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Like with humans, it is not uncommon in the natural world for a group of animals to split apart and form their own independent groups. But what a new study in the journal Science depicts in the largest known community of chimpanzees in the world is exceptionally rare. The researchers describe it as a civil war. NPR's Nate Rott reports.
NATE ROTT, BYLINE: The Ngogo chimpanzee group in Uganda's Kibale National Park has been continuously studied for more than 30 years. Aaron Sandel, a primatologist at the University of Texas at Austin, started working there in 2012.
AARON SANDEL: They were so used to people by then that most of them just ignored me.
ROTT: The researchers stay about 30 feet away, observing behaviors, interactions, movements.
SANDEL: Took me months and months to recognize every individual chimp in the group because there were almost 200 chimps when I started sitting them.
ROTT: Now, Sandel says there were substructures in this community, almost like neighborhoods of chimpanzees that spent more time together.
SANDEL: But still, there was no sign that the group would split until 2014. We started seeing the first signs of these neighborhoods being really distinct.
ROTT: And then it was in 2015...
SANDEL: When the social network changed in a dramatic way.
ROTT: There was one day in particular Sandal remembers when he was out with chimpanzees from the western neighborhood. And when they heard others from the central one...
SANDEL: They got quiet all of the sudden. They started touching each other in this reassurance, like they were really nervous. And to me, this seemed like they were acting as if they were hearing outsider chimps.
ROTT: Chimpanzees are extremely hostile to outside groups. But these groups knew each other. They'd grown up together. They intermingled. But instead of reuniting, Sandel says the western chimps ran away and the groups avoided each other for six weeks.
SANDEL: So this was very clear, like, on the ground, something big has just happened.
ROTT: Over the next few years, Sandel says the polarization between the groups increased. They spent less time together.
SANDEL: And by 2018, they were completely separate groups, no longer peacefully interacting. And that was when we saw the beginning of these lethal attacks.
(SOUNDBITE OF ARCHIVED RECORDING)
SANDEL: Hitch point five-10, 11:22 (ph).
ROTT: Sandel recorded this voice memo of a conflict in 2021.
(SOUNDBITE OF ARCHIVED RECORDING)
SANDEL: Alfred said (ph) westerners attacked Bartley (ph) and Miles (ph). Miles and Jackson (ph) ran.
(SOUNDBITE OF CHIMPANZEES CALLING)
SANDEL: Now they're calling in response.
ROTT: A few days after this, an older male in the central group was found dead. And by that point, the targeted killings had even spread to infants.
ANNE PUSEY: This systematic killing of many individuals is unusual.
ROTT: Anne Pusey is a retired primatologist who worked alongside the late Jane Goodall in Tanzania in the 1970s when the population of chimps they were studying fractured and started killing each other as well. It's the only other documented case of this occurring and was the first time scientists had seen another species engage in civil war.
PUSEY: I mean, it's rather uncomfortably familiar seeing how these relationships can break down and then lead to antagonisms between groups which weren't there before.
ROTT: In both cases, it's not entirely clear what caused the split. A study published in 2018 on the Gombe chimpanzee war suggests it was driven by interpersonal relationships, infighting, ambition, jealousy. Sandel says the Ngogo group may have broken apart because of its sheer size, and he's cautious about drawing too many parallels between chimpanzee conflict and human. But he also says it's worth considering that this conflict occurred...
SANDEL: In the absence of all these aspects of human behavior that we often attribute to conflicts like civil wars, like ethnic divisions and religious differences and political ideologies.
ROTT: Chimps don't have any of those. So maybe, he says, it's more a byproduct of eroding interpersonal relationships. And if that's the case, Sandel sees reason for optimism. That's something individuals can control.
SANDEL: Like with the chimps, it's like you act like a stranger, you become a stranger. I want to avoid that in my own life.
ROTT: A lesson, perhaps, for all of us. Nate Rott, NPR News.
(SOUNDBITE OF MUSIC) Transcript provided by NPR, Copyright NPR.
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