In chimpanzees, cracking nuts cannot be improvised


As in a learning workshop: when chimpanzees manage to crack nuts with stones, it is not the result of chance but of real know-how acquired from their most experienced congeners, according to a published study Monday.

Chimpanzees are often considered the closest primates to humans, especially because they are capable of complicated tasks, such as using tools.

However, it is difficult to determine where this ability comes from. Some scientists attribute it to a “cumulative culture”, by which certain non-human primates would transmit their skills from generation to generation, perfecting their techniques over time.

For other scientists, on the contrary, this form of social learning is specific to humans. In chimpanzees, the use of tools would develop spontaneously – as if each individual was starting from scratch, without copying a model.

This second hypothesis supposes the existence of a “zone of latent solutions” in the brain of non-human primates, which seems to be at work for the use of rudimentary tools, such as sticks for picking up food.

But what about more sophisticated practices such as cracking nuts, using rocks that act as a hammer and anvil?

Ignored tools

Experiments carried out on chimpanzees in Guinea, and described in the journal Nature Human Behaviour, are advancing the debate.

A team of researchers, led by primatologist Kathelijne Koops from the University of Zurich, compared the behavior of a community of wild chimpanzees with that of captive individuals at Bossou, in the Mount Nimba nature reserve (south of Guinea).

Bossou is one of the first places where the use of sophisticated tools by chimpanzees in captivity has been scientifically established.

The researchers presented these same tools to wild chimpanzees, still at Mount Nimba, in different configurations: first with palm nuts in their shells and stones capable of breaking them. We then added walnuts already shelled, then cola nuts, reputed to be easier to crack.

All repeated over several months, between 2008 and 2011, in four different sites, visited by dozens of chimpanzees and filmed with hidden cameras. Result: if they handled the tools well, not a single one deigned to use them to access his pittance, or even tried it. Thus invalidating the hypothesis of spontaneous use.

Just 6 km away, among their fellows at the Bossou study center, cracking nuts is commonplace. “Research carried out in Bossou and other communities of ‘nutcrackers’ has shown that young individuals watched their elders do things up close, and trained,” Kathelijne Koops, a professor in the department of anthropology, told AFP. from the University of Zurich.

His study therefore reinforces the thesis of a “cumulative culture” (transmitted from the eldest to the youngest). This would suppose, according to the researcher, “a common origin with Man in evolution”.

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