A team of scientists led by Dr Tracy Kivell of the University of Kent and University College London has found strong evidence for stone tool use among Australopithecus africanus (3 to 2 million years ago) and several Pleistocene hominins, traditionally considered not to have engaged in habitual tool manufacture.
Australopithecus africanus. Image credit: J.M Salas / CC BY-SA 3.0.
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.
Dr Kivell’s team used new techniques to reveal how fossil species, such as Australopithecus africanus, 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.
“Over time these structures adapt in a way that enables them to handle the daily loads in the best way possible,” said Dr Dieter Pahr from the Vienna University of Technology, Austria, a co-author on the study published in the journal Science.
The scientists 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 study shows that Australopithecus africanus has a human-like trabecular bone pattern in the bones of the thumb and palm consistent with forceful opposition of the thumb and fingers typically adopted during tool use.
“This new evidence changes our understanding of the behavior of our early ancestors and, in particular, suggests that in some aspects they were more similar to humans than we previously thought,” said lead author Dr Matthew Skinner of the Max Planck Institute for Evolutionary Anthropology and the University of Kent.
Dr Jean-Jacques Hublin of the Max Planck Institute for Evolutionary Anthropology, a co-author on the study, added: “there is growing evidence that the emergence of the genus Homo did not result from the emergence of entirely new behaviors but rather from the accentuation of traits already present in Australopithecus, including tool making and meat consumption.”
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Matthew M. Skinner et al. 2015. Human-like hand use in Australopithecus africanus. Science, vol. 347, no. 6220, pp. 395-399; doi: 10.1126/science.1261735
