human evolution: Hominin Evolution
The earliest known hominins are members of the genus Australopithecus, the earliest of which date to more than 4 million years ago. Unlike other primates, but like all hominins, australopithecines were bipedal. Their crania, however, were small and apelike, with an average cranial capacity of about 450 cc in the gracile species and 600 cc in the robust forms. Australopithecines that have been considered ancestral in the lineage leading to the human genus Homo include A. afarensis (an important skeleton of which is popularly known as Lucy) and A. africanus. The exact position of these and other early species on the hominin family tree continues to be disputed.
The first member of the genus Homo, a small gracile species known as H. habilis, was present in east Africa at least 2 million years ago. H. habilis was the first hominin to exhibit the marked expansion of the brain (with an average cranial capacity of about 750 cc) that would become a hallmark of subsequent hominin evolutionary history. By about 1.6 million years ago, H. habilis had evolved into a larger, more robust, and larger-brained species known as Homo erectus (African members of the species are sometimes called H. ergaster). Cranial capacities ranged from about 900 cc in early specimens to 1050 cc in later ones. H. erectus persisted for well over a million years and migrated off the African continent into Asia, Indonesia, and Europe. H. heidelbergensis is believed to arisen from H. erectus as far back as 1.3 million years ago.
Between 400,000 and 350,000 years ago, H. heidelbergensis is believed to have given rise to H. neandertalensis, or Neanderthal man, in Europe, and to an branch in Africa that eventually became H. sapiens. By about 150,000 years ago in Africa and Asia and 40,000 years ago in Europe (see Cro-Magnon man), the transition to H. sapiens was complete, and fully modern humans became the single surviving hominin species. (The possible exception is the humans represented by the remains found on Flores, Indonesia, a dwarf hominin species that survived until about 50,000 years ago.)
The Columbia Electronic Encyclopedia, 6th ed. Copyright © 2012, Columbia University Press. All rights reserved.
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