Chimpanzees aren't known for their charity. Recent experiments with chimps have found that they're generally unwilling to deliver a snack to a fellow ape, even when there's no cost to themselves. A new study, however, breaks with those findings, demonstrating that our closest living relatives do show altruistic tendencies--at least sometimes.
In the wild, chimpanzees engage in apparent acts of kindness such as grooming and sharing food. But behavioral researchers have found little evidence of true altruism: helping an unrelated individual when there's no expectation of payback. For example, a recent study led by primatologist Joan Silk of the University of California, Los Angeles, gave chimps a choice between two levers: By pulling one, a chimp could earn a snack; by pulling the other, it could earn a snack for itself plus a bonus snack for a chimp in a nearby room. But the chimps pulled the levers randomly, showing little regard for their companion (ScienceNOW, 26 October 2005). A 2006 study led by psychologist Michael Tomasello of the Max Planck Institute for Evolutionary Anthropology in Leipzig, Germany, reported similarly inconsiderate behavior.
In the new experiments, Tomasello and postdoctoral fellow Felix Warneken tried a different setup. They placed one chimp in a room where it had a clear view of a tantalizing piece of watermelon or banana in a room next door. The door connecting the two rooms was chained shut. A second chimp, by itself in a third room with a view of the whole setup, could unlock the door by removing a peg to release the chain. Doing so would allow the first chimp to get the fruit. The potential benefactors unlocked the door almost 80% of the time, even though the fruity treat always went to the other chimp, Warneken and Tomasello report in the July issue of PLoS Biology. The researchers argue that their findings suggest that altruistic behavior is not unique to humans, as the previous work might have suggested.
"I think it's a great experiment," says Silk. "It raises really interesting questions about the circumstances in which chimps are motivated to provide help to others." For example, Silk suspects that when chimps are eating or expect to eat, the impulse to help others may go out the window. She points out that unlike the unhelpful chimps in previous experiments, the benefactors in the new study had no chance of getting food themselves. Warneken agrees that the expectation of food puts chimps "in a different mindset." He thinks another factor might be that the recipient chimps in his experiment pushed and banged on the door, making it clear they needed help.