© 1999 Macmillan Magazines Ltd The Thomas Jefferson paternity case The DNA analysis of Y-chromosome haplo- types used by Foster et al.1 to evaluate Thomas Jefferson’s alleged paternity of Eston Hemings Jefferson, the last child of his slave Sally Hemings, is impressive. How- ever, the authors did not consider all the data at hand in interpreting their results. No mention was made of Thomas Jeffer- son’s brother Randolph (1757–1815), or of his five sons2,3. Sons of Sally Hemings con- ceived by Randolph (or by one of his sons) would produce a Y-chromosome analysis identical to that described by Foster et al. Further collaborative data (for example, the whereabouts of any of those who might have been involved at conception) are needed to confirm that Jefferson did indeed father his slave’s last child, as claimed in the title. We know Thomas Jefferson was there, but how about Randolph Jefferson and his sons? David M. Abbey Health Science Center, University of Colorado, 1512 Teakwood Court, Fort Collins, Colorado 80525, USA e-mail: dabbey1000@aol.com If the data of Foster et al. are accurate, then any male ancestor in Thomas Jefferson’s line, white or black, could have fathered Eston Hemings. Plantations were inbred communities, and the mixing of racial types was probably common. As slave families were passed as property to the owner’s off- spring along with land and other property, it is possible that Thomas Jefferson’s father, grandfather or paternal uncles fathered a male slave whose line later impregnated another slave, in this case Sally Hemings. Sally herself was a light mulatto, known even at that time to be Thomas Jefferson’s wife’s half sister3,4. Gary Davis Evanston Hospital, 2650 Ridge Avenue, Evanston, Illinois 60201, USA Foster et al. reply — It is true that men of Randolph Jefferson’s family could have fathered Sally Hemings’ later children. Space constraints prevented us from expanding on alternative interpretations of our DNA analysis, including the interesting one proposed by Davis. The title assigned to our study was misleading in that it repre- sented only the simplest explanation of our molecular findings: namely, that Thomas Jefferson, rather than one of the Carr broth- ers, was likely to have been the father of Eston Hemings Jefferson. It had been suggested to us earlier (by Herbert Barger, who also helped to recruit the descendants of Field Jefferson who par- ticipated in our study) that Isham Jefferson, son of Thomas Jefferson’s brother Ran- dolph, might have been the father of one or more of Sally Hemings’ children. Barger’s proposal was based on a statement5 that Isham was reared by Thomas Jefferson; he suggested that Isham could have been at Monticello or at Snowden (Snowden was across the James River from Scottsville, which is about 20 miles from Monticello) when Eston Hemings was conceived. But it is not known for certain that Isham was at Monticello at that time, whereas it is docu- mented that Thomas Jefferson was. From the historical knowledge we have, we can- not conclude that Isham, or any other member of the Jefferson family, was as likely as Thomas Jefferson to have fathered Eston Hemings. We know from the historical and the DNA data that Thomas Jefferson can neither be definitely excluded nor solely implicated in the paternity of illegitimate children with his slave Sally Hemings. When we embarked on this study, we knew that the results could not be conclusive, but we hoped to obtain some objective data that would tilt the weight of evidence in one direction or another. We think we have provided such data and that the modest, probabilistic interpretations we have made are tenable at present. E. A. Foster*, M. A. Jobling†, P. G. Taylor†, P. Donnelly‡, P. de Knijff§, R. Mieremet§, T. Zerjal¶, C. Tyler-Smith¶ *6 Gildersleeve Wood, Charlottesville, Virginia 22903, USA e-mail: eafoster@aol.com †Department of Genetics, University of Leicester, Adrian Building, University Road, Leicester LE1 7RH, UK ‡Department of Statistics, University of Oxford, South Parks Road, Oxford OX1 3TG, UK §MGC Department of Human Genetics, Leiden University, PO Box 9503, 2300 RA Leiden, The Netherlands ¶Department of Biochemistry, University of Oxford, South Parks Road, Oxford OX1 3QU, UK 1. Foster, E. A. et al. Nature 396, 27–28 (1998). 2. Mayo, B. & Bear, J. A. Jr Thomas Jefferson and his Unknown Brother (Univ. Press of Virginia, Charlottesville, 1981). 3. Brodie, F. M. Thomas Jefferson: An Intimate History (Norton, New York, 1974). 4. Randall, W. S. Thomas Jefferson: A Life (Holt, New York, 1993). 5. History of Todd County, Kentucky (1884). scientific correspondence 32 NATURE | VOL 397 | 7 JANUARY 1999 | www.nature.com qualitative adjustment. Rhea heart mass (267 grams) conforms to that predicted for a mammal of the same body size and aero- bic power. Volume densities of mitochon- dria in leg muscles are similar to those of mammals of the same size and aerobic capacity, whereas those in the relatively inactive flight muscles are only half as large and correspond to values reported for less aerobic mammals (Table 1). Given that 30% of the rhea’s body mass consists of leg musculature, rates of oxygen uptake by mitochondria per millilitre dur- ing locomotion at the aerobic maximum appear to fall within the range reported for mammals. Capillary densities in the rhea leg and flight muscles, like the mitochon- drial volume densities, also parallel values reported for the muscles of athletic and less mobile mammals. In contrast to the apparent conservation of structure–function relationships in most of the respiratory system, our results sug- gest that there are basic differences in the performance of the lungs of birds and mammals. We could not measure the lung volumes of the rheas directly, but in birds these are normally slightly more than half of those of mammals of the same mass7,8. The rheas therefore achieved maximum oxygen flux rates, equal to those of the most aerobic mammals of their size, using lungs that are probably only half as large. This supports the general belief that avian lungs provide relatively more function per unit volume than mammalian lungs8,9. Although the aerobic limits of rheas and athletic mammals are similar, the metabolic power available in practice, and their func- tional needs, are not. Unlike dogs, horses and other athletic mammals that sustain high metabolic rates for hours during pre- dation and migration, rheas do little or no sustained running and are poor at dissipat- ing metabolic heat loads10. Rheas have apparently not been under strong selective pressures like those that promoted the aero- bic power of extant running mammals. Large flightless birds lead fairly inactive lives, and may have lost the ability to fly primarily because of a lack of predation. Why rheas have an aerobic power that greatly exceeds their apparent functional needs remains a puzzle. Matthew W. Bundle*, Hans Hoppeler†, Ruth Vock†, June M. Tester*, Peter G. Weyand* *Museum of Comparative Zoology, Harvard University, Bedford, Massachusetts 01730, USA e-mail: pweyand@oeb.harvard.edu †Department of Anatomy, University of Bern, Buhlstrasse 26, CH 3000 Bern 9, Switzerland 1. Seeherman, H. J., Taylor, C. R., Maloiy, G. M. O. & Armstrong, R. B. Respir. Physiol. 44, 11–23 (1981). 2. Lasiewski, R. C. & Dawson, W. R. Condor 69, 13–23 (1967). 3. Ellington, C. P. J. Exp. Biol. 160, 71–91 (1991). 4. Brackenbury, J. H. & El-Sayed, M. S. J. Exp. Biol. 117, 349–355 (1985). 5. Kooyman, G. L. & Ponganis, P. J. J. Exp. Biol. 195, 199–209 (1994). 6. Weibel, E. R., Taylor, C. R. & Hoppeler, H. Proc. Natl Acad. Sci. USA 88, 10357–10361, (1991). 7. Maina, J. N. & King, S. A. J. Anat. 163, 67–73 (1989). 8. Dubach, M. Respir. Physiol. 46, 43–60 (1981). 9. Piiper, J. & Scheid, P. in Comparative Physiology (eds Bolis, L., Schmidt-Nielsen, K. & Maddrell, S. H. P.) 161–185 (North- Holland, 1973). 10. Taylor, C. R., Dmi’el, R., Fedak, M. & Schmidt-Neilsen, K. Am. J. Physiol. 51, 772–776 (1981).