The largest known group of wild chimpanzees has permanently split in two, prompting a series of violent and deadly attacks. The findings, reported in Science, may tell us something about our own species’ propensity for violence.
You may know the Ngogo chimps of Uganda’s Kibale National Park from the Netflix documentary series Chimp Empire, but scientists have been studying them closely for 30 years.
For the first two decades, the community stuck together. Sometimes, small groups broke away in ‘clusters’ to go foraging or travelling, but the divisions were temporary and amicable. When the groups merged back together, everyone still got along. This is known as fission-fusion, and it’s common in chimp communities.
However, things started to change in 2015, when chimps in the Western and Central clusters began to avoid each other. The bigger population started to split.
Three years later, the division was complete, and the chimps now belonged to two separate groups with two separate territories. This sparked a brutal and bloody period of violence, where members of the Western group attacked members of the Central group. Between 2018 and 2024, 20 adults and more than 25 infants were killed. “What’s especially striking is that the chimpanzees are killing former group members,” says Aaron Sandel from the University of Texas at Austin.
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In many primate species, large groups regularly fragment into smaller ones, often reducing competition for resources. But in chimpanzees, permanent fissions are extraordinarily rare. According to genetic evidence, they occur roughly once every 500 years.
Sandel stops short of calling this civil war but suggests that the violence they witnessed may give insight into our own species.
In humans, collective acts of violence are often explained by cultural disparities, such as ethnic or religious differences, which bind groups together and fuel hostility to outsiders. However, this fails to explain conflicts that arise in previously unified communities, as seen in violent rebellions or civil wars.
An alternate theory blames shifting social relationships. The study supports this view because frictions started simmering after a change in the male dominance hierarchy, and the deaths of several key males.
“If relational dynamics alone can drive polarisation and lethal conflict in chimps without language, ethnicity or ideology, then in humans, those cultural markers might be secondary to something more basic,” says Sandel. “If that’s true, then we may have the potential to reduce societal conflicts in our personal lives, and that gives me hope. It may be in the small, daily acts of reconciliation and reunion between individuals that we find opportunities for peace.”
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