A long-stable community of wild chimpanzees in western Uganda descended into years of lethal violence after splitting into rival factions, in what researchers say is the clearest documented case of such a breakdown within a single group.
Scientists studying the Ngogo chimpanzees in Kibale National Park observed that, after decades of cohesion, the large community divided into two groups that went on to wage sustained, coordinated attacks against each other.
Since 2018, one faction has killed at least 28 members of the other, targeting adult males and infants in assaults that researchers described as brutal and highly organised.
The study, published in the journal Science, tracked the group over nearly 30 years. The Ngogo community, first studied in 1995, was once the largest known group of wild chimpanzees, with around 200 individuals—far exceeding the typical group size of about 50.
Researchers said the split likely stemmed from a combination of pressures, including intense competition for food and mates as the group grew, disease outbreaks that disrupted social bonds, and shifts in leadership among dominant males.
Tensions began to emerge around 2015, when subgroups started avoiding each other. By the end of 2017, the community had fractured into two distinct factions, known as the Western and Central groups.
Violence escalated the following year, with members of the Western group launching repeated attacks on their former companions. Researchers documented killings involving coordinated beatings, biting and prolonged assaults, often resulting in fatal internal injuries.
While chimpanzees are known to attack rival groups, scientists said this case is unusual because the violence occurred between individuals that had grown up together and previously cooperated.
Despite comparisons to human conflict, researchers cautioned against drawing direct parallels, noting that chimpanzees and humans have evolved along separate paths for millions of years.
The findings nevertheless offer rare insight into how social breakdown, competition and environmental pressures can trigger sustained violence—even among closely bonded communities.