ALEX CHADWICK, host:

This is DAY TO DAY. I'm Luke Burbank

MADELEINE BRAND, host:

And I'm Madeleine Brand.

You know, it's hard out there for a chimp, but those animals may be a lot tougher than we thought. A new study of West African chimpanzees shows that they're now making their own weapons, the first animals other than humans to do that. And they're using those weapons to attack other animals. Joining us now is Jill Pruetz. She's an anthropologist at Iowa State University and a lead researcher in the study.

And, welcome to DAY TO DAY.

Dr. JILL PRUETZ (Iowa State University): Well, hi. Thanks.

BRAND: Okay. So what exactly were they doing, these chimps?

Ms. PRUETZ: Well, what they're doing is actually fashioning these sturdy stick tools and using them to incapacitate bush babies, which are small primates themselves. They're prosimian primates. And basically, this is a very clever way of keeping these - their prey from escaping, and then are able to retrieve them later.

BRAND: And they're actually fashioning crude spears?

Ms. PRUETZ: Right. And they have a fairly systematic way of fashioning the tools. They can use up to five or more steps. And some individuals even go so far as to sharpen the tip of the tool with their incisors, in effect, making a point.

BRAND: Wow. And then they go in and find where the bush babies are hiding or sleeping and stab them to death?

Ms. PRUETZ: Well, we haven't been able to see exactly what goes on in the hollow, but often they made tool while they're in a tree that has a hollow. And then they will stab the tool in there multiple times, using a very forceful jabbing motion. They'll do this multiple times. They'll pull the tool out and then either smell it, sniff it or lick it sometimes, and they may proceed to stab it in there again. Sometimes they'll abandon a tool and make another.

BRAND: Well, it sounds quite murderous.

(Soundbite of laughter)

Ms. PRUETZ: I mean, well, you know, they have to eat. So...

BRAND: Yeah. Right.

Ms. PRUETZ: And they do eat other primates at the site. Males eat monkeys. I guess one thing that was really exciting about this finding was the fact that it's not predominantly an adult male behavior. And usually in chimps, we think of males as being the hunters in the species.

BRAND: So, you're saying that it was the females that were carrying out this?

Ms. PRUETZ: Well, individuals we saw that exhibited the behavior most were actually adolescent females. There were some young males that performed the behavior as well, but by and large, the adolescent females were ones that we witnessed doing this the most.

BRAND: Teenage girls.

Ms. PRUETZ: Yeah. Teenage girls.

(Soundbite of laughter)

BRAND: Well, this is kind of surprising, because you think well, they're spending all their time really, you know, taking care of their babies. Do they really have time to go out on the hunt?

Ms. PRUETZ: Right. And well, I think this one way that females are able to go out on a hunt. You know, one of the - the adult female that I saw performing this type of behavior actually had a little, you know, fairly small infant clinging to her belly while she was performing this behavior, and it was just kind of trying to hang on. Females that have infants, especially, are not able to effectively hunt monkeys like males do and immature - or probably not very efficient hunters, but they can perform this type of behavior. It's not a very costly behavior. And I think it's just a really creative, innovative solution to a problem that they get around - basically they use their brains to solve, I guess.

BRAND: Well, what does this mean in terms of understanding humans and evolution?

Ms. PRUETZ: I think it just supports some of the hypothesis and theories that have been around there for a while, that we tend to maybe ignore, that we should consider females in terms of technology - the evolution of technology - a little more seriously. So I think it just supports what others have said. Sometimes it's hard to get away from that old man, the hunter paradigm that I think anthropologists have kind of adhered to for a very long time.

BRAND: Okay. So, the original riot girls, these chimps, huh?

(Soundbite of laughter)

Ms. PRUETZ: Yeah. I guess so.

BRAND: Jill Pruetz is an anthropologist at Iowa State University. Thank you.

Ms. PRUETZ: Thanks.

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