Early Homo: Who, when, and where

The origin of Homo is argued to entail niche differentiation resulting from increasing terrestriality and dietary breadth relative to the better known species of Australopithecus (A. afarensis, A. anamensis, A. africanus). I review the fossil evidence from ~2.5 to 1.5 Ma in light of new finds and analyses that challenge previous inferences. Minimally, three cranial morphs of early Homo (including Homo erectus) exist in eastern Africa (1.9-1.4 Ma), with at least two in southern Africa. Because of taphonomic damage to the type specimen of Homo habilis, in East Africa two species with different masticatory adaptations are better identified by their main specimen (i.e., the 1813 group and the 1470 group) rather than a species name. Until recently, the 1470 group comprised a single specimen. South African early Homo are likely distinct from these groups. Together, contemporary early H. erectus and early Homo are bigger than Australopithecus (~30%). Early H. erectus (including recently discovered small specimens) is larger than non-erectus Homo (~15%-25%), but their size ranges overlap. All early Homo are likely to exhibit substantial sexual dimorphism. Early H. erectus is less "modern" and its regional variation in size more substantial than previously allowed. These findings form the baseline for understanding the origin of the genus.