Orangutan uses stone knife, on its own initiative

And again great apes are more handy than we thought. An orangutan turns out to be able to use a sharp rock cut to open something, even without anyone ever showing it to him.

Orangutans also appear to spontaneously hit with stones when you put them in their cage, in such a way that sometimes such sharp knocks are created. Just as it may have once happened to distant human ancestors when they discovered the use of stone tools, millions of years ago.

This is apparent from a small-scale experiment with a total of five orangutans from zoos in Norway and England. In the wild, orangutans do not use stone tools, unlike chimpanzees and macaques that use them to crack open nuts. Remarkably, the orangutan who used a sharp stone to open something held that stone with its mouth. Perhaps the first hominids also used their mouths when they started using tools, the researchers, led by Alba Motes-Rodrigo and Claudio Tennie (University of Tübingen), suggest in their paper on Wednesday. research report in PLOS ONE†

For a long time it was thought that only the modern human race Homo started with stone tools, about 2.3 million years ago. But in 2015, stone tools — sharp cuts and hammerstones — were found 3.3 million years old, probably made by precursors to Homo, such as Australopithecus or Kenyantropus† Tennie’s research group in Tübingen has long been investigating the role of cultural learning in primates, early humans and also in modern children.

The toolbox of great apes

The current study is a follow-up to previous research in which Tennie and his colleagues established that (other) orangutans are also perfectly capable of cracking nuts with a rock without an example. This is an act that chimpanzees have always thought they had to learn from someone else. With the current research, Tennie and his colleagues want to make it plausible that the use of sharp stones – known only from humans and their ancestors – is also part of the toolbox of great apes.

Previously, chimpanzees, an orangutan and the famous language-using bonobo Kanzi had been able to make and use primitive tools in experiments. But always those were monkeys that had grown up in very close contact with humans and that the fabrication and use of stone tools were first extensively demonstrated by the researchers involved.

In addition to large stones, the orangutan’s cage also contained two boxes of about six inches in size, containing visibly tasty things, such as fruit. One was closed with twine, like an approximation to a piece of meat that required severing the tendons first. The other box could only be opened by cutting open a membrane, as an approximation of a carcass whose skin has to be cut open. Both thus imitated conditions that primitive hominids encountered when they first used tools.

Unexpectedly, one of the orangutans, the young man Loui from Norway’s Kristiansand zoo, soon managed to open the ‘skin box’ with a stick he happened to have brought with him. Later he tried with a thick piece of garden hose, but when that didn’t work he picked up a sharp stone from the floor (man-made and placed there in advance for the experiment). With that knife in his mouth, he poked a hole in the membrane and made it bigger with his hand. So it is not that the orang used a tool that he had made himself. Striking back and forth with the stones in the cage did cause sharp turns, so in theory those could also have been used.