The authors say they have the first archaeological evidence for stone tool use among fossil australopiths 3-2 million years ago. 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. However, it is unclear when these locomotory and manipulative transitions occurred.
University of Kent anthropologists Dr. Matthew Skinner and Dr. Tracy Kivell and colleagues inferred how fossil species were using their hands by examining the internal spongy structure of bone called trabeculae. Trabecular bone remodels quickly during life and can reflect the actual behavior of individuals in their lifetime.
Australopithecus africanus first metacarpal of the thumb, 3-2 million years old. Credit: T.L. Kivell&M. Skinner
The researchers first examined the trabeculae of hand bones of humans and chimpanzees. 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. This unique human pattern is present in known non-arboreal and stone tool-making fossil human species, such as Neanderthals.
The paper says that Australopithecus africanus, a 3-2 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.
These results support other archaeological evidence for stone tool use in australopiths and provide skeletal evidence that our early ancestors used human-like hand postures much earlier and more frequently than previously considered.
Citation: Matthew M. Skinner, Nicholas B. Stephens, Zewdi J. Tsegai, Alexandra C. Foote, N. Huynh Nguyen,Thomas Gross, Dieter H. Pahr, Jean-Jacques Hublin,Tracy L. Kivell, Human-like hand use in Australopithecus africanus, 23 January, Science. doi:10.1126/science.1261735
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