John Mitani

Well, some of them are, not all of them, but that's another thing that because they live together and reproduce together, there are these ties of kinship that develop over time.

Well, group splitting occurs, fissioning occurs in many other primate species, and it also occurred here in 2018.

As the group grew to such a large size, it did finally split in 2018.

Well, actually, it was quite surprising.

As I indicated, things were going along quite swimmingly for the first 20 years of study.

And so it was a bit of a surprise when hostility started to break out.

And there was a particular event in June of 2015 when members of the two sides began to fight with each other instead of coming together peaceably as they had before.

Chimps from one side chased those from the other side.

Members of both started to scream and shout.

unusually they started to give calls that are only used when they're encountering members from other groups.

And this continued and played out.

And so the split was a process.

It wasn't just a single event.

Things played out over the next two and a half years.

They began to avoid each other.

There were occasional aggressive interactions.

And then finally, at the start of 2018, after two and a half years of this, the two sides completely separated.

They became two independent groups.

Chimps and each no longer associated.

They used separate territories and they stopped reproducing with each other.