We owe our generosity to chimps

The Emory researchers decided to undertake the study because of a contradiction in scientific literature. Some lab experiments on chimpanzees failed to show a willingness to help,but primatologists who observed chimpanzees in the wild saw many examples of what looked like helping. “They’re sharing food,they’re helping each other in fights—there was a huge mismatch between what was going on in the field and in the lab,” said Victoria Horner,the lead author of the study. Horner and her colleagues suspected that the design of earlier lab studies had been too complex for the chimpanzees to figure out. They set up what they believed was a much simpler experiment. For an earlier study,they had trained captive chimpanzees to give them coloured tokens in exchange for food. For the current study,they used those tokens to give seven female chimpanzees a chance to help out fellow chimps.

In each trial,a pair of chimpanzees sat next to each other,able to see each other in adjoining cages. They were given 30 tokens,half in one colour and half in another. If a chimp gave the scientists a token of one colour,she got a package of food while her partner got none. If she gave the other colour,both of them got something to eat. If chimpanzees didn’t care about the welfare of other chimpanzees,the scientists predicted,they’d pick both colours equally often. That’s not what happened. All of the chimpanzees were more likely to pick the generous colour,up to 66.7 per cent of the time. They showed no preference for their relatives versus unrelated chimps. The scientists also ran control sessions,in which the chimpanzees got food only for themselves,no matter which colour they chose. “In these control sessions,they had no bias in their colour choice.

This now fits with the evidence we know from the wild,” Horner said. She speculates that human helping evolved from the kind of bias she and her colleagues see in chimpanzees,as the probability of helping rose in our ancestors. “It’s not that we have a unique ability,but it’s the number of instances of when we do it is vastly different,” she said.

Several experts gave Horner and her colleagues high marks. “They have been able for the first time to duplicate what field researchers already knew was a natural ability of chimpanzees,” said Christophe Boesch,a primatologist at the Max Planck Institute for Evolutionary Anthropology in Germany. But Michael Tomasello,also at the Max Planck Institute,found the study poorly designed. He notes that the Emory scientists ran their control sessions after the experimental sessions. “Maybe the chimpanzees were just tired of choosing the two-pieces-of-food option by the time the control conditions were run,” Tomasello said.

Tomasello and his colleagues have published their own experiments on pro-social behaviour in chimps,most recently in July in the journal Nature. His own research led Tomasello to a somewhat different conclusion from Horner’s. “Chimps help others,but what they do not do is give up food themselves so others can have it,” Tomasello said. “So they are pro-social when it is not costly,but when it is,not so much.”CARL ZIMMER