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 color and half in another. If a chimp gave the scientists a token of one color, she got a package of food while her partner got none. If she gave the other color, 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 colors equally often. That’s not what happened. All of the chimpanzees were more likely to pick the generous color, up to 66.7 percent of the time. They showed no preference for their relatives versus unrelated chimps.
Carl Zimmer, "Chimpanzees Clear Some Doubt After Generosity is Questioned," New York Times, Aug. 8, 2011. http://www.nytimes.com/2011/08/09/science/09chimp.html