Chimps: Natural-born killers

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Why do chimpanzees kill one another? For years, many studies have shown that chimps that were observed killing one another had become more aggressive only when humans encroached on their environment. But new studies have lent weight to an alternative theory: Chimpanzees are, like humans, natural-born killers who use violence as a means of expanding their territory and increasing their access to food and mates.

Researchers observed 18 chimp communities in the wild over 50 years, and they observed 152 fatal incidents of chimp-on-chimp aggression. The researchers noted no connection between violence and loss of habitat because of human encroachment: Most of the attacks occurred in fairly remote areas, with groups of male chimps— sometimes as many as 32—attacking single males from other communities. “They’ll tear off pieces of the body, often the genitalia, and sometimes they’ll rip the throat out,” says Michael Wilson, from the University of Minnesota. “It’s really horrific, the sorts of damage they do.”The warfare often led to increased access to females and food, with the most aggressive chimps achieving dominant status in their groups.

Since chimps are our closest evolutionary cousins, researchers said their willingness to kill indicates that violence has “a long evolutionary history” among primates and predates Homo sapiens.