Jonathan Webb at the BBC:
Apart from humans, chimpanzees are the only primates known to gang up on their neighbours with lethal results – but primatologists have long disagreed about the underlying reasons.
One proposal was that human activity, including destroying habitats and providing food, increased aggression.
But the new findings, published in Nature, suggest this is not the case.
Instead, murder rates in different chimp communities simply reflect the numerical make-up of the local population.
The international study was co-written by more than 30 scientists and gathers data from some 426 combined years of observation, across 18 different chimp communities.
A total of 152 killings were reported. This includes 58 that were directly observed by researchers; the rest were counted based on detective work – tell-tale injuries or other circumstances surrounding an animal's death or disappearance.
Interestingly, the team also compiled the figures for bonobos, with strikingly different results: just a single suspected killing from 92 combined years of observation at four different sites. This is consistent with the established view of bonobos as a less violent species of ape.
More here.