Scientists observed a permanent split in Uganda’s Ngogo chimpanzee community beginning in 2015, with two distinct factions forming by 2018 and engaging in lethal violence over the following seven years.
The Ngogo group, described as the largest known community of wild chimpanzees, has been studied since the mid-1990s in Kibale National Park. Researchers documented 24 attacks by members of one faction on the other, resulting in the deaths of at least seven adult males and 17 infants.
This marks the first time scientists have witnessed a civil war-like conflict among chimpanzees characterized by shifting group identities and prolonged hostility, according to the study published in Science in early April.
How the split evolved over decades of observation
When tracking began, the Ngogo chimpanzees numbered over 100 in a 26-square-kilometer area, with researchers noting they were “everywhere.” Over time, the community grew to about 200 individuals moving in slight groups through the forest.
Initially, encounters between individuals were peaceful, with chimpanzees frequently switching between subgroups during the day. This pattern of fluid interaction persisted until behavioral shifts emerged around 2015.
By 2018, the group had permanently divided into two distinct factions, ending the earlier fluidity in social structure and setting the stage for sustained intergroup conflict.
What researchers say this reveals about primate and human conflict
The study’s authors state that territorial conflicts in animals can inform understanding of human war, but civil wars with changing group identities had not previously been observed in non-human species.
They argue the Ngogo conflict shows group identities can escalate to lethal hostility without the cultural markers often considered necessary for human warfare, offering insight into our closest living relatives.
John Mitani, primatologist at the University of Michigan and co-founder of the Ngogo Chimpanzee Project, recalled the early observations when the group first showed signs of unusual cohesion and later fragmentation.
Why is this chimpanzee conflict considered unprecedented?
Researchers say they had not seen a chimpanzee “war” as widespread and prolonged as this one, making it the first documented case of a civil war-like split in the species.
What evidence supports the claim of a permanent fission?
Using 30 years of behavioral observations and network analysis, scientists identified a transition from cohesion to polarization starting in 2015 and the formation of two distinct groups by 2018.