Hadar AL 162-28 endocast as evidence that brain enlargement preceded cortical reorganization in hominid evolution.

On the basis of a description of an endocast from Hadar early hominid AL 162-28, it has been suggested that cerebral organization towards a human pattern occurred as early as 3-4 Myr ago. I have studied a cast of the AL 162-28 calvaria and a copy of an endocast prepared from the original fossil, and report here observations regarding cranial capacity, the relationship between endocast and skull, sulcal pattern, brain shape and cranial venous sinuses. Contrary to the earlier report, all of these features appear to be consistent with an ape-like external cortical morphology in Hadar early hominids and in my view there is no evidence for expansion or reorganization of parietal/occipital regions. Cranial capacity of AL 162-28 is at least 10% and 29% smaller than respective mean capacities of subsequently living gracile and robust australopithecines, who also exhibit ape-like cortical patterns. Thus palaeoneurological evidence from the entire early hominid record suggests that the trend towards brain enlargement preceded cortical reorganization.