Chimpanzees in Uganda are locked in a deadly ‘civil war’ after their group split apart — and scientists don’t know why
In Uganda, wild chimpanzees are waging a rare “civil war,” which appears to have begun when a huge community split, leading to sustained and deadly conflict between animals that were previously allies and friends.
Conflicts between different groups chimpanzees (Pan troglodytes) are relatively common because they compete for key resourcessuch as fruit trees, water supplies and trees that provide suitable nesting material. However, conflicts within previously unified communities are much rarer.
NOW, Aaron Sandelanthropologist at the University of Texas at Austin, and his colleagues described another, much larger, deadly conflict between the group’s members. Ngogo chimpanzee community in Kibale National Park, Uganda. The work was published Thursday April 9 in the journal Science.
Chimpanzees have been studied there for around 30 years, providing extensive data on their interdependence and behavior. Although they were all part of one large group, they tended to form temporary “clusters” that changed throughout the day as individuals moved through their territory.
But between 1998 and 2014, some of these groups became more regular cliques, like three adult men who were constantly together.
The researchers revealed that starting around 2015, the huge Ngogo community – which then numbered around 200 chimpanzees – split into two distinct groups that lived and bred separately. The core of one group was the clique of three adult men.
At this point, there were still connections between many individuals from the two groups, who still cooperated and bonded, but by 2018 the last social bonds disintegrated and aggression increased while patrolling the borders of their separate territories.
“After splitting into two groups, the chimpanzees in one group began attacking and killing those in the other group, which developed into a period of escalating deadly violence,” Sandel told Live Science.
Deadly raids
The raids resulted in multiple killings of adult men, and as of 2021, researchers have also regularly observed infanticide. The actual death toll in what researchers call a civil war is likely higher because many more people have disappeared without a clear cause, Sandel added.
“I’m a little nervous about talking about civil war,” he said. “Civil war means something very specific when we’re talking about humans, and chimpanzees don’t have nations and that sort of thing, but there’s an important conceptual point when you think about war against strangers versus civil war. These are chimpanzees knowing each other.”
James Brooksan evolutionary anthropologist at the German Primate Center in Göttingen who was not involved in the study told Live Science that he recognized that this conflict was not the same thing as a human civil war, but said the term helped people understand the general idea.
It remains unclear why the division within the community led to such aggressive conflict, but Sandel cited various factors that could have destabilized social bonds. These include unusually large group sizes, competition for food and reproduction, the deaths of five adult males and one adult female in 2014, the shift from one alpha male to another in 2015, and a respiratory outbreak that killed 25 chimpanzees in 2017.
Brooks suggested that the size of the group could have been a factor. “Perhaps they no longer faced such an abundance of resources and became too large a group to maintain cohesion,” he said.
Zoologist Samuni Bookalso at the German Primate Center and co-director of the Taï Chimpanzee project, who was not part of this study, said the Ngogo community is one of the most aggressive that researchers know of. “Kibale National Park is considered a fairly rich environment, with chimpanzees living in high density and for a long lifespan. But even before this split, it was one of the most violent chimpanzee communities in terms of encroaching on neighbors,” she told Live Science.
Between 1998 and 2008, the Ngogo’s chimpanzees killed at least 21 chimpanzees from neighboring groupsand expanded across their territory, leading to population growth.
The civil war continues, Sandel said. The research paper covers data collected through 2024, but it claims other attacks took place in 2025 and 2026.
According to him, this work shows that even without ethnicity, religion or political ideology, social networks can divide, leading to collective violence.
Given that chimpanzees are one of man’s two closest relativesThe finding reiterates how group divisions can pose a danger to human societies, Brooks said, but he adds that it doesn’t mean the conflict is biologically determined. He emphasized bonobos (Pan paniscus) — our other closest relatives — which form stable and distinct groups. They are also aggressive, but unlike chimpanzees, they do not engage in such deadly group conflicts but form tolerant and cooperative associations, so such conflicts are not determined by evolution.
“Our evolutionary past does not determine our future,” he said.
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