENAWAN | to A xz eee a ee ee ar ee et ee eres oe VES SAB ey ae 1 1 Z B| ANMiKian V7 : } GG YY 2 | o + oeal om h pen Papoeg grees paeaee panean bonny ntennnd 9 1 st r | 2 re ' oO 1 1 owes 2 Nes Pot oes 2 ' i 1 or be es 1 < ! 1, a! >] ALGOMIAN ) 4) cBra A Sud th aa c 4 ie er Fy joey beetle oe te A gO ost {oat \_ 54 z/5) sueurian |E~ |! aivert | ge? | & | se rs feel Ne ee a? — SJ 7 t &oy, we 4 v NF la 1azl Oo ol \ = Vu te| — (Boi (224, (881) Ze | \ ' Y OO/{| LAURENTIAN! 19) | oo! tga; | a} MANY-CELLED ANIMALS,’ I oaqui 1 Qo] 1 1 fo =| tee! ; <2, 1928! 1 92} \ / “ as 1s! wie rye! oy Be! \ : cm oO x I Lt ! On 1 / 2 Ola tees! 1o8i 163! LES; \: foe? 3 o MAMMALS 3 a UPPER sie g CRETACEOUS 2 ue Q 2 u/s ° LOWER ‘le AGE N CRETACEOUS 838 OF 5 TEOMANCHEANT ce ile REPTILES oO aslo = JURASSIC > &/o 4 e Wage = aan TRIASSIC wu .O 2zyu Gaz PERMIAN Osw eal 2 aos § | PENNSYLVANIAN 154 gue AGE TUPPER 095 “OF 5 CARBONIFEROUS) Tau] 9 = a 2 Bo5| & 5 | Mississippian gue | LOWE! zy CARBONIFEROUS) E°a| 9 y aro} Oh z 8 8 Ole 2042 2/2 Ke Ni] & | Devonian Po oe O| 3 | 8 FISHES Wy) § & D <| ¢ | siLuRiAN u 3/2 S| Sp o saie & g°/9 2578 E | ORDOVICIAN a « AGE 2 OF 2 INVERTEBRATES 5 3 ‘CAMBRIAN, 30 MILLIONS KEWEENAWAN OF 2 YEARS 5 2 zi ANIMIKIAN . ne 3asse 6 N/e ane) EVOLUTION | QO] 3 Z08 OF eg HURONIAN zoo s INVERTEBRATES | Lj 58] % 9| g gaa] fe] & | atcomian cOw| > | = a3 : +0 | 384) 8 e 3fE|o | SUDBURIAN wus boa 80%} o onz|S Qe |? GEO/ zu | LAURENTIAN 45j,{z 4 = £26 | 0 3 Sey|e z zoY|< Ozl ae ui Bou]: r 205 /Z S >a) & Jy | © 3g S. so zty| a Ree EVOLUTION UO 229|G | UNiceLLuLaR |< oezZ)G UFE oO oz N oot} & oO wal P ssi 7 & 5 a < GRENVILLE (KEEWATIN) {(COUTCHICHING) 60 Fic. 40. Totat GEoLocic TIME SCALE, EsTIMATED AT SrxTy MILLION YEARS. These estimates are based upon the relative thickness of the pre-Cambrian and post-Cambrian rocks. Prepared by the author and C. A. Reeds after the time estimates of Walcott and Schuchert. 154 THE ORIGIN AND EVOLUTION OF LIFE The defensive armature finally through change of function makes important contributions to the inner skeleton. The chief advance which has been made in the last fifty years is our abundant knowledge of the modes of adaptation as contrasted with the very limited knowledge yet attained as to the causes of adaptation. The theoretic application of the fundamental law of action, reaction, and interaction becomes increasingly difficult and almost inconceivable as adaptations multiply and are super- posed upon each other with the evolution of the four physico- chemical relations, as follows: Physical environment: succession, reversal, and alternation of habitat zones, Individual development: succession, reversal, and alterna- tion of adaptive habitat phases, A ne Chromatin evolution: addition of the determiners of new aad habitat adaptations while preserving the determiners of . by Competition old habitat adaptations, Succession of life environments: caused by the migrations of the individual and of the life environment itself. THE LAW OF CONVERGENCE OR PARALLELISM OF FORM IN Locomotor, OFFENSIVE, AND DEFENSIVE ADAPTATIONS There arise hundreds of adaptive parallels between the evolution of the Vertebrata and the antecedent evolution of the Invertebrata. Although the structural body type and mechanism of locomotion is profoundly diverse, the combined necessity for protection and locomotion brings about close parallels in body form between such primitive Silurian euryp- terids as Bunodes and the vertebrate armored fishes known as ostracoderms, a superficial resemblance which has led Patten’ to defend the view that the two groups are genetically related. 1 Patten, Wm., 1912. THE LAWS OF ADAPTATION a It must be the similarity of the internal physicochemical energies of protoplasm, the similarity in the mechanics of motion, of offense and defense, together with the constant simi- larity of selection, which under- lies the law of convergence or parallelism in adaptation, name- ly, the production of externally similar forms in adaptation to similar external natural forces, a law which escaped the keen ob- servation of Huxley! in his re- markable analysis of the modes of vertebrate evolution pub- lished in 1880. The whole process of motor adaptation in the vertebrates, whether among fishes, amphib- ians, reptiles, birds, or mam- mals, is the solution of a series of mechanical problems, namely, of adjustment to gravity, of overcoming the resistance of water or air in the develop- ment of speed, of the evolution of the limbs in creating levers, fulcra (joints), and pulleys. The fore and hind fins of fishes 2 « Sfarli-a medern Jioh ¥ Sorpotec-a medeen Noam mal Fic. 41. CONVERGENT ADAPTATION OF Form IN THREE WHOLLY UNRELATED MARINE VERTEBRATES. Analogous evolution of the swift-swim- ming, fusiform body type (upper) in the shark, a fish; (middle) in the ichthyosaur, a reptile; and (lower) in the dolphin, a mammal—three wholly unrelated animals in which the in- ternal skeletal structure is radically different. After Osborn and Knight. and the fore and hind limbs of mammals evolve uniformly where they are homodynamic and divergently where they are heterodynamic. This principle of homodynamy and _ hetero- dynamy applies to the body as a whole and to every one of its 1 Huxley, T. H., 1880. 156 parts, according to two laws: THE ORIGIN AND EVOLUTION OF LIFE first, that each individual part has its own mechanical evolution, and, second, that the same mechanical problem is generally solved on the same principle. HABITAT ADAPTATIONS OF THE VER- TEBRATES TO THE CHANGES OF ENVIRONMENT AERIAL (FLYING, VOLANT TYPES) AERO-ARBOREAL (paRACcHUTE, VOLPLANING types) ARBOREAL {CLIMBING, LEAPING, AND BRACHIATING TYPES) ARBOREO-TERRESTRIAL (WALKING AND CLIMBING, SCANSORIAL TYPES) TERRESTRIAL AMBULATORY, SLOW; SALTATORY, LEAPING ; cumBrous) CURSORIAL, RAPID; GRAVIPORTAL, SLOW, TERRESTRIO-FOSSORIAL WALKING AND BURROWING TYPES) FOSSORIAL (BURROWING TYPES) TERRESTRIO-AQUATIC AMPHIBIOUS TYPES) AQUATIC PALUSTRAL, LACUSTRINE (SUAFACE-LIVING, BOTTOM-LIVING) FLUVIATILE FRESH-WATER, SWIFT CURRENT, SLOW- CURRENT; FLUVIO-MARINE TYPES) MARINE LITTORAL (SURFACE-LIVING AND BURROWING TYPES) MARINE PELAGIC FREE SURFACE-LIVING, DRIFTING, FLOAT- ING, SELF-PROPELLING TYPES) MARINE ABYSSAL (DEEP BOTTOM-LIVING TYPES, SLOW- AND SWIFT-MOVING) Each of the chief habitat zones may be divided into many subzones. The vertebrates may mi- grate from one to another of these habitats, or through geophysical changes the environments themselves may migrate. Conditions of locomo- tion result in forms that are quadrupedal, bipedal, pinnipedal, apodal, etc. This, we observe, is invariably the ideal principle, for, unlike man, nature wastes little time on inferior inventions but imme- diately proceeds to superior in- ventions. The three mechanical prob- lems of existence in the water habitat are: First, overcoming the buoyancy of water either by weighting down and increasing the gravity of the body or by the development of special grav- itating organs, which enable animals to rise and descend in this medium; second, the me- chanical problem of overcom- ing the resistance of water in rapid motion, which is accom- plished by means of warped sur- faces and well-designed entrant and re-entrant angles of the body similar to the ‘stream- of the fastest modern yachts; third, the problem of propulsion of the body, which is lines”’ accomplished, first, by sinuous motion of the entire body, ter- minating in powerful propulsion by the tail fin; secondly, by supplementary action of the four lateral fins; third, by the THE LAWS OF ADAPTATION 157 horizontal steering of the body by means of the median sys- tem of fins. The terrestrial and aérial evolution of the four-limbed types (Tetrapoda) is designed chiefly to overcome the resis- tance of gravity and in a less degree the resistance of the atmos- phere through which the body moves. When the aérial stage evolves, with increasing speed the resistance of the air becomes only slightly less than that of the water in the fish stage, and the warped surfaces, the entrant and re-entrant angles evolved by the flying body are similar to those previously evolved in the rapidly moving fishes. In contrast with this convergence brought about by the sim- ilarity above described of the physicochemical laws of action, reaction, and interaction, and the similarity of the mechanical obstacles encountered by the different races of animals in similar habitats and environmental media, is the law of diver- gence. BRANCHING OR DIVERGENCE OF ForM, THE LAW OF ADAPTIVE RADIATION In general the law of divergence of form, perceived by La- marck and rediscovered by Darwin, has been expanded by Osborn into the modern Jaw of adaptive radiation, which ex- presses the differentiation of animal form radiating in every direction in response to the necessities of the quest for nour- ishment and the development of new forms of motion in the different habitat zones. The psychic rudiments of this ten- dency to divergence are observed among the single-celled Pro- tozoa (p. 114). Divergence is constantly giving rise to differ- ences in structure, while convergence is constantly giving rise to resemblances of structure. The law of adaptive radiation is a law expressing the modes 158 THE ORIGIN AND EVOLUTION OF LIFE of adaptation of form, which fall under the following great principles of convergence and divergence: . Divergent adaptation, by which the members of a primitive stock tend to develop differences of form while radiating into a number of habitat zones. 2. Convergent adaptation, parallel or homoplastic, whereby an- imals from different habitat zones enter a similar habitat zone and acquire many superficial similarities of form. 3. Direct adaptation, for example, in primary migration through an ascending series of habitat zones, aquatic to terres- A Law : : f trial, arboreal, aérial. . s 4. Reversed adaptation, where secondary migration takes a re- Adaptive verse or descending direction from aérial to arboreal, Radiation from arboreal to terrestrial, from terrestrial to aquatic in the — habitat zones. External | 5. Alternate adaptation, where the animal departs from an orig- Body inal habitat and primary phase of adaptation into a sec- Form ondary phase, and then returns from the secondary phase of adaptation into a more or less perfect repetition of the primary phase by returning to the primary habitat zone. 6. Change of adaptation (function), by which an organ serving a certain function in one zone is not lost but takes up an entirely new function in a new zone. 7. Symbiotic adaptation, where vertebrate forms exhibit recip- rocal or interlocking adaptations with the form evolution of other vertebrates or invertebrates. It is very important to keep in mind that the body and limb form developed in each adaptive phase is the starting point of the next succeeding phase. Prolonged residence by an animal type in a single habitat zone results in profound alterations in its chromatin and in consequence the history of past phases is more or less clearly recorded. Among the disadvantages of prolonged existence in one life zone are the following: Through the Jaw of compensation, dis- covered by Geoffroy St. Hilaire early in the last century, every vertebrate, in developing and specializing certain organs sacri- THE. LAWS OF ADAPTATION 159 fices others; for example, the lateral digits of the foot of the horse are sacrificed for the evolution of the central digit as the animal evolves from tridactylism to monodactylism. These sacrificed parts are never regained; the horse can never regain the tridactyl condition although it may re-enter a habitat zone in which three digits on each foot would serve the pur- poses of locomotion better than one. In this sense chromatin evolution is irreversible. The extinction of vertebrate races has generally been due to the fact that the various types have sacrificed too many characters in their structural and func- tional reactions to a particular life habitat zone. A finely spe- cialized form representing a perfect mechanism in itself which closely interlocks with its physical and living environment reaches a cul-de-sac of structure from which there is no possible emergence by adaptation to a different physical environment or habitat zone. It is these two principles of too close adjust- ment to a single environment and of the non-revival of char- acters once lost by the chromatin which underly the law that the highly specialized and most perfectly adapted types become extinct, while primitive, conservative, and relatively unspe- cialized types invariably become the centres of new adaptive radiations. CHAPTER VI EVOLUTION OF BODY FORM IN THE FISHES AND AMPHIBIANS Rapid evolution in a relatively constant environment. Mechanism of motion, of offense, and defense. Early armored fishes. Primordial sharks. Rise of existing groups of fishes. Form evolution of the amphibians. Maxi- mum radiation and extinction. A SIGNIFICANT law of fish evolution is that in a practically unchanging environment, that of salt and fresh water, which is relatively constant both as to temperature and chemical con- stitution as compared with the variations of the terrestrial environment, it is steadily progressive and reaches the great- est extremes of form and of function. This indicates that a changing physicochemical environment, although important, is not an essential cause of the evolution of form. The same law holds true in the case of the marine invertebrates (p. 137), as observed by Perrin Smith. A second principle of signifi- cance is that even the lowliest fishes establish the chief glandu- lar and other organs of action, reaction, and interaction which we observe in the higher types of the vertebrates. Especially the glands of internal secretion (p. 74), the centres of inter- action and coordination, are fully developed. MecwHanismM OF MOTION, OF OFFENSE, AND DEFENSE Ordovician time, the early Paleozoic Epoch next above the Cambrian, is the period of the first vertebrates known, namely, the fossil remains of fish dermal defenses found near Cafon City, Col., as announced by Walcott in 1891, and subse- quently discovered in the region of the present Bighorn 160 EARLIEST KNOWN FISHES 161 Mountains of Wyoming and the Black Hills of South Dakota. Small spines referred to acanthodian sharks are also abundant in the Ordovician of Cafion City, Col. Since they were slow- moving types protected with the beginnings of a dorsal arma- ture composed of small calcareous tubercles, to which the FISHES AMPHIBIANS REPTILES BIRDS MAMMALS: g AGE OF MAN | © QUATERNARY = capes Ye Aa ee to 32 AGE 8g $3 OF 3 TERTIARY 7 MAMMALS. 8 UPPER @ CRETACEOUS = Y 3 O° LOWER, 7 AGE N CRETACEOUS 3 OF 0 (COMANCHEAN) eA Ss Pat eae or REPTILES W) ae oc W JURASSIC 2 = as } ee fe — 2 TRIASSIC PERMIAN zs Ta NP as tS a ee & | PENNSYLVANIAN AGE 2 (UPPER OF 2 CARBONIFEROUS) wo AMPHIBIANS 2 oe z 3 | mississiPPiAN ui ILC WER > CARBONIFEROUS) 0 ea er 8 QO} 2 | vevonian a AGE N/ 8 3 OF ° 3 —g@-——— ——— — — — — — — — — — — —— — J FISHES 5 io <| 2 | siurian 7 2 = x a Q e e 3 | ORDOVICIAN x AGE 2 oF 2 INVERTEBRATES = a cela eS ns el 3 CAMBRIAN ORDER OF APPEARANCE AND EXPANSION OF THE CLASSES OF VERTEBRATE ANIMALS Fic. 42. CHRONOLOGIC CHART OF VERTEBRATE SUCCESSION. Successive geologic appearance and epochs of maximum adaptive radiation (expansion) and diminution (contraction) of the five classes of vertebrates, namely, fishes, amphi- bians, reptiles, birds, and mammals. group name Ostracoderm refers, probably these earliest known pro-fishes were not primitive in external form but followed upon a long antecedent stage of vertebrate evolution. In the form evolution of the vertebrates relatively swift-moving, de- fenseless types are invariably antecedent and ancestral to slow- moving, armored types. Ancestral to these Ordovician chor- dates there doubtless existed free-swimming, quickly darting 162 THE ORIGIN AND EVOLUTION OF LIFE types of unarmored fishes. The double-pointed, fusiform body, in which the segmented propelling muscles are external and a stiffening notochord is central, is the fish prototype, which MYOMERES (Musete, segments) SPINAL NERVE CORD (Provertebral axis) DIGESTIVE TRACT Git SUTS more or less clearly survives in the exist- ing lancelets (Amphi- oxus) and in the lar- val stages of the de- generate ascidians. These animals also furnish numerous ia Fic. 43. THe Extstinc Lancetets (Amphioxus). embryonic and _lar- Fusiform protochordates living in the littoral zone of val Pp roofs of de- the ocean shores, sole survivors of an extremely ancient stage of chordate (pro-vertebrate) evolution. scent from nobler The body is fusiform or doubly pointed, hence the types name Amphioxus. It is stiffened by the continuous Dems central axis (chorda, notochord). All the other or- Followin g the ans are more or less sharply segmented. After Willey. é z sa * pro-fishes of Ordovi- cian time, the great group of true fishes begins its form evolu- tion with (A) active, free-swimming, double-pointed types of fusiform shape, adapted to rapid motion through the water and to predaceous habits in pursuit of swift-moving prey. EARLIEST KNOWN FISHES 163 From this type there radiated many others: (B) the deep, narrow-bodied fishes of relatively slow movements, frequenting the middle depths of the waters; (D) the swift-moving, elongate DEPRESSED (GROVELING) Fic. 44. THE FrvE PrincipAL Types OF Bopy Form IN FIsHEs. These begin with (A) the swift-moving, compressed, fusiform types which pass, on the one hand, into (B) laterally compressed, slow-moving, deep-bodied types, and, on the other, into (C) laterally depressed, round, bottom-dwelling, slow-moving types, also into (D) elongate, swift-moving fusiform types which grade into (£) the eel-like, swift- moving, bottom-living types without lateral fins. These five types of body form in fishes arise independently over and over again in the various groups of this class of vertebrates. Partially convergent forms subsequently appear among amphibians, rep- tiles, and mammals. Prepared for the author by W. K. Gregory and Erwin S. Christman. 164 THE ORIGIN AND EVOLUTION OF LIFE types which increasingly depend upon lateral motions of the body for propulsion and thus tend to lose the lateral fins and PALEOGEOGRAPHY, UPPER SILURIAN (SALINA) TIME AFTER SCHUCHERT, APRIL, 1916 MARINE DEPOSITS © CONTINENTAL DEPOSITS (? SALT DEPOSITS 1x VOLCANOES NortH AMERICA IN UPPER SILURIAN TIME. Fic. 45. During this period of depression of the Appala- chian region and elevation of the western half of the North American continent occurred the maximum evolution of the most primitive armored fishes, known as Ostracoderms, which were widely distributed in Europe, America, and the Antarctic. After Schuchert, 1916. finally to assume (£) an elongate, eel shape, en- tirely finless, for pro- gression along the bot- (C) the bottom- living forms, in which the body becomes later- ally broadened, the head very large relatively and covered with protective the movements of the ani- tom; dermal armature, mals becoming slower and slower as the dermal defenses develop. This law applies to all the vertebrates, including the de- velopment of armor is pari passu with the loss of speed. Conversely, the gain of speed neces- sitates the loss of ar- Smith Wood- ward! has traced similar man, namely: mor. radiations of body form in the historic evolution of each of the great groups of fishes. The interest of this fivefold law of body-form radiation is greatly enhanced when we find it repeated successively under 1 Smith Woodward, A., 1915. EARLY ARMORED FISHES 165 the law of convergence among the aquatic amphibia, reptiles, and mammals as one of the invariable effects of the coordina- tion of the mechanism of locomotion with that of offense and defense. In each of these four or five great radiations of body form, from the swift-moving to the bottom- or ground- living, slow, armored types, Fic. 46. THe Ostracoperm Paleas pis there is usually an increase of OF CLAYPOLE AS RESTORED BY DEAN. bodily size, also an increase of specialization, the maximum in both being reached just before the period of extinction arrives. EARLY ARMORED FISHES The armored Ordovician ostracoderms are very little known. The Upper Silurian ostracoderms enjoyed a wide distribution in Europe and They include both the fusiform, free-swim- America. ming type (Birkenia) and the broadly depressed ray- like types (Lanarkia, etc.). Apparently they had not yet acquired cartilaginous lower jaws and were in a lower stage of evolution than the true fishes. Tue ANTIARCHI. Fic. 47. Armored, bottom-living Ostracoderm type, Bo- thriole pis, from the Upper Devonian of Canada, with chitinous armature anda pair of anterior appendages analogous to those of the euryp- terid crustaceans. This cluster of animals was undoubtedly buried simultaneously while headed against the current in search of food or for purposes of respiration. After Patten. The armature is from the first arranged in shield and plate form, as seen in Paleaspis, from the Upper Silurian Salina time of Schu- chert. In this epoch we 166 THE ORIGIN AND EVOLUTION OF LIFE obtain our first glimpses of North American land life in the presence of the oldest known air-breathing animals, the scorpion Fic. 48. THe ARTHRODIRA. (Above.) Restoration of the gigantic Middle Devonian Arthrodiran (jointed neck) fish Dinichthys intermedius, eight feet in length, of the Cleveland shales (Ohio), showing the bony teeth and bony armature of the head region. (Below.) Lateral view of the same. Model by Dr. Louis Hussakof and Mr. Horter, in the American Museum of Natural History. spiders, also of the first known land plants. There are indica- tions of an arid climate in many parts of the world. In Upper Silurian time the ostracoderms attain the slow, armored, bottom-living stage of evolution, typified in the ptera- spidians and _ cephalaspidians, which were widely distributed in Europe, in America, and pos- sibly in the Antarctic regions, as indicated by recent explora- tions there. Belonging to an- other and very distinct order, or subclass (Antiarchi), are certain armored Devonian forms (Both- riolepis, Pterichthys, etc.), which possessed a pair of jointed lat- eral appendages. Some of these fishes, which are propelled by a pair of appendages at- tached to the anterior portion of the body, present analogies to the eurypterids (Merostomata, or Arachnida). In the fresh-water deposits of Lower Devonian age have been discovered the ancestors of the heavily armored fishes PRIMORDIAL SHARKS 167 known as the Arthrodira, a group of uncertain relationships. They have many adaptations in common with Bothriolepis, such as the jointed neck, dermal jaws, carapace, plastron, and paired appendages (Acanthaspis). the Arthrodira as aberrant lung-fishes. others regard the balance of evidence as in favor of relationship In the Middle Some authorities regard Dean, Hussakof, and with the stem of the Antiarchi (Bothriolepis). Devonian (the Cleveland shales of Ohio) they attain the formi- dable size shown in the species Dinichthys intermedius (Fig. 48). Like the ostracoderms, these animals are not in the central or main lines of fish evolution but represent collateral lines Fic. 49. A Primitive DEVONIAN SHARK. (Above.) Cladoselache, the type of the primitive Devonian shark of Ohio with paired and median lappet fins provided with rod-like cartilaginous supports, from which type by fusion the limbs of which early attained a very high degree of specialization which was followed by extinction. PRIMORDIAL SHARKS, ANCES- TRAL TO HIGHER VER- TEBRATES all the higher land vertebrates have been derived. Model by Dean, Hussa- kof, and Horter from specimens in the American Museum of Natural History. (Below.) The interior structure of the lappet fins of Cladoselache showing the cartilaginous rays (white) within the fin (black). After Dean. The central line of fish evolution, destined to give rise to all the higher and modern fish types, is found in the typical cartilaginous skeleton and jaws and four fins of the primordial sharks, the primitive fusiform stage of which appears in the spine-finned type (acanthodian, Diplacanthus, Fig. 51) of Upper Silurian time. The relatively large-headed, bottom-living types of sharks do not appear until the Devonian, during which epoch the early swift-moving, fusiform, predaceous types through a partly reversed adaptation 168 THE ORIGIN AND EVOLUTION OF LIFE branch off into the elongated eel-shaped forms of the Car- boniferous. The prototype of the shark group is the Cladoselache (Fig. 49), a fish famed in the annals of comparative anatomy since it demonstrates that the fins of fishes arise from lateral skin TERTIARY UPPER CRETACEOUS, LOWER CRETACEOUS (COMANCHEAN! MESOZOIC JURASSIC TRIASSIC PERMIAN PENNSYLVANIAN TUPPER, CARDONIFEROUS! i MISSISSIPPIAN ‘Lower CARBONIFEROUS! DEVONIAN wnp-patatoz0ic SILURIAN PALAEOZOIC ORDOVICIAN RLY PALALOZOR 7 SOFT-SKINNED CHORDATES CAMBRIAN ORIGIN AND ADAPTIVE RADIATION OF THE. Fic. 50. OriciIn AND ApaApTIvE RADIATION OF THE FISHES. This chart shows the now extinct Siluro-Devonian groups, the Ostracoderms and Arthro- dires, in relation to the surviving lampreys (Cyclostomes); sharks and rays (Elasmo- branchs); sturgeons, garpikes, and bowfins (Ganoids); bony fishes (Teleosts); primi- tive and recent lung-fishes (Dipnoi); and finally the fringe-finned or lobe-finned Ganoids (Crossopterygii) from the cartilaginous fins of which the fore and hind limbs of the first land-living vertebrates (Tetrapoda) were derived. Dotted areas represent groups which still exist. Hatched areas represent extinct groups. Prepared for the author by W. K. Gregory. folds of the body, into which are extended internal stiffening cartilaginous rods (Fig. 49). In course of evolution these rods are concentrated to form the central axis of a freely jointed fin, while in a further step of evolution they transform into the cartilages and bones of the limb girdles and limb segments of the four-footed land vertebrates, the Tetrapoda. The manner of this fin and limb transformation has been one of the greatest problems in the history of the origin of RISE OF MODERN FISHES 169 animal form since the earliest researches of Carl Gegenbaur, of Heidelberg, who sought to derive the lateral fins from a modification through a profound change of adaptation (func- tion) of the cartilaginous rods which support the respiratory gill arches. While paleontology has disproved Gegenbautr’s hypothesis that the limbs of the higher vertebrates, including those of man, are derived from the cartilaginous gill arches of fishes, it has helped to demonstrate the truth of Reichert’s anatomical hypothesis that the bony chain of the middle ear of man has been derived through change of adaptation from a portion of a modified gill arch, namely, the mandibular carti- lage of the fish. The cycle of shark evolution in course of geologic time embraces a majority of the swift-moving, predaceous types, which radiate into the sinuous, elongate body of the frilled shark (Chlamydoselache) and into forms with broadly depressed bodies, such as the bottom-living skates and rays. Under the law of adaptive radiation the sharks seek every possible habitat zone except the abyssal in the search for food. The nearest approach to the evolution of the eel-shaped type among the sharks are certain forms discovered in Carboniferous time. Rise oF MopERN FISHES By Upper Devonian time the fishes in general had already radiated into all the great existing groups. The primitive armored arthrodires and ostracoderms were nearing extinc- tion. The sharks were still in the early lappet-fin stage of evolution above described, a common characteristic of the members of this entire order being that they never evolved a solid bony armature, finding sufficient protection in the sha- green covering. The scaled armature of the first true ganoid, enamel-cov- 170 THE ORIGIN AND EVOLUTION OF LIFE ered fishes (Osteolepis, Cheirolepis) now makes its first appear- ance. These armored knights of the sea are descended from simpler scaly forms which also gave rise to the rich stock of sturgeons, garpikes, bowfins, and true bony fishes (teleosts) which now dominate all other fish groups both in the fresh Fic. 51. Fish Typrs FRoM THE OLD RED SANDSTONE OF SCOTLAND. Upper Devonian time. Primitive ganoids, primitive spine-finned sharks, bottom-living Ostracoderms, partly armored ganoids, and the first lung-fishes. 1. Osteolepis, primitive lobe-finned ganoid. 2. Holoptychius, fringe-finned ganoid. 3, 6. Cheiracanthus, spine- finned shark (Acanthodian). 4. Diplacanthus, spine-fmned shark (Acanthodian). 5. Coccosteus, primitive Arthrodiran. 7. Cheirolepis, primitive ganoid. 8,9. Dipterus, primitive lung-fish. Péerichthys, bottom-living Ostracoderm allied to Bothriolepis. Restorations by Dean, Hussakof, and Horter, partly after Traquair. Models in the American Museum of Natural History. waters and the seas. Remotely allied to this stock are the first air-breathing lung-fishes (Dipnoi), represented by Dipterus ; also the ‘“‘lobe-finned,”’ or “fringe-finned”’ ganoids from which the first land vertebrates were derived. From a single locality, in the Old Red Sandstone of Scotland, Traquair has recovered RISE OF MODERN FISHES 171 a whole fossil series of these archaic fish types as they lived together in the fresh water or the brackish pools of Upper De- vonian time. (Fig. 51). In this period the paleogeographers (Schuchert) obtain their first knowledge of the evolution of the terrestrial environment in the indications of the existence of parallel mountain ranges on the British Isles, of active volcanoes in the Gaspé region of EARLY LOWER DEVONIAN PALEOGEOGRAPHY, EARLY LOWER DEVONIAN (HELDERBERGIAN-GEDINNIAN-HERCYNIAN-KONIEPRUSSIAN) TIME. AFTER SCHUCHERT, APRIL, 1916 DEPOSITS DEPOSITS MOUNTAINS AND VOLCANOES Fic. 52. THEORETIC WoRLD ENVIRONMENT IN EARLY Lower DEVONIAN TIMES. The period of the early appearance of terrestrial invertebrates and vertebrates. This shows the hypothetical South Atlantic continent Gondwana and the Eurasiatic inland sea Tethys, according to the hypotheses of Suess. Modified after Schuchert, 1916. New Brunswick, of the mountain formations of South Africa, and of the depressions of the centre of the Eurasiatic continent into the great central Mediterranean Sea, known as the Tethys of the great Austrian geologist, Suess. In the seas of this time, as compared with Cambrian seas, we observe that the trilo- bites are in a degenerate phase, the brachiopods are relatively less numerous, the echinoderms are represented by the bottom- 172 THE ORIGIN AND EVOLUTION OF LIFE living starfishes, sharks are abundant, and arthrodiran fishes are still abundant in Germany. It was long believed that the air-and-water-breathing Am- phibia evolved from the Dipnoi, the air-breathing fishes of the inland fresh waters, and this hypothesis was stoutly main- FIN STAGE FOOT STAGE RHIPIDISTIAN FISH AMPHIBIAN { A (DEVONIAN) (CARBONIFEROUS) I Fic. 53. CHANGE oF ADAPTATION IN THE LIMBS OF VERTEBRATES. The upper figures represent the theoretic mode-of metamorphosis of the fringe-fin of the Crossopterygian fish (left) into the foot of an amphibian (right) through loss of the dermal fringe border and rearrangement of the cartilaginous supports of the lobe. After Klaatsch. The lower figures represent (left) the theoretic mode of direct original evolution of the bones of the fringe-fin (A, B) of a Crossopterygian fish—the Rhipidistia type of Cope— into the bony, five-rayed limb (C) of an amphibian of the Carboniferous Epoch (after Gregory); and (right) the secondary, reversed evolution of the five-rayed limb of a land reptile (4) into the fin or paddle (B, C) of an ichthyosaur (after Osborn). tained by Carl Gegenbaur, who also upheld what he termed the archipterygian theory of the origin of the vertebrate limb, namely, that the prototype of the modern limbed forms of terrestrial vertebrates is to be found in the fin of the modern Australian lung-fish, Ceratodus. This hypothesis of Gegen- baur, which has been warmly supported by a talented group of his students, is memorable as the last of the great hypotheses regarding vertebrate descent to be founded exclusively upon RISE OF MODERN FISHES 173 Fic. 54. EXTREMES OF ADAPTATION IN Locomotion AND ILLUMINATION. Extremes of adaptation in the existing bony fishes (Teleosts) of the Abyssal Zone of the Oceans. Although many different or- ders of Teleosts are represented, each type has independently acquired phosphores- cent organs, affording a fine example of the law of adaptive convergence. The body form in these fishes is of great diversity. 1. Thread-eel, Nemichthys SS scolopaceus Richardson. z. Barathronus S10 Lay diaphanus Brauer. 3. Neoscopelus macrole- pidotus Johnson. 4, 5. Gastrostomus bairdi Gill and Ryder. 6. Gigantactis ranhoeffeni Brauer. 7. Sternoptyx diaphana Lowe. 8. Giganturachuni Brauer. 9. Melanostomias melanops Brauer. 10. Stylophthalmus paradoxus Brauer. 11. Opisthoproctus solcatus Vaillant. After models in the American Museum of Natural History. comparative anatomy and embryology as opposed to the triple evidence afforded by these sciences when reinforced by paleontology. 174 THE ORIGIN AND EVOLUTION OF LIFE It is through the discovery of primitive types of the fringe- finned ganoids, to which Huxley gave the appropriate name Crossopterygia, in reference to the fringe of dermal rays around a central lobe-fin of cartilaginous rods, that the true ancestry of the Amphibia and of the amphibian limb has been traced. This is now regarded as due to a partial change of adaptation, Fic. 55. PHOSPHORESCENT ILLUMINATING ORGANS. The abyssal fishes represented in Fig. 54 as they are supposed to appear in the darkness of the ocean depths. After models in the American Museum of Natural History. incident to the passage of the animal from the littoral life zone to the shore zone, whereby the propelling fin was gradually transformed into the propelling limb. This transformation implies a long terrestrio-aquatic phase, in which the fin was partly used for propulsion on muddy surfaces (Fig. 53). In the reversed parallel retrogressive evolution of the lung- fishes (Lepidosiren, Gymnotus), of the fringe-finned fishes (Cala- moichthys) and of the bony fishes (Anguilla), the final eel-shaped, RISE OF MODERN FISHES 175 finless stage is through convergent adaptation either approached or actually passed. The bony fishes (teleosts), which first emerge as a distinct group in Jurassic time, radiate adaptively into all the great body-form types which had been previously at- tained by the older groups, more or less closely imitating each in turn, so that it is not easy to distinguish su- perficially between the armored catfishes (Lori- caria) of the existing South American waters and their prototypes (Cephalaspis) of the early Paleozoic. The most extreme specializa- tion in the great group : : : of bony fishes is to be ||. | eT eneulans _ DEVONIAN} Seafe found in the radiations career vancouver ee TIME . (PR MARINE DEPOSITS. CONTINENTAL DEPOSITS axs MOUNTAINS AND VOLCANOES of abyssal fishes into ve EEP WELLS slow- and swift-moving Fic. 56. NorTHAMERICA IN UPPER DEVONIAN TIME. . : : The maximum evolution of the Arthrodiran fishes forms which inhabit the (Dinichthys, etc.) and of the ganoids of the Upper great dep ths of the Devonian of Scotland, the establishment of all the great modern orders of fishes excepting the bony ocean and are adapted fishes (Teleosts), and the appearance of the first = = land vertebrates, the amphibians (Thinopus), to tons of water pes took place during this period of depression of the sure, to temperatures western centre of the North American continent. Modified after Schuchert. just above the freezing point, and to total absence of sunlight which is compensated for by the evolution of a great variety of phosphorescent light- 176 THE ORIGIN AND EVOLUTION OF LIFE producing organs in the fishes themselves and in other animals on which they prey. Another extreme of chemical evolution among the fishes is the production of electricity as a protective function, which is even more effective than bony arma- ture because it does not interfere with rapid locomotion. In only a few of the fishes is electricity generated in sufficient amounts to thoroughly pro- tect the organism. It develops through modified body tissues in the form of superimposed plates (electroplaxes) se- parated equally from one another by layers of a peculiar jelly-like connec- tive tissue, all lying parallel to each other and at right angles to the direc- tion of discharge.1 The electric organ is formed from modified muscle and connective tissue and is innervated by Tue EARLIEST Known Limpep ANIMAL. Fic. 57. Footprint of Thinopus anti- quus Marsh, an amphibian from the Upper Devonian of Pennsylvania. Type in the Peabody Museum of Yale University. Photograph of cast presented to the Ameri- motor nerves. The physical principle involved is that of the concentration cell, and the electrolyte used in the process is probably sodium chloride. can Museum of Natural His- tory by the Peabody Museum. The theory is that at the moment of discharge a membrane is formed on one surface of the electroplax which prevents the negative ions from passing through while the positive ions do pass through and form the current. The strength of the current varies from four volts in Mormyrus up to as much as 250 or more in Gymnotus, the electric eel, and consists of a series of shocks discharged 3/1000 of a second apart. 1 Dahlgren, Ulric, 1906, pp. 389-398; 1910, p. 200. EVOLUTION OF THE AMPHIBIANS 177 Form EvoLuTion oF THE AMPHIBIANS A single impression of a three-toed footprint (Thinopus antiquus) in the Upper Devonian shales of Pennsylvania con- stitutes at present the sole paleontologic proof of the long period of transition of the vertebrates from the fish type to the amphibian type. This transition was a matter of thousands of years. It took place in Lower Devonian if not in Upper Silurian time. Under the influence of the heredity- chromatin it is now re- hearsed or recapitulated in a few days in the metamor- phosis from the tadpole to tshirt a eat tas ee Fic. 58. A Primitive AMPHIBIAN. the frog. Theoretic reconstruction of a primitive sala- : mander-like type with large, solidly roofed As co mpare d with skull, four limbs, and five fingers on each of fishes, the significant prin- the fore and hind feet, such as may have ex- x , isted in Upper Devonian time. After Fritsch. ciple of the evolution of amphibians, as the earliest terrestrial vertebrates, is their reac- tion to marked environmental change. Their entire life re- sponds to the changes of the seasons. They also respond to secular changes of environment in the evolution of types adapted to extremely arid conditions. The adaptive radiation of the primordial Amphibia prob- ably began in Middle Devonian time and extended through the great swamp, coal-forming period of the Carboniferous, which afforded over vast areas of the earth’s surface ideal con- ditions for amphibian evolution, the stages of which are best preserved in the Coal Measures of Scotland, Saxony, Bohemia, Ohio, and Pennsylvania, and have been revealed through the studies of von Meyer, Owen, Fritsch, Cope, Credner, and Moodie. The earliest of these terrestrio-aquatic types have 178 THE ORIGIN AND EVOLUTION OF LIFE not only a dual breathing system of gills and lungs, but a dual motor equipment of limbs and of a propelling median fin in the tail region. So far as known, the primordial Amphibia in their form were chiefly of the small-headed, long-bodied, small-limbed, tail-pro- FROGS AND S| ASFOF MANS || ses: QUATERNARY COECILIANS URODELES TOADS S Ss pee ete ee 8 =a AGE 8 7 OF z TERTIARY MAMMALS, 2 UPPER. g CRETACEOUS 2 v poet eee g AGE O creo Bous HYLOEQBATRACHUS. > OF N (COMANCHEAN) 8 REPTILES 9 TRUE ANURA- a s WwW JURASSIC 4 2 = er at eh ee 2 Se a ee = — & TRIASSIC LABYRINTHO- DONTS: ‘St PERMIAN TOP i (SNAKE-LIKE g Per eee NNSYLVANIAN (UPPER. MicROSAURS BRANCHIOSAURS; ASE 2 canseeRPER, ,<) | FIRST REPTILES w | AMPHIBIANS § « PRIMITIVE STEGOCEPHS oO Sos a 8 5 MISSISSIPPIAN ) NI (Lower 8 oO CARBONIFEROUS) - wW FIRST BATRACHIANS o 4 THINOPUS a = a zg DEVONIAN ° FISHES 3 RHIPIDISTIAN FISHES - 5 LUNGFISHES 'LOBE-FINNED GANOIDS) < 3 —_ nN fe i ee i SILURIAN 7.GANOIb STOCK ORDOVICIAN AGE a FISHES WITH GILL-ARCH JAWS OF 3 a sees INVERTEBRATES 2 z CAMBRIAN 7 SOFT-SKINNED CHORDATES. ORIGIN AND ADAPTIVE RADIATION OF THE AMPHIBIA W. GREGORY, 1916 Fic 59. DESCENT oF THE AMPHIBIA The Amphibia—in which the fin is transformed into a limb (Thinopus)—are believed to have evolved from an ancestral ganoid fish stock of Silurian age through the fringe- finned ganoids. From this group diverge the ancestors of the Reptilia and the sala- mander-like Amphibia which give rise to the various salamander types, also to branches of limbless and snake-like forms (Aistopoda, modern Ceecilians). The other great branch of the solid-skulled Amphibia, the Stegocephalia, was widespread all over the northern continents in Permian and Triassic time (Cricotus, Eryops), and from this stock descended the modern frogs and toads (Anura). Prepared for the author by W. K. Gregory. pelled type of the modern salamander and newt. The large- headed, short-bodied types (Amphibamus) were precocious descendants of such primordial forms. In Upper Carbonifer- EVOLUTION OF THE AMPHIBIANS 179 ous and early Permian time the terrestrial amphibians began to be favored by the land elevation and recession of the sea which distinguished the close of the Carboniferous and early Permian time. Under these varied zonal conditions, aquatic, palustral, terrestrio-aquatic, fossorial, and terrestrial, the Am- EUMICRERPETON YONIUS AMPHIBIA CARBONIFEROUS AURHIBIA ia CARBONIFEROUS, DIPLOCAULUS AMPHIBIA CARBONIFEROUS AMPHIBIA PERMO- CARBONIFEROUS AMPHIBAMUS. Fic. 60. CuHrErF AMPHIBIAN TYPES OF THE CARBONIFEROUS. Restorations of the early short-tailed, land-living Amphibamus, the salamander-like Eumicrerpeton, the eel-bodied Ptyonius, and the broad-headed, bottom-living Dzplo- caulus. Prepared for the author by W. K. Gregory and Richard Deckert. phibia began to radiate into several habitat zones and adaptive phases, and thus to imitate the chief types of body form which had previously evolved among the fishes as well as to anticipate many of the types of body form which were to evolve subse- quently among the reptiles. One ancestral feature of the amphibians is a layer of superficial body scales in some types, which appear to be derived from those of their lobe-finned fish ancestors; with the loss of these scales most of the Amphibia also lost the power of forming a bony dermal armature. 180 THE ORIGIN AND EVOLUTION OF LIFE Recent researches in this country, chiefly by Williston, Case, and Moodie, indicate that the solid-headed Amphibia (Stegocephalia) and primary forms of the Reptilia chiefly be- long to late Carboniferous (Pennsylvania) and early Permian time. They are found abundantly in ancient pool deposits, which are now widespread over the southwestern United States aseseaasie, SA and Europe deposited in rocks of a reddish color. This reddish color points to aridity of climate in the northern hemis- phere during the period in which the terrestrial adaptive radiation of the Amphibia occurred. : Sgn ee oI These arid conditions Fic. 61. SKULL AND VERTEBRAL COLUMN OF Diplocaulus. continued during the A typical solid-, broad-headed amphibian from the Permian of northern Texas. Specimen in the American Museum of Natural History. (Com- time, especially in the pare Fig. 60.) greater part of Permian northern hemisphere. In the southern hemisphere there is evidence, on the con- trary, of a period of humidity, cold, and extensive glaciaticn, which was accompanied by the disappearance of the old lyco- pod flora (club-mosses) and arrival of the cool fern flora (Glos- sopteris), which appeared simultaneously in South America, South Africa, Australia, Tasmania, and southern India. The widespread distribution of this flora in the southern hemisphere furnishes one of the arguments for the existence of the great South Atlantic continent Gondwana, a transatlantic land bridge of animal and plant migration, postulated by Suess and sup- ported by the paleogeographic studies of Schuchert. In North America the glaciation of Permian time is believed to EVOLUTION OF THE AMPHIBIANS 181 have been only local. The last of the great Paleozoic seas dis- appeared from the surface of the continents, while the border seas give evidence of the rise of the ammonite cephalopods. Toward the close of Permian time the continent was com- pletely drained. Along the eastern seaboard the Appalachian EARLIEST, PERMIAN 3 5 © » ° OS PALEOGEOGRAPHY. EARLIEST PERMIAN (LOWER ARTINSKIAN-ROTLIEGENDE-AUTUNIAN), A GLACIAL TIME AFTER SCHUCHERT, APAIL, 1916 (pice riecos T bIRECTION OF Ice FLOW ]OLGANOES = »aaMOUNTAINS YY MARINE DEPOSITS < CONTINENTAL DEPOSITS ICE FIELDS xt Fic. 62. THEORETIC WoRLD ENVIRONMENT IN EARLIEST PERMIAN TIME. A period of marked glacial conditions in the Antarctic region. Vanishing of the coal floras and rise of the cycad-conifer floras, along with the rise of more modern insects and the beginning of the dominance of reptiles. Modified after Schuchert, 1916. revolution occurred, and the mountains rose to heights esti- mated at from three to five miles. An opposite extreme, of slender body structure, is found in the active predaceous types of water-loving amphibians such as Cricotus, of rapid movements, propelled by a long tail fin, and with sharp teeth adapted to seizing an actively moving prey. This type retrogresses into the eel-like, bottom-loving Lysorophus with its slender skull, elongate body propelled by 182 THE ORIGIN AND EVOLUTION OF LIFE lateral swimming undulations, the limbs relatively useless. Corresponding to the bottom-living fishes are the large, slug- gish, broad-headed, bottom-living amphibians, such as Diplo- caulus, with heads heavily armored, limbs small and weak, the body propelled by lateral motions of the tail. There were also v1 i i ! vy fe july Hii A \ “KE cRICOTUS PERMO- AMPHIBIA CARBONIFEROUS AMPHIBIA CACOPS PERMO- CARBONIFEROUS: ERYOPS PERMO- CARBONIFEROUS, AMPHIBIA Fic. 63. AMPHIBIA OF THE AMERICAN PERMO-CARBONIFEROUS. Here are found the free-swimming Cricotus, the short-bodied Cacops, and abundance of the amphibious terrestrial type, the large, solid-headed Evyops. Restorations for the author by W. K. Gregory and Richard Deckert. more powerful, slow-moving, long-headed, alligator-like, terres- trio-aquatic forms, such as the Archegosaurus of Europe and the fully aquatic Trimerorachis of America. An extreme stage of terrestrial, ground-living evolution with marked reduc- tion of the use of the tail for propulsion is the large-headed Cacops, short-bodied, with limbs of medium size, but with feeble powers of prehension in the feet. Radiating around these animals were a number of terrestrial types exhibiting the evolution of dorsal protective armature and spines (Aspi- dosaurus); other types lead into the pointed-headed structure and pointed teeth of Trematops. EVOLUTION OF THE AMPHIBIANS 183 The Age of Amphibians passes its climax in Permian time (Fig 63.). In Triassic time there still survive the giant terres- trial forms. Evidences of extensive intercontinental connections in the northern hemisphere are also found in the similarity of type between the great terrestrial amphibians of such widely sepa- rated areas as Texas and Wiirtemberg, which develop into simi- lar resemblances between the great labyrinthodont amphibians of Lower Triassic times of Europe, North America, and Africa. Ancestral to these Triassic giants is the large, sluggish, water- and shore-living Eryops of the Texas Permian, with massive head, depending on its short, powerful limbs and broad, spread- ing feet for land propulsion, and in a less degree upon its tail for propulsion in the water. This animal may be regarded as a collateral ancestor of the labyrinthodonts; it belongs to a type which spread all over Europe and North America and persisted into the Metopias of the Triassic. eae ye a Ae atin Fic. 64. SKELETON oF Eryops FROM THE PERMO-CARBONIFEROUS OF TEXAS. A type of the stegocephalian Amphibia which were structurally ancestral to the Laby- rinthodonts of the Triassic. Mounted in the Amerjcan Museum of Natural History. \ CHAPTER VII FORM EVOLUTION OF THE REPTILES AND BIRDS Appearance of earliest reptile-like forms, the pro-Reptilia, followed by the first higher reptiles. Geologic distribution and environment of the various extinct and existing orders of reptilia. Evolutionary laws exemplified in the origin and development of this great group of animal] life. Direct, reversed, alternate, and convergent adaptation. Modes of offense and defense. Terrestrial, fossorial, aquatic, and marine radiation. Aérial adaptation. The Pterosaurs. First appearance of bird-like - animals. Theories regarding the evolution of flight in birds. Theories as to the causes of arrested evolution. THE environment of the ancestor of all the reptiles was a warm, terrestrial, and semi-arid region, favorable to a sensitive nervous system, alert motions, scaly armature, slender limbs, a vibratile tail, and the capture of food both by sharply pointed, recurved teeth and by the claws of a five-fingered hand and foot. The mechanically adaptive evolution of the Reptilia from such an ancestor is as marvellous and extreme as the subsequent evolution of the mammals; it far exceeds in di- versity the radiation of the Amphibia and extends over a pe- riod estimated at from 15,000,000 to 20,000,000 years. THE PERMIAN REPTILES OF NorTH AMERICA AND SOUTH AFRICA The experiments of the Amphibia in adapting themselves to the Permian continents with their relatively dry surfaces and seasonal water pools and lagoons are contemporaneous with the first terrestrial experiments and adaptive radiations of the Reptilia, a group which was particularly favored in its 184 EARLIEST REPTILES 185 origin by arid environmental conditions. The result is the creation in Permian time of many externally analogous or con- vergent groups of amphibians and reptiles which in external appearance are difficult to distinguish. Yet as divergent from the primitive salamander-like Amphibia and clearly of another EARLIEST PERMIAN cy gy PALEOGEOGRAPHY. EARLIEST PERMIAN (LOWER ARTINSKIAN-ROTLIEGENDE-AUTUNIAN), A GLACIAL TIME AFTER SCHUCHERT, APRIL, 1916 Pe ¥ MARINE DEPOSITS ¢} CONTINENTAL DEPOSITS Giptice FIELOS: f pinection oF ice FLOW ICE FIELDS x*" VOLCANOES «saa MOUNTAINS. Fic. 65. THEORETIC WorLD ENVIRONMENT IN EARLIEST PERMIAN TIME. A period of marked glacial conditions in the Antarctic region. Vanishing of the coal floras and rise of the cycad-conifer floras, along with the rise of more modern insects and the beginning of the dominance of reptiles. Modified after Schuchert, 1916. type these pro-reptiles are different in the inner skeletal struc- ture and in the anatomy of the skull they are exclusively air-breathing, primarily terrestrial in habit rather than ter- restrio-aquatic, superior in their nervous reactions and in the development of all the sensory organs, and have a more highly perfected cold-blooded circulatory system. Neverthe- less, the most ancient solid-headed reptilian skull type (Cotylo- sauria, Pareiasauria, of Texas and South Africa, respectively) 186 THE ORIGIN AND EVOLUTION OF LIFE is very similar to that of the solid-headed Amphibia (Steg- ocephalia). Bone by bone its parts indicate a common descent from the skull type of the fringe- finned fishes Fig. 53). As revealed by the researches of Cope, Williston, and Case, the adaptive radiation of the (Crossopterygia, PERMO- CARBONIFEROUS. REPTILIA VARANOPS reptile life of western America in Permian time is as follows: First there is a variety of swift- moving, alert, predaceous forms corresponding to the fusiform, swift-moving stage in the evolu- tion of the fishes. these reptiles (Varanops) re- semble the modern monitor liz- ards (Varanus); others (Ophi- acodon and Theropleura) are Some of ARAEOSCELIS: PERMO REPTILIA CARBONIFEROQUS Fic. 66. Two of the defenseless, swift-moving, terrestrial reptilian types, Varanops and Ar@oscelis, of the Permo-Carbonif- erous period of Texas. The skull and skeleton of Ar@oscclis foreshadow the ANCESTRAL REPTILIAN TYPES. existing lizard (Lacertilian) type and Williston regards it as the most nearly related Permian representative known of the true Squamata (ancestors of provided with four well-devel- oped limbs and feet, the long tail being utilized as a balancing the lizards, snakes, and mosasaurs). Restorations of Varanops and Ar@os- celis modified from Williston. Drawn for the author by Richard Deckert. organ. ‘These were littoral or lowland reptiles, insectivorous The primitive, lizard-like pelycosaur Varanops, with a long tail and four limbs of equal proportions, represents more nearly or carnivorous in habit. than any known ancient reptile, apart from certain special characters, a generalized prototype from which all the eighteen Orders of the Reptilia might have descended; its structure could well be ancestral to that of the lizards, the alligators, and the dinosaurs. At present, however, it is not determined whether EARLIEST REPTILES 187 the primitive ancestors from which the various orders of reptiles descended belong to a single, a double, or a multiple stock. Passing to the widely different amphibian-like order known as cotylosaurs, we see animals which, on the one hand, grade into the more fully aquatic, pad- dle-footed, free-swimming Lim- noscelis with a short, crocodile- like head, which propelled itself by means of its long tail, and, .’ on the other hand, there devel- oped short-tailed, semi-aquatic the Labido- In adaptation to the more purely terrestrial habitats forms, such as SQUrUs. there is sometimes a reduction in the length of the tail and greater perfection in the struc- ture of the limbs and the various forms of armature. In Pantylus these defenses appear in the form of bony ossicles of the skin and scutes; in Chilonyx the skull top is covered with tuber- culated defenses; in the slow- moving Diadectes the body is partly armored, the animal be- ing proportioned like the exist- ing Gila monster and probably of nocturnal habits, which is in- ferred from the large size of the eyes. REPTILIA REPTILIA LABIDOSAURUS PERMO- CARBONIFEROUS PERMO- SEVMOURIS CARBONIFEROUS DIADECTES PERMO- REPTILIA CARBONIFEROUS REPTILES WITH SKULLS TRANS- ITIONAL IN STRUCTURE FROM THE AMPHIBIAN SKULL. Fic. 67. Typical solid-headed reptiles (Coty- losaurs) characteristic of Permo-Car- boniferous time in northern Texas, including the three forms Seymouria, Labidosaurus, and the powerful Dia- dectes, which resembles the existing Gila monster. The head in the mounted skeleton of Diadectes (lower) in the American Museum of Natural History is probably bent too sharply on the neck. Restorations for the author by W. K. Gregory and Richard Deckert. Labidosaurus and Seymouria chiefly after Williston. 188 THE ORIGIN AND EVOLUTION OF LIFE The most remarkable types in this complex reptilian society of Permian Texas are the giant fin-backed lizards, Clepsydrops, Dimetrodon, Edaphosaurus, of Cope, probably terrestrial and carnivorous in habit. In these animals the neural spines of the dorsal vertebrz are vertically elongated to support a power- ful median membranous fin, the spines of which are sometimes MIDDLE PERMIAN no » 8 PALEOGEOGRAPHY. MIDDLE PERMIAN (THURINGIAN-ZECHSTEIN) TIME AFTER SCHUCHERT, APRIL, 1916 aan MOUNTAINS vy GONDWANA FLORA (POMARINE DEPOSITS Gt CONTINENTAL DEPOSITS AND SALT Fic. 68. THEORETIC WORLD ENVIRONMENT IN MIDDLE PERMIAN TIME. Great extension of the Baltic Sea and of the Eurasiatic Mediterranean Tethys. Rise of the Appalachian, Northern European Alps, and many other mountains. Modified after Schuchert. smooth (Dimetrodon), sometimes provided with transverse rods (Edaphosaurus cruciger). These structures may have devel- oped through social or racial competition and selection within this reptile family rather than as offensive or defensive organs in relation to other reptile families. We now glance at the Permian life of another great zoologic region. Africa has been throughout all geologic time the most stable of the continents, especially since the begin- EARLIEST REPTILES 189 ning of the Permian Epoch. The contemporaneous evo- lution of the pro-Reptilia, traced in a continuous earth section from the base of the Permian to the Lower Trias- sic, as successively explored by Bain, Seeley, Broom, and Watson, has re- realed a far more extensive and more varied adaptive radiation of the reptiles than that which is known on the American continent. Al- Owen, though the adaptations are chiefly terrestrial, we trace certain strong analogies if not actual relationships to the Permo-Triassic reptiles of North America. While the drying pools and lagoons of arid North America were entombing the life of the Permian and Triassic Epochs, there were being deposited in the Karoo series of South Africa some 9,500 feet of strata consist- ing of shales and sandstones, chiefly of river flood-plain and delta origin, and rang- ing in time from the basal EDAPHOSAURUS PERMO- REPTILIA CARBONIFEROUS DIMETROOON PERMO- REPTILIA CARBONIFEROUS Fic. 69. Tar Frin-BAck PERMIAN REPTILES. Restorations (middle and upper figures) of the giant carnivorous reptiles of northern Texas in Permian time; the large-headed Dimetrodon and the contemporary small- headed Edaphosaurus cruciger. In both animals the neural spines of the vertebre are greatly elongated, hence the popular name “fin-back.” Skeleton of Dimetrodon (lower) in the American Museum of Natural History. Restorations for the author by W. K. Gregory and Richard Deckert. 190 THE ORIGIN AND EVOLUTION OF LIFE Permian into the Upper Triassic. Here, up to the year 1909, twenty-two species of fossil fishes had been recorded, mostly ganoids of Triassic age. The eleven species of amphibians dis- covered are of the solid-headed (Stegocephalia) type, broadly REPTILIA PERMIAN IcTIDOPSIS REPTILIA TRIASSIC C¥HNUGNATHUS REPTILIA TRIASSIC Fic. 70. MAMMAL-LIKE REPTILES OF Soutu AFRICA. The relative stability of the African continent favored the early evolu- tion of the free-limbed forms of reptiles known as Anomodonts, in- cluding the powerful Endothiodon, in which the jaws are sheathed in horn like those of turtles; and also of the Cynodonts (dog-toothed reptiles), including the carnivorous, strongly toothed Cynognathus which is allied to the ancestors of the Mammalia. Restorations for the author by W. K. Gregory and Richard Deckert. similar in external appearance to those of the same age discovered in Europe. The one hundred and fifteen species of reptiles described from the Lower and Middle Per- mian deposits include solid-headed pareiasaurs—great, round-bodied, herbivorous reptiles with massive limbs and round heads—which are allied to the cotylosaurs of the Permo-Carboniferous of America, the agile dromosaurs, similar to the lizard-like reptiles of the Texas Permian, with large eye-sockets, and adapted to swift, cursorial movements, also reptiles known as therocephalians in reference to the analogy which the skull bears to that of the mammals, gorganop- sians, and numerous slender- limbed, predatory reptiles with sharp caniniform teeth. The giant predaceous Reptilia of the time are the dinocephalians (7. e., ‘‘ terri- ble-headed’’), very massive animals with a highly arched back, broad, swollen forehead, short, wide jaws provided with mar- ginal teeth. Surpassing these in size are the anomodonts (7. ¢., “lawless-toothed’’) in which the skull ranges from a couple MAMMAL-LIKE REPTILES IQI of inches to a yard in length, and the toothless jaws are sheathed in horn and beaked like those of turtles. This is a nearly typical social group: large and small, herbivorous, omnivorous, and carnivorous, toothed, toothless and horny-beaked, swift- moving, slow-moving, unarmored, partly armored; it lacks only the completely armored, slow-moving type to be a perfect complex. In the Upper Permian the fauna includes pareiasaurs and gorganopsians, which are similar to a large group of reptiles of the same geologic age discovered in Russia by Amalitzky. In Lower and Middle Triassic time the last and most highly specialized of the beaked anomodonts appear together with di- minished survivors (Procolophon) of the very ancient solid-headed order (Pareiasauria of South Africa, Cotylosauria of Texas). Here also are found the true cynodonts, which are the most mammal-like of all known reptiles. In the Upper Triassic of South Africa occur carnivorous dinosaurs, also crocodile-like phy- tosaurs (Fig. 75), allied to those of Europe and North America. ORIGIN OF THE MAMMALS AND ADAPTIVE RADIATION OF THE EIGHTEEN ORDERS OF REPTILES The most notable element in this complex reptilian society of South Africa are those remarkable pro-mammalian types of reptiles (cynodont, theriodont), from which our own most remote ancestors, the stem forms of the Mammalia, the next higher class of vertebrates above the Reptilia, were destined to arise. This is another instance where paleontology has dis- lodged a descent theory based upon anatomy, for at one time from anatomical evidence alone Huxley was disposed to derive the mammals directly from the amphibians. The question at once arises, why were these particular reptiles so highly favored as to become the potential ancestors of the 192 THE ORIGIN AND EVOLUTION OF LIFE mammals? At least two reasons are apparent. First, these larger and smaller types of South African pro-mammals exhibit an exceptional evolution of the four limbs, enabling them to travel with relative rapidity, which is connected with ability to migrate, powers doubtless associated with increasing in- telligence. Another marked characteristic which favors de- velopment of intelligence is the adaptability of their teeth to different kinds of food, insectivorous, carnivorous, and herbiv- orous, which leads to development and diversity of the powers of observation and choice. In this adaptability they in a limited degree anticipate the evo- lution of the mammals, for the other SCYMNOGNATHUS reptiles generally are distinguished by a REPTILIA PERMIAN ‘6 * * ° singular arrest or inertia in tooth de- Fic. 71. A SoutH AFRICAN : alte o “Doc-Tootuep” Reptie, Velopment. Rapid specialization of the Head of one of the South teeth is one of the chief features in the African Cynodonts or “‘dog- 5 A i toothed” reptiles, related to history of the mammals, which display the ancestors of the mam- 4 continuous momentum and advance mals. Restoration for the | : . author by W. K. Gregory in tooth structure, associated with ern specialization of the organs of taste. Of greater importance in its influence on the brain evolu- tion of the early pro-mammalian forms is the internal tem- perature change, whereby a cold-blooded, scaly reptile is transformed into a warm-blooded mammal through a change which produced the four-chambered heart and complete sep- aration of the arterial and venous circulation. This change may have been initiated in some of the cynodonts. This new constant and higher temperature favors the nervous evolution of the mammals but has no influence whatever upon the me- chanical evolution. As pure mechanisms the cold-blooded rep- tiles exhibit as great plasticity, as great diversity, and perhaps ADAPTIVE RADIATION OF REPTILES 103 higher stages of perfection than the mammals. Nor does increas- ing intelligence, as we shall see, favor mechanical perfection. Turning our survey to the origin and adaptive radiation of the reptiles as a whole, we find that in Permian time all of the CENOZOIC TERTIARY UPPER CRETACEOUS MESOZOIC JURASSIC TRIASSIC PERMIAN -- PROGANO- PENNSYLVANIAN (UPPER CARBONIFEROUS) MISSISSIPPIAN TRIRST ower CARBONIFEROUS! DEVONIAN SILURIAN PALAEOZOIC ORDOVICIAN CAMBRIAN ORIGIN AND ADAPTIVE RADIATION OF THE W, K GREGORY, 1916 Fic. 72. ADAPTIVE RADIATION OF THE REPTILIA. The reptiles first appear in Upper Carboniferous and Lower Permian time and radiate into eighteen different orders, three of which—the Cotylosaurs, Anomodonts, and Pely- cosaurs—attain their full evolution in Permian and Triassic time and later become extinct. .Six orders—the Ichthyosaurs, Plesiosaurs, Dinosaurs, Phytosaurs, Pterosaurs, and Turtles—are first discovered in Triassic time, while five of the orders—the Ich- thyosaurs, Plesiosaurs, Mosasaurs, Dinosaurs, and Pterosaurs—dominate the Cretace- ous Period and become suddenly extinct at its close, leaving the five surviving modern orders—Testudinata (turtles, tortoises), Rhyncocephalia (tuateras), Lacertilia (lizards), Ophidia (snakes), and Crocodilia (crocodiles). These great reptilian dynasties seem to have extended over the estimated ten million years of the Mesozoic Era, namely, the Triassic, Jurassic, and Upper Cretaceous Epochs. Prepared for the author by W. K. Gregory. ten early adaptive branches of the reptilian stem had radiated and become established as prototypes and ancestors of the great Mesozoic Reptilia. Five divisions, namely, the coty- losaurs, anomodonts, pelycosaurs, proganosaurs, and phyto- saurs, were destined to become extinct in Permian or Triassic time, in each instance as the penalty of excessive and prema- 194 THE ORIGIN AND EVOLUTION OF LIFE ture specialization. Five other great branches, namely, the ichthyosaurs, plesiosaurs, two great branches of the dinosaurs, and the pterosaurs, were destined to dominate the waters, the earth, and the air during the Mesozoic Era, 7. e., the Tri- assic, Jurassic, and Cretaceous Epochs. Thus altogether thir- teen great branches of the reptilian stock became extinct either before or near the close of the Age of Reptiles. Out of the total of eighteen reptilian branches only five were destined to survive into Tertiary time, namely, the orders which include the existing turtles, tuateras, lizards, snakes, and crocodiles. GEOLOGIC BLANKS AND VISTAS OF REPTILIAN EVOLUTION As pointed out in the introduction of this chapter, the rep- tile ancestor of these eighteen branches of the class Reptilia— a class with an adaptive radiation which represents the mechan- ical conquest of every one of the great life zones, from the aérial to the deep sea—will some day be discovered as a small, lizard- like, cold-blooded, egg-laying, four-limbed, long-tailed terres- trial form, with a solid skull roof, of carnivorous or more prob- ably insectivorous habit, which lived somewhere on the land surfaces of Carboniferous time. Such undoubtedly was the reptilian prototype from which evolved every one of the marvellous mechanical types which we may now briefly re- view. By methods first clearly enunciated by Huxley in 1880 several of the ideal vertebrate prototypes have been theoreti- cally reconstructed, and in more than one instance discovery has confirmed these hypothetical reconstructions. The early geologic vistas of this entire radiation are seen in the reptilian life of the Permian Epoch of North America, Europe, and Africa just described, consisting exclusively of ter- restrial and terrestrio-aquatic forms. In the Triassic we obtain succeeding vistas of the terrestrial and fluviatile life of North ADAPTIVE RADIATION OF REPTILES 195 America, Europe, and Africa, as well as our first glimpses of the early marine life of North America. In Jurassic time deposits at the bottom of the great interior continental seas give us the TERRESTRIAL AND FLUVIATILE MARINE N. AMER. | EUROPE | AFRICA | S. AMER. N. AMER, | EUROPE | AFRICA : | S. AMER. QUATERNARY i | \ | t+——--$——~—+-—— + — TERTIARY ILIAN SEA FAUNA PTILIAN SEA FAU! UPPER CRETACEOUS URS AND MOSASAURS) CRETACEOUS = (COMANCHEAN! Z LLL D DINOSAUR STAGES MJ ZZ pe Eg arate PODA) ZZ LA LEZ ID REPTILIAN SEA FAUNA LEE Zz E JURASSIC ZL a A! IRS-AND ICHTHYOSAURS) SSAURS 0 2 | | ZAAarst REPTILIAN SEA FAUNA PRIMITIVE ICHTHYOSAURS) ' TRIASSIC a Fic. 73. Grortocic Recorps oF REPTILIAN EVvoLUTION, TERRESTRIAL AND Marine. Shaded areas represent the geologic vistas of reptilian life which have been discovered from fossils entombed in ancient TERRESTRIAL, FLUVIATILE, and MARINE habitats of different portions of the northern and southern hemispheres. Triassic. We begin with the deposits of the continental surfaces of North America, Europe, and Africa. During Triassic time the FIRST DINOSAUR STAGES appear, as well as some of the semi-aquatic forms which frequented fluviatile regions, while the PRrmI- TIVE ICHTHYOSAURS were then fully adapted to marine life. Jurassic and Lower Cretaceous. We continue with geologic vistas of the succeeding marine life and the evolution of the SECOND REPTILIAN SEA FAUNA, indicated by the shaded areas of the Jurassic and the Lower Cretaceous of North America and Europe. The remains of these animals are found in the deposits of deep or shallow sea waters. There is one great vista, the SECOND DINOSAUR STAGES, which includes the terrestrial dinosaurs known as SAUROPODA, found in Upper Jurassic and Lower Cretaceous de- posits in North America, Europe, Africa, and South America. Upper CRETACEOUS. Then there was a long interval, followed by the FINAL DINOSAUR STAGES and a long vista of the terrestrial reptilian life of Upper Cretaceous time, especi- ally in North America. Contemporary with this is the FINAL REPTILIAN SEA FAUNA. Chart by the author. second reptilian sea fauna of plesiosaurs and ichthyosaurs within the continents of North America and Europe. The story of the marine pelagic evolution of the reptiles is continued with some interruptions through the Lower Cretaceous into the final rep- 196 THE ORIGIN AND EVOLUTION OF LIFE tilian sea fauna of plesiosaurs and mosasaurs of Upper Creta- ceous time. In the meanwhile the life of the continents is revealed in the terrestrial and fluviatile deposits of the Triassic Epoch, in the first stages of the terrestrial evolution of the dinosaurs, in the early stages of the fluviatile evolution of the Crocodilia, and in the final stages of the terrestrial phases of the Amphibia and pro-Reptilia. A long interval of time elapses at this period in the earth’s history, during which the life of the con- tinents is entirely unknown, until the close of the Jurassic and beginning of Cretaceous time, when there appears a sec- ond great stage of dinosaur evolution, revealed especially in the lagoon deposits of North Africa and South America, which have yielded remains of giant Sauropoda. Then another gap occurs in the story as told by continental deposits. Finally, in Upper Cretaceous time we again discover great flood-plain and shore-line deposits, which give a prolonged vista of the ter- restrial life of the Reptilia, especially in North America and Europe. Thus it will be understood that, while the great tree of reptilian descent has been worked out through a century of scientific researches, beginning with those of Cuvier and con- tinued by Owen, Leidy, Cope, Marsh, and our contemporary paleontologists, there are enormous gaps in both the terres- trial and the marine history of several of the reptilian orders which remain to be filled by future exploration. We piece to- gether fossil history on the continents and in the seas from the animals entombed in these deposits, partly by means of the real relationships observed in widely migrating forms, such as the land dinosaurs and the marine ichthyosaurs, ple- siosaurs, and mosasaurs. Many of these reptiles ranged over every continent and in every sea. On the whole, the physio- ADAPTIVE RADIATION OF REPTILES 197 graphic condition most favorable to the preservation of life in the fossil condition is that known as the flood-plain, in which the rising waters and sediments of the rainy season rapidly entomb animal remains which are deposited on the surface Anderson Bphertitsis we Fic. 74. CLose oF THE AGE oF Rreptites. A RELIc oF ANCIENT FLOOD-PLAIN ConprI- TIONS. Iguanodont dinosaur lying upon its back. Integument impressions preserved. The “dinosaur mummy,” Trachodon, from the Upper Cretaceous flood-plain deposits of Converse County, Wyoming. Due to arid seasonal desiccation, the skin folds and impressions are preserved over the greater part of the body and limbs. Discovered by Sternberg. Mounted specimen in the American Museum of Natural History. or in small water pools during the drier seasons. Fossils buried in old flood-plain areas of South Africa tell us the story of the life evolution which is continued by the ancient shore and lagoon deposits in other parts of the world as well as by fossils found in the broad, intermittent flood-plain areas of the American Triassic and Cretaceous, which close with the 198 THE ORIGIN AND EVOLUTION OF LIFE great delta deposits of the Upper Cretaceous lying to the east of the present Rocky Mountain range. The more re- stricted deposition areas of drying pools and lagoons, such as those observed in the Permian and Triassic shales and sand- stones of Texas, entomb many forms of terrestrial life. Vistas of the contemporaneous evolution of fluviatile, aquatic, and marine life are afforded by the animals which perish at the surface and sink to the calcareous bottom oozes of the conti- nental seas of Triassic, Jurassic, and Cretaceous time. It is only in the Tertiary of the Rocky Mountain region of North America that we obtain a nearly continuous and uninterrupted story of the successive forms of continental life, among the mammals entombed in the ancient flood-plains, in the volcanic ash-beds, in the lagoons, and more rarely in the littoral deposits. AQuATIC ADAPTATION OF THE REPTILIA, DIRECT AND REVERSED From the distinctively terrestrial radiations of Permian time we turn to the development of aquatic habitat phases among the reptiles which lived along the borders of the great interior rivers and continental seas of Permian, Triassic, and Jurassic time. This reversal of adaptation from terrestrial into aquatic life is, as we might theoretically anticipate, a reversal of func- tion rather than of structure, because, as above stated (p. 159), it is a universal law of form evolution that ancient adaptive characters once lost by the heredity-chromatin are never reacquired. In geologic race evolution there is no process analogous to the wonderful phenomena of individual regenera- tion or regrowth, such as is seen among amphibians and other primitive vertebrates, whereby the original limb may be com- pletely restored from the mutilated remnant of an amputation. AQUATIC REPTILES 199 Such regeneration is attributable to the potentiality of the heredity-chromatin which still resides in the cells of the am- putated surfaces. The heredity-chromatin determiners of the bones of the separate digits or separate phalanges if once lost in geologic time are never reacquired; on the contrary, each phase of habitat adapta- tion is forced to commence with the elements remain- ing in the organism’s hered- ity-chromatin, which may rePrin ont have been impoverished in previous habitats. When : Lm - f? oi a ‘ae G~l 1 ff an ancient habitat zone is reentered there must be readaptation of the parts ~ —=a= which remain. Thus, REPTILIA RHYTIDODON TRIASSIC when the terrestrial rep- Itc. 75. Reprires Lreavinc A TERRESTRIAL til is _ FOR AN AQUATIC HABITAT, THE BEGINNING les reenter the aquatic oF AQUATIC ADAPTATION. zone of their amphibian Littoral-fluviatile types independently evolve t fy t in the Triassic (Rhytidodon, a phytosaur) and ancestors ey cannot re- in the Upper Cretaceous (Champsosaurus). sume the amphibian char- These animals belong to two widely different orders of reptiles, neither of which is closely acters, for these have been akin to the modern alligators and crocodiles. : The adaptation is convergent to that of the lost by the chromatin. existing gavials and crocodiles. Restorations This invariable princi- for the author by W. K. Gregory and Richard Deckert. ple underlying reversed evolution is partly illustrated (Fig. 53) in the passage from the reptilian foot into the fin of the aquatic reptile and with equal clearness in the passage of the wing of the flying bird into the fin of the swimming bird (Fig. r1o). In no less than eleven out of the eighteen orders of reptiles reversed adaptation to a renewal of aquatic life, like that of the fishes and amphibians, took place in the long and slow 200 4 CYMBOSPONDYLUS REPTILIA TRIASSIC GEOSAU! REPTILIA ise TYLOSAURUS SBELOGEOUS CRICOTUS PERMO- AMPHIBIA CARGONIFEROUS, Fic. 76. CONVERGENT AQuaTIC ADAP- TATION INTO ELONGATE FusirormM TYPE In Four DIrFERENT ORDERS OF AMPHIBIANS AND REPTILES. Independently convergent evolution of four long- bodied, free-swimming, swift-moving, surface-liv- ing aquatic types in which the fins and limbs are retained as paddles: Cricotus, an amphibian; Ty- losaurus, an Upper Cretaceous mosasaur; Geo- Saurus, a Jurassic crocodilian; Cymbospondylus, a Triassic ichthyosaur. A very similar fusiform type evolves among the mammals in the Eocene ceta- ceans (Zeuglodon), as seen in Fig. 123. Restora- tions prepared for the author, independent of scale, by W. K. Gregory and Richard Deckert. THE ORIGIN AND EVOLUTION OF LIFE passage from a terrestrial phase, through palustral, swamp-living phases into a littoral, fluviatile phase, and from this into littoral and marine salt-water phases; so that finally in no less than six orders of reptiles the pelagic phase of the high seas was inde- pendently reached. The réle in the economy of oceanic life which is now taken by the whales, dolphins, and por- poises was assumed by families of the plesiosaurs, ichthyosaurs, mosasaurs, snakes, and croco- diles, all flourishing in the high seas, together with families of the turtles, which are the only high-sea reptiles surviving at the present day. Moreover, under the alternating adaptations to terrestrial and marine life, which prevailed during the 10,000,000 years of late Paleozoic and Mesozoic time, several families of the existing orders of reptiles sought a seafaring existence more than once and gave off numerous side branches from the main stem. The adapta- tions to marine life have been especially studied by Fraas. 201 AQUATIC REPTILES Even to-day there are tendencies toward marine invasion observed among several of the surviving families of lizards and crocodiles of seashore frequenting habits. ADAPTIVE RADIATION OF AQUATIC REPTILES T | vitig00089 LOO KS a SOQ IF gr | | IF is | S | LY | rrncooonuy CC EF FEE | eS Ne | \ (YS SONp wrs3071 Wass som il | | | | | | viunvsvsow Ki | + viunvsonvooud { ANS | | aed jc, \ | VIENVSOAHLHO! NOOO ee Ci yet eg VINOTSHO ERS WS NII Nw SUVSOSTY TOE EX XXQQ J J Xx ™™ Kx TNR SS WSs | > TERRESTRIAL (LAND LIVING PALUDAL (SWAMP LIVING LITTORAL- FLUVIATILE (FRESH WATER) LITTORAL- MARINE (SALT WATER) PELAGIC | | | | | | INDEPENDENT REVERSED ADAPTATION TO THE AQuaTic ZONES IN TWELVE ORDERS OF REPTILES, ORIGINATING ON LanD AND ENTERING THE SEAS. Fic. 77. Diagram showing the manner in which twelve of the eighteen orders of. reptiles descend from the terrestrial (land-living) zone into the paludal (swamp-frequenting) zone, thence into the littoral-fluviatile (fresh-water and brackish-water) zone, thence into the littoral- This final marine pelagic phase of evolution is attained in only six orders, namely, the plesiosaurs, water) zone, and finally into the pelagic zones of the high seas. marine (salt- ichthyosaurs, mosasaurs (marine lizards), crocodiles, and Chelonia (sea-tortoises) Nine of the reptilian orders give off not only one but from two to five independent branches seeking aquatic life, of which six independently reach the full pelagic high-sea phase. certain ophidians (true sea-snakes found far out at sea in the Indian Ocean). Still more remarkable than the law of reversed adaptation is that of alternate adaptation, which has been brilliantly 202 THE ORIGIN AND EVOLUTION OF LIFE developed by Louis Dollo, of Brussels. This is applied hypo- thetically to the evolution of the existing leatherbacks (Sphar- 1) ANCESTRAL CHELONIANS, O TERR2 AQUATIC wit so.io carapace 2( PRIMARY LITTORAL STAGE) (SECONDARY LITTORAL STAGE WITH UNIMPAIRED CARAPACE PRIMARY CARAPACE AND PLASTRON REOUCED AND PLASTRON A SECONDARY CARAPACE AND PLA ol SECONDARY PELAGIC STAGE PRIMARY PELAGIC STAGE. WITH CARAPACE AND PLASTRON SECONDARY CARAPACE REGRESSIVE PROGRESSIVELY ATROPHIED SECONDARY PLASTRON REDUCED » ABYSSAL Fic. 78. CHetonta. D1acRAmM ILLUSTRATING THE ALTERNATE Hapitat MIGRATION OF THE ANCESTRAL ‘‘LEATHERBACKS,” SPHARGID&. Dollo’s theory is that these animals originate in armored land forms with a solid bony shell, and pass from the terrestrio-aquatic into the littoral and then into the pelagic zone, in which the solid bony shell, being no longer of use, is gradually atrophied. After prolonged marine pelagic existence these animals return secondarily to the littoral zone and acquire a new armature of rounded dermal ossicles which develop on the upper and lower shields of the body. The animals (Sphargis) then for a second time take up existence in the pelagic zone, during which the dermal ossicles again tend to disappear. gide), an extremely specialized type of sea turtles. It is be- lieved that after a long period of primary terrestrial evolution in which the ancestors of these turtles acquired a firm, bony carapace for land de- fense, they then passed through various transitions into a primary marine phase during which they gradually g ost all their first bony arma- Fic. 79. Tue Existmyc “Leataersack” ture. Following this sea Comvomian Spharess, phase the animals returned In this form the solid armature adapted to a former terrestrial existence is being replaced tO shore and entered a by a leathery shield in which are embedded ° ee small polygonal ossicles. After Lydekker. secondary littoral, shore-liv ing phase, also of long dur- ation, in course of which they developed a second bony armature quite distinct in plan and pattern from the first. AQUATIC REPTILES 203 Descendants of these secondarily armored, shore-living types again sought the sea and entered a secondary marine pelagic phase in course of which they lost the greater part of their ARCHELON REPTILIA CRETACEOUS REPTILIA PLACOCHELYS TRIASSIC Fic. 80. ARMORED TERRESTRIAL CHELONIA INVADE THE SEAS AND Lose THEIR ARMA- TURE. Convergent or analogous evolution (two upper figures) in the inland seas of the paddle-propelled chelonian Archelon (after Williston), the gigantic marine turtle of the Upper Cretaceous continental seas of North America, and of Placochelys (after Jaekel in part), a Triassic reptile belonging to the entirely distinct order Placodontia. Skeleton of Archelon (lower) in which the bony armature of the carapace has largely disappeared, exposing the ribs. Specimen in the Peabody Museum of Yale Univer- sity. After Wieland. second armature and acquired their present leathery covering, to which the popular name “‘leatherbacks”’ applies.! In general the law of reversed aquatic adaptation is most brilliantly illustrated in the fossil ichthyosaurs, in the internal 1 This law of alternate adaptation may be regarded as absolutely established in the case of certain land-living marsupials in which anatomical records remain of an alterna- tion of adaptations from the terrestrial to the arboreal phase, from an arboreal into a secondary terrestrial phase, and from this terrestrial repetition to a secondary arboreal phase. The relics of successive adaptations to alternations of habitat zones and adap- tive phases are clearly observed in the so-called tree kangaroos (Dendrolagus) of Australia. 204 THE ORIGIN AND EVOLUTION OF LIFE anatomy of which land-living ancestry is clearly written, while reversed adaptation for marine pelagic life has resulted in a superficial type of body which presents close analogies to that of the sharks, porpoises, and shark-dolphins (Fig. 41). Integu- mentary median and tail fins precisely similar to those of the Fic. 8t. EXTREME ADAPTATION oF THE IcHTHyosAURS TO Marine Petacrc Lire. Although primarily of terrestrial ‘origin the ichthyosaurs become quite independent of the shores through the viviparous birth of the young as evidenced by a fossil female iehthyosaur (upper figures) with the foetal skeletons of seven young ichthyosaurs within or near the abdominal cavity. A fossil ichthyosaur (lower figure) with preserved body integument and fin outlines re- sembling those of the sharks and dolphins (see Fig. 41). Both specimens in the American Museum of Natural History from Holzmiaden, Wiirtem- berg. sharks evolve, the anterior lateral limbs are secondarily con- verted into fin-paddles, which are externally similar to those of sharks and dolphins, while the posterior limbs are reduced. As in the shark, the tail fin is vertical, while in the dolphin the tail fin is horizontal. In the early history of their marine pelagic existence the ichthyosaurs undoubtedly returned to shore to deposit their eggs, but a climax of imitation of the dol- phins and of certain of the sharks is reached in the develop- ment of the power of viviparity, the growth of the young within AQUATIC REPTILES 205 the body cavity of the mother, resulting in the young ichthyo- saurs being born in the water fully formed and able to take care of themselves immediately after birth like the young of modern whales and dolphins. When this viviparous habit finally released the ichthyosaurs from the necessity of return- ing to land for breeding they developed the extraordinary powers of migration which car- ried them into the Arctic seas of Spitzbergen, the Cordilleran seas of western North America, and doubtless into the Antarc- tic. So far as we know this viviparous habit was never de- veloped among the seafaring turtles, which always return Pe REBTILTA CYMBOSPONDYLUS. TRIASSIC to shore to deposit their eggs. pre. 35. RESTORATIONS OF Two IcH- While the ichthyosaurs vary CEOS UES: ‘ : Cymbospondylus, a primitive ichthyosaur greatly In size, they present a from the Triassic seas of Nevada (after reversed evolution from the ter- Merriam), and the highly specialized Baptanodon, a Cretaceous ichthyosaur restrial, quadrupedal type into _ of the seas of that period in the region the swithanovine. fusiform bed of Wyoming, in which the teeth are 8) y greatly reduced. Restorations for the type of the fishes, which is author by W. K. Gregory and Richard : Deckert. finally reduced in predaceous power through the degeneration of the teeth, as observed in the Baptanodon, an ichthyosaur of the Upper Jurassic seas of the ancient Rocky Mountain region. While the continental seas of Jurassic time were favorable to this remarkable aquatic marine phase of the reptiles, still greater inundations both of North America and of Europe occurred during Upper Cretaceous time. This was the period of the maximum evolution of the sea reptiles, the ultimate food supply of which was the surface life of the oceans, the 206 THE ORIGIN AND EVOLUTION OF LIFE marine Protozoa, skeletons of which were depositing the great chalk beds of Europe and of western North America. The Plesiosaurs had begun their invasion of the sea during Upper Triassic time, as shown in the primitive half-lizard Fic. 83. NortH AMERICA IN UPPER CRETACEOUS TIME. The great inland continental sea extending from the Gulf to the Arctic Ocean, was favor- able to the evolution of the mosasaurs, plesiosaurs, and giant sea turtles (Archelon). This period is marked by the greatest inundation of North America during Mesozoic time, by mountains slowly rising along the Pacific coast from Mexico to Alaska, and by volcanic activity in Antillia. Detail from the globe model in the American Museum by Chester A. Reeds and George Robertson, after Schuchert. Lariosaurus, discovered in northern Italy, which still retains its original lacertilian appearance, due to the fact that the limbs and feet are not as yet transformed into paddles. In the subsequent evolution of paddles the number of digits re- mains the same, namely, five, but the number of the phalanges on each digit is greatly increased through the process known as hyperphalangy, an example of the numerical addition of AQUATIC REPTILES 207 new characters. Propulsion through the water was rather by means of the paddles than by the combined lateral body-and- Fic. 84. CONVERGENT Forms oF AQuaTIC REPTILES OF DIFFERENT ORIGIN. Lariosaurus (left), the Triassic ancestor of the plesiosaurs from northern Italy, and Mesosaurus (right), from the Permian of Brazil and South Africa, representing another extinct order of the Reptilia, the Proganosauria. Drawn by Deckert after McGregor. tail motion seen among the ichthyosaurs, because all plesiosaurs exhibit a more or less abbreviated tail and a more or less broadly depressed body. It is also significant that the fore sds A kaw b AY Shag: SEL He we Fic. 85. A PLESIOSAUR FROM THE JURASSIC OF ENGLAND. Skeleton of Cryptocleidus oxoniensis seen from above. Mounted in the American Museum of Natural History. 208 THE ORIGIN AND EVOLUTION OF LIFE and hind paddles are homodynamic, 7. ¢., exerting equal power; they are so exactly alike that it is very difficult to distinguish them, whether they are provided with four broad paddles or with four long, narrow, slender paddles. The plesiosaurs Ure TRINACROMERION CRETACEOUS REPTILIA Fic. 86. Types or Marine PELacic PLESIOSAURS OF THE AMERICAN CON- TINENTAL CRETACEOUS SEAS. The slow-moving, long-necked Elasmo- saurus and the swift-moving, short- necked Trinacromecrion. The limbs are completely transformed into pad- dles. The great differences in the pro- portions of the neck and body repre- sent adaptations to greater or less speed. Restorations for the author by W. K. Gregory and Richard Deckert, chiefly after Williston. afford the first illustration we have noted of another of the great laws of form evolution, namely, adaptation occurs far more frequently through changes of existing proportions than through numerical addi- tion of new characters. It is proportional changes which separate the swift-moving plesiosaurs (Trinacromerion os- borni), which are invariably provided with long heads, short necks, and broad paddles, from the slow-moving plesiosaurs (Elasmosaurus), which are pro- vided with narrow paddles, short bodies, extremely long necks, and small heads. It is believed that the lizard- like ancestors of the mosasaurs left the land early in Cretaceous time; it is certain that through- out the three or four million years of the Cretaceous epoch they spread into all the oceans of the world, from the conti- nental seas of northern Europe and North America to those of New Zealand. In Europe these animals survived to the very close of Mesozoic time since the type genus of the great AQUATIC REPTILES 209 order Mosasauria (Mosasaurus), taking its name from the River Meuse, was found in the uppermost marine Cretaceous. Detailed knowledge of the structure of these remarkable sea lizards is due chiefly to the researches of Williston and Fic. 87. A SEA Lizarp. Tylosaurus, a giant mosasaur from the inland Cretaceous seas of Kansas, chasing the giant fish Portheus. After a restoration in the American Museum of Natural History, by Charles R. Knight under the author’s direction. Osborn of this country and to those of Dollo in Europe. The head is long and provided with recurved teeth adapted to seiz- ing active fish prey (Fig. 87); the neck is extremely short; as in the plesiosaurs the fore and hind limbs are converted into paddles, symmetrical in proportion; the body is elongate and 210 THE ORIGIN AND EVOLUTION OF LIFE propulsion is not chiefly by means of the fins but by the sinu- ous motions of the body, and especially of the very elongate, broad, fin-like tail. These sea lizards of Upper Cretaceous time (Fig. 76) are analogous or convergent to the sea Croco- dilia (Geosaurus) of Jurassic time and present further analogies with the Triassic ichthyosaur Cymbospondylus and the small Permo-Carboniferous amphibian Cricotus (Fig. 76). In the American continental seas these animals radiated into the small, relatively slender Clidastes, into the somewhat more broadly finned Platecarpus, and into the giant Tylosaurus, which was capable (Fig. 87) of capturing the great fish of the Cretaceous seas (Portheus). TERRESTRIAL LIFE. CARNIVOROUS DINOSAURS Widely contrasting with these extreme adaptations to aquatic marine life, the climax of terrestrial adaptation in the reptilian skeleton is reached among the dinosaurs, a branch which separated in late Permian or early Triassic time from small quadrupedal, swiftly moving, lizard-like reptiles and before the time of their extinction at the close of the Creta- ceous had evolved into a marvellous abundance and variety of types. In the Upper Triassic of North America, late New- ark time, the main separation of the dinosaurs into two great divisions, (a) those with a crocodile-like pelvis, known as Saurischia, and (6) those with a bird-like pelvis, known as Orni- thischia, had already taken place, and the dinosaurs domi- nated all other terrestrial forms. When Hitchcock in 1836 explored the giant footprints in the ancient mud flats of the Connecticut valley he quite nat- urally attributed many of them to gigantic birds, since at the time the law of parallel mechanical evolution between birds and dinosaurs was not comprehended and the order Dino- CARNIVOROUS DINOSAURS 211 = STEGOMUS PODOKESAURUS ANCHISAURUS CONNECTICUT TRIASSIC REPTILES Fic. 88. Lire oF THE ConneEcTICUT RIVER VALLEY IN Upper Triassic (NEWARK) TIME. Anchisaurus, a primitive carnivorous bipedal dinosaur. Rhkytidodon, a phytosaur analo- gous but not related to the modern gavials. Stegomus, a small armored phytosaur related to Rhytidodon. Anomepus, a herbivorous bipedal dinosaur related to the “duckbills” or Iguanodonts. Podokesaurus, a light, swift-moving, carnivorous dino- saur of the bird-like type. Restorations (except Rhytidodon) after R. S. Lull of Yale University. Drawn to uniform scale for the author by Richard Deckert. PHYLOGENY AND ADAPTIVE RADIATION OF THE DINOSAURS. MAINLY AFTER LULL, ED OF (AST SAUROPODA CARPE ARI OROUS DINOSAURS LAST BIRDLIKE DINOSAURS LAST GEAKED DINOSAURS LAST ARMORED DINOSAURS UPPER (CRETACEOUS Lower CRETACEOUS TOuANEHEANO — varico DINOSAURS LUKE. DINOSAURS DINOSAURS ARMORED DINOSAURS —| JURASSIC PRIMITIVE SAUROPODA FIRST ARMORED DINOSAURS Z ANCESTRAL SAUROPODA PRIMITIVE CARNIVOROUS DINOSAURS. FIRST HORNY-BEAKED DINOSAURS (BIPEDAL, First et BIRO-LIKE DINOSAURS. FIRST CARNIVOROUS DINOSAURS PERMIAN COMMON STOCK OF DINOSAURS, CROCODILES. BIRDS PTEROSAURS ETC, PENNSYLVANIAN (UPPER CARBONIFEROUS! FIRST REPTILES Fic. 89. TERRESTRIAL EVOLUTION OF THE DINOSAURS. The ancestral tree of the dinosaurs, originating in Lower Permian time, and branching into five great lines during a period estimated at twelve million years. A, The giant herbivorous Sauropoda which sprang from Lower Triassic carnivorous ancestors. B, Giant carnivorous dinosaurs, which prey upon all the larger herbivorous forms. C, Swift-moving, ostrich-like, carnivorous dinosaurs, related to B. D, Herbivorous Iguanodonts, swift-moving, beaked, or “duck-bill” dinosaurs, related to FE. E, Slow- moving, quadrupedal, heavily armored or horned herbivorous dinosaurs, related to D. Prepared for the author by W. K. Gregory, chiefly after Lull. O12 THE ORIGIN AND EVOLUTION OF LIFE sauria was not known. It has since been discovered that many of the ancient dinosaurs, especially those of carnivorous habit, were bird-footed and adapted in structure for rapid, cursorial locomotion; the body was completely raised above Fic. 90. Norta AMERICA IN Upper Triassic (NEWARK) TIME. The period of the primitive bipedal dinosaurs, with semi-arid, cool to warm climate, and a prevailing flora of cycads and conifers. Remains of amphibians, primitive crocodiles, and dinosaurs are found in the reddish continental deposits. Detail from the globe model in the American Museum by Chester A. Reeds and George Robertson, after Schuchert. the ground, the forward part being balanced with the aid of the long tail. This primitive type of body structure is com- mon to all the dinosaurs, and is evidence that the group underwent a long period of evolution under semi-arid conti- nental conditions in late Permian and early Triassic time. The reptilian group discovered in the Connecticut valley (Fig. CARNIVOROUS DINOSAURS 213 88) is not inconsistent with the theory of a semi-arid climate advocated by Barrell to explain the reddish continental de- posits not only in the region of the Connecticut valley but over the southwestern Great Plains. The flora of ferns, cycads, and conifers indicates moderate conditions of temperature. Along the Pacific coast there was a great overflow of the seas along the western continental border and an archipelago of volcanic islands. In this region there were numerous coral reefs and an abundance of cephalopod ammonites. In the Fic. 91. A Carnivorous Dinosaur PREYING UPON A SAUROPOD. Skeletons (left) and restoration (right) of the bipedal dinosaur Allosaurus of Upper Jurassic and Lower Cretaceous time in the act of feeding upon the carcass of A patosaurus, one of the giant herbivorous Sauropoda of the same period. Mounted specimens and restoration by Osborn and Knight in the American Museum of Natural History. interior continental seas great marine reptiles (Cymbospondylus, Fig. 82), related to the ichthyosaurs, were abundant. The primitive light-bodied, long-tailed type of dinosaur of bipedal locomotion originates in this country with Marsh’s Anchisaurus of the Connecticut valley (Fig. 88) and develops into the more powerful form of the Allosaurus of Marsh from the Jurassic flood-plains east of the Rocky Mountains (Fig. 91). Contemporaneous with this powerful animal is the much more delicate Ornitholestes, which is departing from the carnivorous habits of its ancestors and seeking some new form of food. It is in turn ancestral to the remarkable “ostrich dinosaur” of the Upper Cretaceous, Struthiomimus (Ornithomimus), which is bird-like both in the structure of its limbs and feet and in 214 THE ORIGIN AND EVOLUTION OF LIFE its toothless jaw sheathed in horn. In this animal the car- nivorous habit is completely lost; it is secondarily herbivorous. Its limbs are adapted to very rapid motion. In the meantime the true carnivorous dinosaur line was evolving over the entire northern hemis- phere stage by stage with the evolution of the varied herbivorous group of the dinosaurs. These animals Recently restored skeleton of the light-limbed, f bird-like, toothless “ostrich”? dinosaur, Struth- preserved per ect me- tomimus (Ornithomimus), after Osborn. chanical unity in the evo- = si - jution of the very swift motions of the hind limb and prehensile powers both of the jaws and of ae) oe the hind feet, adapted to er N seizing and rapidly over- : coming a struggling mY : 3 i ei =" powerful prey. This series e reaches an astounding Lateral view of the “tyrant” dinosaur, Tyran- nosaurus (left), and the “ostrich” dinosaur, Struthiomimus (right), to the same scale. Tyrannosaurus vex, de- Fic. 92. EXTREMES oF ADAPTATION IN THE : : “TYRANT” AND THE “OsTRICH” DINOSAURS. scribed by Osborn from Skeletons mounted in the American Museum of the Upper Cretaceous of Natural History. : - Montana (see frontis- piece). This “king of the tyrant saurians” is in respect to speed, size, power, and ferocity the most destructive life climax in the gigantic engine which has ever evolved. The excessively small size of the brain, probably weighing less than a pound, which is less CARNIVOROUS DINOSAURS 215 than 1/4000 of the estimated body weight, indicates that in animals mechanical evolution is quite independent of the evolution of their intelligence; in fact, intelligence compensates for the absence of mechanical perfection. Tyrannosaurus is Ne. GPE ole # “ 4 yi Fic. 93. Four Rresrorations or THE “OstricH” Dinosaur, Siruthiomimus (Ornithomimus). A. Showing the mode of progression. B. Illustrating the hypothesis that the animal was an anteater which used the front claws like those of sloths in tearing down anthills. C. Illustrating the hypothesis that it was a browser which supported the fore part of the body by means of the long, curved claws of the fore limb while browsing on trees. D. Illustrating the hypothesis that it was a wading type, feeding upon shrimps and smaller crustaceans. Restorations by Osborn. No satisfactory theory of the habits of this animal has as yet been advanced. an illustration of the law of compensation, first enunciated by Geoffroy St. Hilaire, first, in the disproportion between the diminutive fore limb and the gigantic hind limb, and second, in the fact that the feeble grasping power and consequent degeneration of the fore limb and hand are more than com- pensated for by the development of the tail and the hind claws, 216 THE ORIGIN AND EVOLUTION OF LIFE which enables these animals to feed practically in the same manner as the raptorial birds. HERBIVOROUS DINOSAURS, SAUROPODA As analyzed by Lull along the lines of modern interpreta- tion, beside the small carnivorous dinosaurs there may be PLATEOSAURUS REPTILIA TRIASSIC RZ AE ANCHISAURUS. EPTILIA TRIASSIC Ri Fic. 94. ANALOGY BETWEEN THE CARNIVO- Rous Anchisaurus TYPE OF THE TRIASSIC AND THE ANCESTRAL HERBIVOROUS SAURO- pop Type Plateosaurus. The upper restoration (Plateosaurus) repre- sents a bipedal stage of sauropod evolution which was discovered in the German Trias, in which the transition from carnivorous to herbivorous habits is observed. Recent discovery renders it probable that the herbivorous Sauropoda descend from carniv- orous ancestors like Anchisaurus. Restoration of Plateosaurus modified from Jae- kel. Restoration of Anchisaurus after Lull. traced in the Connecticut Triassic footprints the be- ginnings of an herbivorous offshoot of the primitive carnivorous dinosaur stock, leading into the elephantine types of herbivorous dino- saurs known as the Sauro- poda, which were first brought to our knowledge in this country through the pioneer studies of Marsh and Cope. As there is never any need of haste in the capture of plant life these animals underwent a reversed evo- lution of the limbs from the swift-moving primitive bi- pedal type into a secon- dary slow-moving quadru- pedal ambulatory type. The original power of occa- sionally raising the body on the hind limbs was stil] retained in some of these gigantic forms. The half-way stage between the bipedal and the HERBIVOROUS DINOSAURS 217 quadrupedal mode of progression is revealed in the recently described Plateosaurus of Jaekel from the Trias of Germany (Fig. 94), an animal which could progress either on two or on four legs. The Sauropoda reached the climax of their evolution dur- ing the close of Jurassic (Morrison formation) and the be- & YL LOWER CRETACEOUS 80 oe « ° ) PALEOGEOGRAPHY, LOWER CRETACEOUS (UPPER NEOCOMIAN-VELANGIAN-HILS-WEALDEN-TRINITY-MORISSON) TIME AFTER SCHUCHERT, APRIL, 1916 MARINE DEPOSITS DEPOSITS sy SIERRA NEVADA Fic. 95. THEorEtIC WorLtD ENVIRONMENT IN LOWER CRETACEOUS TIME. The dominant period of the great sauropod dinosaurs. This shows the theoretic South Atlantic continent Gondwana connecting South America and Africa, and the Eurasiatic Mediterranean sea Tethys. Shortly afterward comes the rise of the modern flowering plants and the hardwood forests. The shaded patch over the existing region of Wyo- ming and Colorado is the flood-plain (Morrison) centre of the giant Sauropoda (see Fig. 97). After Schuchert, 1916. ginning of Cretaceous time (Comanchean Epoch). Meanwhile they attained world-wide distribution, migrating throughout a long stretch of the present Rocky Mountain region of North America, into southern Argentina, into the Upper Jurassic of Great Britain, France, and Germany, and into eastern Africa. The last named region is the one most recently explored, and 218 THE ORIGIN AND EVOLUTION OF LIFE the widely heralded Gigantosaurus (== Brachiosaurus), de- scribed as the largest land-living vertebrate ever found, is Fic. 96. NortH America IN LowEeR CRETACEOUS (COMANCHIAN) TIME. This period, also known as the Trinity-Morrison time, is marked by the maximum develop- ment of the giant herbivorous dinosaurs, the Sauropoda. The Sierra Nevada and coast ranges are elevated, also the mountain ranges of the Great Basin which give rise east- ward to the flood-plain deposits (Morrison) in which the remains of the Sauropoda are entombed. This epoch is prior to the birth of the Rocky Mountains, which arose be- tween Cretaceous and Eocene time. Detail from the globe model in the American Museum by Chester A. Reeds and George Robertson, after Schuchert. structurally closely related to and does not exceed in size the sauropods discovered in the Black Hills of South Dakota. Their size is indeed titanic, the length being roo feet, while the $ HERBIVOROUS DINOSAURS 219 longest whales do not exceed go feet. In height these sauropods dwarf the straight-tusked elephant of Pleistocene time, which is the largest land product of mammalian evolution. The Sauropoda for the most part inhabited the swampy meadows and flood-plains of Morrison time. They include, besides the BRACHIOSAURUS CRETACEOUS OwLoDgCcUS StRA= CAMARASAUIRUS: Jul CRETACEOUS, REPTILIA CRETACEOUS REPTILIA Fic. 97. THREE PRINCIPAL TYPES OF SAUROPODS. The body form of the three principal types of giant herbivorous Sauropoda which ap- pear to have been almost world-wide in distribution. Camarasaurus, a heavy-bodied, short-limbed quadrupedal type. Diplodocus, a light- bodied, relatively swift-moving quadrupedal type. Brachiosaurus, a short-bodied quadrupedal type in which the fore limbs are more elevated than the hind limbs. Brachiosaurus attained gigantic size, being related to the recently discovered Giganto- saurus of East Africa. Restorations by Osborn, Matthew, and Deckert. gigantic type Brachiosaurus (== Gigantosaurus), with its greatly elevated shoulder and forearm, massive quadrupedal types like Camarasaurus Cope and A patosaurus (= Brontosaurus) Marsh, and the relatively long, slender, swiftly moving Dzplodocus. According to Lull and Depéret the Sauropoda survived until the close of the Cretaceous Epoch in Patagonia and in southern France. In North America they became extinct in Lower Cretaceous time. 220 THE ORIGIN AND EVOLUTION OF LIFE In the final extinction of the herbivorous sauropod type we find an example of the selection Jaw of elimination, attributable Fic. 98. AMPHIBIOUS OR TERRESTRIO-FLUVIATILE THEORY OF THE HABITS OF APATOSAURUS. (Upper.) A patosaurus (=Brontosaurus), a typical sauropod of Morrison age, quad- rupedal, heavy-limbed, herbivorous, inhabiting the flood-plains (Morrison) and lagoons of the region now elevated into the Rocky Mountain chain of Wyoming and Colorado. (Lower.) Mounted skeleton of A patosaurus (= Brontosaurus) in the American Museum of Natural History. to the fact that these types had reached a cul-de-sac of mechan- ical evolution from which they could not adaptively emerge HERBIVOROUS DINOSAURS 221 when they encountered in all parts of the world the new en- vironmental conditions of advancing Cretaceous time. THE IGUANODONTIA Contemporaneous with the culminating period of the evo- lution of the Sauropoda is the world-wide appearance of an ] Fic. 99. Prumutive IcuaNoponr Camptosaurus FROM THE UPPER JURASSIC OF Wyominc. This swift bipedal form was contemporary with the giant sauropod A patosaurus and the lighter-bodied Diplodocus. These iguanodonts were defenseless and dependent wholly on alertness and speed, or perhaps on resort to the water, for escape from their enemies. They were the prey of Allosaurus (see Fig. 91). Mounted specimen in the American Museum of Natural History. entirely different stock of bipedal herbivorous dinosaurs in which the pelvis is bird-like (Ornithischia, Seeley). These animals may be traced back (von Huene) to the Triassic Naosaurus. The front of the jaws at an early stage lost the teeth and developed a horny sheath or beak like that of the birds, within which a new bone (predentary) evolves, giving to this order the name Predentata. Entirely defenseless at this stage (Camptosaurus), these relatively small, bipedal types 222 THE ORIGIN AND EVOLUTION OF LIFE Fic. too. A Parr oF UPPER CRETACEOUS IGUANO- DCNTS FROM MONTANA. After a lapse of 5a0,000 years of Cretaceous time the Camptosaurus (Fig. 99) evolved into the giant “ duck- billed” dinosaur Trachodon, described by Leidy and Cope from the Upper Cretaceous of New Jersey and Dakota. Two skeletons of Tvachodon annectens (upper) discovered in Montana, as mounted in the American Museum of Natural History, and restoration of the same (lower) by Osborn and Knight. (Compare Fig. 74.) spread all over the northern hemisphere and attained an extra- ordinary adaptive radi- ation in the river- and shore-living ‘‘duck- bill’’ dinosaurs, the iguanodonts of the Cre- taceous Epoch (Fig. tor). The adaptive radiation of these ani- mals has only recently been fully determined; it led into three great types of body form, all unarmored. First, the less specialized types which retain more or less the body structure of the earlier Jurassic forms and the famous iguanodont of Bernis- sart, Belgium. Related to these are the krito- saurs of the Cretaceous of Alberta, with a com- paratively narrow head, the protection of which was facilitated by a long, backwardly pro- jecting spine. Second, there are the broadly HERBIVOROUS DINOSAURS 223 duck-billed, wading dinosaurs (Trachodon), with stalking limbs and elevated bodies. Third, there are more fully aquatic, free- swimming forms with crested skulls (Corythosaurus). The Page We Fic. 1o1. ADAPTIVE RADIATION OF THE IGUANODONT DINOSAURS INTO THREE GROUPS. (Upper.) Three characteristic types: A, Typical “duck-bill” Trachodon; B, Corytho- saurus, the hooded “duck-bill,” with a head like a cassowary, probably aquatic; C, Kritosaurus, the crested “duck-bill”’ dinosaur. Restorations by Brown and Deckert. (Lower.) Mounted skeleton of Corythosaurus in the American Museum of Natural His- tory, recently discovered in the Upper Cretaceous of Alberta, Canada, with the integ- ument impressions and body lines preserved. anatomy and habits of all these forms have been made known recently by American Museum explorations in Alberta, Canada, under Barnum Brown (Fig. ror). The partly armored dinosaurs known as stegosaurs are related to the iguanodonts and belong to the bird-pelvis group 224 THE ORIGIN AND EVOLUTION OF LIFE (Ornithischia). The small Triassic ancestors of this great group of herbivorous, ornithischian dinosaurs also gave rise to a number of secondarily quadrupedal, slow-moving forms, in which there developed various forms of defensive and offen- sive armature. Of these the Jurassic stegosaurs exhibit a reversed evolution in their locomotion since they pass from a bipedal into a quadrupedal type in which the armature takes Fic. 102, OFFENSIVE AND DEFENSIVE ENERGY COMPLEXES. The carnivorous “tyrant” dinosaur Tyrannosaurus approaching a group of the horned herbivorous dinosaurs known as Ceratopsia. Compare frontispiece. The Ceratopsia are related to the armored Stegosaurus and to the armorless, swift-moving Tguanodontia. Restoration by Osborn in the American Museum of Natural History, painted by Charles R. Knight. the form of sharp dorsal plates and spiny defenses, the exact arrangement of which has been recently worked out by Gil- more. Doubtless when this animal was attacked it drew its head and limbs under its body, like the armadillo or porcu- pine, and relied for protection upon its dorsal armature, aided by rapid lateral motions of the great spines of the tail to ward off its enemies. During the progress of Cretaceous time these stegosaurs became extinct, and by the beginning of the Middle Cretaceous two other herbivorous types are given off from the predentate stock. The first of these are the aggressively and defensively horned Ceratopsia, in which two or three front horns evolved HERBIVOROUS DINOSAURS 225 step by step, with a great bony frill protecting the neck. This evolution took place stage by stage with the evolution of the predatory mechanism of the carnivorous dinosaurs, so that the climax of ceratopsian defense (Triceratops) was reached simultaneously with the climax of Tyrannosaurus offense. This is an example of the counteracting evolution of offensive and defensive adaptations, analogous to that which we observe to-day in the evolution of the lions, tigers, and leopards, which counteracts with that of the horned cattle and antelopes of Africa, and again in the evolution of the wolves simultaneously with the horned bison and deer in the northern hemisphere. It is a case where the struggle for existence is very severe at every stage of development and where advantageous or dis- advantageous chromatin predispositions in evolution come con- stantly under the operation of the law of selection. Thus in the balance between the reptilian carnivora and herbivora we find a complete protophase of the more recent balance between the mammalian carnivora and herbivora. The climax of defense was reached, however, in another line of Predentata, in the herbivorous dinosaurs, known as Ankylosaurus, in which there developed a close imitation of the armadillo or glyptodon type of mammal, with the head and entire body sheathed in a very dense, bony armature. In these animals not only is motion abandoned as a means of escape, but the teeth become diminutive and feeble, as in most other heavily armored forms of reptiles and mammals. The herbivorous function of the teeth is replaced by the develop- ment of horny beaks. Thus these animals reach a ground- dwelling, slow-moving, heavily armored existence. 226 THE ORIGIN AND EVOLUTION OF LIFE PTEROSAURS There is no doubt that the pterosaurs, flying reptiles, were adapted to fly far out to sea, for their remains are found min- gled with those of the mosasaurs in deposits far from the ancient shore-lines. There is no relation whatever between the feathered birds and these animals, whose analogies in their modes of flight are rather with the bats among the mammals. These flying reptiles are perhaps the most extraor- dinary of all extinct ani- mals. While some ptero- saurs were hardly larger than sparrows, others sur- passed all living birds in the spread of the wings, Fic. 103. RESTORATION OF THE PTERODACTYL, although inferior to many SHOWING THE SOARING FLIGHT. birds in the bulk of the After the Aéronautical Journal, London. body. Te 3 teclieedd that they depended almost entirely upon soaring for progression. The head in the largest types of the family (Pteranodon) is converted into a great vertical fin, used, no doubt, in directing flight, with a long, backwardly projecting bony crest which served in the balancing of the elongate and compressed bill. The feeble development of the muscles of flight in these an- cient forms is compensated for by the extreme lightness of the body and the hollowness of the bones. ORIGIN OF BIRDS It is believed that in late Permian or early Triassic time a small lizard-like reptile of partly bipedal habit and remotely related to the bipedal ancestors of the dinosaurs passed from ORIGIN OF BIRDS 227 a terrestrial into a terrestrio-arboreal mode of life, probably for purposes of safety. This early arboreo-terrestrial phase is indicated in the most ancient known birds (Archeopteryx) by the presence of claws at the ends of the bones of the wing, fit- ting them for clinging to trees, it is argued, through analogy to the tree-clinging habits of existing young hoatzins of South [QUATERNARY TERTIARY FLIGHTLESS RUNNING BIRDS MODERNIZED BIRDS UPPER CRETACEOUS TOOTHED DIVERS PRIMITIVE TOOTHED BIROS cRETACEOUS 7 FIRST RADIATION FROM ARBOREAL INTO (COMANCHEAN! __ TERRESTRIAL AND AQUATIC BIRDS JURASSIC. =. ______ ARSOREAL BIRDS OF FEEBUE FLIGHT IARCHAEOPTERYX) TRIASSIC 7 FIRST BIROS-BIPEDAL. CURSORIAL CLIMBING (HIGH BODY TEMP. RELATIVELY HIGH REPTJLIAN GRAIN) PERMIAN COMMON ANCESTORS OF CROCODILES, PHYTOSAURS, a ee IN SAURS PTEROSAURS AND IBIRDS oa PENNSYLVANIAN R CARBONIFEROUS! MISSISSIPPIAN (LOWF CARBONIFEROUS: ORIGIN AND ADAPTIVE RADIATION OF THEBIROS, WK GREGORY, 1916 Fic. 104. ANCESTRAL TREE OF THE Birps. The ancestors of the birds branch off in Permian time from the same stock that gives rise to the dinosaurs, adding to swift, bipedal locomotion along the ground the power of tree climbing and, with their very active life, the development of a high and uniform body temperature. Primitive types of birds exhibit a fore limb terminating in claws, probably for grasping tree branches. The power of flight began to develop in Triassic time through the conversion of scales into feathers either on the fore limbs (two-wing theory) or on both fore and hind limbs (four-wing theory). From the Jurassic birds (Arch@opteryx), capable of only feeble flight, there arises an adaptive radiation into aérial, arboreal, arboreo-terrestrial, terrestrial, and aquatic forms, the last exhibiting a a reversal of evolution. Diagram prepared for the author by W. K. Gregory. America. Ancestral tree existence is rendered still more prob- able by the fact that the origin of flight was apparently sub- served in the parachute function of the fore limb and perhaps of both the fore and hind limbs for descent from the branches of trees to the ground. Two theories have been advanced as to the origin of flight in the stages succeeding the arboreal phase of bird evolution. First, the pair-wing theory, developed from the earlier studies on Archeopteryx, in which the transformation of lateral scales 228 Fic. SKELETON OF Archeopteryx (left) CoMPARED WITH THAT OF THE PIGEON (right). 105. Showing the abbreviation of the tail into the pyg ostyle and the conversion of the grasping fore limb into the bones of the wing. After Heilman. THE ORIGIN AND EVOLUTION OF LIFE into long primary feathers on the fore limbs and at the sides of the extended tail would afford a glissant parachute support for short flights from trees to the ground (Fig. 106). Quite recently a four-wing theory, the tetrapteryx theory, has been pro- posed by Beebe, based on the observation of the presence of great feathers on the thighs of embryos of modern birds and of supposed traces of similar feathers on the thighs of the old- est known fossil bird, the Ar- cheopteryx of Jurassic age. Ac- cording to this hypothesis after the four-wing stage was reached the two hind-leg wings degen- erated as the flight function evolved in the spreading feathers of the forearm-wings and the rudder function was perfected in the spreading feathers of the tail (Fig. 107). Both of these 4 N <= “a, Lx ‘- G, a on “ dua ha él i ww HY 3) [ae Fic. 107. Ceeeegat “ys a ) Wii y wae Fic. 106. SILHOUETTES OF Archaeop- teryx (A) AND PHEASANT (B). Based on the two-wing theory. After Heilman. > wie Bas egy ty ae > oa ys Four Evolutionary STAGES IN THE HypoTHETICAL Four-WINGED BIRD. After Beebe. ORIGIN OF BIRDS 229 hypotheses assign two phases to the origin of flight in birds: first, a primary terrestrial phase, during which the peculiar characters of the hind limbs and feet were developed with their strong analogies to the bipedal feet of dinosaurs; second, a purely arboreal phase. It is believed by the adherents of both the two- Fic. 108. THroretic Mop or Para- CHUTE FLIGHT OF THE PRIMITIVE Brirp. Based on the four-wing theory. After Beebe. wing and the four-wing theory that following the arboreal phase, in which the powers of flight were fully developed, there occurred among the struthious birds, such as the ostriches, a secondary terres- trial phase in which the powers of flight were secon- darily lost and rapid cursorial locomotion on the ground was secondarily developed. This Fic. 109. RESTORATION OF THE ANCIENT , . Tie Bra, Archeopterys. interpretation of the foot and Capable of relatively feeble flight. After limb structure associated ae with the loss of teeth, which is characteristic of all the higher birds, will explain the close analogies which exist between the ostrich-like dinosaur Stru- 230 THE ORIGIN AND EVOLUTION OF LIFE thiomimus and the modern cursorial flightless forms of birds, such as the ostriches, rheas, and cassowaries. In the opposite extreme to these purely terrestrial forms, the flying arboreal birds also gave off the water-living birds, one phase in the evolution of which is represented in the loon- like Hesperornis, the companion of the pterosaurs and mosa- saurs in the Upper Cretaceous seas. It was on the jaws of the Fic. 110. REVERSED AQuaTic EvoLuTION oF WING AND Bopy Form. Wing of a penguin (A) transformed into a fin externally resembling the fin of a shark (B). Skeleton of Hesperornis (C) in the American Museum of Natural History and restora- tion of Hesperornis (D) by Heilman, both showing the transformation of the flying bird into a swimming, aquatic type, and its convergent evolution toward the body shape of the shark, ichthyosaur, and dolphin (compare Fig. 41). Hesperornis and smaller Ichthyornis that Marsh made his sen- sational announcement of the discovery of birds with teeth, a discovery confirmed by his renewed studies of the classic fossil bird type, the Jurassic Archeopteryx. These divers of the Cretaceous seas (Hesperornis) are analogous to the modern loons, and represent one of the many instances in which the tempting food of the aquatic habitat has been sought by ani- mals venturing out from the shore-lines. As in the most highly specialized modern swimming birds, the Antarctic penguins, the wing secondarily evolves into a fin or paddle, while the ARRESTED REPTILIAN EVOLUTION 231 body secondarily develops a fusiform shape in order to dimin- ish resistance to the water in rapid swimming. PoOssIBLE CAUSES OF THE ARRESTED EVOLUTION OF THE REPTILES Of the eighteen great orders of reptiles which evolved on land, in the sea, and in the air during the long Reptilian Era of 12,000,000 years, only five orders survive to-day, namely, the turtles (Testudinata), tuateras (Rhynchocephalia), lizards (Lacertilia), snakes (Ophidia), and crocodiles (Crocodilia). The evolution of the members of these five surviving or- ders has either been extremely slow or entirely arrested during the 3,000,000 years which are generally assigned to Tertiary time; we can distinguish only by relatively minor changes the turtles and crocodiles of the base of the Tertiary from those living to-day. In other words, during this period of 3,000,000 years the entire plant world, the invertebrate world, the fish, the amphibian, and the reptilian worlds have all remained as relatively balanced, static, unchanged or persistent types, while the mammals, radiating 3,000,000 years ago from very small and inconspicuous forms, have undergone a phenomenal evolution, spreading into every geographic region formerly occupied by the Reptilia and passing through multitudinously varied phases not only of direct but of alternating and of reversed evolution. During the same epoch the warm-blooded birds were doubtless evolving, although there are relatively few fossil records of this bird evolution. This is a most striking instance of the differences in chroma- tin potentiality or the internal evolutionary impulses under- lying all visible changes of function and of form. If we apply our law of the actions, reactions, and interactions of the four physicochemical energies (p. 21), there are four reasons why 232 THE ORIGIN AND EVOLUTION OF LIFE we may not attribute this relatively arrested development of the reptiles either to an arrested physicochemical environment, to an arrested life environment, or to the relative bodily iner- tia of reptiles which affects the body-protoplasm and body- chromatin. These four reasons appear to be as follows: First: We have noted that among the reptiles the velocity of purely mechanical adaptation is quite independent both of brain power and of nervous activity, a fact which seems to strike a blow at the psychic-direction hypothesis (p. 143), on which the explanations of evolution by Lamarck, Spencer, and Cope so largely depend. The law that perfection of mechan- ical adaptation is quite independent of brain power also holds true among the mammals, because the small-brained mammals of early Tertiary time, the first mammals to appear, evolve as mechanisms quite as rapidly or more rapidly than the large- brained mammals. Second: The law of rapidity of character evolution is inde- pendent also of body temperature, for, while the mechanical evolution of the warm-blooded birds and mammals is very rapid and very remarkable it can hardly be said to have ex- ceeded that of the cold-blooded reptiles. Thus the causes of the velocity of character evolution in mechanism need not be sought in the psychic influence of the brain, in the nervous system, in the “Lamarckian” influence of the constant exer- cise of the body, nor in a higher or lower temperature of the circulatory system. Third: Nor has the relatively arrested evolution of the Reptilia during the period of the Age of Mammals been due to arrested environmental conditions, for during this time the environment underwent a change as great as or greater than that during the preceding Age of Reptiles. Fourth, and finally, there is no evidence that natural selec- ARRESTED REPTILIAN EVOLUTION 233 tion has exerted less influence on reptilian evolution during the Age of Mammals than previously. Thus we shut out four out of five factors, namely, physical environment, individual habit and development, life environment, and selection as reasonable causes of the relative arrest of evolution among the reptiles. Consequently the causes of the arrest of evolution among the Reptilia appear to lie in the internal heredity-chromatin, i. €., to be due to a slowing down of physicochemical inter- actions, to a reduced activity of the chemical messengers which theoretically are among the causes of rapid evolution. The inertia witnessed in the entire body form of static or per- sistent types is also found to occur in certain single characters of the individual. Recurring to the view that evolution is in part the sum of the acceleration, balance, or retardation of the velocity of single characters, the five surviving orders of the reptiles appear to represent organisms in which the greater number of characters lost their velocity at the close of the Age of Reptiles, and consequently the order as a whole re- mained relatively static. CHAPTER VIII EVOLUTION OF THE MAMMALS First mammals, of insectivorous and tree-living habits. Single character evolution, physicochemical interaction, coordination, and complexity. Problem as to the causes of the origin of new characters and of new bodily proportions. Adaptations of the teeth and of the limbs as observed in direct, reversed, alternate, and counteracting evolution. Physiographic and climatic environment during the period of mammalian evolution, in a measure deduced from adaptive variations in teeth and feet of mammals. Conclusions, present knowledge of biologic evolution among the verte- brate animals. Future lines of inquiry into the causes of evolution. It required a man of genius like Linneus to conceive the inclusion within the single class Mammalia of such diverse Fic. 111. THE SE1 WHALE, BALZNOPTERA BOREALIS, Which attains a total length of forty-nine feet. Restoration (upper) and photograph (lower) after Andrews. forms as the tiny insect-loving shrew and the gigantic preda- ceous whale. It has required one hundred and twenty-five years of continuous exploration and research to establish the fact that the whale type (Fig. 111), is not only akin to but : 234 ORIGIN OF MAMMALS 235 is probably a remote descendant of an insectivorous type not very distant from the existing tree shrews (Fig. 112), the transformation of size, of func- tion, and of form between these two extremes having taken place within a period broadly estimated in our geologic time scale at about 10,000,000 years. Fic. 112. THE Tree Ssarew Tupaia. Insectivore, considered to be near the pro- totype form of all the higher placental mammals. ORIGIN OF THE Mammats, INSEC- TIVOROUS, ARBOREAL To the descent of the mammals Huxley was the first, in essaying the reconstruction of the great ancestral tree, to apply Darwin’s principles on a large scale and to prophesy that the very remote ancestral form of all the mammals was of an MOoNOTREME AND MARSUPIAL. insectivore type. Subsequent re- is : yP dq (Below.) Monotreme type—Echid- search! has all tended in the same na, the spiny ant-eater. d eaves : : (Above.) Marsupial type—Didel- direction, pointing to insectivorous phys, the arboreal opossum of habits and in many ways to arboreal = South = America. After photo- graphs of specimens in the New modes of existence as characteristic York Zoological Park. 1This insectivorous and tree-inhabiting theory of mammalian origin has recently been advocated by Doctor William Diller Matthew of the American Museum of Natural History, by Doctor William K. Gregory of Columbia University (‘‘The Orders of Mam- mals”), and Doctor Elliot Smith of the University of Glasgow. 236 THE ORIGIN AND EVOLUTION OF LIFE of the earliest mammals. Proofs of arboreal habit are seen in the limb-grasping adaptations of the hind foot in many prim- itive mammals, and even in the human infant. Thus the ORIGIN AND ADAPTIVE RADIATION OF THE MAMMALS. WK GAtcony i910 RECENT HooFco MAMMALS. PLEISTOCENE QUATER- NARY PLIOCENE, MIOCENE CENOZOIC OLIGOCENE AUSTRALIAN TERTIARY PALECCENE PLACENTALS Prunrive oFossuMS UPPER CRETACEOUS, yaiconoponrs: MESOZOIC TRIASSIC PERMIAN RePTiuce CARBONIFEROUS PALAEOZOIC Fic. 114. ANCESTRAL TREE OF THE MamMALs. Adaptive radiation of the Mammalia, originating from Triassic cynodont reptiles and dividing into three main branches: (A) the primitive, egg-laying, reptile-like mammals (Monotremes); (B) the intermediate pouched, viviparous mammals (Marsupials— opossums, etc.); and (C) the true Placentals which branch off from small, primitive, arboreo-insectivorous forms (Trituberculata) of late Triassic time into the four grand divisions (1) the clawed mammals, (2) the Primates, (3) the hoofed mammals, and (4) the cetaceans. Dividing into some thirty orders, this grand evolution and adaptive radiation takes place chiefly during the four million years of Upper Cretaceous and Tertiary time. As among the Reptilia, the primary arboreo-terrestrial adaptive phases radiate by direct evolution into all the habitat zones, and by reversed and alternate evolu- tion develop backward and forward in adaptation to one or another habitat zone. Dia- gram prepared for the author by W. K. Gregory. existing tree shrews, the tupaias of Africa (Fig. 112), in many characters resemble the hypothetic ancestral forms of Creta- ceous time from which the primates (monkeys, apes, and man) may have radiated. ORIGIN OF MAMMALS 237 Following Cuvier, Owen, and Huxley in Europe, a period of active research in this country began with Leidy in the middle of the nineteenth century and was continued in the arid regions of the West by Cope, Marsh, and their succes- sors with such energy that America has become the chief cen- tre of vertebrate paleontology. When we connect this research with the older and the more recent explorations by men of all countries in Europe, Asia, Africa, Australia, and South Amer- ica, we are enabled to reconstruct the great tree of mammalian descent (Fig. 114) with far greater fulness and accuracy than that of the reptiles, amphibians, or fishes (Pisces). The connection of the ancestral mammals with a reptilian type of Permian time is theoretically established through the survival of a single branch of primitive egg-laying mammals (Monotremata, Fig. 113) in Australia and New Guinea; while the whole intermediate division, consisting of the pouched mammals (Marsupialia) of Australia, which bring forth their young in a very immature condition, represents on the great continent of Australia an adaptive radiation which also sprang from a small, primitive, tree-living 1. Whales. type of mammal, typified by the ex- 2. Seals (marine carnivores). isting opossums of North and South pe CARnvorts (terrestrial). . : : 4. Insectivores. America (Fig. 113). The third great «. Bats. group (Placentalia) includes the © fo mammals in which the unborn ke young are retained a longer period Apes, within the mother and are nourished Man. é . se +. Hoofed mammals. through the circulation of nutrition _¢_ fanatees. in the placenta. 9. Rodents. ro. Edentates. The adaptive radiation of the ten great branches of the placental stock from the primitive insec- tivorous arboreal ancestors produced a mammalian fauna which 238 THE ORIGIN AND EVOLUTION OF LIFE inhabited the entire globe until the comparatively recent period of extermination by man, who through the invention of tools in Middle Pleistocene time, about 125,000 years ago, became the destroyer of creation. SINGLE CHARACTER EVOLUTION AND PHYSICOCHEMICAL CORRELATION The principal modes of evolution as we observe them among the mammals are threefold, namely: I. The modes in which new characters first appear, whether suddenly or gradually and continuously, whether accidentally or according to some law. II. The modes in which characters change in proportion, quantitatively or intensively, both as to form and color. III. The modes in which all the characters of an organism respond to a change of environment and of individual habit. The key to the understanding of these three modes is to be sought first in changes of food and in changes of the medium in which the mammals move, whether on the earth, in the water, or in the air. The complexity of the environmental influence becomes like that of a lock with an unlimited number of combinations, because the adaptations of the teeth to varied forms of insectivorous, carnivorous, and herbivorous diet may be similar among mammals living in widely different habitat zones, while the adaptations of the locomotor apparatus, the limbs and feet, to the primary arboreal zone may radiate into structures suited to any one of the remaining ten life zones. Thus there is invariably a double adaptive and inde- pendent radiation of the teeth to food and of the limbs to pro- gression, and therefore two series of organs are evolving. For example, there always arises a more or less close analogy be- tween the teeth of all insect-eating mammals, irrespective of CHARACTER EVOLUTION 239 the habitat in which they find their food. Similarly there arises a more or less close analogy between the motor organs of all the mammals living in any particular habitat; thus the glis- sant or volplaning limbs of all aéro-arboreal types are exter- nally similar, irrespective of the ancestral orders from which HABITAT CHANGE ACCOMPANYING CHANGE OF FUNCTION AERIAL (FLYING) AER? ARBORE WGURDARIRG! FLYING" PHALANGERS GALEOPITHECUS FLYING” LIZARD ees Gere eee eee et “FLYING” SQUIRRELS (LEAPING OR ARBOREAL = Stivaincn ARBORS TERRE seavemomen, YO (WALKING TERRESTRIAL —fwnnins JUMPING) JUMPING RODENTS _ KANGAROOS MANY CLAWED MAMMALS MANY REPTILES TERR? FOSSORE = “FESR FOSSORIAL (DIGGING! 10 (TRANSITIONAL, TERR AQUATIC PARTIALLY AQUATIC) POLAR BEARS OTTERS MANY TURTLES: LE {LIVING IN FRESH SROCOBILES: AQUATIC,FLUVEE Waters se BATS PTEROSAURS PHALANGERS.LEMURSSSOsS=~C<“=~S~S*~“~S*~*C‘“=:S~S*~CS~CSSSS SQUIRRELS ‘TREE KANGAROG MACGAQUES GORILLA MANY INSECTIVORES: BABOONS, MANY RUNNING TYPES MOLES POUCHED MOLES SHREWS, YAPOK. BEAVER CAPYBARA, HIPPOPOTAMUS, MANY LIZAROS: SEA-OTTER (LIVING ALONG SHORE NOTHOSAURS » LITTORAL OR IN ESTUARIES) Re cialis MANY EXTINCT REPTILES (EXCLUSIVELY Wines SEA TURTLES om PELAGIC MARINE? ICHTHYOSAURS (LIVING AT GREAT DEPTHS: FIN BACK WHALES SOME MOSASAURS: 2 ABYSSAL oroivine To creat ofPTHS) MOTOR ADAPTATIONS OF DIFFERENT ANIMALS TO SIMILAR LIFE ZONES Fic. 115. ADAPTIVE RADIATION oF THE MAMMALS. The mammals, probably originating in arboreal leaping or climbing phases, radiate adaptively into all the other habitat zones and thus acquire many types of body form and of locomotion more or less convergent and analogous to those previously evolved among the reptiles (shown in the right-hand column), the amphibians, and the fishes. Diagram by Osborn and Gregory. they are derived. A mammal may seek any one of twelve different habitat zones in search of the same general kind of food; conversely, a mammal living in a single habitat zone may seek within it six entirely different kinds of food. This principle of the independent adaptation of each organ of the body to its own particular function is in keeping with the heredity law of individual and separate evolution of ‘“char- acters” and ‘character complexes” (p. 147), and is fatal to 240 THE ORIGIN AND EVOLUTION OF LIFE some of the hypotheses regarding animal structure and evolu- tion which have been entertained since the first analyses of animal form were made by Cuvier at the beginning of the last century. The independent adaptation of each character group to its own particular function proves that there is no such essen- tial correlation between the structure of the teeth and the struc- ture of the feet as Cuvier claimed in what was perhaps his most famous generalization, namely, his ‘“‘ Law of Correlation.’’! Again this principle, of twofold, threefold, or manifold adap- tation, is fatal to any form of belief in an internal perfecting tendency which may drive animal evolution in any particular direction or directions. Finally, it is fatal to Darwin’s original natural-selection hypothesis, which would imply that the teeth, limbs, and feet are varying fortuitously rather than evolving under certain definite although still unknown laws. The adaptations which arise in the search of many varieties of food and in overcoming the mechanical problems of loco- motion, offense, and defense in the twelve different habitat zones are not fortuitous. On the contrary, observations on successive members of families of mammals in process either of direct, of reversed, or of alternate adaptation admit of but one interpretation, namely, (that the evolution of characters is in definite directions toward adaptive ends; nor is this definite direction limited by the ancestral constitution of the heredity- chromatin as conceived in the logical mind of Huxley., The passage in which Huxley expressed this conception is as follows: “The importance of natural selection will not be impaired even if further inquiries should prove that variability is definite, and is determined in certain directions rather than in others, by 1 Cuvier’s law of correlation has been restated by Osborn. There is a fundamental correlation, coordination, and cooperation of all parts of the organism, but not of the kind conceived by Cuvier, who was at heart a special creationist. Contrary to Cuvier’s claim, it is impossible to predict from the structure of the teeth what the structure of the feet may prove to be. CHARACTER EVOLUTION 241 conditions inherent in that which varies. It is quite conceiv- able that every species tends to produce varieties of a limited number and kind, and that the effect of natural selection is to favor the development of some of these, while it opposes the development of others along their predetermined lines of modification.’’! ism are in some respects limited in the heredity-chromatin, as Huxley imagined; on the contrary, every part of a mammal It is true that the variations of the organ- may exhibit such plasticity in course of geologic time as enables it to pass from one habitat zone into another, and from that into still others until finally traces of the adaptations to pre- vious habitats and anatomical phases may be almost if not entirely lost. The heredity-chromatin never determines be- forehand into what new environment the lot of a mammal family may be cast; this is determined by cosmic and plane- tary changes as well as by the appetites and initiative of the organism (p. 114). For example, one of the most remarkable instances which have been discovered is that of the reversed aquatic adaptation of Zeuglodon,* first terrestrial, then aquatic, in succession a dog-like, a fish-like, and finally an eel-like mammal. These peculiar whales (Archeoceti) appear to have originated in the littoral and pelagic waters of Africa in Eocene time from a purely terrestrial ancestral form of mammal (allied to Hyenodon), in which the body is proportioned like that of the wolf or dog, and this terrestrial mammal in turn was descended from a very remote arboreal ancestor. Thus in its long history the Zeuglodon passed through at least three habitat zones and as many life phases. Yet in another sense Huxley was right, for palzontolo- 1 Huxley, Thomas, 1893, p. 223 (first published in 1878). 2 Zeuglodon itself is a highly specialized side branch of the primitive toothed whales. The true whales may have arisen from the genera Protocetus, probably ancestral to the toothed whales, and Patriocetus which combines characters of the zeuglodonts and whalebone whales. 242 THE ORIGIN AND EVOLUTION OF LIFE gists actually observe in the characters springing from the heredity-chromatin a predetermination of another kind, namely, the origin through causes we do not understand of a tendency toward the independent appearance or birth at different periods of geologic time of similar new and useful characters. In fact, a very large number of characters spring not from the visible ancestral body forms but from invisible predispositions and tendencies in the ancestral heredity-chromatin. For example, all the radiating descendants of a group of hornless mammals may at different periods of geologic time give rise to similar horny outgrowths upon the forehead. This heredity principle partly underlies what Osborn has termed the law of rectigra- dation. Moreover, once a new character or group of characters makes its visible appearance in the body its invisible chromatin evolution may assume certain definite directions and become cumulative in successive generations in accordance with the principle of Mutationsrichtung, first perceived by Neumayr (p. 138); in other words, the tendency of a character to evolve in one direction often accumulates in successive generations until it reaches an extreme. The application of our law of quadruple causes, namely, of the incessant action; reaction, and interaction of the four physicochemical complexes under the influence of natural selection, to the definite and orderly origin of myriads of char- acters such as are involved in the transformation of a shrew type of mammal ifto the quadrupedal wolf type and of the wolf type into the Zeuglodon eel type, has not yet even ap- proached the dignity of a working hypothesis, much less of an explanation. The truth is that the causes of the orderly co- adaptation of separable and independent characters still remain a mystery which we are only beginning to dimly penetrate. As another illustration of the complexity of the evolution CHARACTER EVOLUTION 243 process in mammals, let us observe the operation of Dollo’s law of alternate adaptation (p. 202) in the evolution of the tree. kangaroo (Dendrolagus), belonging to the marsupial or pouched division of the Mammalia. This is a case where many of the intermediate stages are known to survive in existing types. These tree kangaroos theoretically have passed through four phases, as follows: (1) An arboreo-terrestrial phase, including primitive marsupials like the opossum, with no special adap- AERIAL AEROARBORE IARBOREAL i(i‘(‘ééC of Pech orctivanatyee crear Tor oprosae | IBten Wee Sor neaoarreD ron ARBOR® TERRE "ERE BEEATSreaens en ee weet eee al Df ee ee fh eg Se es a ee ee Ss ee aN ee KAN . TERRESTRIAL | cAEAT TOE RCUceD OnABSENT Fic. 116. Four PHASES oF ALTERNATING ADAPTATION IN THE KANGAROO MARSUPIALS, Accorpinc To DoLto’s Law. Primitive arboreo-terrestrial phase—tree and ground living forms. Primitive arboreal phalanger phase—tree-living forms. Kangaroos—terrestrial, saltatorial phase—ground-living, jumping forms. Tree kangaroos—secondarily arboreal, climbing phase. POND H tations for climbing; (2) a true arboreal phase of primitive tree phalangers with the feet specialized for climbing purposes through the opposability of the great toe (hallux), the fourth toe enlarged; (3) a cursorial terrestrial phase, typified by the kangaroos, with feet of the leaping type, the big toe (hallux) reduced or absent, the fourth toe greatly enlarged; (4) a second arboreal phase, typified by the tree kangaroos (Dendrolagus), with limbs fundamentally of the cursorial terrestrial leaping type but superficially readapted for climbing purposes. It is clear that there can be no internal perfecting tendency or predetermination of the heredity-chromatin to anticipate such a tortuous course of evolution from terrestrial into arbo- real life, from arboreal back to a highly specialized terrestrial 244 THE ORIGIN AND EVOLUTION OF LIFE life, and finally from the leaping over the ground of the kan- garoo into the incipiently specialized arboreal phase of the tree kangaroo. In the evolution of the tree kangaroos adap- tation is certainly not limited by the inherent tendencies of the heredity-chromatin to evolve in certain directions. The physicochemical theory of these remarkable alternate adap- tations is that an animal leaving the terrestrial habitat and taking on arboreal habits initiates an entirely new series of actions, reactions, and interactions with its physical environ- ment, with its life environment, in its body cell and individual development, and, in some manner entirely unknown to us, in its heredity-chromatin, which begins to show new or modified determiners of bodily character. That natural selection is continuously operating at every stage of the transformation there can be no doubt. One interpretation which has been offered up to the pres- ent time of the mode of transformation of a terrestrial into an arboreal mammal is through a form of Darwinism known as the “organic selection” or “coincident selection’? hypothesis, which was independently proposed by Osborn,! Baldwin, and Lloyd Morgan, namely: that the individual bodily modifications and adaptations caused by growth and habit (while not them- selves heritable) would tend to preserve the organism during the | long transition into arboreal life; they would tend to nurse the family over the critical period and allow time to favor all pre- dispositions and tendencies in the heredity-chromatin toward arboreal function and structure, and would tend also to elim- inate all structural and functional predispositions in the hered- ity-chromatin which would naturally adapt a mammal to life in any one of the other habitat zones. This interpretation is consistent with our law that selection is constantly operating 1Osborn, H. F., 1897. CAUSES OF EVOLUTION 245 on all the actions, reactions, and interactions of the body, but it does not help to explain the definite origin of new characters which cannot enter into ‘‘organic selection” before they exist. Nor is there any evidence that while adapting itself to one mode of life fortuitous variations in the heredity-chromatin for every other mode of life are occurring. THEORETIC CAUSES OF EVOLUTION IN MAMMALS We have thus far described only the modes of evolution and said nothing of the causes. In speculating on the causes of character evolution in the mammals, in comparison with similar body forms and characters in the lower vertebrates and even in the invertebrates, it is very important to keep in mind the preceding evidence that mammalian heredity-chromatin may preserve all the useful functional and structural properties of action, reaction, and interaction which have accumulated in the long series of ancestral life forms from the protozoan and even the bacterial stage. Since structurally the mammalian embryo passes through primitive protozoan (single-celled) and metazoan (many-celled) phases, it is probable that chemically it passes through the same. The heredity-chromatin even in the development of the highest mammals still recalls primitive stages in the devel- opment of the fishes, for example, the gill-arch structure at the side of the throat, which through change of function serves to form the primary cartilaginous jaws (Meckelian cartilages) of mammals as well as the bony ossicles which are connected with the auditory function of the middle ear (Reichert’s theory). Similarly profound structural ancestral phases in protozoan, fish, and reptile structure pervade every part of the mammalian body. In race evolution there may be changes of adaptation as in the Jaw of change of function (Prinzip des Funk- 246 THE ORIGIN AND EVOLUTION OF LIFE tionswechsels), first clearly enunciated by Anton Dohrn in 1875. But no function is lost without good cause, and the heredity- chromatin retains every character which through change of function and adaptation can be made useful. The same law which we observe in the conservation of all adaptive characters and functions will probably be discovered also in the conservation of ancestral physicochemical actions, reactions, and interactions of the organism from the protozoan stages onward. The primordial chemical messengers—enzymes or organic catalyzers, hormones and chalones, and other accele- rators, retarders, and balancers of organ formation (see p. 72)— are certainly not lost; if useful, they are retained, built up, and unceasingly complicated to control the marvellous coordina- tions and correlations of the various organs of the mammalian body. The principal endocrine (internal secretory) as well as duct secretory glands established in the fish stage of evolution (p. 160), through which they can be partly traced back even to the lancelet stage (chordate), doubtless had their beginnings among the ancestors (protochordates) of the vertebrated animals, which extend back into Cambrian and pre-Cambrian time. Since these chemical messenger functions among the mammals are enormously ancient, we may attribute an equal antiquity to the powers of chemical storage and entertain the idea that the chromatin potentiality of storing phosphate and carbonate of lime for skeletal and defensive armature in the protozoan stage of 50,000,000 years’ antiquity is the same chromatin potentiality which builds up the superb internal skeletal struc- tures of the Mammalia and the highly varied forms of offen- sive and defensive armature either of the calcium compound or the chitinous type. It is, moreover, through the fundamental similarity of the physicochemical constitution of the fishes, amphibians, reptiles, CAUSES OF EVOLUTION 247 birds, and mammals that we may interpret the similarities of form evolution and understand why, the other three causes being similar, mammals repeat so many of the habitat form phases in adaptation to the environments previously passed through by the lower orders of life. Thus advancing struc- tural complexity is the reflection or the mirror of the invisible physicochemical complexity; the visible structural complexity of a great animal like the whale (Fig. 234), for example, is something we can grasp through its anatomy; the physico- chemical complexity of the whale is quite inconceivable. In research relating to the physicochemical complexity of the mammals, so notably stimulated by the work of Ehrlich and further advanced by later investigators, there are perhaps few studies more illuminating than those of Reichert and Brown! on the crystals of oxyhemoglobin, the red coloring matter of the mammalian blood. Their research proves that every species of mammal has its highly distinctive specific and generic form of hemoglobin crystals, that various degrees of kinship and specific affinity are indicated in the crystallog- raphy of the hemoglobin. For example, varieties of the dog family, such as the domestic dog, the wolf, the Australian dingo, the red, Arctic, and gray fox, are all distinguished. by only slightly differing crystalline forms of oxyhemoglobin. The authors’ philosophic conclusions arising from this research are as follows:? “The possibilities of an inconceivable number of constitu- tional differences in any given protein are instanced in the fact that the serum-albumin molecule may, as has been estimated, have aS many aS 1,000,000,000 stereoisomers. If we assume that serum-globulin, myoalbumin, and other of the highest pro- 1 Reichert, E. T., and Brown, A. P., 1909, pp. iii-iv. ; 1 Certain insertions in brackets being made for purposes of comparison with other portions of this series of lectures. 248 THE ORIGIN AND EVOLUTION OF LIFE teins may have a similar number, and that the simpler proteins and the fats and carbohydrates and perhaps other complex organic substances, may each have only a fraction of this number, it can readily be conceived how, primarily by differ- ences in chemical constitution of vital substances, and secon- Fic. 117. EvoLuTION OF PRoporTION. ADAPTATION IN LENGTH oF NECK. Short-necked okapi (left), the forest-living giraffe of the Congo, which browses upon the lower branches of trees. Long-necked giraffe (right), the plains-living type of the African savannas, which browses on the higher branches of trees. After Lang. darily by differences in chemical composition, there might be brought about all of those differences which serve to charac- terize genera, species, and individuals. Furthermore, since the factors which give rise to constitutional changes in one vital substance would probably operate at the same time to cause related changes in certain others, the alterations in one may logically be assumed to serve as a common index to all. “In accordance with the foregoing statement it can readily be understood how environment, for instance, might so affect CAUSES OF EVOLUTION 249 the individual’s metabolic processes as to give rise to modifica- tions of the constitutions of certain corresponding proteins and other vital molecules which, even though they be of too subtle a character for the chemist to detect by his present methods, may nevertheless be sufficient to cause not only physiological and morphological differentiations in the individual, but also Fic. 118. SHORT-FINGEREDNESS (BRACHYDACTYLY) AND LoNG-FINGEREDNESS (DOLICHO- DACTYLY). CONGENITAL, AND DUE TO INTERNAL SECRETION. (Left.) Congenital brachydactyly, theoretically due either to a sudden alteration in the chromatin or to a congenital defect in the pituitary gland. After Drinkwater. (Centre.) Brachydactyly, after birth, due to abnormally excessive secretions of the pituitary gland. After Cushing. (Right.) Dolichodactyly, after birth, due to abnormally insufficient secretions of the pituitary gland. After Cushing. become manifested physiologically [functionally] and morpho- logically [structurally] in the offspring.” The above summary adumbrates the lines along which some of the chemical interactions, if not causes, of mammalian ev- olution may be investigated during the present century. The cause of different bodily proportions, such as the very long neck of the tree-top browsing giraffe, is one of the classic problems of adaptation. In the early part of the nineteenth century Lamarck (p. 143) attributed the lengthening of the neck 250 THE ORIGIN AND EVOLUTION OF LIFE to the inheritance of bodily modifications caused by the neck- stretching habit. Darwin attributed the lengthening of the neck to the constant selection of individuals and races which were born with the longest necks. Darwin was probably right. This is an instance where length or shortness of neck is ob- viously a selective survival character in the struggle for existence, because it directly affects the food supply. But there are many other changes of proportion in mam- mals, which are not known to have a selective survival value. We may instance in man, for example, the long head-form Fic. 119. RrEsutt oF REMOVING THE (dolichocephaly) and the broad THYROID AND PARATHYROID GLANDS. head-form (brachycephaly), or en Normal sheep fourteen months the long- fingered form ( dnltehos (Left.) A sheep of the same age from dactyly) and the short-fingered which the thyroids and parathyroids , were removed twelve months previ- form (brachydactyly), which ani: ; have been interpreted as con- After Sutherland Simpson. genital characters appearing at birth and tending to be transmitted to offspring. Brachy- dactyly may be transmitted through several generations, but until recently no one has suggested what may be its possible cause. It has now been found! that both the short-fingered con- dition (brachydactyly) and the slender-fingered condition may be induced during the lifetime of the individual in a previously healthy and normal pair of hands by a diseased or injured con- dition of the pituitary body at the base of the brain. If the 1 Cushing, Harvey, rorr, pp. 253, 256. MODES OF EVOLUTION secretions of the pituitary are abnormally active (hyperpitui- tarism) the hand becomes broad and the fingers stumpy (Fig. 118, B). If the secretions of the pituitary are abnormally re- duced (hypopituitarism) the fingers become tapering and slender (Fig. 118, C). Thus in a most remarkable manner the internal secretions of a very ancient ductless gland, attached to the brain and originating in the roof of the mouth in our most remote fish-like ancestors, affect the proportions both of flesh and bones in the fingers, as well as the proportions of many other parts of the body. Whether this is a mere co- incidence of a heredity-chro- Fic. 120. Rrsutt oF REMOVING THE Piruirary Bopy. matin congenital character & (Right.) Normal dog twelve months with a mere bodily chemical old. i it ld (Left.) A dog of the same age and litter messenger C aracter 1t wou from which the pituitary body was e mature to sav. It cer- removed at the age of two months. b . Dae y 7 , After Aschner. tainly appears that chemical in- teractions from the pituitary body control the normal and ab- normal development of proportions in distant parts of the body. Cuter Mopes oF EVOLUTION OF MAMMALIAN CHARACTERS What we have gained during the past century is positive knowledge of the chief modes of evolution; we know almost the entire history of the transformation of many different kinds of mammals. These modes as distinguished from the unknown causes are expressed in the following general laws: first, the Jaw of con- tinuity; Natura non facit saltwm, there is prevailing continuity 252 THE ORIGIN AND EVOLUTION OF LIFE in the changes of form and proportion in evolution as in growth. Second, the Jaw of rectigradation, under which many important new characters appear definitely and take an adap- tive direction from the start; third, the Jaw of acceleration and retardation, witnessed both in racial and individual develop- ment, whereby each character has its own velocity, or rate of development, which displays itself both in the time of its origin, in its rate of evolution, and its rate of individual development. This last law underlies the profound changes of proportion in the head and different parts of the body and limbs which are among the dominant features of mammalian evolution. In the skeleton of mammals very few new characters originate; most of the changes are in the loss of characters and in the profound changes of proportion. For example, by the addi- tion of many teeth and by stretching or pulling, swelling or contracting, the skeleton of a tree shrew may almost be trans- formed into that of a whale. The above laws are the controlling ones and make up four- fifths of mammalian evolution in the hard parts of the body. So far as has been observed the remaining fifth or even a much smaller fraction of mammalian evolution is attributable to the law of saltation, or discontinuity, namely, to the sudden appearance of new characters and new functions in the hered- ity-chromatin. For example, the sudden addition of a new vertebra or vertebre to the backbone, which gives rise to the varied vertebral formule in different orders and even the dif- ferent genera of mammals, or the sudden addition of a new tooth are instances of saltatory evolution in the hard parts of the body. There are also many instances of the sudden appearance of new functional, physiological, or physicochem- ical characters, such as immunity or non-immunity to certain diseases. ADAPTATION TO ENVIRONMENT 253 RESPONSES OF MAMMAL CHARACTERS TO CHANGING ENVIRONMENT Buffon was the first to observe the direct responses of mam- mals to their environment and naturally supposed that en- vironment was the cause of animal modification, chiefly in adaptation to changes of climate. It did not occur to him to inquire whether these modifications were heritable or not, any more than it did to Lamarck. It is now generally believed that these reactions are for the most part modifications of the body cells and body chro- matin only, which give rise to what may be known as environ- mental species, as distinguished from true chromatin species which are founded upon new or altered hereditary characters. Of the former order are many geographic varieties and doubtless many geographic species. These visible species of body cell characters are quite distinct from the invisible species of heredity-chromatin characters. Both occur in nature. Geologic and secular changes of environment have preceded many of the most profound changes in the evolution of the mammals, which interlock and counteract with their physical and life environments quite as closely as do the reptiles, am- phibians, and fishes; yet a very large part of mammalian evo- lution has proceeded and is proceeding quite independently of change of environment. Thus environment holds its rank as one of the four complexes of the causes of evolution instead of being the cause par excellence as it was regarded in the brilliant speculations of Buffon. The interlocking of mammals with their life environment is extremely close, namely, with Bacteria, Protozoa, Insecta, and many other kinds of Invertebrata, with other Vertebrata, as well as with the constantly evolving food supply of the plant 254 THE ORIGIN AND EVOLUTION OF LIFE world; consequently the vicissitudes of the physical environ- ment as causes of the vicissitudes of the life environment of mammals afford the most complex examples of interlocking which we know of in the whole animal world. In other words, the mammals interlock in relation to all the surviving forms of the life which evolved on the earth before them. Although suggested nearly a century ago by Lyell, the demonstration is comparatively recent that one of the principal causes of the extinction of certain highly adaptive groups of mammals is their non-immunjty to the infections spread by Bacteria and Protozoa.!. Thus a change of environment and of climate may not affect a mammal directly but may profoundly affect it in- directly through insect life. These closely interlocking relations of the mammals with their physicochemical environment and their life environment have been subject to constant disturbances through the geo- logic and geographic shifting of the twelve or more habitat zones which they occupy. Yet the earth changes during the Tertiary, the era during which mammalian evolution mainly took place, were less extreme than those during Mesozoic and Paleozoic time. This is because the trend of development of the earth’s surface and of its climate during the past 3,000,000 years has been toward continental stability and lowering of general temperature in both the northern and southern hemi- spheres, terminating in the geologically sudden advent of the Glacial Epoch, with its alternating periods of moisture and aridity, cold and heat, which exerted the most profound influ- ence upon the food supply, insect barriers, and other causes affecting the migrations of the Mammalia. These causes com- pletely change the general aspect of the mammalian world in 1 For the history and discussion of this entire subject see Osborn, H. F.: ‘‘The Causes of Extinction of Mammalia,” Amer. Naturalist, vol. XL, November and December, 1906, pp. 769-795, 829-859. ADAPTATION TO ENVIRONMENT 255 the whole northern hemisphere, South America, and Australia, and leave only the world of African mammalian life untouched. The water content of the atmosphere during the 3,000,000 years of the Age of Mammals has tended toward a repetition of the environmental conditions of Permian and Triassic times in the development of areas of extreme humidity as well as areas of extreme aridity, interrupted, however, by widespread humid conditions in the Pleistocene Epoch. Marine invasion of the continents of Europe and North America, while far less ex- treme than during Cretaceous time, has served to give us the complete history of the littoral and marine Mollusca, both in the eastern and western hemispheres, which is the chief basis of the geologic time scale as discovered in the Paris basin by Brogniart at the beginning of the eighteenth century. The clearest conception of the length of Tertiary time is afforded (Fig. 121) by the completion in Eocene time of the Rocky Mountain uplift of America and the eastern Alps of Europe, by the elevation of the Pyrenees in Oligocene time, by the rise of the wondrous Swiss Alps between the Oligocene and Miocene Epochs, and finally by the creation of the titanic Himalaya chain in the latter part of Miocene time. Through the phenomena of the migration of various kinds of mammals from continent to continent, we are able to date with some precision the rise and fall of the land bridges and the alternating periods of connection and separation of the two northern continental masses, Eurasia and America, as well as of the northern and southern continents. Few writers maintain seriously for Tertiary time the “equatorial theory”’ of connection between the eastern and western hemispheres such as figures largely in the speculations of Suess, Schuchert, and others in relation to plant and animal migrations of Paleozoic and Mesozoic time. The less radical “bipolar theory” that 256 THE ORIGIN AND EVOLUTION OF LIFE the eastern and western hemispheres were connected both at the north pole and at the south pole, or through Arctic and Antarctic land areas, still has many adherents, especially in PERIOD GLACIAL 4 [QUATERNARY GLACIAL HIMALAYAS (LEC OGERE ts AGE MIOCENE oe! b Ss ey) SWISS ALPS a FI ee re OF PYRENEES 3] Bi ota MOD AT AIN MAMMALS EOCENE, EASTERN ALPS Pepa mr Ha KUARAMIE) |. scsedearesvibeca etrtedecco een erred tected tt ny Pei] Lay (ogrAbeguy 1 oon Ie tilititititit B) | vGRASRIC SIERRA NEVADA AGE = Det ad Faby daguye iTRAPSIEL ! i itt] PaLIsAe OF REPTILES I | APPALACHIAN AND THE HERCYNIAN BELT 7 ENTRAL EUROPE ? G AMERIBIANS x Mes Z Z we Z he ae ACADIAN 2} [70 8] bz oO e 2 SCOTTISH HIGHLA 3 &) | sfturian 15000 7 AGE TACONIC ‘eo OF oRDOvICYy ORDOVICIAN i006 FISHES AND CAMBRIAN CAMBRIAN jana 4 INVERTEBRATES ? PRE-CAMBRIAN ALGONKIAN ! ALGONKIAN ESC ANDINAVIA 5 = oe ? ARCHAEAN BROREMIA c ARCHAEAN ae ‘CERTAIN MOUNTAIN CHIEF MOUNTAIN REVOLUTIONS OF” REVOLUTIONS OF EUROPE AND ASIA NORTH AMERICA Fic. 121. Marin SuBDIVISIONS OF GEOLOGIC TIME. The subdivisions are not to the same scale. The notches at the sides of the scale (which is simplified from that on p. 153) represent chiefly the periods of mountain uplift in the northern hemisphere of the Old World (left) and of the New World (right). regard to the former relations of the Australian continent and South America through the now partly sunKen continent of Antarctica. The still more conservative ‘north polar ADAPTATION TO ENVIRONMENT 257 theory” of Wallace, of an exclusively northern land connection of the eastern and western hemispheres during Tertiary time, has recently been maintained by Matthew! as adequate to explain all the chief facts of mammalian migration and geo- graphic evolution. The feet and the teeth of mammals become so closely adapted to the medium in which they move and the kind of food consumed that through the interpreta- tion of their structure we shall in time write a fairly complete physio- graphic and climatic his- tory of the Tertiary Epoch along the lines of the investigations in- itiated by Gaudry and Kowalevsky. Through th ‘ a Fic. 122. THe NortH Potar THEORY OF THE € SUCCESSIVE a apta- DISTRIBUTION OF MAMMALS. tions of the limbs and A zenith view of the earth from the north pole, showing (arrows) the North Polar theory of the sole of the foot and the geographic migrations and distribution of the adaptations of the teeth, mammals, especially of the Primates (monkeys, lemurs, and apes). After W. D. Matthew, rors. which are most delicately adjusted—the former to impact with varying soils and the latter to the requirements of the consumption of various forms of nourishment—we may definitely trace the influences or rather the adaptive responses to the habitat subzones, such as the forest, forest-border, meadow, meadow-border, river-border, the lowland, the upland, the meadow-fertile, the meadow-arid, the plains, and the desert-arid. This mirror of past geography, climate, evolution of plant life in the anatomy of the limbs 1 Matthew, W. D., rors. 258 THE ORIGIN AND EVOLUTION OF LIFE and feet, is one of the most fascinating fields of philosophic study. In the more humid, semi-forested regions, which preserve the physiographic conditions of early Eocene times (Fig. 123), we discover most of the examples of the survival of primitive mammalian forms and functions. The borderland between the extremes of aridity and humidity has afforded the most Fic. 123. SCENE IN WESTERN WyomInc IN MippLe Eocene TIMe. The period of the four-toed mountain horse, Orohippus (right), of the Uintathere (left), and of the Titanothere (left lower). From study for a mural decoration in the American Museum of Natural History by Charles R. Knight under the author’s direction. favorable habitats for the rapid evolution of all the forms of terrestrial life. From these favored regions the mammals have entered the semi-arid and arid deserts, in which also evolution has been relatively rapid. Since Tertiary geologic succession is nearly unbroken we can now trace the evolution of many families of the carnivores, the greater number of the hoofed mammals, and the rodents, with few interruptions through the entire 3,000,000 years of Tertiary time. It is through our very close observation of the origin and history of numerous single characters as exhibited in paleontologic lines of evolution that the three chief modes (p. 251) of mam- GEOGRAPHIC DISTRIBUTION 259 malian evolution and the continued definite direction and dif- ferences of velocity in the development of characters have been discovered. GENERAL SUCCESSION OF MAMMALIAN LIFE IN NortTH AMERICA In Upper Cretaceous and Palaocene time we find that the northern hemisphere is covered with an archaic adaptive radi- Ee ation of mammals distinguished bythe extremely small size of the brain and clumsy mechanics of the skeleton. Of these the carnivorous forms radiate into a number of families adapted to a great variety of feeding and lo- comotor habits which are anal-__. ogous to the families of existing Carnivora. Similarly the hoofed Fic. 124. Two STAGES IN THE EARLY EvoLurION OF THE UNGULATES. mammals (Condylarthra, Am- Pantolambda (A), an archaic Palxocene cae : Pa form which transforms into Coryphodon blypoda) divide into swift (B), a Lower Eocene form of increased footed (cursorial) and heavy- size, with greatly enlarged head, ab- . breviated tail, and defensive tusks. footed (graviportal) for ms, the This transformation occupied a period : . estimated at 500,000 years, nearly one- latter including the Amblypoda sixth of Tertiary time. Restorations (Coryphodon and Dino ceras) F in the American Museum of Natural Pe 3 History, by Osborn and Knight. From surviving members of this archaic adaptive radiation of small-brained mammals there arise all the stem forms of the orders existing to-day, which almost without exception have now been traced back to the close of Eocene time, namely, the ancestors of the whales, of the modern families of carnivores, insectivores, bats, lemurs, rodents, and the edentates (armadillos and ant-eaters). Especially remark- able is the discovery in the Lower Eocene of the ancestors of 260 THE ORIGIN AND EVOLUTION OF LIFE the modern horses, tapirs, rhinoceroses, and various types of cloven-footed animals. A very general principle of mammalian evolution is illus- trated in Fig. 124 (A, B), namely, the increase of size character- istic of all the herbivorous mammals, which almost without exception are in the beginning extremely small forms that evolve into massive forms possessing for defense either power- Fic. 125. A PrimittvE WHALE FROM THE EOCENE OF ALABAMA. Zeuglodon cetoides exhibits a secondary elongate, eel-shaped body form analogous to that of many of the aquatic, free-swimming, surface-dwelling reptiles, aquatic amphibians, and fusiform fishes. Restoration by Gidley and Knight in the American Museum of Natural History. ful tusks or horns. The most conspicuous example of very rapid evolution which has taken place prior to the close of Eocene time is that of the great primitive whale Zeuglodon cetoides, discovered in the Upper Eocene of Alabama, and now known to have been distributed eastward to the region of the Mediterranean. As described above (p. 241), as an example of reversed adaptation and evolution, this animal had already passed through a prior terrestrial phase and had reached a stage of extreme specialization for marine life. These zeu- glodonts parallel several of the marine groups of reptiles (Figs. 76, 87), also certain of the amphibians and fishes (Figs. 60, 44); GEOGRAPHIC DISTRIBUTION 261 in the extreme elongation and eel-like mode of propulsion of the body. A zoogeographic feature of Eocene life is the strong and in- creasing evidence of migration between South America and North America by means of land connection in late Cretaceous or basal Eocene time, between the northern and southern hemispheres, which was then interrupted for 1,000,000 or per- haps 1,500,000 years until the middle of the Pliocene Epoch, when the South American types again appear in North Amer- ica. Another relation which has been established by recent discoveries is seen in the resemblance between certain Rocky Mountain primates (lemurs) and those existing at the present time in the Malayan Peninsula. ; North America and western Europe pass alike through three great phases of mammalian life in Eocene time: first, the archaic phase of the Paleocene; second, a long phase in which the archaic and modern mammals of the Lower Eocene inter- mingle; third, a very prolonged period from the Lower to the Upper Eocene, in which Europe and North America are widely separated and each of the ancestral types of mammals undergoes an independent evolution. This is followed in Oligocene time by a phase in which the animal life of western Europe and North America was reunited. Again in Miocene time a fur- ther wave of European mammalian life sweeps over North America, including the advance wave of the great order Pro- boscidea embracing both mastodons and elephants which ap- pear to have originated in Africa or in southern Asia. During the entire Miocene and Pliocene Epochs there is more or less unity of evolution between North America, Europe, and Asia, but it is a very striking fact that in Middle Pliocene time, when a wave of South American life enters North America, certain very highly characteristic forms of North American 262 THE ORIGIN AND EVOLUTION OF LIFE mammals (camels) enter Europe. In late Pliocene and early Pleistocene time the grandest epoch of mammalian life is reached; certain great orders like the proboscidians and the horses, with very high powers of adaptation as well as of migra- tion, spread over every continent except Australia. Fic. 126. NortH AMERICA IN UPPER OLIGOCENE TIME. East of the recently born Rocky Mountains the region of the Great Plains was made up of broad fluviatile flood-plains, fan-deltas, and lagoons, accumulating the detritus of the Rocky Mountains on the west and with a general eastern drainage. It was the scene of a continuous evolution of a plains fauna of mammals for a period of 1,500,000 years. Detail from the globe model in the American Museum by Chester A. Reeds and George Robertson, after Schuchert. This great epoch of mammalian distribution is followed by the Pleistocene phases in the northern and southern hemi- spheres, at the close of which the world wears a greatly im- poverished aspect; the northern hemisphere banishes all the forms of mammalian life evolving in the southern hemisphere CHANGES OF PROPORTION 263 and in the tropics, and the high table-lands of Africa alone retain the grandeur of the Pliocene Epoch. THe DEFINITE CouRsE OF CHROMATIN EVOLUTION IN THE ORIGIN OF NEW CHARACTERS PARTLY PREDETERMINED BY ANCESTRY Some of the most universal laws as to the modes (p. 251) of evolution emerge from the comparative study of the horses, Fic. 127. Two STAGES IN THE EVOLUTION OF THE ‘TITANOTHERES. Transformation of the small hoofed quadruped Eotitanops (A) of the Eocene—a relatively light-limbed, swift-moving, cursorial herbivore—into the gigantic Brontotherium (B) of the Lower Oligocene—a ponderous, slow-moving, graviportal type, horned for offense and defense. These titanotheres were remotely related to the existing rhinoceroses, horses, and tapirs, but they became suddenly extinct on attaining this impressive stage of evolution. They exemplify the increase of size characteristic of the evolution of the greater number of the hoofed Herbivora. The time during which this trans- formation occurred is estimated at 1,200,000 years—about one-third of the whole Tertiary Epoch. the proboscidians, and the rhinoceroses, from areas so widely separated geographically that there was no possibility of hy- bridizing or of a mingling of strains. For example, during a period estimated at not less than 500,000 years the horses of France, Switzerland, and North America evolve in these widely 264 THE ORIGIN AND EVOLUTION OF LIFE separated regions in a closely similar manner and develop closely similar characteristics in approximately a similar length of time. The same is true of the widely separated lines of Tic. 128. STAGES IN THE EVOLUTION OF THE Horn IN THE TITANOTHERES. This shows that these important weapons arise as rectigradations, 7. e., orthogenetically and not as the result of the selection of chance or fortuitous variations. Horns, large, 4, Bron- totherium platyceras, Lower Oligocene; horns, small, 3, Protitanotherium emarginatum, Upper Eocene; horns, rudimentary, 2, Manteoceras manteoceras, Middle Eocene; hornless stage, 1, Eotitanops borealis, Lower Eocene. Models in the American Museum of Natural History, prepared for the author by Erwin S. Christman. descendants from the mas- todons, elephants, and rhi- noceroses. This law of uniform evolution and of the development inde- pendently in descendants from the same ancestors of closely similar characters is confirmed in Osborn’s study of the evolution of the titanotheres (Fig. 127). In these animals, which have been traced through discoveries of their fossil remains over a period of time extending from the beginning of the Lower Eocene to the beginning of the Middle Oligocene, inclusive, is exhibited a nearly continuous,’ un- broken transformation from the diminutive Eoti- tanops of the Lower Eocene to the massive Brontothe- rium of the Lower Oligocene, the latter form being so far as known the most imposing product of mammalian evolution, 1 The continuity is broken by the extinction of one branch and the survival of an- other. It is a continuity of character rather than of lines of descent. In some cases there is a continuity both of characters and of branches. CHANGES OF PROPORTION tc with the exception of the Proboscidea. Every known step in this transformation is determinate and definite, every additional character which has been observed arises according to a fixed law and not according to any principle of chance. In the eleven principal branches which radiate from the earliest known forms (Hotitanops gregoryi) of this family exactly similar new characters arise quite independently at different periods of geologic time which are separated by the lapse of tens of thou- sands of years. The titanotheres exhibit an absolutely independent but definite origin and development in each branch; so far as ob- served, every new character has its own rate of evolution and its own peculiar kind of form change; for example, in cer- tain branches of the family the horns will appear many thou- sands of years later in the evolution history than in other branches, and after their appearance in many instances they may exhibit a singular inertia, or lack of momentum, over a long period of time, which is exactly in accord with our gen- eral principle (p. 149) that every character has its own rate of velocity both in individual development and in racial de- velopment. THE ORIGIN OF NEW PROPORTIONAL CHARACTERS NOT PREDETERMINED BY ANCESTRY The titanotheres exhibit another very important principle, namely, that the linear proportions of the bones of the limbs are exactly adapted to the weight they are destined to carry and to the speed which they are destined to develop; in other words, the speed and the weight of all these great herbivora may be very precisely estimated by ratios and indices of the proportionate lengths of the different segments of the limbs, upper, middle, and lower. These proportionate lengths are 266 THE ORIGIN AND EVOLUTION OF LIFE not predetermined by the heredity-chromatin, because the same law of limb proportion prevails in all heavy, slow-mov- ing mammals, whatever their descent; for example, this law holds among the heavy, slow-moving reptiles, the Sauropoda (Fig. 97), as well as among the heavy, slow-moving mammals. The most beautiful adjustment of the proportions of the limb segments to speed is observed in the evolution of: the horses (Fig. 130). Here we see that the upper segments (hu- merus, femur) are abbreviated, while the lower segments (fore- arm, lower leg, manus, and pes) are elongated. This is precisely Fic. 129. Horsrs oF OLIGOCENE TIME. The horses frequenting the semi-arid the reverse of the conditions plains of Oligocene times present an obtaining among the slow-mov- intermediate stage in the evolution of . . : of cursorial motion—Mesohippus, with Ng titanotheres and proboscid- a narrow, three-toed type of foot, elongate, graceful limbs, and teeth with crowns beginning to be adapted to the horses, too, the same law pre- comminution of silicious grasses in 5 accommodation to the contemporane- vails and governs the ver y ous world-wide evolution of grassy precise adjustment of the ratios plains. This law of the contemporane- ous evolution of an environment of of each of the limb segments, grassy plains and of swift-moving 5 : é f Herbivora was first clearly enunciated quite irrespective 0 ancestry. by Kowalevsky in 1873. In the swift Hipparion of Amer- Restorations by Osborn, painted by ef ; Charles R. Knight, in the American ica, for example, the highest Museum of Natural History. ians (Fig. 131). Among the phase of equine adaptation to speed, the indices and ratios of the limb segments are very similar to those in the existing prong-horn antelopes (Antiloca- pra) of our western plains. Contemporary with the Hipparion of Pliocene time, adapted to racing over hard, stony ground, is the relatively slow-moving, forest-living horse (Hypohip pus) of the river borders of western North America (Fig. 130), in which the limb proportions are quite different. There is reason Fic. 130. STAGES IN THE EVOLUTION OF THE Horse. (Left.) An ascending series of Oligocene three-toed horses (A, B, C), showing their evolu- tion in size, form, and dental structure, which involved continuous change in thousands of distinct characters and occupied a period of time estimated at 100,000 to 200,000 years. (Right.) Two Upper Miocene American types of horses, Hipparion (F), with limbs pro- portioned like those of the deer, representing the climax of the swift-moving, grassy plains type, in contrast with Hypohippus (D, E), a conservative forest and browsing type. This is an instance of the survival of an ancient browsing type in an ancient forested environment (D, £), while in the adjacent grassy plains there exists contem- poraneously the fleet Hipparion (F). Skeletons mounted in the American Museum of Natural History. Restoration under the direction of the author, painted by Charles R. Knight. 207 268 THE ORIGIN AND EVOLUTION OF LIFE to believe that this animal, like the existing okapi, was protected by coloration and by its swamp-living habits. The above examples illustrate the general fact that changes of proportion make up the larger part of mammalian evolution and adaptation. The gain and loss of parts, the presence and absence of parts, which is so conspicuous a phenomenon in heredity as studied from the Mendelian standpoint, is a com- paratively rare phenomenon. These changes of proportion are brought about through the greater or less velocity of single characters and of groups of characters; for example, the trans- formation of the four-toed horse of the base of the Lower Eocene! into the three-toed embryo of the modern horse is brought about by the acceleration of the central digit and the retardation of the side digits. This process is so gradual that it required 1,000,000 years to accomplish the reduction of the fifth digit, which left the originally tetradactyl horse in the tridactyl stage (Fig. 130); and it has required 2,000,000 years more to complete the retardation of the second and fourth digits, which are still retained in the chromatin and develop side by side with the third digit for many months during the early intrauterine life of the horse. No form of sudden change of character (saltation, muta- tion of de Vries) or of the chance theory of evolution (pp. 7, 8) accounts for such precise steps in mechanical adjustment; be- cause for all proportional changes, which make up ninety-five per cent of mammalian evolution, we must seek a similar cause, namely, the cause of acceleration, balance or persistence, and retardation. This cause may prove to be in the nature of phys- icochemical interactions (p. 71) regulated by selection. The great importance of selection in the evolution of proportion is 1 The earliest-known fossil horses are four-toed, having lost the first digit (thumb). No five-toed fossil horse has yet been found. CHANGES OF PROPORTION 269 demonstrated by the universal law that the limb proportions of mammals are closely adjusted to provide for escape from enemies at each stage of development. AFRICA AS A GREAT THEATRE OF RADIATION The part which Africa has played in the early stages of mammalian evolution is a matter of comparatively recent dis- covery, and we are not yet positive whether the great life centre of North Africa was not closely related to that of south- ern Asia in Eocene and early Oligocene time, as the most re- cent discoveries appear to indi- cate. At all stages of geologic history Africa was, as it is to- day, a great theatre of evolu- tion of terrestrial life. Accord- ing to present knowledge, North Africa developed a highly varied fauna, including three chief ele- ments: first, types which are closely ancestral to the higher monkeys and apes, and which may thus be related to man him- self; second, a series of forms which attained gigantic size and never migrated from the con- tinent of Africa, but became . eS Pe Fic. 131. EprroMe oF PRoporTION Evo- LUTION IN THE PROBOSCIDEA. These animals originated in the Pal@o- mastodon (lower), frequenting the an- cient borders of the Nile in Egypt dur- ing Oligocene time, which developed during a period of 1,500,000 years into the existing types of the Indian and African elephants and into the ancient type of the Elephas (upper). Restoration in the American Museum of Natural History under the direction of the author, painted by Charles R. Knight. extinct; and, thirdly, a series of forms, such as the zeuglodons, ancestral whales, sirenians, manatees, and dugongs, which emerged from this African home and enjoyed a very wide dis- 270 THE ORIGIN AND EVOLUTION OF LIFE tribution in the northern hemisphere and in the equatorial regions. Among the giant tribes which issued from this ancient con- tinent the evolution of the proboscidians gives us an instance of the most extreme divergence of a terrestrial type from a related family, the sirenians, which evolve into the aquatic, fluviatile, and littoral type of the existing sea-cows and man- atees. In the transformation of Paleomastodon (Fig. 131) into Elephas there are notable changes of proportion as well as the loss of many characters, as seen in the disappearance of eae the lower tusks, the enlarge- Fic. 132, THe Icr-FIELDS OF THE ment and curvature of the up- FourtTH GLACIATION. . per tusks, the elongation of the Southward extension of the ice-fields over the northeastern United States proboscis, the abbreviation of during the period of the fourth glacia- tion. After studies of Chamberlain. the skull, the elongation of the eta aas limbs, the relative abbreviation of the vertebree of the neck and of the backbone, the reduction of the tail. The limbs become of the weight-bearing type, the hind limbs attaining proportions which converge toward those of the titanothere Brontotherium (Fig. 127). The final numerical loss of characters as witnessed in the very gradual reduction of the lower tusks affords an instance of the leisurely methods of nature, for the process requires 2,000,000 years in the elephant line while in the mastodon line the lower tusks were still pres- ent at the time of the comparatively recent extinction of this animal, which occurred since the final glaciation of North America. The loss of parts through retardation is also seen CHANGES OF PROPORTION in the reduction of the number of the pairs of grinding teeth, from seven to six and finally in the adult modern elephant stage to one. The addition of new characters is principally observed in the remarkable evolution of the plates of the grind- ing teeth and of the elaborate muscular system of the pro- boscis. It is very important to note that, as in the evolution of the horses (p. 263), this evolution independently follows sim- ilar lines among the Proboscidea throughout all parts of the world. In other words, the unity of the evolution of the proboscidians in various parts of the world was not main- ae a Fic. 133. GRoUPS OF REINDEER (Rangifer tarandus) AND WooLtty Mammotu (Elephas primigenius). Conditions of the reindeer-mammoth period of Europe during the maximum cold of the fourth glaciation of the Glacial Epoch. Mural painting in the American Museum of Natural History, painted by Charles R. Knight, under the direction of the author. tained by interbreeding, but by the unity of ancestral heredity and the unity of the actions, reactions, and interactions of the animals with their environment. Widely separated de- scendants of similar ancestors may evolve in a closely but not entirely similar manner. The resemblances are due to the independent gain of similar new characters and loss of old characters. The differences are chiefly due to the unequal ve- locity of characters; in some lines certain characters appear or disappear more rapidly than others. The general fact that the slow-breeding elephants evolved very much more rapidly than the frequently breeding rodents, such as the mice and rats (Muridz), is one of the many evi- dences that the rate of evolution may not be governed by the frequency of natural selection and elimination. For example, 272 THE ORIGIN AND EVOLUTION OF LIFE in the murine family of rodents, the annual progeny is very numerous and reproduction is very frequent, while among the elephants there is only a single offspring and reproduction is comparatively infrequent, yet the grinding teeth of the Pro- boscidea evolve far more rapidly and into much more highly complicated structures than the grinding teeth of any of the Fic. 134. PLEISTOCENE OR GLACIAL ENVIRONMENT OF THE WOooOLLy RHINOCEROS. Rhinoceros tichorhinus, of northern Europe, a contemporary of the woolly mammoth. Restoration in the American Museum of Natural History, painted by Charles R. Knight, under the direction of the author. rapidly breeding rodents. If evolution were due to the natural selection of chance variations this would not be the case. The elephants, like the horses, afford an example of superb mechanical perfection in a single organ, the teeth, evolved in relatively slow-breeding forms, within a relatively short period of geologic time. In their grinding-tooth structure the Probos- cidea closely interlock with their environment, that is, there are complete transitions of dental structure between partly grazing, partly browsing, and exclusively browsing forms, such CHANGES OF PROPORTION 273 as the mastodon. The psychic and bodily adaptability and plasticity of the Proboscidea to extreme ranges of habitat is paralleled only by the human adaptation to extremes of climate which is achieved through the intelligence of man. The woolly Fic. 135. PyGMiEs oF THE HILLS CoMPARED WITH THE PLAINSMEN OF WEST CENTRAL New GuIneEa. From Rawling’s Land of the New Guinea Pigmies, by permission of Seeley, Service & Co.—The question arises whether the dwarfing is due to natural selection, to prolonged unfavorable environment, or to abnormal internal secretions of certain glands like the thyroid. It will be observed that the dwarfing is disproportional, the heads being relatively large. Compare the dwarfed sheep and dog in Figs. 119 and 120. mammoth (Fig. 131) presents one extreme of proboscidian adaptation, comparable to the Eskimo among human races as superbly adapted to the rigors of the arctic climate, while the hairless African and Indian elephants are comparable to the hairless human races living under the equator. 274 THE ORIGIN AND EVOLUTION OF LIFE Undoubtedly the most promising field for future paleon- tological research and discovery is in Asia. The links in the series of mammals—especially in the line known as the Pri- mates leading into the ancestors of man, namely, the Lemurs, Monkeys, and Apes—are probably destined to be found in this still very imperfectly explored continent, for it is indicated by much evidence that the still unexplored region of northern Asia was a great centre of animal population and of adaptive radiation into Europe on the west and into North America on the northeast. Ancient vertebrate fossils from this vast region are as yet absolutely unknown, but will doubtless be discovered, and it is here that the Eocene, and perhaps the Oligocene ancestors of man are likely to be unearthed, that is, in deposits of the first half of the Tertiary Period. Fos- sil records of the descent of man during the second half of the Tertiary also, namely, from the Oligocene Epoch to the close of the Pliocene time, we believe may -be discovered in Asia, most probably in the region lying south of the Hima- layas. _ This subject of prehuman ancestry and evolution is re- served for the concluding series of Hale Lectures, but in our search for suggestions as to the causes of evolution, especially along the lines of internal physicochemical factors and the doctrine of energy, man himself is proving to be one of the most helpful of all mammals because chemically, physically, and experimentally man is the best known of all organisms at the present time. RETROSPECT AND PROSPECT 275 RETROSPECT AND PROSPECT The initial question raised in this volume arises as soon as we undertake a summary of evolution as we see it in the retrospect of the ages. Does the energy conception of evolution bring us nearer to the causes either of the origin or of the transformation of characters? Before answering these crucial questions let us see what our brief survey has taught us as to the kind of causes to look for. The foregoing comparison in the second part of this vol- ume of the evolutionary development that has taken place in many series of animals belonging to the five great classes of vertebrates—fishes, reptiles, amphibians, birds, and mam- mals—in response to twelve different kinds of environment, gives repeated evidence of their continuous powers of ever- plastic adaptation, not only to one kind of physical and life environment, but to any direct, reversed, or alternating change of environment which a group of animals may en- counter either on its own initiative or by force of circum- stances. In the large vertebrates we are enabled to observe and often to follow in minute details this continuous adaptation not merely in one, but in hundreds and sometimes in thou- sands of characters. In this respect a vertebrate differs from a relatively simple plant organism like the pea or the bean on which some of the prevailing conceptions of evolution have been grounded. In the well-ordered evolution of these single characters we have a picture like that of a vast army of sol- diers; the organism as a whole is like the army; the “‘char- acters”? are like the individual soldiers; and the evolution of each character is coordinated with that of every other char- 276 THE ORIGIN AND EVOLUTION OF LIFE acter. Sometimes a character lags behind and through failure to keep pace produces the dysteleogy or imperfect fitness of certain parts of the organism observed by Metchnikoff in the human body. Sometimes there are serial regiments of such well-ordered characters which are exactly or closely alike—for example, the 1og2 teeth in the upper jaw of the iguanodont dinosaur, Trachodon, all very similar in appearance, all evolving and all perfectly coordinated in form and function with the gro teeth in the lower jaw of the same animal. There are other serial regiments of characters, however, like the vertebre in the backbone of a large dinosaur, for example, in which every single character, large and small, is different in form from every other. These are among the many miracles of adapta- tion referred to in the Preface. The evidence for this continuous and more or less adaptive direction in the simultaneous evolution of numberless char- acters which can be observed only by means of an ancestral fossil series was unknown to the master mind of Darwin during the preparation of his ‘Origin of Species” through his observations on the variations of domestic animals and plants between 1845 and 1858; for it was not until the dis- covery by Waagen, in 1869, of a continuous series of fossil ammonites, in which minute changes originate and can be followed continuously, that the rudiments of a true concep- tion of the orderly and continuous modes of evolution which prevail in nature were reached. Among invertebrates and vertebrates, this conception has been abundantly confirmed by modern paleontology in all its branches, namely, that of a well-ordered continuity as the prevailing mode of evolu- tion. This is the greatest contribution which paleontology has made to biology and to natural philosophy. RETROSPECT AND PROSPECT 277 Discontinuity is found chiefly in those characters in which a continuous mode of change is impossible. As to the physico- chemical constitution of animals and plants it has been well said that there can be no continuity between two distinct chemical formule, or in many physicochemical functions and reactions. There are also certain form and proportion char- acters in which continuity is impossible—for example, the sudden addition of a new tooth to the jaw, or of a new verte- bra to the backbone. From these well-ascertained facts of the sudden or salta- tory appearance of characters, some have rashly inferred that there can be no continuity between species, whereas it is now known in mammalogy, in paleontology, and to a less extent in ornithology that a large number of so-called species in nature show a complete continuity. Although the part which sudden changes or “‘saltations” from character to char- acter play in experimental evolution and artificial selection is very prominent, it remains to be seen how large a part they play under natural conditions. We realize that it is far more difficult to ascertain the causes of such continuous independent and more or less orderly and adaptive evolution of single characters than to comprehend evolution as Darwin’s adherents of the present day imagine it to be, namely fortuitous and saltatory, for it is incumbent upon us to discover the cause of the orderly origin of every single character. The nature of such a law we cannot even dream of at present, for the causes of the majority of vertebrate adap- tations remain wholly unknown. Negatively we may say from paleontology that there is positive disproof of the existence of an internal perfecting principle or entelechy of any kind which would impel animals to evolve in a given direction regardless of the direct, reversed, THE ORIGIN AND EVOLUTION OF LIFE or alternating directions taken by the organism in seeking its life environment or physical environment. It is true, we have found (p. 264) among the descendants of similar, though remote, ancestors something determinate or definite—a similarity which reminds us of the potential of the physicist—as to the origin of certain characters rather than others in the heredity-chromatin. It is as if certain latent power or potency of character-origin in the chromatin were there waiting to be called forth. It is partly due to this, as well as to inheritance of a similar ancestral form, that the “mammals, as studied by the comparative anatomist, are so much alike, despite their superficial differences as seen by the student of adaptation. This definite or determinate origin of certain new characters appears to be partly a matter of hereditary predisposition. That is, animals from a common ‘stock independently give rise at different times to similar new characters, as seen, for example, in the origin of similar horn defenses and similar bony and dental structures. The conclusive evidence against an éan vital or internal perfecting tendency, however, is that these characters do not spring up autonomously at any time; they may lie dor- mant or remain rudimentary for great periods of time, and here we find a correspondence which may be only an analogy with the principle of Jatent energy in physics. They require something to call them forth, to make them active, so to speak. It is in this function of arousing such character predis- positions that the chemical messenger phenomena of inter- action in the organism present some analogy to latent energy, although future experiment may prove that this does not con- stitute a real cause or likeness. If the transformation of energy ‘is accelerated in certain organs or parts of existing organs by the RETROSPECT AND PROSPECT 279 arrival of interacting chemicai messengers and these parts thereby change their form and proportions, it is not incon- ceivable that chemical messengers may arouse a latent new character by stimulating the transformation of energy at a specific point. Then character-velocity must be considered. Although we may find that in the course of evolution in one group of animals a character moves extremely slowly, it lags along, it is retarded, as if partly suffering from inertia, or perhaps, for a while it stops altogether; yet in another group we may find that the very same character is full of life and velocity, it is accelerated like the alert soldier in the regiment. Here again is a point where the energy conception of evolution may throw a gleam of light. Some of the phenomena of interaction in the organism give us the first insight into the possible causes of the slow or rapid movement of character evolution—of its acceleration and retardation. Such individual character move- ments may govern the proportions of certain parts as well as of all parts of the organism. Combined, these character velocities and movements create all the extraordinary differences of proportion which dis- tinguish the mammals—for example, the extraordinarily long neck of the giraffe, the short neck of the elephant, the elongated skull of the ant-eater, the abbreviated head of the tree sloth. Wherever such changes of proportion weigh in the struggle for existence they may be hastened or retarded by natural selection. We discover that the chief principles of comparative anatomy formulated by Aristotle, Cuvier, Lamarck, Goethe, St. Hilaire, Dohrn, and other philosophic anatomists' may all be expressed anew in terms treating the organism as a 1 Russell, E. S., 1916. 280 complex of energies. THE ORIGIN AND EVOLUTION OF LIFE This is shown in a final scheme of action, reaction, and interaction! which is an elaboration of the simplified scheme expressed on page 16 of the Introduction, as follows: COORDINATED ACTIVITY OF THE ORGANISM WITHIN ITSELF ACTION AND REACTION of certain parts Chemical synthesis proteins, fats, carbohydrates Heat and Motion Nutrition, digestion Respiration oxidation, etc. Secretion Circulation Muscular and Skeletal system, etc. organs of Jocomotion Reproductive system: ovary and testis tis- sues surrounding heredity-germ cells All other phenomena under the laws of Transformation, Stor- age, and Release of Energy. INTERACTION Physicochemical A gents Catalyzers enzymes Internal secretions hormones (accelerators), chalones (retarders), Nervous system accelerators, retarders, inhibitors Functions of Organs Balance, Equilibrium arrested development Acceleration growth, development Retardation atrophy, degeneration Correlation Compensation reciprocal atrophy and hypertrophy ACTION _ AND REACTION of other parts Chemical synthesis proteins, fats, carbohydrates Heat and Motion Nutrition, digestion Respiration oxidation, etc. Secretion Circulation Muscular and Skeletal system, etc. organs of locomotion Reproductive system: ovary and testis tis- sues surrounding heredity-germ cells All other phenomena under the laws of Transformation, Stor- age, and Release of Energy. io The eternal question remains, How do these energy phe- nomena which govern the life, form, and function of the organ- ism interact with the supposed latent and potential energy phenomena of the heredity-germ cells? As stated in the Pref- ace and Introduction, this question can only be answered by experiment. There is no proof at present. 1This notion of coordinated activity is particularly well expressed in Mathews’s Physiological Chemistry (1916), a volume which came to the author after this work was written (see Appendix, Notes V and VI). CONCLUSION 281 CONCLUSION In the foregoing pages we have attempted to sketch in broad outlines the course of the origin and evolution of life upon the earth in the light of our present imperfect knowl- edge, which offers few certainties to guide us and probabilities and possibilities innumerable among which to choose. The difference between the non-living world and the living world seems like a vast chasm when we think of a very high organism like man, the result of perhaps a hundred million years of evolution. But the difference between primordial earth, water, and atmosphere and the lowliest known organisms which secure their energy directly from simple chemical com- pounds is not so vast a chasm that we need despair of bridging it some day by solving at least one problem as to the actual nature of life—namely, whether it is solely physicochemical in its energies, or whether it includes a plus energy or element which may have distinguished Lire from the beginning. The energy conception of the origin and evolution of life, on which are based our fresh stimulus to experiment and re- newed hope of progress in solving the riddle of Heredity, is as yet in its infancy. Our vision will doubtless be amplified by experiment. In seeking the causes of the complex adapta- tions even of the simplest organisms described in Chapters III and IV we soon face the boundaries of the unknown, boundaries which human imagination entirely fails to pene- trate, for Nature never operates as man expects her to, and we believe that imagination itself is strictly limited to recombina- tions of ideas which have come through observation. It may be said that the bulk of experimental work hitherto has been in the domain of action and reaction—here lie all the simple energy processes of growth, of waste and repair, of use 282 THE ORIGIN AND EVOLUTION OF LIFE and disuse, of circulatory, muscular, digestive, and nervous action. Lamarckism has sought in vain for evidences of the inheritance of the effects of such action and reaction processes. Experiment and observation in the mysterious field of in- teraction are relatively new, yet they are now being pressed with intensity by many workers. There is an encouraging likeness—pointed out in many parts of this volume—between some of the effects visibly produced in the body by internal secretions and other chemical messengers, and certain of the familiar processes of germ evolution, especially in adaptation through changes of proportion (see p. 268) of various parts of the body—a kind of adaptation which is of great importance in all animals. And while this likeness between interaction and germ evolution may be mere coincidence and have no deeper significance, it is also possible that it may betoken some real similarity of cause. For our theory of action, reaction, and interaction—which is fully set forth and illustrated in the second and third chap- ters of this work, dealing with biochemical evolution and the evolution of bacteria and alge, as well as in certain sections of the chapters describing the evolution of the vertebrates— it may be claimed that it brings us somewhat nearer a consis- tent physicochemical conception of the original processes of life. If our theory is still far from offering any conception of the nature of Heredity and the causes of elaborate Adaptation in the higher organisms, it may yet serve the desired purpose of directing our imagination, our experiment, and our observa- tion along lines whereby we may attain small but real advances into the unknown. As pointed out in our Preface and Intro- duction the only processes in inorganic Nature and in living organisms themselves which are in the least suggestive of the processes of Heredity are some of the processes of interaction. CONCLUSION 283 We know, for example, that certain cells of the reproduc- tive glands' have a profound and commanding influence on all the body cells, including even the brain-cell centres of thought and intelligence—all this is, in a sense, an outflowing from the heredity-germ region, a centrifugal interaction. Is there any reversal of this process, any inflowing or centripetal in- teraction whereby chemical messengers from any part of the body specifically affect the heredity-germ, and thus the new or- ganism to which it will give rise? This is one of the first | things to be ascertained by future experiment. Being still at the very beginning of the problem of the causes of germ evolution—a problem which has aroused curi- osity and baffled inquiry throughout the ages—it were idle to entertain or present any settled conviction in regard to it, yet we cannot avoid expressing as our present opinion that these causes are internal-external rather than purely internal— in other words, that some kind of relation exists between the actions, reactions, and interactions of the germ, of the organ- ism, and of the environment. Moreover, this opinion is prob- ably capable of experimental proof or disproof. We may well conclude with the dictum of Francis Bacon,? one of the first natural philosophers to counsel experiment, who in his Novum Organum (1620) shows that living objects are well adapted to experimental work, and points out that it is possible for man to produce variations experimentally: “ They |i. e., the deviations or mutations of Na- ture] differ again from singular instances, by being much more apt for practice and the operative branch. For it would be very difficult to generate new species, but less so to vary known species, and thus produce 1 Goodale, H. D., 1916; Lillie, Frank R., 1917. 2 Bacon, Francis, 1620, book II, sec. 29, p. 180. \ | 284 THE ORIGIN AND EVOLUTION OF LIFE many rare and unusual results. The passage from the miracles of nature to those of art is easy; for if nature be once seized in her variations, and the cause be manifest, it will be easy to lead her by art to such deviation as she was at first led to by chance; and not only to that but others, since deviations on the one side lead and open the way to others in every direction.” APPENDIX In the following citations from the recent works of friends all but one of which have come into the author’s hands since the present volume was written, the reader will find not only an amplification by Gies (Note I) and Loeb (Notes III and IV) of certain passages in the text, but in Notes V and VI original views previously and independently expressed by Mathews, which are somewhat similar to those the author has developed under the law of interaction. NOTE I DIFFERENT MODES OF STORAGE AND RELEASE OF ENERGY IN LIVING ORGANISMS! “The elements referred to” (‘This energy is distributed among the eighty or more chemical elements of the sun and other stars,” p. 18) “are available to plants, in the first place, in the form of compound substances only, simple though those substances are, such as water, carbon dioxid, nitrate, phosphate, etc. When these substances are taken from the air and soil into plants they are reduced in the main, that is, the elements are combined there into new groupings with a storage of energy, the effective radiant kinetic energy from the sun becoming potential energy in the con- stituents of plants. Plant substances are eaten by herbivorous animals, that is to say, these substances are hydrolyzed and oxidized in such animals; the elements are, in the main, ‘burst asunder’ into new group- ings, with the release of energy, the stored potential energy becoming kinetic. Carnivorous and omnivorous animals obtain plant substances, either directly or in the form of animal matter from herbivorous animals, thus, in effect, doing what herbivorous animals do, namely, using plant substances by disintegrating them with the release of energy.” NOTE II BLUE-GREEN ALG POSSIBLY AMONG THE FIRST SETTLERS OF OUR PLANET? “Tn 1883 the small island of Krakatau was destroyed by the most vio- lent volcanic eruption on record. A visit to the islands two months after the eruption showed that ‘the three islands were covered with pumice 1W. J. Gies, letter of May 16, 1917. 2 Loeb, Jacques, 1916, The Organism as a Whole, p. 21. 285 286 APPENDIX and layers of ash reaching on an average a thickness of thirty metres, and frequently sixty metres.’} Of course all life on the islands was extinct. When Treub in 1886 first visited the island, he found that blue-green alge were the first colonists on the pumice and on the exposed blocks of rock in the ravines on the mountain-slopes. Investigations made during sub- sequent expeditions demonstrated the association of diatoms and _ bac- teria’’ [with the alge]. “All of these were probably carried by the wind. The alge referred to were according to Euler of the nostoc type. Nostoc does not require sugar, since it can produce that compound from the CO, of the air by the activity of its chlorophyll. This organism possesses also the power of assimilating the free nitrogen of the air. From these obser- vations and because the Nostocacee generally appear as the first settlers on sand the conclusion ‘has been drawn that they or the group of Schizo- phycee to which they belong formed the first settlers of our planet.’’? NOTE III ONE SECRET OF LIFE—-SYNTHETIC TRANSFORMATION OF INDIFFERENT MATERIAL? “The essential difference between living and non-living matter con- sists then in this: the living cell synthetizes its own complicated specific material from indifferent or non-specific simple compounds of the sur- rounding medium, while the crystal simply adds the molecules found in its supersaturated solution. This synthetic power of transforming small ‘building stones’ into the complicated compounds specific for each or- ganism is the ‘secret of life’ or rather one of the secrets of life.” NOTE IV INTERACTION THROUGH CATALYSIS—-THE ACCELERATION OF CHEMICAL REACTIONS THROUGH THE PRESENCE OF ANOTHER SUBSTANCE WHICH IS NOT CONSUMED BY THE REACTION! “The discovery of Lavoisier and La Place left a doubt in the minds of scientists as to whether after all the dynamics of oxidations and of chemical reactions in general is the same in living matter and in inanimate matter. ... The way out of the difficulty was shown in a remarkable article by Berzelius.» He pointed out that in addition to the forces of 1Ernst, A., The New Flora of the Volcanic Island of Krakatau, Cambridge, 1908. 2 Euler, H., Pflanzenchemie, 19009, ii and iii, 140. 3 Loeb, Jacques, 1916. The Organism as a Whole, p. 23. 4 Loeb, Jacques, 1906. The Dynamics of Living Matter, pp. 7, 8. 5 Berzelius, Einige Ideen tiber eine bei der Bildung organischer Verbindungen in der lebenden Natur wirksame aber bisher nicht bemerkte Kraft. Berzelius u. Woehler, J ahresberichkt, 1836. APPENDIX 287 affinity, another force is active in chemical reactions: this he called cata- lytic force. As an example he used Kirchhoff’s discovery of the action of ilute acids in the hydrolysis of starch to dextrose. In this process the acid is not consumed, hence Berzelius concluded that it did not act through _ its affinity, but merely by its presence orits contact. . . . He then suggests that the specific and somewhat mysterious reactions in living organisms might be due to such catalytic bodies as act only by their presence, without being consumed in the process. He quotes as an example the action of diastase in the potato. ‘In animals and plants there occur thousands of catalytic processes between the tissues and the liquids.’ The idea of Berzelius has proved fruitful. . .. We now know that we have no right to assume that the catalytic bodies do not participate in the chemical reaction because their quantity is found unaltered at the end of the reac- tion. On the contrary, we shall see that it is probable that they can ex- ercise their influence only by participating in the reaction, and by form- ing intermediary compounds, which are not stable. The catalyzers may be unaltered at the end of the reaction, and yet participate in it. “Tn addition we owe to Wilhelm Ostwald! the conception that the cata- lyzer does not as a rule initiate a reaction which otherwise would not occur, but only accelerates a reaction which otherwise would indeed occur, but too slowly to give noticeable results in a short time.” NOTE V THE CAUSES OR AGENTS OF SPEED AND ORDER IN THE REACTIONS OF LIVING BODIES—ENZYMES, COLLOIDS, ETC.? “There is still another feature of cell chemistry which must strike even the most superficial observer, and that is the speed with which growth and the chemical reactions occur in it... . Starch boiled with water does not easily take on water and split into sweet glucose, but in the plant cell it changes into sugar under appropriate conditions very rapidly. How does it happen then that the chemical changes of the foods go on so rapidly in living matter and so slowly outside? This is owing to the fact, as we now know, that living matter always contains a large number of sub- stances, or compounds, called enzymes (Gr. en, in; zyme, yeast; in yeast) because they occur in a striking way in yeast. These enzymes, which are probably organic bodies, but of which the exact composition is as yet unknown, have the property of greatly hastening, or as is generally said, catalyzing, various chemical reactions. The word catalytic (kata, down; lysis, separation) means literally a down separation or decomposition, but 1Qstwald, W., Lehrbuch der allgemeinen Chemie, vol. II, 2d part, p. 248, 1902. 2 Mathews, Albert P., Physiological Chemistry, pp. 10-12. 288 APPENDIX it is used to designate any reaction which is hastened by a third substance, this third substance not appearing much, if at all, changed in amount at the end of the reaction. Living matter is hence peculiar in the speed with which these hydrolytic, oxidative, reduction, or condensation reactions occur in it; and it owes this property to various substances, catalytic agents, or enzymes, found in it everywhere. Were it not for these sub- stances reactions would go on so slowly that the phenomena of life would be quite different from what they are. Since these catalytic substances are themselves produced by a chemical change preceding that which they catalyze, we might, perhaps, call them the memories of those former chem- ical reactions, and it is by means of these memories, or enzymes, that cells become teachable in a chemical sense and capable of transacting their chemical affairs with greater efficiency. Whether all our memories have some such basis as this we cannot at present say, since we do not yet know anything of the physical basis of memory. “Living reactions have one other important peculiarity besides speed, and that is their ‘orderliness.’ The cell is not a homogeneous mixture in which reactions take place haphazard, but it is a well-ordered chemical factory with specialized reactions occurring in various parts. If proto- plasm be ground up, thus causing a thorough intermixing of its parts, it can no longer live, but there results a mutual destruction of its various structures and substances. The orderliness of the chemical reactions is due to the cell structure; and for the phenomena of life to persist in their entirety that structure must be preserved. It is true that in such a ground- up mass many of the chemical reactions are presumably the same as those which went on while structure persisted, but they no longer occur in a well-regulated manner; some have been checked, others greatly increased by the intermixing. This orderliness of reactions in living protoplasm is produced by the specialization of the cell in different parts... . Thus the nuclear wall, or membrane, marks off one very important cell region and keeps the nuclear sap from interacting with the protoplasm. Pro- found, and often fatal, changes sometimes occur in cells when an admix- ture of nuclear and cytoplasmic elements is artificially produced by rup- ture of this membrane. Other localizations and organizations are due to the colloidal nature of the cell-protoplasm and possibly to its lipoid char- acter. By a colloid is meant, literally, a glue-like body; a substance which will not diffuse through membranes and which forms with water a kind of tissue, or gel. It is by means of the colloids of a protein, lipoid, or car- bohydrate nature which make up the substratum of the cell that this localization of chemical reactions is produced; the colloids furnish the basis for the organization or machinery of the cell; and in their absence there could be nothing more than a homogeneous conglomeration of re- actions. The properties of colloids become, therefore, of the greatest APPENDIX 289 importance in interpreting cell life, and it is for this reason that they have been studied so keenly in the past ten years. The colloids localize the cell reactions and furnish the physical basis of its physiology; they form the cell machinery.” NOTE VI INTERACTIONS OF THE ORGANS OF INTERNAL SECRETION AND HEREDITY! The following table expresses the action of some of the organs of internal secretion: On PROTEIN METABOLISM Stimulating Inhibiting (accelerating) (retarding) Thyroid Pancreas Pituitary body Parathyroids Suprarenal glands and _ other adrenalin-secreting tissue Reproductive glands On Catcrtum RETENTION Favorable to Inhibiting Pituitary body Reproductive glands Thyroids Parathyroids The facts that are here presented show that the action of the anterior lobe of the pituitary body upon the chemical changes or transformations taking place in the vertebrate organism or in any of its cells strongly re- sembles the action of the thyroid, although less pronounced. It is clear from its relation to the reproductive organs, to the adrenalin-secreting tissues of the suprarenal glands and other similar tissues, and to the formation of an abnormal amount of glucose in the urine, that the pituitary body, thyroids, reproductive glands, suprarenals, and thymus are a closely related series of organs which mutually influence each other’s growth. Important as these organs are, it must be remembered that the co- ordination of all the chemical changes and transformations within the body—all processes of renewal, change, or disorganization such as respira- tion, nutrition, excretion, etc.—embraces every organ in it. The body is an organic whole, and the so-called organs of internal secretion are not unique, but the bones, muscles, skin, brain, and every part of the body are furnishing internal secretions necessary to the development and proper 1 Mathews, Albert P., 1916. Physiological Chemistry, pp. 649, 650 (modifled). 290 APPENDIX functioning of all the other organs of the body. A scheme of the organs of internal secretion, to be complete, must embrace every organ, and so far only the barest beginning has been made in this study so important, so necessary for the understanding of development and jnheritance. Prob- lems of development and inheritance cannot be solved until these physio- logical questions are answered. As for the bearing of these processes upon Heredity, the internal secre- tions of the body appear to Mathews to constitute strong evidence against the existence of such things as inheritance by means of structural units in the germ which represent definite characters in the body. We see in the internal secretions, he observes, that every character in the body involves a large number of factors (i. e., determiners). The shape and size of the body, the coarseness of the hair, the persistence of the milk-teeth, a ten- dency toward fatness—all these may easily depend on the pituitary body, on the thyroid, and on the reproductive organs, and these—in their turn —are but the expression of other influences played upon them by their surroundings and their own constitution. An accurate examination shows the untrustworthiness of any such simple or naive view as that of unit characters. NOTE VII TABLE—RELATIONS OF THE PRINCIPAL GROUPS OF ANIMALS REFERRED TO IN THE TEXT Phylum Class PAGES PROTOZOA { 1Rhizopoda [ Lobosa—A meba, etc........... 93, 112, 114, 116 (the simplest Foraminifera (porous-shelled protozoa) animals) 32, 103, 115 Radiolaria (siliceous-shelled protozoa)..... II5 Mastigophoraiccciccase bso ssee eG Damemece ine en ead ey 112,115 Infusoria—ciliates, etc...... 0. cece eee eee 112,115 | Sporozoa PoRIFERA 1Calcarea Calcareous sponges (sponges) 1Non-Calcarea { Siliceous Ee PP iisie nsitele tat deta 130 Fibrous # C@LENTERATA 1Hydrozoa Hydroids—millepores. ............0.00 0 113 Siphonophores Graptolithida 1Scyphozoa Jelly fishes’. cio dey seyse teens sees 120, 129, 130 1Actinozoa Sea-anemones, corals, sea-fans, etc........ 103 Ctenophora 1¥Fossil and recent forms. All other classes listed are as yet unknown in the fossil state. APPENDIX Phylum PLATYHELMINTHES Class Turbellaria Trematoda Cestoda Nematoda Acanthocephala 1Chetognatha NEMATHELMINTHES TROCHELMINTHES Rotifera Mo.Liuscompa 1Polyzoa Phoronida 1 Brachiopoda 1Asteroidea 1Ophiuroidea 1Echinoidea 1Holothuroidea 1Crinoidea 2Cystoidea 2Blastoidea EcHINODERMATA (true worms) Gephyrea ANNULATA 1Chetopoda Hirudinea Branchiata 1Crustacea ARTHROPODA *Trilobita !Xiphosura Tracheata Onychophora 'Myriapoda 1Arachnoidea | UInsecta Mo.tusca 1Pelycypoda 1Amphineura 1Gastropoda 1Scaphopoda 1Cephalopoda 1 Fossil and recent forms. 2 Extinct fossil forms. 291 PAGES Flat worms Flukes Tape-worms Round worms Hook-headed worms AITOW-WOIMS . 0.20066 c ee cee ee eee es 6120, 129 Wheel-animalcules Bryozoa (moss animals) Lamp-shells............. 120, 123, 130, 138, 140 Sea-stars, starfishes................. 136, 172 Brittle stars SeA-UTCHINGE aa wiAvomawaiekedscckanes eee 94 Sea-cucumbers.................0000- 125,127 Sea-lilies (stone-lilies).................. 66 primitive echinoderms Sea-worms, earthworms................ 128 Sipunculids Leeches Crabs, lobsters, shrimp, barnacles, ostra- COS a camsanetare am lanng sane Arn I0ts 120, 124,134 Trilobites, eurypterids....... I21, 125, 132,133 Horseshoe crabs................. 124, 125,132 Peripatus Centipedes, millepedes Spiders, scorpions, mites, ticks... .130, 132, 136 INSECtS oo feisediew one aut ee eo 105, 130, 136, 254 Clams, oysters, mussels................. 130 Chitons Limpets, snails, slugs, sea-hares, etc... .120, 130 Tusk-shells Nautilus, cuttle-fish, ammonites. ..130, 137-139 All other classes listed are as yet unknown in the fossil state. 292 APPENDIX Phylum Class CHORDATA Sub-phylum Adelochorda.................04. Uroehord as ys aseelawiex sbatnew s4% Vertebrata Acrania Cyclostomata 1 Pisces (fishes) 1 Amphibia 1Reptilia 1Aves (birds) 1Mammalia 1 Fossil and recent forms. PAGES Balanoglossus, etc-—worm-like chordates Ascidians, salps, etc.—sessile and secon- darily free-swimming marine chordates, 162, 168 Amphioxus (lancelets)...............4.. 162 Lampreys; bagsis¢ 24.15 eae ene ienemen es 168 ( Ostracodermata (Palzozoic shelly-skinned || ARSHES ices aia-as ced aeicke Rpcaaanomaan | 101, 165-168 Arthrodira (Paleozoic joint-necked fishes) 166-168 Elasmobranchii—sharks, rays, chimeroids 161, 167-169 Dipnoi (lung-fishes).............. 168, 170, 172 Teleostomi.. 1... ..... 000000 e ee eee 173 lobe-finned ganoids (Crossopterygii) 168, 172,174 true ganoids—sturgeons, garpike, Dowfins, €tCi cic. s eniuad ea eee age 168, 170 teleosts (bony fishes).........168, 170,175 Frogs, toads, newts, mud-puppies, Stego- GepWalia, Cte 2 cnccece ap adaes wean eac 177-183 Turtles, tortoises, tuateras, lizards, mosa- saurs, snakes, crocodilians, dinosaurs, mammal-like reptiles, ichthyosaurs, ple- siosaurs, pterosaurs (flying reptiles), etc. 184-226 Reptile-like birds (Arch@opteryx)...... 226-229 Modernized birds.................... 227-231 “Ratite” birds—ostriches, moas, etc. 228, 229 “Carinate” birds—toothed birds and all other birds................. 230, 231 Monotremes (egg-laying mammals)— duck-bills, etc... 0... 0. 235,273 Marsupials (pouched mammals)—opos- sums, kangaroos, etc...... 235, 237, 243, 244 Placentals insectivores, carnivores, primates, ro- dents, bats, whales, artiodactyls (cattle, deer, pigs, antelopes, giraffes, camels, hippopotami, etc.), ungulates including proboscidea (mastodons and elephants) and perissodactyls (horses, tapirs, rhi- noceroses, titanotheres, etc.), and many other orders... 0.2.0... 2: eee ee eee 259-274 All other classes listed are as yet unknown in the fossil state. 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