Comparative analyses of human stone tool behaviours and chimpanzee feeding behaviours have revealed a distinctive set of forceful pinch grips by humans that are effective in the control of stones by one hand during manufacture and use of the tools. Journal reference: Science, DOI: 10.1126/science.Was stone tool making a factor in the evolution of human hand morphology? Is it possible to find evidence in fossil hominin hands for this capability? These questions are being addressed with increasingly sophisticated studies that are testing two hypotheses (i) that humans have unique patterns of grip and hand movement capabilities compatible with effective stone tool making and use of the tools and, if this is the case, (ii) that there exist unique patterns of morphology in human hands that are consistent with these capabilities. But now, it’s possible to tie the stones to the hands that held them, and were shaped by them. People have found stone tools at archaeological sites, and they have found bones lying close by, but McPherron points out that no one ever finds a million-year-old hand still holding a tool. Skinner’s approach makes it possible to say something about how individual hands were used. Whether or not their hands were already wrapped around flints, they were at least laying the foundations for their descendants to do so. They were more dextrous and more precise. africanus was already starting to use its hands differently to its ancestors. Or they might have been using their strong precision grips to get at food in new ways, such as peeling tough skins off fruit – a task that chimps tend to do with their teeth.īut the study does suggest that 3 million years ago – 400,000 years before the oldest known Oldowan hand axes – A. africanus were using other types of tools, like bones or pieces of wood.

Whether that grip was used to manoeuver delicate flakes of flint remains to be seen, though. “The best explanation is that the difference reflects some powerful thumb-to-finger gripping,” he says. africanus and human bones are relatively convincing. John Hawks of the University of Wisconsin-Madison says the similarities between A. “This study is really interesting because it shows how the hand was actually used, and that’s consistent with stone tool use,” says McPherron. This revealed that their owners had been tree swingers but had also spent a lot of energy tightly pinching small objects, suggesting they were indeed early tool users. When Skinner and his colleagues looked at the metacarpals of early human species and neanderthals – who also used stone flakes for tasks like scraping and butchering – they found bone ends that were shaped like modern human bones, and unlike ape bones.įinally, they looked at metacarpals from four Australopithecus africanus individuals, up to 3 million years old. This precision squeeze between thumb and fingers is uniquely human and a legacy from our flint-wielding ancestors. Most of our activities involve some kind of pinching – think of how you hold a pencil or pick up a cup. Modern human metacarpals looked different because we use our hands differently. Bottom row: CT scans of the same specimens, showing the structure inside (Image: T.L. Top row: a selection of metacarpal bones. Skinner and his colleagues predicted how this should shape the soft bone in ape hands, then looked at modern ape bones, finding their predictions were right. That exerts a great deal of force on the joints in its hands, in a specific way. Because the bone ends are made of soft, spongy bone tissue, they are shaped over a lifetime of use and moulded by what that hand has done.Ī chimp, for instance, spends a lot of time swinging from branches and knuckle-walking. Specifically, they looked at metacarpal bones – the five bones in the palm of the hand that articulate the fingers. They decided to look at the hands that held them.

Matthew Skinner at the University of Kent in the UK and his colleagues have now found something they think is as exciting as finding an earlier tool.

Chimpanzee hand axe