The deadly inheritance of chimps and humans

Illustration for article titled The deadly inheritance of chimps and humans

A new study of chimp behavior reveals that humans share something deadly with our genetic cousins. Chimps routinely wage war on their own species, murdering neighbors to gain new territory. Did we inherit warlike urges from a common ancestor?


For ten years, a group of researchers tailed a large group of chimps through Uganda's Kibale National Park. They dubbed this group of over one hundred strong the "Ngogo chimps," after the region where they live - and make war. Over the past decade the researchers observed that the Ngogo went on raids into the territory of nearby chimp groups about every ten days. If they came upon a lone member of the "enemy," they would kill him. If it was a female, her life would be spared but they would eat her children. The researchers dubbed these behaviors "patrolling," since they mostly took place at the boundaries of the Ngogo territory.

But last year, the raids stopped - the Ngogo had simply annexed a territory nearby that had once belonged to another troop. The scientists speculated that the chimps were making war in order to expand their territory. Similar kinds of behaviors have been observed among other chimp troops, but this was the first study where the scientists were eyewitnesses to the carnage. Primate expert Jane Goodall also observed chimp war, but it was never clear whether her involvement with the chimps, feeding them bananas to gain their trust, had caused the behavior.


Nicholas Wade writes in the New York Times:

But can the chimps themselves foresee the outcome of their behavior? Do they calculate that if they pick off their neighbors one by one, they will eventually be able to annex their territory, which will raise their females' fertility and the power of their group? "I find that a difficult argument to sustain because the logical chain seems too deep," says Richard Wrangham, a chimp expert at Harvard.

A simpler explanation is that the chimps are just innately aggressive toward their neighbors, and that natural selection has shaped them this way because of the survival advantage that will accrue to the winner.

Warfare among human groups that still live by hunting and gathering resembles chimp warfare in several ways. Foragers emphasize raids and ambushes in which few people are killed, yet casualties can mount up with incessant skirmishes. Dr. Wrangham argues that chimps and humans have both inherited a propensity for aggressive territoriality from a chimplike ancestor. Others argue the chimps' peaceful cousin, the bonobo, is just as plausible a model for the joint ancestor.

Humans and chimps diverged on the evolutionary tree only about 5 million years ago. Studies like this inevitably raise the question of whether homo sapiens' territorial aggression is an ancient urge that we share with chimps. Most scientists say we'll never know for sure. We may have inherited behaviors that resemble those of another genetic cousin, the peaceful bonobos. And of course, human behavior has evolved radically over the millions of years since we parted ways with chimps. Even a strict evolutionary psychologist type like Steven Pinker would argue that humans are hardwired to invent ethical strategies, so our urge to stop making war may be just as ancient as the urge to start one.

via New York Times

Image by researcher John Mitani


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"And of course, human behavior has evolved radically over the millions of years since we parted ways with chimps."

Absolutely. What less often gets mentioned, for whatever reason, is that chimpanzees have also been evolving and there is no reason to outright assume that their habits and behaviours today represent those of our last common ancestor. Any evolutionary modeling done using chimps or other great apes should acknowledge that these animals have also had to adapt to a changing planet, even if they didn't manage to conquer the globe like their human cousins.

Cladistically we are equally close to chimps and bonobos on the ape family tree. It's telling that the behaviours of both groups are so markedly different from each other. I don't think studying ape behaviour is without merit, it gives us insight into how certain social behaviours might evolve. It seems mainstream culture likes to extrapolate grand statements about human society from these studies, though, and that's where we should be skeptical.