A rare case of prolonged internal violence among chimpanzees documented in a recent study may have been driven by leadership changes and a breakdown in social cohesion within the group, a primate expert said.
The study, published last week, tracked a chimpanzee community in Uganda over nearly two decades and documented a violent split that led to the deaths of 28 chimpanzees, including infants, in attacks researchers likened to a human civil war.
Dr. Tamar Federman, founder and director of Israel’s Monkey Sanctuary, said in an interview that such internal aggression is highly unusual.
“Chimpanzees live in complex social groups based on family ties and very intricate relationships,” she said. While they are often aggressive toward neighboring groups, violence within the same group is rare because of reconciliation mechanisms that help maintain stability.
Federman said one possible factor behind the case was a change in leadership, noting that dominant individuals play a key role in maintaining group cohesion.
“Leaders have a very important role in keeping the group together, and it depends on their character,” she said.
She also pointed to the loss of key individuals who may have acted as intermediaries between subgroups.
“There were individuals in the group who had the ability to bridge between different parts of the community,” she said. “Once they were gone, there was no one to connect those individuals, and gradually the subgroups drifted apart.”
Over time, chimpanzees that had once cooperated began to perceive one another as members of rival groups, leading to escalating violence between the factions.
Federman noted that a similar case was documented in the 1970s by primatologist Jane Goodall in Tanzania, though that case involved human intervention, including food provisioning.
“In this case, we are seeing the same kind of process without external intervention,” she said.
Researchers have drawn parallels between the case and human societies, particularly theories about the causes of civil wars. Federman said the findings support the idea that social fragmentation alone can be sufficient to trigger internal conflict.
“Once the social fabric unravels, that is when groups can become very aggressive toward each other,” she said.
Federman also warned about the continued illegal trafficking of monkeys, including into Israel, driven in part by demand for social media content.
“These animals are treated like objects for status,” she said, describing videos that often show monkeys restrained next to luxury items.
She said many rescued monkeys arrive with severe physical and psychological trauma, including broken limbs or removed teeth, and require lengthy rehabilitation to recover normal behavior.