A few years ago, Robert Provine, who is probably the world's leading laughter scientist, set out to discover what cracks us up. He and his researchers monitored thousands of human interactions, noting who said what, and who laughed in response. Strap on your surgical ribcage support right now, because I'm about to reveal some of the most hilarity-inducing lines: "I know." "I'll see you guys later." "I see your point." "It was nice meeting you." (Dry your eyes, take a few deep breaths, and we'll continue.) "Most pre-laughing dialogue," Provine later wrote in his book Laughter: A Scientific Investigation, "is like that of an interminable television situation comedy, scripted by an extremely ungifted writer."

This is great news for extremely ungifted sitcom writers, but a little mystifying for everyone else. Most of us, presumably, want to laugh more than we do; after all, we spend about a third as much time laughing as people did in the 1930s, according to "laughter therapist" Carole Fawcett, and as adults we laugh vastly less than we did as children. Yet seeking out humorous people, books or TV shows wouldn't seem to be the answer: laughter and humour, Provine's research indicated, aren't very closely related.

"Laughter existed before humour," Provine told me, shortly before doing an impression of a chimpanzee laughing, the brilliance of which I sadly can't convey in print. "It's the ritualised sound of rough-and-tumble play." The sound primates have always made, in other words, when they're socialising energetically. It's not a response to something funny, but an instinctive bonding mechanism. Or as Provine puts it: "The key ingredient to laughter is another person, not a joke."

Nowhere is this clearer than in sexual politics. Provine analysed thousands of personal ads and found that women disproportionately sought men with a good sense of humour, while men disproportionately claimed to possess one. In fact, he reckons, nobody was really talking about humour: the women wanted men who made them laugh, and the men wanted women who would laugh when they spoke. This suggests one way to diagnose the health of any given heterosexual relationship: notice how frequently the female partner laughs.

Looking at things this way also casts doubt on the notion of laughter as medicine - the "laugh your way to wellness" approach pioneered by the radical American doctor Patch Adams. Perhaps the real reason that people who laugh more seem to recover more effectively from illness - in a handful of studies - is simply because they spend time with others.

"If you want to laugh more, place yourself in situations where laughter's more common," Provine said. "Not a comedy club, but simply spending more time with your friends." And can laughter make you well? He sighed. In fact, overall, there's a negative correlation between a happy outlook on life and longevity, he said, perhaps because optimism encourages risky behaviour. "I don't want to come off as a total curmudgeon... but laughter makes us feel good. Our lives will be better if there's more of it. Isn't that enough?"

· oliver.burkeman@theguardian.com