Every pet owner knows that animals love to play, but laughter seems reserved for humans, a few apes, and maybe a few birds good at mimicking humans and apes. As it turns out, according to a new article published in the journal Bioacoustics, laughter has been “documented in at least 65 species,” Jessica Wolf writes at UCLA Newsroom. “That list includes a variety of primates, domestic cows and dogs, foxes, seals, and mongooses, as well as three bird species, including parakeets and Australian magpies.” This is a far cry from just a few years ago when apes and rats were the “only known animals to get the giggles,” as Liz Langley wrote at National Geographic in 2015.
Yes, rats laugh. How do scientists know this? They tickle them, of course, as you can see in the video just above. (Rat tickling, it turns out, is good for the animals’ well being.) The purpose of this experiment was to better understand human touch — and tickling, says study author Michael Brecht, “is one of the most poorly understood forms of touch.”
Laughter, on the other hand, seems somewhat better understood, even among species separated from us by tens of millions of years of evolution. In their recent article, UCLA primatologist Sasha Winkler and UCLA professor of communication Greg Bryant describe how “play vocalizations” signal non-aggression during roughhousing. As Winkler puts it:
When we laugh, we are often providing information to others that we are having fun and also inviting others to join. Some scholars have suggested that this kind of vocal behavior is shared across many animals who play, and as such, laughter is our human version of an evolutionarily old vocal play signal.
Generally, humans are unlikely to recognize animal laughter as such or even perceive it at all. “Our review indicates that vocal play signals are usually inconspicuous,” the authors write. Rats, for example, make “ultrasonic vocalizations” beyond the range of human hearing. The play vocalizations of chimpanzees, on the other hand, are much more similar to human laughter, “although there are some differences,” Winkler notes in an interview. “Like, they vocalize in both the in-breath and out breath.”
Why study animal laughter? Beyond the inherent interest of the topic — an especially joyful one for scientific researchers — there’s the serious business of understanding how “human social complexity allowed laughter to evolve from a play-specific vocalization into a sophisticated pragmatic signal,” as Winkler and Bryant write. We use laughter to signal all kinds of intentions, not all of them playful. But no matter how many uses humans find for the vocal signal, we can see in this new review article how deeply non-aggressive play is embedded throughout the animal world and in our evolutionary history. Read “Play vocalisations and human laughter: a comparative review” here.