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 forest habitats or food supplies.
The research indicates this is wishful thinking. In reality, chimps fight and kill to get what they want and “eliminate rivals”, say the authors.
Competing groups of the animals go to war over resources such as territory, food or mates, the study found. And, just as in human conflict, it is often the innocent who are victims. In the violent clashes investigated by the scientists, nursing infants were frequently killed, sometimes after being snatched from their mothers. A 30-strong team of researchers analysed five decades of data from 18 chimpanzee and four bonobo study sites in east, west and central Africa. Bonobos, another member of the ape genus Pan, are endangered close relatives of chimpanzees said to display positive human behavioural traits such as altruism and empathy.
Attackers were usually males acting together, and victims mostly males and nursing infants of other groups who were unlikely to be close kin.
Intercommunity attacks accounted for 66 per cent of killings and usually victims were strongly out-numbered, typically with odds of eight to one.
A key finding was that killing rates bore no relation to measures of human impacts.
The researchers considered three human variables likely to influence chimp behaviour – artificial feeding of wild apes, the size of a protected area − with those that are smaller experiencing more impacts − and environmental disturbance.
They found that killings increased as the number of males and population density rose, but none of the human factors had any effect.
Writing in the journal Nature, the researchers concluded: “Patterns of lethal aggression in Pan show little correlation with human impacts, but are instead better explained by the adaptive hypothesis that killing is a means to eliminate rivals when the costs of killing are low.”