BioEd Online

You can tell a lot about someone from how they treat their friends. As the results of a study of captive chimpanzees seem to show, our ape cousins are only in it for themselves.

The study, led by Joan Silk of the University of California, Los Angeles, looked for evidence that chimpanzees (Pan troglodytes) will help other members of their group. But the apes seem to be indifferent at best to the welfare of their fellows.

Silk and her colleagues presented captive chimps with an apparatus that allowed them to get food by pulling on one of two ropes. Choosing one of the ropes meant that the chimp could haul in a tasty titbit. Selecting the other yielded exactly the same reward, but another chimp in an adjacent cage also received a morsel to eat.

Given that the chimp in charge got the same food reward regardless of which rope was selected, one might expect them to have shown some compassion and chosen the one that gave food to their companion too. "All they had to do was be nice," Silk says.

But the 29 chimps tested were no more likely to choose the generous option than the selfish one, Silk and her colleagues report in this week's Nature¹. This shows that the apes are not motivated to help others as a matter of course, they conclude.

Helping hands

Helpful behaviour is widespread in humans, and can even extend to situations in which the helper harms their own interests while aiding another, whether it be intervening in a fight or giving to charity.

But the chimps showed no such inclination, despite the fact that it wouldn't cost them anything. "We wanted to make it as easy for the chimps as possible," Silk says. "It's not as if we were asking them to give blood or write cheques to tsunami victims."

The results were particularly surprising because the chimpanzees had been living in the same groups for at least 15 years. So although they were not related, they were very close.

And chimpanzees are known to be able to master cooperation if both parties stand to gain something on which they would have otherwise missed out (see ' Modern cooperation').

Share and share alike

We need to be cautious about drawing conclusions from the behaviour of laboratory chimps, warns Brian Hare, who studies the animals at the Max Planck Institute for Evolutionary Anthropology in Leipzig, Germany. "It's a very complicated topic, and this is one measurement made in a contrived situation," he says.

Wild chimpanzees are known to share food with other group members, Hare adds. It remains to be seen how such arrangements arise, whether through trust-building or a genuine desire to help those less fortunate.

Silk would like to repeat the experiment with related chimps to see if they can be encouraged to do a good turn for a family member. And she wonders whether chimps would behave differently if they swapped roles several times, so learning what it's like to be on the other side of the fence and perhaps building a reciprocal arrangement by which both parties would benefit.

Silk would also like to try out the experiment with human children, to see how their unique brand of selfishness measures up.