The Ngogo chimpanzees may be at an unusual advantage over their neighbors due to the impressive size of their community, which may explain the surprisingly high level of violence observed, the researchers say. There are more than 150 Ngogo chimpsabout three times the number found in chimp communities studied elsewhere.
Despite humans' close evolutionary ties with chimpanzees, Mitani and his colleagues tend not to think that studies of chimps' aggressive tendencies will reveal much at all about the varied and complex reasons that humans go to war. In fact, they say, the findings may have more to tell us about why humans so often work together.
"Using our results to address an enduring question about why humans are an unusually cooperative species may prove to be a more productive line of inquiry," the researchers write. "Our observations indicate that territorial conflict leads chimpanzees in some groups to cede land to members of other groups as a consequence of lethal coalitionary aggression. In the process, chimpanzees in communities that gain territory obtain increased access to resources that are then available to others in the group. Whether this selective factor can override the fitness costs suffered by individuals who cooperate within groups remains a theoretically and empirically challenging problem."
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