Humans Likely Not The Reason That Chimps Attack And Kill Each Other

Chuck Bednar for redOrbit.com – Your Universe Online
Chimpanzee-on-chimpanzee violence is not the result of increased aggression resulting from exposure to human activities, researchers from the University of Minnesota and an international team of colleagues report in the latest edition of the journal Nature.
Rather, an in-depth analysis of lethal aggression among different groups of mankind’s closest relatives revealed that the behavior is an adaptive strategy which evolved so the creatures can eliminate rivals and gain better access to resources or territory, lead author Michael L. Wilson and his associates explain in the study.
Wilson and his colleagues spent five decades studying the behavior of chimpanzees in Africa, attempting to solve the mystery as to why they are the only creatures other than humans to engage in coordinated attacks on other members of the same species – behavior first observed by British anthropologist Jane Goodall in the 1970s.
“Observations that chimpanzees kill members of their own species have influenced efforts to understand the evolution of human violence,” said University of Michigan anthropologist John Mitani, who helped come up with the idea for and was one of more than 30 experts from the US, Germany and elsewhere involved in the research.
According to the researchers, the study provides “compelling evidence” that this type of killing is an evolved tactic, not an incidental result of aggression made worse by human activities such as deforestation. The findings indicate that human interference and encroachment is not actually an influential predictor of chimp-on-chimp aggression.
Wilson, Mitani and their colleagues compiled and analyzed roughly 50 years worth of research data pertaining to 18 different chimpanzee communities and four groups of bonobos, the creatures’ kinder, gentler cousins. The authors found that chimps were no more likely to attack each other when human interference like feedings or habitat destruction occurred, and the bonobos would not kill one another, even when exposed to those same manmade disturbances, said Rachel Feltman of the Washington Post.
The study authors reported that approximately 150 chimpanzees were confirmed or suspected to have been killed by other members of their own species during the course of the study, noted USA Today’s Traci Watson. Richard Wrangham, a primatologist at Harvard University and co-author of the study, told Watson that chimps patrol their territories in large groups and that their social structure leads to “a tendency… to kill neighbors.”
The chimpanzees responsible for the attacks were invariably male members of the species who acted together in groups, the researchers said. Their victims tended to be other males and nursing infants of other communities, and were unlikely to be closely related to the aggressors. When young chimps were killed, the attackers sometimes removed them from their mothers in situations where they could have also killed her, but chose not to do so.
“Humans have long impacted African tropical forests and chimpanzees, and one of the long-standing questions is if human disturbance is an underlying factor causing the lethal aggression observed,” said co-author Dr. David Morgan, a research fellow with the Lester E. Fisher Center for the Study and Conservation of Apes at Chicago’s Lincoln Park Zoo.
“A key take-away from this research is that human influence does not spur increased aggression within or between chimpanzee communities,” he added. “The more we learn about chimpanzee aggression and factors that trigger lethal attacks among chimpanzees, the more prepared park managers and government officials will be in addressing and mitigating risks to populations particularly with changing land use by humans in chimpanzee habitat.”