These Wild Chimps Have Been Fighting in a ‘Civil War’ for Nearly a Decade. It’s the Bloodiest Split Ever Seen Among Their Kind

The Ngogo chimpanzees in Uganda have divided themselves into two main factions, and dozens of deaths have been recorded since the split in 2018. A new study details the unprecedented violence, which could shed light on the evolutionary underpinnings of human warfare

Sara Hashemi | Daily Correspondent

April 10, 2026

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Since 1995, scientists have kept a watchful eye on the Ngogo chimpanzees in Uganda’s Kibale National Park. For around two decades, the wild apes coalesced as a unified group that mated and hunted together, although they divided themselves into three tighter-knit factions: the Western, Central and Eastern clusters.

However, on June 24, 2015, researchers witnessed an unusual change.

That day, Aaron Sandel, now a primatologist at the University of Texas at Austin, and his colleague John Mitani, a primatologist at the University of Michigan, watched as chimpanzees from the Western cluster approached members of the Central one. Instead of their usual mingling, “all hell broke loose,” Mitani tells Carl Zimmer at the New York Times.

Screaming and fighting ensued. The Western chimps ran away, but the Central ones chased them. “Nothing like that had been observed before,” Sandel tells Scientific American’s Jason P. Dinh.

After that confrontation, things got more violent—and two distinct groups eventually emerged, culminating in an ongoing “civil war” among the largest-known community of wild chimpanzees. Details about the fallout and deadly conflict, described in a study published April 9 in the journal Science, could help scientists understand the evolutionary underpinnings of human warfare.

Tensions grew after the first witnessed hostile encounter. Western and Central males began patrolling their territories for one another, and aggressive interactions escalated. In 2017, Western chimps attacked and severely injured the Central cluster’s alpha male, even though he had previously been part of the Western group. By the next year, the Ngogo chimps had split into two distinct factions.

From 2018 to 2024, Sandel, Mitani and their colleagues found evidence that Western chimpanzees killed seven adult males and 17 infants from the Central group. Another 14 animals in the cluster disappeared, although without bodies, the scientists don’t know whether Western chimps are to blame. The Central males have not killed any Western chimps in that time, despite outnumbering them. Meanwhile, the Eastern cluster seems to have allied with the Central group, although they’re not engaging in the fight, per the Times.

While violence among wild chimpanzees is not unusual, researchers have never witnessed it at this level. Genetic evidence suggests that such a “civil war” probably happens once every 500 years among the animals.

The scientists aren’t sure what sparked the lethal aggression, although they suspect the Ngogo group’s massive size of nearly 200 individuals played a part. Perhaps competition for food or mates drove a wedge between the animals, or maybe there were too many group members to maintain social relationships.

“If you’re not engaging in those daily practices holding everything together, the social glue starts to fall apart,” says Catherine Hobaiter, a primatologist at the University of St. Andrews in Scotland, who was not involved in the research, to Christina Larson at National Geographic.

The bloodshed among the Ngogo chimps might shed some light on what violence looked like among our human ancestors. “These findings tell us indeed that these civil-war-like types of conflicts were possible in the course of human evolution,” says Sylvain Lemoine, a primatologist at the University of Cambridge in England, who did not participate in the research, to the Times.

Although it’s tempting to attribute human war to ethnic, religious or political divisions, the study authors write, that overlooks the social processes—shared by many of our close relatives, like chimps—that shape human behavior.

“You do not need ideology to generate hostilities,” says Richard Wrangham, a primatologist at Harvard University, who was not involved in the study, to Science’s Jon Cohen. “The motivations for warfare are much more concerned with our biology than people would have believed a long time ago.”

Sara Hashemi | Read More

Sara Hashemi is a science writer and fact-checker currently based in New York City. Her work has appeared in Sierra, The Body, Maisonneuve magazine and more.