From Australopithecus to Homo: the transition that wasn't.
Although the transition from Australopithecus to Homo is usually thought of as a momentous transformation, the fossil record bearing on the origin and earliest evolution of Homo is virtually undocumented. As a result, the poles of the transition are frequently attached to taxa (e.g. A. afarensis, at ca 3.0 Ma versus H. habilis or H. erectus, at ca 2.0-1.7 Ma) in which substantial adaptive differences have accumulated over significant spans of independent evolution. Such comparisons, in which temporally remote and adaptively divergent species are used to identify a 'transition', lend credence to the idea that genera should be conceived at once as monophyletic clades and adaptively unified grades. However, when the problem is recast in terms of lineages, rather than taxa per se, the adaptive criterion becomes a problem of subjectively privileging 'key' characteristics from what is typically a stepwise pattern of acquisition of novel characters beginning in the basal representatives of a clade. This is the pattern inferred for species usually included in early Homo, including H. erectus, which has often been cast in the role as earliest humanlike hominin. A fresh look at brain size, hand morphology and earliest technology suggests that a number of key Homo attributes may already be present in generalized species of Australopithecus, and that adaptive distinctions in Homo are simply amplifications or extensions of ancient hominin trends.This article is part of the themed issue 'Major transitions in human evolution'.
Institute of Human Origins, and School of Human Evolution and Social Change, Arizona State University, Tempe, AZ 85287, USA wkimbel.iho@asu.edu.
William H
WH
Kimbel
Department of Anthropology, University of Nevada Las Vegas, Las Vegas, NV 89154, USA Department of Anthropology, University College London, London UK WC1H 0BW.
Brian
0000-0003-1012-9388
B
Villmoare
D000818:Animals; D005075:Biological Evolution; D001921:Brain / Q000033:anatomy & histology / Q000502:physiology; D003468:Cultural Evolution; D005580:Fossils / Q000033:anatomy & histology; D006225:Hand / Q000033:anatomy & histology; D015186:Hominidae / Q000033:anatomy & histology* / Q000502:physiology*; D006801:Humans; D013672:Technology; D053001:Tool Use Behavior
Australopithecus; early Homo; transition