Ngogo Chimpanzee Fission: The First Documented Natural Split of a Wild Chimp Community

In April 2026, Aaron Sandel (UT Austin) and John Mitani (University of Michigan, emeritus) published in *Science* the first clearly documented permanent fission of the largest known wild chimpanzee community — the approximately 190-member **Ngogo** group in Kibale National Park, Uganda. The Ngogo community was the subject of Netflix's *Chimp Empire* documentary series. ## The Split Beginning in June 2015, the Ngogo community began separating into two geographic clusters: a **Central** group of approximately 107 individuals and a **Western** group of approximately 83. The split was not instant — it emerged gradually as ranging patterns diverged and social bonds weakened between the two clusters. ## The Violence Between 2018 and 2024, researchers documented lethal inter-group violence between the two factions: **7 lethal attacks on adult males** and **17 lethal attacks on infants**. These were former allies — individuals who had groomed, patrolled, and hunted together for years — now killing each other over territory and reproductive access. ## Scientific Significance Community fission in wild chimpanzees had been theorized but never clearly documented in real time with confirmed outcomes. The Gombe community studied by Jane Goodall experienced a split in the 1970s (the "Four-Year War"), but that event lacked the long-term demographic data and genetic analysis available at Ngogo. The Ngogo dataset, built over decades of continuous observation, provides the most complete record of a fission event in any wild great ape population. The researchers' characterization of such events as occurring perhaps "once every 500 years" reflects the rarity of the phenomenon — communities must be large enough to split viably, and researchers must be present continuously for decades to document the process. ## Context Ngogo has been studied since the 1990s. At its peak, the community had over 200 members, making it the largest known wild chimpanzee group — roughly twice the size of typical communities. The unusually large size may itself have been a factor in the fission: larger groups face increasing coordination costs, feeding competition, and internal power dynamics that eventually make cohesion unsustainable. The pattern — a group growing beyond a threshold, developing internal factions along geographic or social lines, then splitting violently — has parallels to models of human group dynamics, though direct analogies should be drawn cautiously given the differences in cognitive and social complexity.