The 84th Annual Meeting of the American Association of Physical Anthropologists (2015)


Did an increase in body size play a role in the origin of Homo?

MARK W. GRABOWSKI1, KEVIN G. HATALA1,2, WILLIAM L. JUNGERS3 and BRIAN G. RICHMOND1,4.

1Center for the Advanced Study of Hominid Paleobiology, The George Washington University, 2Deparment of Human Evolution, Max Planck Institute for Evolutionary Anthropology, 3Department of Anatomical Sciences, Stony Brook University, 4Division of Anthropology, American Museum of Natural History

March 27, 2015 1:15, Grand Ballroom E/F/G Add to calendar

Body size directly influences an animal's place in the natural world, including its energy requirements, home range size, relative brain size, locomotion, diet, life history and other aspects of behavior. Thus, an informed understanding of the biology of extinct organisms, including species in our own lineage, requires accurate estimates of body size. Since the last major review of hominin body size based on postcranial morphology over 20 years ago, new fossils have been discovered, species attributions have been clarified, and methods have improved. Here, we reevaluate individual fossil hominin body mass estimates based on a large sample of modern humans (n=220) and common chimpanzee (n=25) of known body masses; our human sample included many small-bodied people. We also present species and sex-specific averages based on fossils with reliable taxonomic attributions. Our results show that early hominins were generally smaller bodied than previously thought. This outcome is due in part to estimates in earlier studies deriving from larger bodied modern human reference samples. Our analyses show that modern human-like large size first appears 3-3.5 Ma in individuals of Australopithecus afarensis. There is little reliable evidence that body size of pre-erectus Homo differed from that of some australopiths, and the pattern of hominin body size evolution appears more complex than previously thought. Our results challenge what we thought we knew about hominin body size evolution and suggest the origins of Homo did not coincide with, and thus presumably were not driven by, an increase in body mass.

Funding for this research was provided by NSF DGE-0801634, NSF BCS-1128170, NSF BCS-1028699, and The George Washington University's Selective Excellence Program.