As many of us know, laughter is contagious. It can ripple through a movie theater, a classroom, and even business meetings.
But infectious laughter isn’t just good for a quick giggle. New research suggests that it provides important social benefits—benefits that might have served our ancestors well through millions of years of evolution.
In a recent study, published in the journal Emotion, researchers investigated whether chimpanzees, some of our closest relatives in the animal kingdom, are prone to the same type of contagious laughter as humans, where we reflexively imitate someone else’s laugh even if we’re not feeling the same emotion that they are.
Prior research suggests that this type of laughter—say, a polite guffaw in response to a joyous bellow—could promote cooperation and positive communication, making laughter and smiles essential to emotional intelligence. This kind of laughter had been observed in humans but never before in our primate relatives.
The researchers observed 59 chimpanzees of various ages, split among four colonies at a sanctuary in Zambia. Two of these colonies were new—the chimps in them had only lived together for five years—and two were old, where the chimps had lived together for more than 14 years.
As the researchers watched pairs of chimpanzees playing together, they consistently found that one chimp would laugh in response to another’s laughter. But this second laugh was distinct from the original laugh; it was shorter and had a different vocal quality.
This kind of contagious, responsive laughter showed “a striking similarity to [the] conversational laughter of humans,” write the authors, who are all based in the department of psychology at the University of Portsmouth in the United Kingdom. “Both vocalizations are significantly short and seem to promote social interactions.” Indeed, the chimpanzees would play together for a longer period of time when one of them laughed in response to the other’s laugh, suggesting that their shared laugh reinforced their social bond.
Chimpanzees in the new colonies were more likely to imitate laughter than were chimps in the older colonies. “It therefore seems likely that laugh replications have a more important role in the social communication of chimpanzees when their social partners are less predictable and/or when the need for social cohesion increases,” the authors write.
The study is the first to document this kind of polite, contagious laughter among non-humans. The results indicate that this type of laughter could have deep evolutionary significance, according to Marina Davila-Ross, the study’s lead author.
“These findings suggest that laughter first emerged into an expression of positive social communication that provided our ape ancestors important advantages,” says Davila-Ross, “before it evolved to become an ubiquitous tool of human communication with not only positive functions, but also negative ones (e.g., to mock).”