Human-like hand use in Australopithecus africanus

Getting a grip The evolution of the hand—particularly the opposable thumb—was key to the success of early humans. Without a precise grip, involving forceful opposition of thumb with fingers, tool technology could not have emerged. Skinner et al. analyzed the internal bone structure of Pliocene Australopithecus hands, dated at 3.2 million years old. Internal bone structure reveals the patterns and directions of forces operating on the hand, providing clues to the kinds of activities performed. Modern human-like hand postures consistent with the habitual use of tools appeared about half a million years earlier than the first archaeological evidence of stone tools. Science, this issue p. 395 The internal bone structure of Pliocene australopiths suggests that precision grip evolved 3.2 million years ago. The distinctly human ability for forceful precision and power “squeeze” gripping is linked to two key evolutionary transitions in hand use: a reduction in arboreal climbing and the manufacture and use of tools. However, it is unclear when these locomotory and manipulative transitions occurred. Here we show that Australopithecus africanus (~3 to 2 million years ago) and several Pleistocene hominins, traditionally considered not to have engaged in habitual tool manufacture, have a human-like trabecular bone pattern in the metacarpals consistent with forceful opposition of the thumb and fingers typically adopted during tool use. These results support archaeological evidence for stone tool use in australopiths and provide morphological evidence that Pliocene hominins achieved human-like hand postures much earlier and more frequently than previously considered.