In the mid-1970s, more than a decade into her study of chimpanzees at Tanzania’s Gombe National Park, Jane Goodall witnessed something that shocked her: a single community fractured into two factions that turned on one another. Chimps that had lived and grown up together began systematically killing each other — a phenomenon Goodall described as resembling a civil war. It altered her view of our close relatives. “I used to think, ‘Well, they’re very [much] like people but nicer,’” she told Fresh Air in 1993. “And then I realized that when opportunity arises, they have this nasty, brutal side to them just like we do.”
Goodall could not be sure what had precipitated that first observed war. Now researchers report a second, prolonged “civil war” among wild chimpanzees, described in Science. The study draws on more than 30 years of observations of the Ngogo community in Uganda’s Kibale National Park — the largest known group of wild chimpanzees.
At its peak nearly 200 individuals in Ngogo lived cohesively in smaller intermingling subgroups, or “clusters.” Males and females from different clusters mated, hunted and cooperated to repel outside groups; researchers even filmed males from different clusters holding hands. But in 2015 observers began to notice clear changes.
Aaron Sandel, the study’s lead author and a primatologist at the University of Texas at Austin, points to one day in June as a turning point. While watching many chimps from the Western cluster, he heard others nearby, presumably from the larger Central cluster. The Western chimps suddenly grew quiet and touched each other in reassurance as if uneasy at hearing outsiders. Then they fled, and the Central chimps chased them. The two clusters avoided one another for six weeks — a behavior never seen before at Ngogo.
Polarization increased over the next few years and by 2018 the clusters were essentially separate groups. Lethal violence followed. The first observed victim was Errol, an adolescent male from the Central cluster whom Sandel had watched grow up. Over the subsequent seven years, the Western group killed at least six other adults and 17 infants from the Central cluster. The fighting is ongoing.
Why the Ngogo group split and turned violent remains unclear. The authors suggest several possible contributors: the sheer size of the community, competition for food, male–male competition, and the natural deaths of five adult males and one adult female in 2014 that may have weakened social networks and alliances. Michael Wilson, a primatologist at the University of Minnesota not involved in the study, notes that such conflicts can arise without the trappings we often ascribe to human wars. “Lions don’t have religion and political parties or ideologies. Neither do wolves or ants for that matter,” he said.
That absence of human-like ideologies in chimpanzee conflict is, for Sandel, a sobering clue and a reason for cautious optimism. If chimps can descend into lethal, factional violence without religion, ideology or political institutions, perhaps interpersonal relationships and social bonds play a larger role in human conflict than we sometimes acknowledge. Strengthening ties, forgiving old grievances and preventing people from becoming interpersonal strangers, he suggests, might help reduce the risk of larger-scale violence. “Like with the chimps: If you act like a stranger, you become a stranger,” Sandel said. “I want to avoid that in my own life.”