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Lethal conflict after group fission in wild chimpanzees
Aaron A Sandel1, Yixuan He2, Junpeng Ren3
1Department of Anthropology, University of Texas at Austin, Austin, TX, USA.
Science (New York, N.Y.)
|April 9, 2026
Summary
Wild chimpanzees (Pan troglodytes) experienced a permanent group fission, leading to lethal intergroup conflict. This study documents the first observed civil war in a non-human primate, revealing escalating violence and shifting group identities.
Area of Science:
- Primate Behavior
- Evolutionary Anthropology
- Animal Conflict Studies
Background:
- Territorial conflicts are common in animals and offer insights into human warfare.
- Civil war, characterized by shifting group identities, has not been previously documented in non-human species.
- Understanding the evolutionary roots of conflict requires studying social dynamics in closely related species.
Purpose of the Study:
- To report and analyze a rare, permanent fission in a large wild chimpanzee group (Pan troglodytes).
- To investigate the transition from group cohesion to polarization and subsequent lethal intergroup aggression.
- To determine if shifting group identities can lead to warfare in our closest living relatives without human-like cultural markers.
Main Methods:
- Long-term behavioral observations spanning 30 years.
- Social network analyses to track group dynamics and cohesion.
- Documentation of intergroup attacks, including casualties.
Main Results:
- A permanent fission occurred in the largest known wild chimpanzee group, transitioning from cohesion to polarization by 2015, with two distinct groups emerging by 2018.
- Over seven years, one group launched 24 attacks against the other.
- These attacks resulted in the deaths of at least seven mature males and 17 infants from the targeted group.
Conclusions:
- Wild chimpanzees exhibit the capacity for civil war, demonstrating permanent group fission and lethal intergroup hostility.
- Shifting group identities in chimpanzees can escalate into organized violence, challenging previous assumptions about the necessity of cultural markers for warfare.
- This study provides crucial insights into the evolution of conflict and sociality in primates, including humans.
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