Ngogo Chimps Split in First Documented Permanent Fission
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- The Ngogo chimpanzee community of Kibale National Park, Uganda, has permanently split in two, according to a new study in Science — the first clearly documented permanent fission in wild chimpanzees, drawing on three decades of field observations.
- Aaron Sandel of UT Austin and colleagues report the community polarized in 2015, following a shift in the male dominance hierarchy and the deaths of several adult males who may have served as social bridges; by 2018, the split into separate Western and Central groups was complete.
- The Western group carried out lethal attacks on the Central group between 2018 and 2024, including seven attacks on adult males and 17 on infants, some inferred with high confidence — violence Sandel describes as former groupmates killing one another.
- Permanent fissions in wild chimpanzees are extraordinarily rare — genetic evidence suggests they occur roughly once every 500 years — and the only previous case, at Gombe, Tanzania, in the 1970s, remains debated because researchers provisioned those chimpanzees with food.
- Sandel argues the findings challenge the hypothesis that human warfare depends on cultural markers like ethnicity or religion, noting that relational dynamics alone appear to have driven polarization and lethal conflict in the Ngogo chimps.
- The study rests on nearly three decades of continuous fieldwork by John Mitani, emeritus professor of anthropology at the University of Michigan, and a large team of researchers and Ugandan field staff who never provisioned the Ngogo animals.
Why it matters: For primatologists, the Ngogo split is the cleanest natural-experiment case of ape fission ever recorded — the Gombe case from the 1970s was muddied by food provisioning. With 17 infant and 7 adult male killings documented over six years, the finding gives researchers a rare window into how group identities override years of cooperation, and it gives Sandel and colleagues a direct counterargument to theories of human warfare built on ideology or ethnicity.
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