- [Narrator] And one behavior spreads their fame more than any other, a startling reminder of our own human journey.

- [Reporter 1] Researchers reported they've seen wild chimpanzees in West Africa making weapons.

- He's hunting.

- [Reporter 2] A new study of West African chimpanzees shows that they're now making their own weapons.

- [Narrator] In a step up from termite fishing, the Fongoli chimps are hunting for bush babies, nocturnal primates that hide in tree hollows.

- [Johnny] First time seeing the chimpanzees killing a bush baby was difficult for me.

I feel sorry for the bush baby.

- This to me, I think is kind of a classic in terms of the length.

They'll go out of their way to find this type of tree and make a tool out of that.

They're stripping all the branches, leaves, and then they'll also trim the tip.

(tense music) Or they'll like stab into the cavity and then smell it.

They're jabbing and like this.

(tense music) - [Narrator] This is a game-changing response to living in an extreme environment.

- [Jill] Our ancestors started hunting with tools, and nobody else does that.

It's one of the things that made us human.

- [Narrator] For Jill, making and using a weapon to hunt another creature creates a detachment from the act of killing.

- What they're doing is they're removing an emotional stage that some scientists say was also what we did as humans.

Changed the way that people though about chimps, but it also changed how we think about ourselves.