Researchers have documented a permanent split between the largest-known group of wild chimpanzees, which erupted into a lethal civil war over the past several years — findings that could help scientists better understand the roots of human conflict.
The study, published Thursday in the Science journal, traced 30 years of chimp behavior in Kibale National Park in Uganda and found a transition from cohesion to polarization among the Ngogo population starting in 2015.
The journal reported that in June 2015, some chips from the Central and Western clusters, which had previously “peacefully intermingled,” met near the center of the territories, and the Central chimps chased the others away.
The two clusters stopped reproducing with each other, and Western males began regularly patrolling Central territory to expand their domain, according to the journal.
The research found that by 2017, Western chimps began attacking Central chimps, starting with the group’s alpha male. It is estimated that the Western group killed at least seven adult males and 17 infants in the Central group between 2018 and 2024.
Study co-author John Mitani, a primatologist at the University of Michigan, told the journal of one contributing factor: “The Ngogo chimps were victims of their own success.”
“The group continued to grow and grow and grow, and it reached the size that individuals couldn’t pull together anymore,” he said. The population was once as many as 200 primates.
Heightened feeding competition and male-male competition exacerbated by reproductive isolation may also have played a role in the fission, the study found.
Researchers pointed to three additional factors that may have acted as catalysts: weakening social ties following the deaths of five adult males in 2014, a change in the alpha male in 2015 and a respiratory epidemic in January 2017 that killed 25 chimpanzees, including four adult males and 10 adult females.
“Taken together, these events suggest how networks may fracture in the face of multiple demographic and social changes,” the study noted.
The authors suggested that the results showed collective violence in humans may have deeper evolutionary roots than previously thought, given that chimpanzees — one of humanity’s closest living relatives — do not have ethnicity, religion or language.
“If chimpanzee groups can polarize, split, and engage in lethal aggression without human-type cultural markers, then relational dynamics may play a larger causal role in human conflict than often assumed,” they wrote.
