"Overall, aggression makes a small percentage of their daily lives," Wilson said, adding that, "our behavior affects them, but it's not affecting them as people have suggested in the past, resulting in aggression."
During the 14 years it spent following the apes, Wilson's team saw two killings - one when a neighboring community killed an infant, and another when a male chimpanzee consumed an infant.īut chimps, an endangered species, are not always warlike, he said.
Wilson and his colleagues followed the chimps and noted the apes' daily activities, such as mating, feeding, grooming, resting and fighting. "But we can learn something about circumstances that may favor the evolution of this type of aggression, such as opportunities to encounter members of neighboring groups when they are on their own," she said. "This is a very important study, because it compiles evidence from many sites over many years, and shows that the occurrence of lethal aggression in chimpanzees is not related to the level of human disturbance," Joan Silk, a professor in the school of Human Evolution and Social Change at Arizona State University, who was not involved in the study, told Live Science in an email.īecause chimps and bonobos do not have the same levels of coordinated lethal aggression, it's impossible to say how the common ancestor acted, Silk said. Some study sites had about 55 chimpanzees living together, he said. When Morgan first arrived, in 1999, the chimpanzees were not afraid of humans, suggesting that this was the animals' first encounter with people, he said.Ĭhimpanzees can live in groups made up of as many as 150 individuals, but group size varies, Wilson said. Fisher Center for the Study and Conservation of Apes at Lincoln Park Zoo in Chicago, have followed the chimpanzees in the study for years. Many of the researchers, including Dave Morgan, a research fellow with the Lester E. "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. Unsurprisingly, the bonobos showed little violence. Also, chimpanzees in East Africa killed more frequently than did chimps in West Africa, the study found. Instead, attacks were more common at sites with many males and high population densities. The different acts of violence did not depend on human impacts, Wilson said. The bonobos had one suspected killing, the researchers said. 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. In all, the scientists collected data on 18 chimpanzee groups and four bonobo groups living in Africa. He and his colleagues collaborated with researchers who are studying chimpanzees and bonobos, another ape that shares a common ancestor with humans. "People have argued that these increasing human impacts could also be putting more pressure on chimpanzee populations, leading to more chimpanzee violence," Wilson said. Loggers cut down forests farmers clear land for crops, and hunters kill chimps for food. As populations in Africa grow, people are infringing on chimpanzee habitats. Yet other scientists counter that human intrusions are to blame for the chimps' coordinated, lethal aggression. Perhaps this behavior originated with a common ancestor some 5 to 7 million years ago, Wilson said. After all, humans and chimpanzees are the only two species in the world known to attack each other in organized onslaughts. But observations of chimpanzees by legendary primatologist Jane Goodall and other researchers challenged the idea that warfare is a modern human development.
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