Despite our wars and crime, humans tend to be nice. We bake for our neighbors, give directions to strangers, and donate money to far-off disaster victims. But does the same go for our closest cousin, the chimpanzee? A new study suggests that it does.
People who study chimpanzees in the field have known for a long time that the apes console their comrades when they're upset and support each other in a fight. And when one chimp has a good hunting day and kills a nice, juicy monkey, it shares the meat with the other members of its group.
But scientists have found that chimps don't share in lab experiments, creating a bit of a primatology mystery. For instance, when researchers gave captive chimps the opportunity to get rewards just for themselves or for both themselves and another chimpanzee from an apparatus with multiple interconnected trays, the apes were equally likely to choose the selfish and sharing options.
Comparative psychologist Victoria Horner of Emory University in Atlanta thought she knew the reason why experiments didn't find sharing: the experimental setups other scientists used to test the chimps were just too confusing—"tables with pulley systems and whatnot." For one study, she says, "I had to read it several times before I understood the apparatus, and I'm a human." She thinks the chimps didn't understand how what they did affected their partner.
With her colleagues at Emory, including renowned primatologist Frans de Waal, Horner devised a new way to test chimps' generosity. "We did the same basic idea but from a more chimpy perspective," she says. In each experiment, two female chimps that live at the Yerkes National Primate Research Center in Lawrenceville, Georgia, were put in side-by-side rooms with a mesh-covered opening between them. Both chimps had been trained to "buy" food from the researchers with tokens, colored, 5-centimeter-long pieces of PVC pipe. The team taught one chimp of the pair that a token of one color would get her a piece of banana, whereas the other color would get fruit for her and her partner. Then she was given 30 chances to choose from a bucket containing both kinds of tokens. The researchers tested seven female chimps three times each with different partners. The partner watched the whole time, sometimes fussing when the other chimp didn't reward her.
Chimps picked the token that gave them and their partners a piece of banana between 53% and 67% of the time, the team reports online today in the Proceedings of the National Academy of Sciences. That result means this kind of generosity isn't a uniquely human trait, Horner says. In fact, she thinks humans should get over the idea that we have abilities that no other animals have.
It's not just generosity, she says. Chimps have culture and make tools, both of which have been thought of as uniquely human traits. "We need to stop trying to find what makes us unique and come to peace with the fact that we are members of the animal kingdom."
These results make sense to Christophe Boesch, a primatologist at the Max Planck Institute for Evolutionary Anthropology in Leipzig, Germany. He studies chimpanzees in the field, so he was perplexed by earlier studies that found captive chimpanzees weren't nice to each other. "I personally felt, from my knowledge of chimpanzees, something had to be wrong with the experiment," he says. He thinks Horner and her colleagues got it right. "By increasing the social and ecological validity of their experiments, they have been able for the first time to duplicate what field researchers already knew was a natural ability of chimpanzees."
Now that researchers know how to get captive chimpanzees to respond like wild chimpanzees, they can do more experiments to study chimp altruism and understand more about how it evolved.
Samuel Bowles, a behavioral scientist at the Santa Fe Institute in New Mexico, points out that altruism usually refers to an action that hurts the one who's doing it. "Me giving you something at no cost to myself is not altruistic. It's just non-nasty." Because a lot of animals are nasty, it's worthwhile to find out that chimps aren't, he says. But because the chimps in this study weren't hurting themselves by getting a piece of banana for their partner, the behavior doesn't count as altruism.