Killing among wild chimpanzees has deep evolutionary roots and is not due to human interference, a major global study on the contentious topic has suggested.
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 amongst chimpanzees.
But the new findings, published in Nature, suggest this is not the case, the BBC reported.
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.
The key findings indicate that a majority of violent attackers, and victims of attack, were male. This was consistent with the theory that these acts of violence are driven by adaptive fitness benefits, rather than human impacts, the researchers said.
Chimpanzees live in well-defined colonies, and groups of males patrol the borders of each colony's territory. This is where violent conflicts are known to arise, particularly if a patrol encounters a single chimp from a neighbouring community - but never before has this much data on the lethality of those interactions been combined in a single study.
When the scientists compared the figures across chimpanzee research sites, they found that the level of human interference had little effect on the number of killings.
Instead, it was basic characteristics of each community that made the biggest difference: the number of males within it, and the overall population density of the area.
These parameters link the violence to natural selection: killing competitors improves a male chimp's access to resources like food and territory - and crucially, it will happen more frequently when there is greater competition from neighbouring groups, and when the males can patrol in large numbers, with less risk to their own survival.
Prof Frans de Waal, an animal behaviour expert from Emory University in the US, said the new study was an important contribution.
"I'm very glad they're publishing this," he told BBC News. It answers a "long, long history of resistance", Prof de Waal explained, to the idea of natural, inter-community violence in chimpanzees.
"It has always been contentious - we've had meetings where people screamed at each other.
