From the brains behind brains on, this is the Moment of Um.

Moment of Um comes to you from APM Studios. I'm producer Anna Goldfield.

Um.

I love making Moment of Um. I've talked to geologists about lava, computer scientists about

Wi-Fi, and Wolf researchers about whether wolves get the zoomies. Spoiler, they do.

I always learn a lot, but the thing about science is, there's always more to learn, because new

science keeps happening. Gorillas are a great example. On Moment of Um, we already did an episode about why gorillas beat their chests. But there's some newer research that gives us some really cool extra information. Last time, we learned that chest pounding was often a way for big male gorillas to say, hey, I'm in charge here. Don't mess with me.

But it turns out, it communicates other things too. I asked a friend of mine,

primatologist Andrea DeGiorgio, to tell me about it.

Gorillas beat their chests in two contexts, and in both of them, the goal is communication.

Hi, I'm Andrea DeGiorgio. I teach at Princeton University, and I am a primatologist.

There's a lot of differences between male and female gorillas. The males can be up to about 400 pounds.

So big animals. When a male gorilla

beats their chest, they're either doing it when they're playing, which is most likely to learn how to do it

as an adult, or they're doing it as a display. And they are displaying for one of two reasons. They are

either trying to defend their territories and tell

other males, hey, this is where I am. My family is here. Don't come near us. Or they are trying

to attract females and say, hey, I'm a big, strong male, and I would be a good mate for you. I think one of the

neatest things about gorilla chest beating is that it's what we call an honest signal. So when

you're signaling something, it can be honest or dishonest in the behavioral ecology world.

Some animals might sing the loudest, but they're actually the smallest animal, so they're just showing off the singing.

Whereas with guerrillas, recent research found that when a male gorilla is larger, his chest beating produces a lower, more booming sound.

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