From the NYT:
Lethal Violence in Chimps Occurs Naturally, Study Suggests
By JAMES GORMAN SEPT. 17, 2014
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.
Obviously, stereotype threat is at fault. Or lack of universal pre-K. Redlining no doubt plays a role. Clearly, the police dressing in military body armor contributes. Whatever it is, we know that chimps have no agency and thus can’t possibly be responsible for their high rate of chimp-on-chimp violence.
Here’s the abstract:
Observations of chimpanzees (Pan troglodytes) and bonobos (Pan paniscus) provide valuable comparative data for understanding the significance of conspecific killing. Two kinds of hypothesis have been proposed. Lethal violence is sometimes concluded to be the result of adaptive strategies, such that killers ultimately gain fitness benefits by increasing their access to resources such as food or mates. Alternatively, it could be a non-adaptive result of human impacts, such as habitat change or food provisioning. To discriminate between these hypotheses we compiled information from 18 chimpanzee communities and 4 bonobo communities studied over five decades. Our data include 152 killings (n = 58 observed, 41 inferred, and 53 suspected killings) by chimpanzees in 15 communities and one suspected killing by bonobos. We found that males were the most frequent attackers (92% of participants) and victims (73%); most killings (66%) involved intercommunity attacks; and attackers greatly outnumbered their victims (median 8:1 ratio). Variation in killing rates was unrelated to measures of human impacts. Our results are compatible with previously proposed adaptive explanations for killing by chimpanzees, whereas the human impact hypothesis is not supported.
I’d recommend my 1999 National Review article on what we can learn about human nature from comparing five Great Apes species, “Chimps and Chumps” for a review of the epistemological issues:
Looking for insight into human nature by studying our closest relatives in the evolutionary tree, our fellow primates, has become a popular intellectual pastime. For guidance on how to live, we increasingly look less to scriptures and more to our cousins with the low foreheads. Now, there are limits to how valuable a role model our furry friends can provide. While no ape would have been so stupid as to have gotten America into our current Banana War with the European Union, none would be smart enough to get us out either. Conversely, those things that all us primates clearly agree upon (e.g., Bananas: Good! Mother Love: Good! Falling out of Tree: Bad!) tend to be unilluminating.
No, what we want apes to tell us are the answers to those fundamental questions about sex and violence that we humans can’t agree upon. What makes this mode of inquiry so popular — yet so fruitless — is that anybody can turn to their favorite primate for support for their favorite lifestyle. Consider sex and family structure. As any upper-middle class American in 1999 can tell you, nature intended us to live in monogamous, egalitarian, affectionate pairs, like Helen Hunt and Paul Reiser on Mad About You. If you doubt it, just ask our fifth closest cousins, those elegant tree-swinging gibbons.
If you’re an NBA star, however, who likes to drop in only every so often on the various mothers of your babies, our fourth closest cousin, the orangutan of Southeast Asia provides all the justification you need..
Each of our three closest relatives is just as useful (if just as inconclusive) an example to somebody. If ayatollahs took up Darwinism, they would find the Koran vindicated by the noble silverback gorilla, who broods in dignified mastery over his harem. …
Similarly, anti-utopian philosophers find their pessimism about human nature vindicated by the thuggish common chimpanzee, whose basic social unit resembles the Hell’s Angels, complete with murderous raids on other troops and frequent gang-bangs.
However, feminists, aging hippies, and queer theorists have recently discovered to their delight that there is a rare second species of chimp, the bonobo or pygmy chimp.