Chimps Lend a Hand

Altruism--helping another when there's nothing to gain--is so rare in the animal kingdom that some researchers think it's a uniquely human trait. Even chimpanzees, our closest primate kin, won't go out of their way to press a lever that delivers food to an unrelated individual (ScienceNOW, 26 October 2005). But a new study indicates that the primates aren't always so selfish. Chimps seemed to understand when a human was having difficulty and helped out. Another experiment by the same team reveals sophisticated cooperation among chimps, although they were not altruistic in that situation.

For the first study, comparative psychologists Michael Tomasello and Felix Warneken of the Max Planck Institute for Evolutionary Anthropology in Leipzig, Germany, had a caretaker drop a marker while a chimp looked on. All three chimps tested picked up the marker and gave it back. The chimps' behavior shows that they can understand the goals of another and do have some altruistic motivation, Tomasello and Warneken conclude 3 March in Science. But the chimps couldn't hold a candle to human infants, who responded about twice as quickly to the same situation. The babies also seemed to grasp that help was needed in more complicated situations where chimps were clueless, such as when someone needed help opening a cabinet to put magazines inside.

"I think it's extremely interesting that these very young children are behaving in a helpful way," says University of California, Los Angeles, biological anthropologist Joan Silk, who led the food-lever study. "It suggests that just like infants are wired up to imitate, they're wired up to help." As for the chimps, the new experiments suggest that they may have a more altruistic nature than the food experiments suggested, Silk says. "It may be that when chimps see food, they can only think of themselves." An alternative explanation, she says, is that chimps may be more likely to help a human caretaker than one of their own.

In a second study--published in the same issue of Science--Tomasello and colleagues Alicia Melis and Brian Hare suggest that chimps cooperate with each other in sophisticated ways--at least when they stand to benefit. The researchers put food on a platform rigged so that a chimp would have to pull both ends of a rope to get it. When the ends were too far apart for the chimp to manage, he opened a door to let in another chimp, who helped tug the rope and get the food. Given a choice between two previous collaborators, chimps consistently let in the one who'd been more effective at helping retrieve the food.

"The paper shows that chimps are able to solve cooperative problems that are pretty complicated when they're motivated to do so," Silk says. But because both chimps benefit from the joint effort, the experiment doesn't speak to their willingness to help others, she adds. "We need to pursue that issue further."

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