Human Evolution: Early Radiations

Abstract

We interpret the early radiations within the hominin clade as including all of the taxa in genera other than Homo . While the taxa in Australopithecus , Kenyanthropus and Paranthropus are almost certainly hominins, others in the genera Ardipithecus , Orrorin and Sahelanthropus may not be hominins but belong in one or more closely related clades. All of the taxa in Australopithecus , Kenyanthropus and Paranthropus have brain sizes one third (or less) to one half the average size of later Homo , postcranial skeletons that combine adaptations for bipedalism with retention of upper limbs adapted for climbing, and postcanine teeth that are relatively larger than those of chimpanzees and bonobos, covered by enamel that is thicker than that seen in chimpanzees and bonobos. Some (e.g. Paranthropus boisei ) have exceptionally large postcanine teeth with hyper‐thick enamel cusps. Key Concepts Morphological and genetic features separate humans from our closest relatives in the genus Pan The earliest potential hominins retain many ‘ape‐like’ features such as arms adapted for climbing All early hominins have chewing teeth that are relatively larger, and with thicker enamel, than in the genus Pan By the time of Australopithecus afarensis , hominins were fully bipedal A radiation of megadont and hyper‐megadont hominins ( Paranthropus ) is found in eastern and southern Africa