Chimpanzees and humans have one key trait in common – both are natural born killers, scientists have shown.
Evidence suggests our closest animal relatives have an almost psychopathic tendency towards violence and slaughter that is not the result of human interference.
A widely held theory is that chimps only turn on each other when humans disrupt their habitats. The new research indicates chimps fight and kill to get what they want and "eliminate rivals", say the authors. Killing rates bore no relation to measures of human impact, while competing groups may fight over territory, food or mates.
It is often the innocent who are the victims. In the violent clashes that were investigated, infants were frequently killed, sometimes after being snatched from their mothers.
This is an important question to get right. If we are using chimpanzees as a model for understanding human violence, we need to know what really causes chimpanzees to be violent.
US lead scientist Dr Michael Wilson, from the University of Minnesota