Humans Ancestors Using Stone Tools For Much Longer Than Previously Estimated

New research suggests pre-Homo human ancestral species used human-like hand postures much earlier than was previously thought.

 

Hand precision grip – Example of a human forceful precision grip, grasping a Australopithecus africanus first metacarpal of the thumb (3-2 million years old)

Picture by Tracy Kivell & Matthew Skinner.

University anthropologists, working with colleagues from University College London , the Max Planck Institute for Evolutionary Anthropology in Leipzig (Germany) and theVienna University of Technology (Austria), have produced the first research findings to support 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.

The first metacarpals of a chimp, the fossil australopiths, and a human (top row). The bottom row constists of images from micro-computertomography-scans of the same specimens, showing a cross-section of the trabecular structure inside.

Credit; © Tracy Kivell

Dr Matthew Skinner, Senior Lecturer in Biological Anthropology and Dr Tracy Kivell, Reader in Biological Anthropology, both of Kent’s School of Anthropology and Conservation, used new techniques to reveal how fossil species were using their hands by examining the internal spongey structure of bone called trabeculae. Trabecular bone remodels quickly during life and can reflect the actual behaviour of individuals in their lifetime.

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 research, titled Human-like hand use in Australopithecus africanus, shows 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 previously published 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.

Human-like hand use in Australopithecus africanus, (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) is published on 23 January in Science magazine.

 

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By Martin Herrema |