A new paper from the University of California has found a very simple way to determine whether people are friends.
Almost 1,000 individuals from 24 societies around the world were asked to listen to short recordings of pairs of people laughing together.
Even though the recordings were only one second long, the test subjects were surprisingly good at correctly identifying which people laughing together were friends, and which were new acquaintances.
61 percent of the respondents could reliably tell which relationships were which.
Greg Bryant, a cognitive psychologist at the University of California and a co-author of the study said:
Laughing isn't necessarily just about communication between the people who are laughing, but potentially it might be a signal to outsiders that gives them some information.
A group of people laughing at a bar might be producing a chorus of signals to others without really being aware of it.
Non-verbal communication like laughter is a powerful tool that could give insights into language and speech formation in early societies, the researchers said.
Based on the findings, an outsider or newcomer to a group could make very quick judgements about a group of people by the way they laugh.
H/T: Smithsonian Magazine