Endocranial capacity in Sts 71 (Australopithecus africanus) by three-dimensional computed tomography.

Abstract

In a recent report on early hominid endocranial capacity, it was predicted that future studies would show that: (1) "several key early hominid endocranial estimates may be inflated"; (2) "current views on the tempo and mode of early hominid brain evolution may need reevaluation"; and (3) endocranial capacity in one of these, Sts 71, was "probably closer to 370 cm(3), very near the mean value for female chimpanzees, and not the currently accepted 428 cm(3)" (Conroy et al., Science, 1998; 280: 1730-1731; Falk, Science 1998; 20:1714). Subsequent studies tend to support the first two predictions, but not the third (Culotta, Science, 1999; 284: 1109; Falk, Am. J. Phys. Anthropol. Suppl., 1999; 28: 126; Falk et al., J. Hum. Evol. [in press]). Here we detail the reasons for thinking the currently accepted endocranial value for Sts 71 is probably correct by providing the first quantitative details of endocranial reconstruction in Sts 71 using three-dimensional computed tomography. Relative brain expansion in the hominid lineage started some half-million years before the earliest appearance of the genus Homo, possibly coincident with enhanced tool-making skills and carnivory.