A once-unified community of wild chimpanzees in Uganda has fractured into warring factions, engaging in a brutal conflict that has lasted eight years and resulted in dozens of deaths, according to new research.
Scientists studying the Ngogo chimpanzee group in Kibale National Park—the world's largest known wild chimpanzee community—documented 24 targeted killings since 2018, including 17 infants. The violence represents what researchers describe as a "civil war" among primates who previously lived in harmony.
"These were chimps that would hold hands," said lead researcher Aaron Sandel, an anthropologist from the University of Texas and co-director of the Ngogo Chimpanzee Project. "Now they're trying to kill each other."
The study, published in the journal Science, reveals how the nearly 200 chimpanzees split into Western and Central groups after decades of peaceful coexistence. Researchers first noticed polarization in June 2015 when Western chimpanzees fled from their Central counterparts, followed by a six-week avoidance period.
"Chimpanzees are sort of melodramatic," Sandel explained, noting that typical disputes involve "screaming and chasing" followed by reconciliation through grooming and cooperation. But following the 2015 incident, interactions became increasingly infrequent and aggressive.
By 2018, the separation became permanent, and Western group members began systematically attacking Central chimpanzees. The 24 documented attacks claimed at least seven adult males and 17 infants, though researchers believe the actual death toll is higher.
Scientists identified several potential catalysts for the conflict:
- The 2014 deaths of five adult males and one adult female, which may have disrupted social networks
- A 2015 change in alpha male leadership that coincided with the initial separation
- A 2017 respiratory epidemic that killed 25 chimpanzees, including key individuals who connected the groups
"In the case of the Ngogo fission, individuals who lived, fed, groomed and patrolled together for years became targets of lethal attacks on the basis of their new group membership," the researchers wrote.
The findings offer insights into the origins of human conflict, suggesting that chimpanzees—our closest genetic relatives—can engage in prolonged warfare without human constructs like religion, ethnicity, or political beliefs.
"If chimpanzees could do so without human constructs... then relational dynamics may play a larger causal role in human conflict than often assumed," the researchers added.
James Brooks, a researcher at the German Primate Center, commented that the study serves as "a reminder of the danger that group divisions can present to human societies."
"Humans must learn from studying the group-based behaviour of other species," he wrote, "while remembering that their evolutionary past does not determine their future."