Chimpanzees Turn on Former Friends After Brutal Attack on Mothers and Babies

In a rare and violent turn of events, researchers have documented a “civil war” among a community of chimpanzees in Uganda, where former social partners and allies turned into lethal enemies. The conflict, occurring within the world’s largest known chimpanzee group, has rewritten scientific understanding of primate violence by demonstrating a permanent group fission that resulted in targeted, years-long campaigns of aggression.

The study, published in Science, focuses on the Ngogo chimpanzees living in Kibale National Park, Uganda. Whereas inter-group conflict between stranger chimpanzees is well-documented, this event is distinct because it involved individuals who had previously shared grooming ties and long-term social bonds. Scientists estimate that such a level of internal community fracture and subsequent warfare occurs only once every 500 years.

The transition from a cohesive community to warring factions was not immediate but unfolded over several years. Starting around 2015, the community—which consisted of approximately 200 chimpanzees—began to polarize. Social ties frayed and neighborhoods within the group hardened into distinct factions. By 2018, the split became permanent, dividing the population into two primary groups: the Central group and the Western group.

What followed was a brutal shift in power dynamics. The smaller Western group launched a series of targeted raids into the territory of the larger Central group. Over a six-year period, these attacks resulted in the deaths of at least seven adult males and 17 infants, according to data detailed by BBC Science Focus. These figures are believed to be an undercount, as an additional 14 adult and adolescent Central males disappeared or died unexpectedly between 2021 and 2024 without any prior signs of illness.

The Anatomy of a Chimpanzee Civil War

The Ngogo conflict is fundamentally different from typical chimpanzee aggression. Most primate warfare occurs between unrelated groups competing for territory. However, the Ngogo split involved “friend to enemy” transformations. Prof Aaron Sandel of the University of Texas at Austin, the lead author of the study, noted that this provides a rare window into the chimpanzee mind, showing how former companions and groomers can turn on one another.

The process of polarization began with the hardening of neighborhoods. As social bonds broke down, shared territory—once a communal resource—became a contested border. The Western group’s strategy involved systematic raids, which eventually allowed them to surpass the larger Central group and become the dominant force in the jungle.

This level of documentation is unprecedented in primatology. While a suspected fission in Gombe, Tanzania, during the 1970s too resulted in lethal violence between former groupmates, that case was complicated by limited observational data and the effects of provisioning practices. In contrast, the Ngogo community has been studied continuously for three decades, allowing scientists to watch the violent split unfold in “slow motion.”

Comparing the Ngogo Split to Previous Observations

To understand why the Ngogo event is so significant, This proves helpful to compare it to previous documented instances of primate fission. The following table outlines the key differences between the Ngogo “civil war” and earlier suspected events.

The Human-Like Complexity of Primate Violence

The findings published in Science suggest that chimpanzee social structures are more fragile and complex than previously assumed. The fact that a single cohesive group of 200 individuals could fracture into warring factions indicates a level of social volatility that mirrors some aspects of human conflict. The targeted nature of the raids, specifically against infants and adult males, suggests a strategic effort to destabilize the rival faction’s future and current leadership.

The impact of this conflict has been devastating for the Central group. The loss of 17 infants and the disappearance of 14 additional adult or adolescent males between 2021 and 2024 represent a massive blow to the group’s demographic stability. This attrition allowed the Western group, despite starting as the smaller entity, to seize dominance through a campaign of lethal attrition.

According to ScienceBlog, this event rewrites the understanding of primate violence by proving that permanent group fission backed by lethal, targeted aggression is a reality in wild chimpanzee populations, provided the social conditions for polarization are met.

Key Takeaways from the Ngogo Conflict

• Rare Event: Scientists estimate this type of internal community “civil war” occurs only once every 500 years.
• Social Polarization: The split began around 2015, with social ties fraying and neighborhoods hardening into factions.
• Lethal Outcomes: The Western group killed at least 7 adult males and 17 infants from the Central group.
• Shift in Dominance: Through targeted raids, the smaller Western group eventually became the dominant force in the jungle.
• Scientific Significance: This is the first permanent group fission in wild chimpanzees backed by extensive, long-term documentation.

As researchers continue to monitor the surviving populations in Kibale National Park, the focus remains on understanding the triggers that lead to such extreme polarization. The Ngogo case serves as a stark reminder of the capacity for violence within our closest living relatives, particularly when social bonds—the very things that maintain peace—are severed.

The scientific community continues to analyze the data from this three-decade study to determine if there are early warning signs of such fissions in other chimpanzee communities. Further updates on the stability of the now-dominant Western group and the remnants of the Central group are expected as longitudinal observations continue.

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