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26 October 2005 (All day)
When it comes to gift-giving, chimps are chumps. An experiment with captive chimpanzees finds they are not motivated to help others even if it costs them nothing.
There are plenty of examples of apparently altruistic behavior among animals, such as sharing food and grooming. But implicit in these acts is a reward, either because the receiver is a close relative or because the giver expects reciprocation in the future. In contrast, humans often commit acts of kindness for complete strangers, such as giving blood, where the reward is mostly the feeling of doing a good deed. Are nonhuman animals also capable of such relatively selfless acts? One theory predicts that humans may be unique in this regard because such behavior only arises in social groups as large and extended as ours, where altruism between strangers is required to keep society stable.
To see if chimpanzees share the same selflessness, a team led by Joan Silk, a behavioral biologist at the University of California at Los Angeles, designed a charity-giving machine. When inside the main chamber, a chimp had the option of two levers. The first simply produced a snack. The second yielded the same food but also delivered a similar serving to a chimp that could be seen waiting in a second chamber. As a control, the researchers also presented chimps with the same options while the second chamber was empty.
This setup "maximizes" the chances of catching chimps acting selflessly, says Silk, because there is no cost to giving the gift. To rule out the possible motivation of family ties, the researchers tested both related and unrelated chimps.
The chimps only cared that they got their own snack. They were not significantly more likely than chance to give a gift under any circumstances, no matter who the receiver was, the team reports 27 October in Nature. And it doesn't seem to be for a lack of understanding how the system worked. When on the receiving end, chimps often begged the chimp controlling the levers.
"This is a pathbreaking paper," says Ernst Fehr, an experimental economist at the University of Zurich, Switzerland, because it is throws into doubt the view of primate researchers who have emphasized the similarity of altruism in chimps and humans. In related experiments with human teenagers, almost all give the gift, he says.