Civil War Among Chimpanzees

Carl Zimmer, These Chimps Began the Bloodiest ‘War’ on Record. No One Knows Why. NYTimes, Apr. 9, 2026.

Near the end:

And the researchers are still trying to figure out what set off the conflict in the first place. “All of a sudden, yesterday’s friend becomes today’s foe,” said Dr. Mitani.

Within any group of chimpanzees, violence will flare from time to time — when apes converge on a tree full of fruit, for example, or when lower-ranked males vie to replace an old alpha male.

But this aggression can be dampened by the friendships that form over years. Some chimpanzees are especially social, jumping between many cliques. “They’re these important social bridges,” Dr. Sandel said.

In 2014, five adult males died, perhaps because of disease. Dr. Sandel speculated that these deaths ripped away some of the bridges that previously held the Ngogo groups together. Low-level conflicts blew up into something akin to civil war.

The Ngogo conflict could offer a glimpse at the kind of violence that might have flared up in our ancient forebears, given that chimpanzees and humans descend from common ancestors that lived about six million years ago.

“These findings tell us indeed that these civil-war-like types of conflicts were possible in the course of human evolution,” said Sylvain Lemoine, a primatologist at the University of Cambridge who was not involved in the study.

The Ngogo chimpanzees show how our ancestors could have gotten dragged into years of lethal fighting without ideology or cultural identity — let alone the language to talk about them.

Instead, shifting social bonds might have been enough to light the fire.

There's more at the link.