Australopithecus to Homo:: Transformations in body and mind

Significant changes occurred in human evolution between 2.5 and 1.8 million years ago. Stone tools first appeared, brains expanded, bodies enlarged, sexual dimorphism in body size decreased, limb proportions changed, cheek teeth reduced in size, and crania began to share more unique features with later Homo. Although the two earliest species of Homo, H. habilis and H. rudolfensis, retained many primitive features in common with australopithecine species, they both shared key unique features with later species of Homo. Two of the most conspicuous shared derived characters were the sizes of the brain and masticatory apparatus relative to body weight. Despite the shared derived characters of H. habilis and H. rudolfensis, one unexpected complication in the transition from australopithecine to Homo was that the postcranial anatomy of H, habilis retained many australopithecine characteristics. H. rudolfensis, however, seems to have had a more human-like body plan, similar to later species of Homo. H. rudolfensis may therefore represent a link between Australopithecus and Homo.