Lethal Violence in Chimps Occurs Naturally, Study Suggests

Are chimpanzees naturally violent to one another, or has the intrusion of humans into their environment made them aggressive?

A study published Wednesday in Nature is setting off a new round of debate on the issue.

The study’s authors argue that a review of all known cases of when chimpanzees or bonobos in Africa killed members of their own species shows that violence is a natural part of chimpanzee behavior and not a result of actions by humans that push chimpanzee aggression to lethal attacks. The researchers say their analysis supports the idea that warlike violence in chimpanzees is a natural behavior that evolved because it could provide more resources or territory to the killers, at little risk.

But critics say the data shows no such thing, largely because the measures of human impact on chimpanzees are inadequate.

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In studying chimpanzee violence, “we’re trying to make inferences about human evolution,” said Michael L. Wilson, an anthropologist at the University of Minnesota and a study organizer.

There is no disagreement about whether chimpanzees kill one another, or about some of the claims that Dr. Wilson and his 29 co-authors make.

The argument is about why chimpanzees kill. Dr. Wilson and the other authors, who contributed data on killings from groups at their study sites, say the evidence shows no connection between human impact on the chimpanzee sites and the number of killings.

He said the Ngogo group of chimpanzees in Uganda “turned out to be the most violent group of chimpanzees there is,” even though the site was little disturbed by humans.

They have a pristine habitat, he said, and “they go around and kill their neighbors.”

Robert Sussman, an anthropologist at Washington University who supports the idea that human actions put pressure on chimpanzee societies that results in killings, was dismissive of the paper. “The statistics don’t tell me anything,” he said. “They haven’t established lack of human interference.”

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