Aaron Sandell

Now my focus has gone from understanding friendship to sort of how do friendships fall apart, how do communities fall apart.

They were so used to people by then that most of them just ignored me.

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.

And then it was really in 2015.

When the social network changed in a dramatic way.

They got quiet all of a 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.

And then when the chimps from the central neighborhood got closer, rather than reuniting in this typical chimpanzee fashion where they're constantly mixing and mingling, and instead of doing that, the western chimpanzees ran and the central chimpanzees chased them.

And nothing really like that had ever been observed before.

And then they avoided each other for six weeks.

And by 2018...

They were completely separate groups, no longer peacefully interacting, and that was when we saw the beginning of these lethal attacks.

Definitely.

I saw the first two lethal attacks and like the first lethal attack was a chimp that I'd really watched grow up.

I even remember the night before he was killed, I saw him and he was sort of running around and grooming with this adolescent female.

And I remember even coming back at the end of the day that night to the campsite and sharing with the other researchers, oh, Errol, this chimp.

He's really acting like an adult.

And then the next morning I saw them kill him.