Wild Laughter

When a slack-mouthed chimpanzee lets loose a husky guffaw, you know he's having a good time. Homo sapiens isn't always so transparent—sometimes when we laugh, we're just being polite—but it turns out that when we really find something funny, we show hints of that happy chimp.

Just think of the last time you cracked up at your favorite comedy. The sound you made was probably relatively loud and high-pitched, open-throated and uncontrolled. "We think that these spontaneous laughs are produced by an emotional vocal system that's shared with many other animals," including primates, says UCLA psychology professor Gregory A. Bryant. In contrast to spontaneous laughter, volitional laughter—the kind we produce when we're humoring someone, or deceiving them, or being ironic—seems connected to a distinctly human speech system.

Bryant and evolutionary biologist C. Athena Aktipis exposed the primal side of laughter with a quiz of sorts. After slowing audio samples of laughter to make it less obvious that they were human-made, the researchers asked participants to identify whether they came from humans or nonhuman animals. Volitional laughter, produced on command, was correctly identified as human 65 percent of the time. But when participants heard slowed-down spontaneous laughs, guesses were evenly divided between "human" and "animal," suggesting that genuine laughs are more closely related to the sounds of our hairier ancestors.

We're actually pretty good at distinguishing this form of laughter from the more willful kind. When participants listened to samples of both types, they could tell the difference on about two-thirds of their attempts.

Credit: Laughing boy scout and monkey from Everett Colleciton/Shutterstock