Cerebral brain endocast pattern of Australopithecus afarensis hominid

Abstract

It is rare for cerebral convolutional details to be imprinted on the internal table of cranial bone of fossil hominids. To date, the South African examples have shown the best detail, although surrounded by considerable controversy^1–3. Given that the Hadar specimens are the oldest hominids known (3–4 Myr BP)^4,5, and have been the subject of considerable debate and interpretation, it is fortunate that such details are found on the cranial bones of at least one specimen, AL 162-28, a small adult⁶. I report here a preliminary description of that endocast and it appears that despite its smallish pongid-sized brain, some degree of cerebral organization had occurred almost 3–4 Myr ago towards a more human pattern. If correct, this would mean that brain size increase may well have followed locomotion, but that brain organization may have occurred early in hominid evolution. Such a finding would call for a re-examination of our understanding about human evolution, and would require much more caution in assuming either ‘gradualist’ or ‘punctuated equilibria’ models in hominid evolution^7,8.