In the dense tropical rain forests of Kibale National Park, a long-studied chimpanzee community has revealed a darker side of primate social life, as researchers document a rare and deeply unsettling incident: a once-unified group splitting into rival factions and descending into years of deadly conflict.
The findings, published in the journal Science and spanning nearly three decades of observation, chronicle how the Ngogo chimpanzee community, once the largest ever recorded in the wild, fractured and turned violently against itself. What followed was a sustained campaign of coordinated attacks that left at least 28 chimpanzees dead, including adult males and infants.
For over 20 years, researchers observed the Ngogo Community living what appeared to be a stable and cooperative existence. The chimpanzees spent their days feeding on fruits and leaves, grooming one another, and traveling through the forest in cohesive social units. At its peak, the group numbered around 200 individuals, far exceeding the typical chimpanzee community size of about 50. But beneath this apparent stability, tensions were quietly building.
By 2015, subtle fractures had begun to emerge. Social clusters within the group started to avoid one another, a shift that researchers say marked the beginning of a gradual but profound breakdown. Within two years, the once-unified community had split into two distinct factions, later identified as the Western and Central groups. What followed was unprecedented.
Unlike previously documented cases where chimpanzees attack outsiders or neighboring groups, this conflict involved individuals who had grown up together, shared alliances, and cooperated for years.
“It is hard to grasp that yesterday’s companion becomes today’s enemy,” noted one of the study’s senior researchers, reflecting on the dramatic reversal of social bonds.
The Western group soon began launching coordinated and often brutal attacks on members of the Central group. These assaults were swift and violent, typically involving multiple attackers targeting a single victim. Adult males were frequent targets, but infants were particularly vulnerable.
Researchers described scenes of chimpanzees biting, kicking, dragging, and repeatedly striking victims. In many cases, attacks lasted less than 15 minutes but proved fatal, likely due to severe internal injuries rather than visible wounds.
Infants, by contrast, were often killed quickly, snatched from their mothers, and dispatched with blunt force or bites.
Between 2018 and 2024, researchers recorded 24 confirmed deaths linked to the violence. Subsequent killings in 2025 and early 2026 pushed the total to 28. However, many chimpanzees have disappeared without explanation, suggesting the actual toll could be higher.
Notably, the Western faction, which initiated the attacks, appears to have suffered no casualties. Over time, it also expanded its territory and numbers, eventually surpassing the Central group in both size and dominance.
Scientists point to a combination of factors that may have destabilized the Ngogo community.
Its unusually large population likely intensified competition for food and mating opportunities, particularly among males. The death of several chimpanzees due to illness in 2014 and again in 2017 may have further disrupted social bonds, creating conditions for mistrust and hostility.
A significant leadership change also occurred around 2015, when a chimpanzee named Jackson rose to alpha status after deposing a rival. Leadership transitions in chimpanzee societies are often turbulent, and researchers believe this shift may have exacerbated existing tensions. By late 2017, the division was complete.
While chimpanzees are known to engage in lethal aggression against neighboring groups, documented cases of internal splits followed by sustained violence are exceedingly rare.
Researchers note only one comparable instance, observed in Tanzania in the 1970s. However, that case involved human intervention through feeding, leaving uncertainty about whether the behavior was natural.
The Ngogo case, by contrast, unfolded in a largely undisturbed environment, offering one of the clearest insights yet into how internal divisions can escalate into deadly conflict among wild chimpanzees.
Given the scale and organization of the violence, comparisons to human conflict may seem inevitable. However, researchers caution against drawing direct parallels.
Chimpanzees and humans share a common evolutionary ancestor, but their paths diverged millions of years ago. While certain behavioral similarities exist, scientists emphasize that chimpanzee violence should be understood within its own ecological and social context—not as a mirror of human warfare.
Still, the events at Ngogo raise profound questions about the roots of conflict, cooperation, and social cohesion in one of humanity’s closest relatives.
As research continues in Kibale National Park, scientists hope to better understand what drives such dramatic social breakdowns and whether similar incidents may be unfolding unnoticed in other primate communities.
