The research shows that Australopithecus africanus, a three to two million-year-old species from South Africa traditionally considered not to have engaged in habitual tool manufacture, has a human-like trabecular bone pattern in the bones of the thumb and palm (the metacarpals) consistent with forceful opposition of the thumb and fingers typically adopted during tool use. This unique human pattern is present in known non-arboreal and stone tool-making fossil human species, such as Neandertals. They found clear differences between humans, who have a unique ability for forceful precision gripping between thumb and fingers, and chimpanzees, who cannot adopt human-like postures. The researchers first examined the trabeculae of hand bones of humans and chimpanzees. “Over time these structures adapt in a way that enables them to handle the daily loads in the best way possible“, says Dieter Pahr of the Institute of Lightweight Design and Structural Biomechanics at the Vienna University of Technology where special computer algorithms for the analysis of the computer tomography images of the bones had been developed. Trabecular bone remodels quickly during life and can reflect the actual behaviour of individuals in their lifetime. Matthew Skinner and Tracy Kivell of the Max Planck Institute for Evolutionary Anthropology and the University of Kent used new techniques to reveal how fossil species were using their hands by examining the internal spongey structure of bone called trabeculae. However, it is unclear when these locomotory and manipulative transitions occurred. The distinctly human ability for forceful precision (e.g., when turning a key) and power “squeeze” gripping (e.g., when using a hammer) is linked to two key evolutionary transitions in hand use: a reduction in arboreal climbing and the manufacture and use of stone tools.
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