Rare ‘Chimpanzee Civil War' in Uganda Is Leaving Scientists Searching for Answers
These animals used to be friends, but now they attack each other on sight.
Deep in the forests of Kibale National Park, scientists are closely watching what can only be described as a chimpanzee civil war in Uganda, a rare and unsettling conflict unfolding within one of the largest known groups of wild chimpanzees. Once a closely-knit community of almost 200 people, they've now broken off into rival groups. Their ongoing, coordinated aggression over the years is something researchers find unusual and difficult to fully explain.
@cbcnews Why did these chimps turn on each other? A new study published in the journal Science documents a violent rift among a large group of chimpanzees in Uganda. Researchers estimate that 24 chimpanzees have been killed since January 2018. #science#chimpanzee#cbcradio
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Over the span of a decade, researchers observed how chimpanzees form rival groups and attack individuals who used to be their friends. This unusual phenomenon first became apparent in 2015, when two subgroups from the same community of chimps became scared instead of excited upon reuniting.
How One of the Largest Chimpanzee Groups Split Into Rival Factions
Aaron Sandel, the codirector of the Ngogo Chimpanzee Project, spoke to CNN about the day the Ngogo chimpanzees began to split. While observing apes in Uganda's Kibale National Park, he noticed the chimps falling silent and showing clear signs of nervousness when a group of other chimps appeared. Normally, the animals would greet one another with excited screaming, holding hands, and pats on the back, but this time, some chimps even ran away.
Since then, the Ngogo chimpanzee community has split into two factions named after the areas of the National Park they inhabit: Western and Central. Sandel told CNN, "I think it planted the seeds of polarization, which resulted in the group's downfall."
Related: Grieving Chimpanzee Refuses to Let Go of Baby Who Passed at Spanish Zoo
Violence and competition among the wild animals have only grown since the initial conflict. The first recorded death occurred in 2018 when five Western adult males attacked a Central young adult male named Errol. This was an especially difficult loss for Sandel, who studied Errol for his dissertation.
Currently, the death toll includes seven adults and 17 infants, all from the Central group. Another 14 missing individuals may also be victims of this animals' civil war.
What This Chimpanzee Conflict Could Reveal About Humans
Even though researchers can't be certain what triggered this horrific conflict, examining the origins of this conflict can shed light on human behavior and the reasons behind wars.
"It was the largest known chimpanzee community, so maintaining effective relationships with so many individuals may have become challenging for community members," explained Katie Slocombe, a professor of psychology at the University of York. Interpersonal relationships, environmental factors, and changing social dynamics could all play a role, just as they do in human conflicts.
Scientists may not know how this chimpanzee civil war will end, but being able to observe it firsthand has already provided priceless information into their species and our own.
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This story was originally published April 27, 2026 at 2:45 PM.