People in 24 different cultures can recognize the status of a relationship based on this one-second social cue

Wondering who your true friends really are? Try sharing a laugh. A new study published last week in the Proceedings of the National Academy of Sciences demonstrates that we can evaluate the nature of a relationship just based on the sound of shared laughter.

I read somewhere that the single most commonly sought after trait listed in personal ads is “a sense of humour.” Of course we all like to be with someone we can laugh with and who enjoys mocking the same targets as we do. But perhaps this new research shows that there is something more scientific at play than simply looking for someone you find (or who finds you) funny.

Researchers from the University of California’s Center for Behaviour, Evolution, and Culture have found that overhearing even just a second of laughter can reveal the level of intimacy in a relationship.

For this study, the research team conducted an experiment that involved recording pairs of university students engaged in conversations. Some of these groups were friends, while others were strangers. The experimenters then cut the recordings down to just the sounds of the two parties sharing a laugh.

Psychologist Gregory Bryant and the research team played one second clips of the laughter for 966 volunteers from 24 cultures around the world. The participants were asked to determine if the two people they heard laughing were friends or not, based only the sound of their laughter.

Most of the time (61%) participants were able to distinguish the friends from the strangers by the laughter. When the couple sharing a laugh were both women, participants were able to accurately determine their friendship level more than 80% of the time. (Interestingly, people in the US were better recognizing the male friend relationships.) However, because the results were so similar across cultures, the researchers concluded that laughter is a fairly accurate and universal indicator of friendship levels.

“In a highly cooperative species such as ours, it is important for individuals to correctly identify the social alliances of others,” Bryant said. “If laughter helps people accomplish that, it has likely played a role in social communication leading to cooperative interactions.”

The next time you want to evaluate your relationships, try cracking a joke and listening for their reactions. Genuine laughter among friends sounds different from fake or restrained laughter with strangers or acquaintances. Real laughter tends to be higher pitched, louder, longer, and faster.

Then again, maybe you’re just not that funny and the fake laughter is just an attempt to be polite rather than an indication of a lack of intimacy.

Also, I have a friend who laughs with that snake-like S sound, “Sss-ss-sss-ss.” The study did not indicate what was up with that.

Read the full release for more details and quotes from the research team.