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Like Humans, Chimp Males Cooperate With Kin and Non-Kin Alike

Sean Markey and Victoria Jaggard
for National Geographic News
April 25, 2007
 
Bees do it. Monkeys do it. We do it. Cooperate, that is.

Why humans cooperate and why we select particular collaborators are questions scientists have puzzled over for years.

Now research into the behavior of chimpanzees—our closest confirmed genetic relations—is providing new insights into the ways kinship affects cooperation.

The work also offers some of the first evidence that humans are not the only species to develop complex cooperation with both relatives and nonrelatives.

Kevin Langergraber, a biological anthropologist at the University of Michigan, led the six-year study of chimps in Kibale National Park, Uganda.

By combining field observations with DNA analysis of fecal samples, his team found that male chimps prefer to work with their brothers by the same mother.

The chimps often teamed up with these siblings to perform one of six observed behaviors, such as grooming fur or forming a two-chimp alliance to beat up a third individual.

But the scientists also discovered that male chimps frequently cooperate with unrelated or distantly related males in their community to perform tasks such as group hunts for red colobus monkeys or patrolling territory boundaries for intruders.

Langergraber team's results appear today in the early online edition of the Proceedings of the National Academy of Sciences.

Kin Selection

Why humans, chimps, or any other animal evolved cooperative behavior gets at the age-old question, What's in it for me?

(Related news: "Monkeys Show Sense of Fairness, Study Says" [September 17, 2003].)

"Well, like everything in biology, we assume that it's going to increase our reproductive success," Langergraber said.

That success can be direct, like finding a mate and having offspring. Or it can be indirect, like helping out a relative and thus advancing the family bloodline.

The family-bloodline scenario is the basis of a theory called kin selection, which holds that animals should prefer to cooperate only with their relatives.

In so doing, they reap the indirect but substantial benefit of seeing their family genes passed on—by becoming an uncle or an aunt in addition to, or instead of, a parent.

"Most people had assumed that in animals it's mainly … through kin selection that cooperative behavior can evolve," Langergraber said.

"But here we're suggesting that's not entirely the case with chimpanzees, who are famous for being one of the most cooperative animals in the world."

Emory University primatologist Frans de Waal said: "I think we have long known or suspected that chimpanzee males cooperate very well with nonrelatives."

Nonetheless, some economists and anthropologists have "preferred to depict chimpanzee cooperation as mainly kin-based" to make the claim that human cooperation is unique, he noted.

"Now we finally have a study that includes not only [chimp] behavior but also genetics, giving us the ultimate proof that non-kin cooperation is extremely well-developed in wild chimpanzees," de Waal wrote in an email.

"This study will put to rest once and for all that only humans know reciprocity-based cooperation. As such, it is highly significant."

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