The bonobo ape Mali is laughing uncontrollably, huffing and chuffing, arms waving, face lit up. She’s just heard a seven-minute laughter track, a recording of baby apes at their most joyous and uninhibited. Mali’s eh-eh-eh sound is delightful and charming, and clearly contagious. But for UCLA biologists it’s also serious, straight-faced science.

The 17-year-old bonobo is a key figure in the relatively new research sector of animal laughter. She tickled the world’s funny bone in 2021, when UCLA researcher Sasha Winkler M.A. ’20 and communications professor Greg Bryant announced that they’d discovered that humans are not alone in guffawing — it appears that an estimated 65 other species, from foxes to cows, also love a good giggle. 

Over the last three years, Winkler, a Ph.D. candidate researching under the aegis of anthropology professor Erica Cartmill, has been working with Mali and three other “super-friendly” bonobos at the Ape Initiative compound in Des Moines, Iowa. She’s been seeking proof that mammalian laughter is not only socially “sticky” — it’s proven that human conversations that contain humor last longer — but that it leaves the happy subject in a more positive mood, which can influence decision-making. It’s what psychologists call “optimism bias.”

To test the hypothesis, Winkler set up two boxes, one white and empty, the other black and hiding a grape. When the apes had learned which color of box held the prize, Winkler introduced a gray box. 

Apes that had been energized by the laughter track were quite likely to approach the gray boxes, optimistic they would find food inside; those who had not were less likely to.

“This is a small sample, but it suggests how laughter can affect behavior and optimism bias,” says Winkler. “So now we have to expand the tests to other great apes. We have also been conducting similar trials with UCLA volunteers, but using computer rewards rather than grapes. Interestingly, humans seem to need more information before laughing — like seeing a friend laugh — than the bonobos.”

So laughter is common to both humans and great apes, despite a family tree that split eight million years ago. And it serves a similar purpose: “It allows us,” Winkler says, “to bond, to connect, to show our joy.

Read more from UCLA Magazine’s Spring 2024 issue.