Capuchin monkeys have a skill previously seen only in chimpanzees and humans: They know how to share. One capuchin monkey will help another get food, and in return the second monkey will hand over some of the goodies, researchers have now observed. They speculate that the monkeys may have developed a concept of gratitude or compensation.
Cooperative behavior has been observed before among capuchins--the smartest New World monkeys--both in the wild and in captivity. But there are different levels of cooperation. In "mutualism," which is seen in many species--for example, when dogs hunt in packs--each animal automatically shares in the rewards, and none of them can easily deny the reward to others. It's much more unusual for an animal to share deliberately when it could easily hoard the goodies.
To see if he could evoke this kind of behavior in the capuchins, primatologist Frans de Waal of the Yerkes Regional Primate Research Center at Emory University in Atlanta designed an experiment in which two monkeys had to combine their strength to pull a weighted shelf holding a bowl of apple slices. Although both monkeys could see the bowl, a screen blocked one monkey from reaching it. Despite having nothing to gain, this monkey helped its partner about 40% of the time. The monkey who did get the food usually brought it near the other monkey, which could reach through the mesh and take some. In contrast, monkeys who could access the food bowl without help from a second monkey were much less likely to share, de Waal reports in the 6 April issue of Nature. A video  shows the monkeys cooperating.
"This is the first experiment I can think of that shows these monkeys share when they aren't forced to," says Lee Dugatkin, a behavioral ecologist at the University of Louisville in Kentucky. The capuchins probably evolved the sharing behavior because they live in stable social groups and hunt squirrels together, says Paul Garber, a specialist in monkey behavior at the University of Illinois, Urbana-Champaign. And they live for as many as 45 years, he says, "so they have plenty of opportunities to reciprocate."