Researchers studying different African communities of wild chimpanzees have pooled their data and found that the apes sometimes kill each other nearly everywhere they’ve been studied. Chimp homicides occurred most frequently in groups with the most adult males, anthropologist Michael Wilson reported at the American Association of Physical Anthropologists’ annual meeting.

Chimps spend most of their time in peaceful pursuits, such as playing, foraging and grooming each other. Yet researchers have long described occasional chimp homicides. Some investigators have speculated that these animals get lethally riled up by human intrusions, such as deforestation, hunting and feeding of chimps by eco-tourists. But the new study found that chimp communities with the most documented killings had no or only rare encounters with humans. Groups of males carried out most killings, and most victims were male adults and infants in neighboring communities.