Uncaring Chimps May Shed Light on Humans, Study Says

John Roach
for National Geographic News
October 26, 2005
The recent outpouring of support for victims of natural disasters may be
the sign of a uniquely human trait: Chimpanzees—our closest living
relatives—are apparently indifferent to the needs of others,
according to a new study.

The research probes the question of why humans have altruistic tendencies.

"This is a very hard question and [is] bound to be very complicated," said Joan Silk, an anthropologist at the University of California, Los Angeles. "We are trying to converge towards an answer by using different methods."

With her colleagues, Silk, who studies the evolution of primate behavior, tested two groups of captive-raised chimpanzees for signs of empathy and concern for others.

The team found chimpanzees are indifferent about doing their neighbor a good deed, even if it causes them no inconvenience. Sometimes they'll do it, sometimes they won't.

Craig Stanford, an anthropologist at the University of Southern California in Los Angeles, said the study is "intriguing" but cautioned against drawing firm conclusions from the results.

"My feeling is insight gained from [captive] raised chimps that have to do with bonding and human-chimpanzee interactions are limited," he said. The behavior of wild chimps may be different, he suggested.

John Mitani, an anthropologist at the University of Michigan in Ann Arbor who studies apes in the wild, said this is "a lovely experiment" that points to a behavioral difference between humans and chimpanzees.

"There are some things you can't examine in the wild, which is why you bring the problem into the lab," he said. "One of the strong points of this experiment is they are looking at a question that is very hard to address in the wild."

Silk's team reports its findings in tomorrow's issue of the journal Nature.

Food Tray

In the study Silk and colleagues presented chimpanzees with an apparatus that gave them two options: They could pull a rope to serve food only to themselves or they could serve themselves and another chimpanzee in an adjacent cage.

According to the results, the chimpanzees were no more likely to choose the second option, even though they could see it would help another chimpanzee at no personal cost. Begging gestures on behalf of some of the recipients had no effect.

As a control the researchers performed the experiment with only one chimpanzee present.

"What we know is they didn't differentiate between situations when another chimpanzee was there and was not there," Silk said.

Whether or not another chimpanzee was present, the chimp in charge chose to the two-food-item option about half the time.

Mitani, the Michigan anthropologist, said that while the result shows indifference among chimps, he wonders why solo chimps chose the two-food-item option so often.

"Put yourself in this experiment, and after you do it for a while you'd notice that that food is going to waste, so you'd say, I'll just do it for myself," he said. "You have to wonder what's going on in their minds."

Interpreting Results

Silk and colleagues said the finding suggests that chimpanzee behavior is not motivated by so-called other-regarding preferences—empathy and a concern for the welfare of others.

They note in Nature that previous research has shown chimpanzees participate in a variety of group activities such as patrolling territory, hunting, sharing food, and guarding mates.

This suggests that in at least some circumstances chimpanzees are cooperative. Anecdotal accounts suggest chimpanzees show empathy toward injured individuals.

But this cooperative behavior is selective, according to Mitani. Research also shows that chimpanzees will kill strangers they encounter in the wild.

"They form strong social bonds with specific individuals and preferentially direct their cooperative behaviors towards those chimpanzees with whom they have developed ties," he said.

What the current study fails to examine, Mitani added, is whether the chimpanzees would show more concern toward individuals with whom they have already formed a bond.

"I can imagine they might pull that bar to get two rewards more often if in fact one of their buddies is next door, compared to somebody they don't like or who they have a rivalry with," he said.

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