Capuchin monkeys in Brazil work stones in such a way that they look suspiciously like the stone tools of prehistoric humans. But they don't use them for anything, they just lick them. What does this mean for our interpretation of the stone objects that prehistoric man left behind?
Many an archaeologist has made it his life's work:studying the stone tools that the ancestors of man made hundreds of thousands of years ago.
Such a stone tool consists of a boulder where large, flat splinters have been knocked off with another boulder. The sharp edges on the boulder, or the sharp splinters themselves (the 'flashes'), served as tools for cutting or scraping. So much for the common wisdom among archaeologists.
Primitive tools
But this week, a team of Brazilian and British psychologists and archaeologists released videos and photos of capuchin monkeys busily carving rocks in exactly the same way. If worked stones are not tools, shouldn't the entire prehistory of man be revised? In some cases, those stone tools are the only evidence that a distant ancestor was not an ape, but a hominid. It is undisputed that our species, Homo Sapiens, have always made tools, but that is much more difficult to prove for distant ancestors such as Homo Erectus or Australopithecus.
Wil Roebroeks, professor of Ancient Stone Age archeology at Leiden University, is quite laconic about this:“Debates about stones that are sold as man-made tools already existed in the nineteenth century. Especially with the most primitive tools, which are created by tapping a stone on another, you can never be sure whether they were not created by natural events, for example because a stone fell from a cliff."
The article about the capuchin monkeys reenacting the Stone Age was published this week in Nature, but Roebroeks saw the videos and the story of the researchers at a conference a month ago. “The fact that these monkeys in Brazil also make such stone artifacts is a complicating factor,” he says. “In that area there are two archaeological sites of artifacts that are already very controversial.”
But according to Roebroeks, this discovery really does not call into question the entire prehistory of man. “We know stone tools in Africa that are 3.3 million years old, which have very large turnings. That couldn't have been done by little monkeys. And there are sites of stone tools from that time where bones with cutting marks have also been found.”
Fist axes
From about 1.7 million years ago, stone tools become much more complex and you can speak of hand axes:stones with multiple, apparently targeted turns. According to Roebroeks, you cannot confuse these with these stones worked by capuchin monkeys. "I've already read reports that those monkeys were making 'hand axes', but that's nonsense."
It is also a mystery why the Brazilian capuchin monkeys smash stones. They have no interest in the splinters, nor do they use the boulder as a tool or weapon; they just lick it. The stones contain no nutrients or salt. At most, the monkeys can benefit from licking siliceous grit, as this is a trace element in the body, but that is far-fetched.
The stones they work on lie at the base of a cliff from which stones sometimes spontaneously fall, and it is full of splinters and broken boulders. Maybe the monkeys just do what they do proverbially:imitate.