Sexual dimorphism in Australopithecus afarensis was similar to that of modern humans
- *Matthew Ferrini Institute of Human Evolutionary Research, Department of Anthropology and Division of Biomedical Sciences, Kent State University, Kent, OH 44242; and †Division of Basic Medical Science, School of Medicine, Mercer College, Macon, GA 31207
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Communicated by Tim D. White, University of California, Berkeley, CA, May 29, 2003 (received for review January 5, 2003)
Abstract
The substantial fossil record for Australopithecus afarensis includes both an adult partial skeleton [Afar Locality (A.L.) 288-1, “Lucy”] and a large simultaneous death assemblage (A.L. 333). Here we optimize data derived from both to more accurately estimate skeletal size dimorphism. Postcranial ratios derived from A.L. 288-1 enable a significant increase in sample size compared with previous studies. Extensive simulations using modern humans, chimpanzees, and gorillas confirm that this technique is accurate and that skeletal size dimorphism in A. afarensis was most similar to that of contemporary Homo sapiens. These data eliminate some apparent discrepancies between the canine and skeletal size dimorphism in hominoids, imply that the species was not characterized by substantial sexual bimaturation, and greatly increase the probability that the reproductive strategy of A. afarensis was principally monogamy.
Footnotes
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↵ ‡ To whom correspondence should be addressed. E-mail: olovejoy{at}aol.com.
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Abbreviations: A.L., Afar Locality; BDI, Binomial Dimorphism Index; MMR, maximum/minimum ratio; TSD, template sexual dimorphism; CV, coefficient of variation; FHD, femoral head diameter; C.A., Combined Afar.
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See commentary on page 9103.
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↵ § In fact, the known range of female body mass of one subspecies of chimpanzee (Pan troglodytes troglodytes) exceeds that of all known males from another (Pan troglodytes schweinfurthii) (22, 23). If samples from each were combined (as could occur, for example, in the assembly of fossil fragments from different sites or time periods), dimorphism would be overestimated.
- Copyright © 2003, The National Academy of Sciences
