BioEd Online

Chimps can not only use tools, but also seem to follow the fashion in how they are used.

Researchers have found that a group of chimpanzees will stick to the same method used by their peers, even if they stumble across a different way of using a tool by themselves. That shows that chimps follow a cultural norm that is socially learned and maintained, the researchers say - proof, perhaps, that chimpanzees really do have culture.

Chimpanzees are known to have many complex behaviours, including tool use and grooming, that place them second only to humans. Scientists have long assumed that chimpanzee populations maintain such traditions the same way humans do: by learning to imitate each other.

But proof for social learning in wild chimpanzees has been hard to come by. One problem is that simply observing one animal watching another doesn't prove that he is learning a behaviour. If he picks up the same tricks, it could be that he learned them by himself.

The solution is to check whether chimpanzees can start and maintain a cultural tradition in a controlled environment, says Andrew Whiten of the University of St Andrews in Fife, UK, the lead author of the study that appears this week in Nature¹.

Grape games

To do this, he and his colleagues used chimpanzees kept at the Yerkes Primate Center at Emory University in Atlanta, Georgia. The researchers placed a grape on a platform inside a box, with an obstructing block to stop it falling out. They then taught two different chimpanzees two different ways to use a stick to get the grape.

One used the stick to lift the block out of the box, allowing the grape to fall out. The other learned to poke the block backwards, pushing the grape off the back of the platform and again allowing it to fall out.

Once trained, the animals were returned to their social groups. As expected, most of the peers used the same technique as the one they observed from the trained chimp. Animals that didn't have an example to follow simply couldn't get the grape out.

Some animals did spontaneously switch from one behaviour to the other when they tried to retrieve the grape, figuring out the alternative method themselves. But two months later, most animals had switched back to the majority behaviour in their group.

Whiten points out that even animals who initially poked - a behavior more natural for chimpanzees than lifting - reverted to lifting eventually. "This is an even stronger social learning tendency than we went out to test for," Whiten says. "It's very exciting. We were surprised."

Closing the gap

Whiten isn't the only one who is excited. "This is narrowing the gap between humans and non-humans," says William McGrew, a cultural primatologist at Miami University in Oxford, Ohio. He says it is the first proof that animals pick up a tradition by imitation.

But Michael Tomasello, a comparative psychologist of the Max Planck Institute for Evolutionary Anthropology in Leipzig, Germany, isn't convinced. The chimps might have learned how to get the grape by watching how the boxes themselves work, rather than by watching other chimps.

But does this show that chimpanzees have 'culture'? Some experts think so. But Bennett Galef, who studes animal behaviour at McMaster University in Hamilton, Ontario in Canada, says he doesn't think the study provides sufficient proof to call chimpanzee traditions by that name.

Besides, Galef adds, the most interesting thing is to investigate how chimp and human behaviours are alike, and how they are different. Lumping them together with the word 'culture' might foreclose those questions, he says.