From the NYT:

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

A new study, published Wednesday in Nature, is setting off a new round of debate around this question.

The study’s authors argue that a review of all known cases when chimpanzees or bonobos in Africa killed members of their own species shows that violence is a natural part of chimp behavior and not the result of actions by humans that push chimp aggression to lethal attacks.

The researchers say their analysis supports the idea that warlike violence in chimps is a natural behavior that evolved because it can provide more resources or territory to the killers, at little risk.

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

While the study ostensibly is about chimpanzees, it is also the latest salvo in a long and profound argument about the nature of violence in people, as chimpanzees are humans’ closest relatives in the animal world.

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

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

Males are more likely to kill than females. Killing chimps in other groups is more common than killings within groups. And chimps tend to attack when they have overwhelming odds on their side.

The argument is about why chimps 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 chimp sites and the numbers of killings.

He said that 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. …

Robert Sussman, an anthropologist at Washington University who supports the idea that human impacts put pressure on chimp societies that result in killings, was dismissive of the paper. “It doesn’t establish anything, really,” he said.

“The statistics don’t tell me anything,” he said. Two sites provided most of the data, he said, while the other 20 communities had few killings. The paper also grouped together killings that were observed, inferred and suspected. There were male killings of males, but also killings of females and infants. And, he said, “They haven’t established lack of human interference.”

… Lurking behind the discussion of chimps is a long-running dispute over whether chimp behavior offers insights about human behavior, as well as an even deeper and older philosophical dispute over whether violence and war are natural for human beings.