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For years, anthropologists have watched wild chimpanzees "go ape" and attack each other in coordinated assaults. But until now, scientists were unsure whether interactions with humans had brought on this violent behavior or if it was part of the apes' basic nature.
A new, 54-year study suggests this coordinated aggression is innate to chimpanzees, and is not linked to human interference.
"Violence is a natural part of life for chimpanzees," Michael Wilson, the study's lead researcher and an associate professor of anthropology at the University of Minnesota in Minneapolis, told Live Science in an email. "They don't need to be fed bananas to kill each other." [Image Gallery: Lethal Aggression in Wild Chimpanzees]
As one of humanity's closest living relatives, chimps can shed light on the evolution of people, such as when humans adopted warlike behaviors, Wilson said.
He and his colleagues collaborated with researchers who are studying chimpanzees and bonobos, another ape that shares a common ancestor with humans. In all, the scientists collected data on 18 chimpanzee groups and four bonobo groups living in Africa.
The chimpanzees exhibited 152 killings, including 58 that the scientists observed, 41 that were inferred and 53 suspected killings in 15 communities, the researchers said. The bonobos had one suspected killing, the researchers said. The different acts of violence did not depend on human impacts, Wilson said.
Instead, attacks were more common at sites with many males and high population densities. Also, chimpanzees in East Africa killed more frequently than did chimps in West Africa, the study found.
Unsurprisingly, the bonobos showed little violence. "We didn't find any definite cases of killing by bonobos, though there was one case of a male bonobo who was severely attacked by members of his own group and never seen again," Wilson said.
The study was published Wednesday (Sept. 17) in the journal Nature.