Laughter hasn't been much of a philosophical topic, historically, and yet isn't it quite a puzzling phenomenon? In fact, it has often been rejected by philosophers because It appears paradoxal, irrational.
Philosophers are serious folks. One rare quasi-philosopher who practiced comic literature was Rabelais:
« Mieulx est de ris que de larmes escripre, Pour ce que rire est le propre de l'homme. » (Gargantua) (Better laugh than cry, for laughter is unique to man)
There's a Bergson essay about laughter, which I found disappointing. Bergson speaks mainly of slapstick comedy, very much in fashion at the turn of the century, and what puzzles him is why do we laugh when someone is hurt? It seems cruel, or at least paradoxal. I guess it's one of the paradoxes with laughter, but to me the big mystery was always the way it overtakes you, even when it goes against your best interest in a given (say solemn) situation. The SEP article on Philosophy of Humor explains that:
In laughter, ... we lose muscle control in our torsos, arms, and legs. In extremely heavy laughter, we fall on the floor and wet our pants.
This is probably the only SEP entry where someone wets his pants...
The same article shares the insights of ethologists on apes, where something like a smile signals playfulness:
In the last century an early play theory of humor was developed by Max Eastman (1936), who found parallels to humor in the play of animals, particularly in the laughter of chimps during tickling. He argues that “we come into the world endowed with an instinctive tendency to laugh and have this feeling in response to pains presented playfully”....
In chimps and gorillas, as in other mammals, play usually takes the form of mock-aggression such as chasing, wrestling, biting, and tickling. .... In mock-aggressive play, it is critical that all participants are aware that the activity is not real aggression. Without a way to distinguish between being chased or bitten playfully and being attacked in earnest, an animal might respond with deadly force. .... Jan van Hooff (1972, 212–213) and others speculate that the first play signals in humans evolved from two facial displays in an ancestor of both humans and the great apes that are still found in gorillas and chimps. One was the “grin face” or “social grimace”: the corners of the mouth and the lips are retracted to expose the gums, the jaws are closed, there is no vocalization, body movement is inhibited, and the eyes are directed toward an interacting partner. This “silent bared-teeth display,” according to van Hooff (1972, 217), evolved into the human social smile of appeasement.
Similarly, laughter would come from tickling, as a play signal. So it has a social function.
The SEP article also highlights the psychological function of helping us take distance with annoying stuff. Better laugh than cry about it, as Rabelais put it...
Still, I can't understand why laughter overtakes us so powerfully at times. Where does its power come from? It's like some deamon taking control of our body.