A study found that the violence displayed by chimpanzees was not caused by human disturbances, but rather the behavior is innate to the species. 

Ian Gilby, an anthropologist and study leader from Arizona State University, worked with his colleagues to determine if the violence observed in wild chimpanzees is part of the animals' natural behavior or if it is caused by human interferences.

In the 1970s, Jane Goodall first reported about violence seen in chimpanzees. Since then, researchers attempted to find out the cause of their violence. Some experts postulated that it could be a reflection of primitive warfare, and others assumed that the violence was due to human disruptions, such as artificial feeding or destruction of habitats. 

"This study debunks the idea that lethal aggression among wild chimpanzees is an aberrant behavior caused by human disturbances, like artificial feeding or habitat loss," Gilby said in a press release.

The latest research is backed by five decades of compiled data on 18 chimpanzees and four bonobo (pygmy chimps) groups. Researchers reviewed the data to trace the relationship of violence as an evolved trait to gain more access to food, mates and territory, along with the role that human activities play in the animals' behavior. 

Analyses of 52 attacks revealed that violence toward other members of the group came naturally in the chimpanzees, and was present regardless of any human intervention. Bonobos did not kill members of their group, even with the presence of humans. 

The study comes with a companion article written by ASU scientist, Joan Silk. Silk's research focused on behavioral ecology of primates. In the article, she discussed that debates arguing about human warfare might influence the research in understanding chimpanzee behavioral changes due to human intervention.

"Morally desirable features, such as empathy and altruism, have deep evolutionary roots, whereas undesirable features, such as group-level violence and sexual coercion, do not," Silk wrote.

Further details of the study were published in the Sept. 18 issue of Nature.