Cranial capacity in hominid evolution

Abstract

We present an analysis of cranial capacity of 118 hominid crania available from the literature. The crania belong to both the genus Australopithecus and Homo and provide a clear outline of hominid cranial evolution starting at more than 3 million years ago. Beginning with A. afarensis there is a clear increase in both absolute and relative brain size with every successive time period. H.s. neandertal has an absolutely and relatively smaller brain size (1412cc, E.Q.=5.6) than fossil modern H.s. sapiens (1487cc, E.Q.=5.9). Three evolutionary models of hominid brain evolution were tested: gradualism, punctuated equilibrium, and a mixed model using both gradualism and punctuated equilibrium. Both parametric and non-parametric analyses show a clear trend toward increasing brain size with H. erectus and a possible relationship within archaic H. sapiens. An evolutionary stasis in cranial capacity could not be refuted for all other taxa. Consequently, the mixed model appears to more fully explain hominid cranial capacity evolution. However, taxonomic decisions could directly compromise the possibility of testing the evolutionary mechanisms hypothesized to be operating in hominid brain expansion. © 1993 International Institute for the Study of Man.