Civil war among wild chimpanzees

Related: Lethal conflict after group fission in wild chimpanzees (Science)

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Source: Science

Civil war among wild chimpanzees

A violent split in a group of chimpanzees highlights the evolutionary roots of war and peace

James Brooks Authors Info & Affiliations
Science
9 Apr 2026
Vol 392, Issue 6794
pp. 146-147
DOI: 10.1126/science.aeg6719

Groups exist in the minds of their members and are reflected in their behavior. They are not always permanent and can split as a consequence of changing social relations, cultural dynamics, and—in humans—geopolitical trends. Groups, and how they are understood by individuals, are dynamic systems shaped by evolution (1). Therefore, studying these systems across species can help to reveal the selective forces and behaviors that promote or moderate divisions among members. On page 216 of this issue, Sandel et al. (2) report a shift in group structure before, during, and after a permanent split in a population of wild chimpanzees, the closest relatives of humans.

Approximately 50 years ago, primatologist Jane Goodall reported a similar fission event among the Kasekela chimpanzee community in Gombe, Tanzania (3). Several adult males, adult females, and young individuals splintered into a new group. Many of them were then killed by former groupmates. Sandel et al. studied the social dynamics of the second group split observed in wild chimpanzees, which took place in the Ngogo community in Uganda. This group, which has been followed systematically for nearly 30 years, grew to become the largest habituated community of chimpanzees (a population that tolerates humans) at more than 200 individuals. Then, it began to split into two spatially and socially segregated parts. Sandel et al. combined classic observational and modern analytical techniques to describe and quantify how this fission unfolded. They found that this change was not abrupt but that there was a period of partitioning until all association between the two sides ceased. Before then, network clusters could be detected by analysis of social associations, but many chimpanzees switched clusters year by year, and all clearly belonged to a single group. As connecting ties waned and some individuals that bridged these clusters were killed by disease, a division into two distinct groups became complete and irreversible. Bonds between pairs of individuals did not fade randomly but split along the new line that divided the original group. The relationship between former groupmates turned hostile within the first years of the split, starting with individuals from both groups patrolling their new borders and continuing into lethal violence that targeted adult males and eventually infants.

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Read more: https://www.science.org/doi/10.1126/science.aeg6719