Credit: PexelsGive an orangutan a choice between two places to find a snack, and you’d expect it to pick the one that has offered the best treats. But what if both places have been equally rewarding? What could possibly tip the scales?
According to a new experiment, the answer might be laughter.
Scientists played recordings of orangutans laughing before six captive apes searched for food. Days later, when the researchers gave them a choice between equally rewarding options, the orangutans substantially favored the one they had learned to associate with laughter.
Positive emotions may influence how orangutans remember experiences and assign value to them. But how can we tell whether animals experience joy, and what does that joy actually do?
Like Grandma’s Pancakes
Ph.D. student Emma Nelson conducted part of the laughter research on one of the zoo’s orangutans while completing a research internship there. Credit: Indianapolis ZooThe experiment involved six orangutans, ranging in age from 8 to 51, living at zoos in Belgium and the United States.
Researchers led by Daan Laméris of Indiana University first taught the apes to forage for treats, including almonds and cashews, hidden beneath materials such as wood chips, shredded paper, or yarn.
The orangutans quickly learned which materials concealed food. In a preliminary test, four of the six also demonstrated that they could remember which materials had previously yielded larger rewards.
Then the researchers spiced things up.
Over four days, the orangutans learned to associate two different materials with identical food rewards. Before searching through one material, the apes listened to five minutes of recordings of unfamiliar young orangutans laughing and squeaking during play. Before searching through the other, they heard ordinary wind-like sounds.
On the fifth day, the researchers brought back both materials and gave the animals 30 opportunities to choose between them, with equivalent reward schedules.
All six orangutans favored the material associated with laughter. Four showed a statistically significant individual preference. Across the group, the laughter-associated material attracted roughly 67% of choices.
The sounds didn’t appear to make the apes learn any faster. Rather, laughter seemed to change how much they valued what they had learned.
“It is surprising to find these effects with orangutans, because they are the least social of all the great apes,” Laméris said in a statement. “So even among relatively nonsocial animals, laughter is important.”
Erica Cartmill, the study’s senior author, compared the phenomenon to preferring your grandmother’s pancakes. They likely aren’t objectively better than most other pancakes, but because of the happy memories associated with eating them, you’re likely to subjectively favor them.
Measuring Joy
Credit: PexelsAnimal behavior research has traditionally devoted considerable attention to negative emotions, particularly fear, stress, and suffering, and how they change how animals manifest. Positive emotions such as joy have received comparatively less scrutiny, partly because they are so difficult to measure.
After all, an orangutan cannot tell scientists that it’s happy.
But researchers can investigate whether experiences associated with positive emotions change how an animal behaves later.
A growing body of evidence suggests they do. In a 2025 study involving bonobos, researchers found that the apes tended to behave more optimistically after hearing recordings of laughter, although the findings were not conclusive. Previous experiments have also linked play and laughter-like vocalizations to more positive expectations in rats.
The orangutan study suggests that playful sounds can influence the value animals attach to remembered experiences. One possible explanation is emotional contagion, the phenomenon in which another individual’s emotional expression influences our own feelings.
However, the experiment included only six orangutans, and scientists didn’t directly measure their emotional states. The animals’ preferences are consistent with laughter producing a more positive mood, but they cannot prove that the orangutans actually felt joy.
Still, the implications are intriguing. The same mechanisms might help explain why humans develop lasting preferences for experiences or subjects associated with positive feelings, even when the objective rewards are no different.
For Cartmill, the larger ambition is to understand animal lives at an intimate level.
“Part of this project was to ask, ‘What are the moments that help shape the lives of the animals we share a planet with?’” she said. “It isn’t just about surviving to reproduce, but it’s actually about creating a narrative that also involves friendships and memories and building toward the things that give life meaning.”
The answer, it seems, may involve something as simple as hearing someone else having a good time.
The study was published in the journal Biology Letters.
