Is warfare in our genes?

Over a decade ago, I became engrossed in Demonic Males: Apes and the Origins of Human Violence, which said chimpanzee males form violent gangs who sneak into neighboring chimp territory to beat isolated males and babies to death and, over time, reduce the neighboring male population to the point that they can seize all their females and territory. It seemed compellingly analogous to human warfare. And the authors argued that modern chimps and modern humans share a genetic propensity for warfare we have inherited from our common ancestors who lived millions of years ago.

One huge caveat is that humans are also about equally related to bonobos, extremely peaceful animals who prefer to solve their differences through sex rather than violence. Also, human existence is not completely Hobbesian. The degree to which our genes predispose us to gang violence remains a hot scientific topic. (I recommend any book by Frans de Waal.)

The factual case for male chimp gang violence has been strengthened:

Every day, John Mitani or a colleague is up at sunrise to check on the action among the chimpanzees at Ngogo, in Uganda’s Kibale National Park. Most days the male chimps behave a lot like frat boys, making a lot of noise or beating each other up. But once every 10 to 14 days, they do something more adult and cooperative: they wage war.

A band of males, up to 20 or so, will assemble in single file and move to the edge of their territory. They fall into unusual silence as they penetrate deep into the area controlled by the neighboring group. They tensely scan the treetops and startle at every noise. “It’s quite clear that they are looking for individuals of the other community,” Dr. Mitani says.

When the enemy is encountered, the patrol’s reaction depends on its assessment of the opposing force. If they seem to be outnumbered, members of the patrol will break file and bolt back to home territory. But if a single chimp has wandered into their path, they will attack. Enemy males will be held down, then bitten and battered to death. Females are usually let go, but their babies will be eaten.

These killings have a purpose, but one that did not emerge until after Ngogo chimps’ patrols had been tracked and cataloged for 10 years. The Ngogo group has about 150 chimps and is particularly large, about three times the usual size. And its size makes it unusually aggressive. Its males directed most of their patrols against a chimp group that lived in a region to the northeast of their territory. Last year, the Ngogo chimps stopped patrolling the region and annexed it outright, increasing their home territory by 22 percent…

The objective of the 10-year campaign was clearly to capture territory, the researchers concluded. The Ngogo males could control more fruit trees, their females would have more to eat and so would reproduce faster, and the group would grow larger, stronger and more likely to survive. The chimps’ waging of war is thus “adaptive,” Dr. Mitani and his colleagues concluded, meaning that natural selection has wired the behavior into the chimps’ neural circuitry because it promotes their survival.

The article notes that many scientists remain sceptical about “group selection.” I’ve long been a big believer in group selection. I was fully persuaded after reading Unto Others: The Evolution and Psychology of Unselfish Behavior in 1999. Most interestingly, group selection can explain both warfare and altruism (or, at least, apparently altruistic behavior). Group selection leads organisms to cooperate within their group and fight collectively against other groups for resources. Many human institutions seem to operate this way.

Posted by James on Wednesday, June 23, 2010