Among humans, laughter can signify a lot of different things, from intimacy to discomfort. Among animals, however, laughter usually communicates something along the lines of “this is playtime—I’m not actually going for your throat.”

According to new research from the University of California, Los Angeles, there are likely at least 65 different creatures, including humans, that make these vocalizations. They’re most commonly found in primates, but they have also been noted in distant relatives like birds. It’s not clear whether this is because laughter has arisen several times over the course of evolution or if it’s more widespread and we just haven’t noticed.

Laughter in the library stacks

To reach this number, Sasha Winkler, a PhD student in UCLA’s anthropology department, searched high and low for any mention of animals making noises during play sessions. Some of the articles she found were quite old—one paper on mink dates back to 1931—so she ended up dusting off some aged tomes in the university’s library.

Finding this data wasn’t always easy, as play vocalizations haven’t been extensively studied across species. “Maybe a lot of animals do have play vocalizations [and] they’re just really quiet,” Winkler told Ars. “We just need to study them better.”

Not all of these noises sound like human laughter—or even the kind of “chuckles” of various other primates, she said. The Rocky Mountain elk, for instance, makes a kind of squealing sound. Conversely, a hyena’s characteristic laugh may sound eerily like a human giggle, but it’s not a play signal.

According to Winkler, animals often use these play vocalizations to indicate that they are not acting aggressively during play fights or other “rough and tumble” interactions. They also act to defuse the possibility of escalation. “[Some actions] could be interpreted as aggression. The vocalization kind of helps to signal during that interaction that ‘I’m not actually going to bite you in the neck. This is just going to be a mock bite,’” she said. “It helps the interaction not escalate into real aggression.”

Among some species on the list, such as dogs, there are other play indicators as well. Dogs make a characteristic “bow” before playing with their peers, and they also adopt a distinctive kind of panting.

Primates and others

The list of “laughing” animals is mostly made up of primates, but there are a few other mammals on the list, such as the degu—whose laugh is described as purring or grumbling—and the killer whale. There are even three birds on the list, such as the kea parrot, which uses play vocalizations discovered in 2017.

According to Winkler, there have been other surveys of the primates who laugh, but little work has been done outside that group. “To my knowledge, no one has gone through and tried to see a comprehensive look of all the vocalizations during play across all mammals, and we even found some birds,” she said.

Winkler told Ars that understanding animal laughter could help us understand the origins of human laughter. Laughter in humans plays several other functions beyond play, such as indicating membership in a group.

Andreas Nieder, a professor of animal physiology at the University of Tübingen, has looked into animal vocalizations in the past. He told Ars that Winkler’s paper is an interesting one, as it brings together a good amount of data from the past. He also noted that there are other kinds of non-linguistic sounds animals make; these sounds, such as moaning and sighing, perform similar functions in humans.

In humans, laughter is innate—deaf infants still laugh—but there is a cultural component to it. Some cultures might simply laugh less than others, Nieder said. But in the animal kingdom, these noises are likely innate and genetically determined rather than learned. “These non-linguistic vocalizations are guided by moods or arousal states of the animals,” she said, adding that, broadly, these sounds help animals form social bonds. “I would say this is one of the prime functions of such vocalizations,” she told Ars.

Winkler also said that other species she didn’t find may make these play noises, though she tried to be as comprehensive as possible. As such, future discoveries could add members to this list.

“There could be more that, we think, are out there. Part of the reason they probably aren’t documented is because they’re probably really quiet, or just [appear] in species that aren’t well-studied for now,” she said. “But hopefully there could be more research in the future.”

Bioacoustics, 2021. DOI: 10.1080/09524622.2021.1905065

Doug Johnson (@DougcJohnson) is a Canadian freelance reporter. His works have appeared in National Geographic, Undark, and Hakai Magazine, among others.

https://arstechnica.com/?p=1765400