It’s obvious that humans are fundamentally different from other animal species. It’s not so easy, though, to identify the traits that make human beings so special. Scientists realized long ago that other animals make tools, play jokes and even have a sense of justice and altruism—all things we once thought were unique to our species.
Now a paper in the journal Current Biology has added another behavior to the list of what other animals share with us—and this one isn’t quite so charming. After years of field observations in Uganda’s Kibale National Park, John Mitani of the University of Michigan and several colleagues have concluded that chimps wage war to conquer new territory.
"We already knew that chimps kill each other," says Mitani. "We’ve known this for a long time." What scientists didn’t know for certain, at least in cases in which groups of chimps banded together to kill others, was why. One hypothesis, advanced more than a decade ago by anthropologist Richard Wrangham, was the idea of territorial conquest; circumstantial evidence from both Gombe and Mahale national parks in Tanzania bolstered the theory.
In Mahale, for example, male members of one group mysteriously vanished, and another group then expanded into what had been their land. In Gombe, an existing group dissolved into civil war, resulting in killings and land takeovers.
What’s especially chilling about the observation is that the murder rate appears to be so high. The anthropologists couldn’t be certain of how big a band the victims belonged to because they weren’t used to a human presence and thus couldn’t be accurately counted. But even a conservative estimate suggests that the death rate is significantly higher than you would see in war between human hunter-gatherer groups.
Mitani isn’t oblivious to the lesson some people might draw from the study. "Invariably, some will take this as evidence that the roots of aggression run very deep," he says, and therefore conclude that war is our evolutionary destiny. "Even if that were true," says Mitani, "we operate by a moral code that chimps don’t have."
Apart from that, he points out, the Pan troglodytes chimps he studies are one of two subspecies. The other is called Pan paniscus, also known as bonobos, and, says Mitani, "the latter, as far as we know, aren’t nearly as aggressive with respect to intergroup relations. Yet they’re equally close to us." That means that if we’re wired for warfare, we’re wired for peace too. Ultimately, the route we choose is still up to us.
John Mitani concludes that chimps（）
A. are hard to approach under some circumstances
B. tend to be aggressive against others on some occasions
C. have many similar traits as human beings
D. may kill each other for some reasons unknown
