Nate Rott

That includes ants and lions and wolves.

But these kinds of permanent fissions that result in violence, like a group of animals breaking apart forever and fighting each other, is super rare.

With chimpanzees, they think this only happens like once every 500 years.

Yeah, from the very start, before it began, and even as it's ongoing right now.

And what it can teach us about how communities fall apart.

And I'm Nate Rott.

And you're listening to Shortwave, the science podcast from NPR.

Yeah, it's happening on the western border of Uganda in this densely forested national park.

There are multiple communities of wild chimpanzees that are studied there, but the ones we're going to be focused on are part of what's called the Ngogo group.

Researchers have been observing this group for more than 30 years.

It is.

And that's part of what makes this so interesting.

Because the primatologists who were working there had decades of observations of these chimpanzees.

So they knew who was hanging out with who, who mated with who.

They knew the chimps' social bonds.

Aaron Sandell, the primatologist we heard from earlier, started working there in 2012.

He's now at the University of Texas at Austin.

Yeah, so when researchers started tracking them in the mid-90s, there were about 100, which is a lot.

Aaron says that the average group of chimpanzees is about 50.

But by the time Aaron started working there, there were nearly 200 individuals in this group.