boisei a mean capacity of 463.3 (Changeux and Chavaillon pg.65, table 4.1). When the limited sample size is taken into account, is there a significant difference? "The modern human inter-racial mean is of the order of 1350 cm3, which is 3.52 times that of the chimpanzee, 2.68 times that of the gorilla value, and 3.33 times the orang-utan value, the comparative inter-hominoid index values for Australopithecus species are seen to have hardly increased at all (Changeux and Chavaillon pg. 67)." If we compare the modern chimpanzee, as modern human's closest living ancestor, to the australopithecines we find that they "show a small but definite advance over the chimpanzee in both absolute and relative brain size (Changeux and Chavaillon pg. 67)".
With the advance of Homo habilis, 2.3 to 1.6 myp, we see significant advances in the brain. The mean capacity of H. habilis is 640 cm3. This is a 45% increase over A. africanus. The typically enlarged brain size of modern man, that is the ratio of brain to body mass that is a hallmark off the human species is present in H. habilis (Changeux and Chavaillon pg. 74&75). H. habilis indicates an enlargement of the cerebral hemisphere and "detectable impressions of the superamarginal and angular gyri are present for the first time in the hominid lineage (Changeux and Chavaillon pg.76)". This ensures that two of the three basic neurological needs for language are present. The third need, the superior speech cortex, is in the superomedial surface of the cerebral hemisphere. This can not be detected on an endocast (Changeux and Chavaillon pg.76). H. habilis may have been the first to have language capabilities. .
Using brain mass or cranial capacity as a measure of brain evolution is not universally accepted. Holloway states that it is not a useful measure only a statistic for estimating parameters (Jerison pg.388). Studying endocasts as if they are a brain and extracting and applying this information to possible brain development is also debated.