Move over Homo habilis, you're being dethroned. A growing body of evidence – the latest published this week – suggests that our "handy" ancestor was not the first to use stone tools. In fact, the ape-like Australopithecus may have figured out how to be clever with stones before modern humans even evolved.
Humans have a way with flint. Sure, other animals use tools. Chimps smash nuts and dip sticks into ant nests to pull out prey. But humans are unique in their ability to apply both precision and strength to their tools. It all began hundreds of thousands of years ago when a distant ancestor began using sharp stone flakes to scrape meat off skin and bones.
So who were those first toolmakers?
In 2010, German researchers working in Ethiopia discovered markings on two animal bones that were about 3.4 million years old. The cut marks had clearly been made using a sharp stone, and they were at a site that was used by Lucy's species, Australopithecus afarensis.
The study, led by Shannon McPherron of the Max Planck Institute for Evolutionary Anthropology in Leipzig, Germany, was controversial. The bones were 800,000 years older than the oldest uncontested stone tools, and at the time few seriously thought that australopithecines had been tool users. Plus, McPherron hadn't found the tool itself.
The problem, says McPherron, is that if we just go on tools that have been found, we must conclude that one day somebody made a beautifully flaked Oldowan hand axe, completely out of the blue. That seems unlikely.
Answers at hand
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.
They decided to look at the hands that held them. Specifically, they looked at metacarpal bones – the five bones in the palm of the hand that articulate the fingers. 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.
A chimp, for instance, spends a lot of time swinging from branches and knuckle-walking. That exerts a great deal of force on the joints in its hands, in a specific way. 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.
Modern human metacarpals looked different because we use our hands differently. Most of our activities involve some kind of pinching – think of how you hold a pencil or pick up a cup. This precision squeeze between thumb and fingers is uniquely human and a legacy from our flint-wielding ancestors.
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.
Finally, they looked at metacarpals from four Australopithecus africanus individuals, up to 3 million years old. 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.
Getting a grip
"This study is really interesting because it shows how the hand was actually used, and that's consistent with stone tool use," says McPherron.
John Hawks of the University of Wisconsin-Madison says the similarities between A. africanus and human bones are relatively convincing. "The best explanation is that the difference reflects some powerful thumb-to-finger gripping," he says.
Whether that grip was used to manoeuver delicate flakes of flint remains to be seen, though. It's possible A. africanus were using other types of tools, like bones or pieces of wood. 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.
But the study does suggest that 3 million years ago – 400,000 years before the oldest known Oldowan hand axes – A. africanus was already starting to use its hands differently to its ancestors. They were more dextrous and more precise. Whether or not their hands were already wrapped around flints, they were at least laying the foundations for their descendants to do so.
There's one more twist to the tale. Skinner's approach makes it possible to say something about how individual hands were used. 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. But now, it's possible to tie the stones to the hands that held them, and were shaped by them.
Journal reference: Science, DOI: 10.1126/science.1261735
If you would like to reuse any content from New Scientist, either in print or online, please contact the syndication department first for permission. New Scientist does not own rights to photos, but there are a variety of licensing options available for use of articles and graphics we own the copyright to.
No comments:
Post a Comment