Why Do We Laugh?

Philosopher John Morreall believes that the first human laughter may have begun as a g­esture of shared relief at the passing of danger. And since the relaxation that results from a bout of laughter inhibits the biological fight-or-flight response, laughter may indicate trust in one's companions.

Many researchers believe that the purpose of laughter is related to making and strengthening human connections. "Laughter occurs when people are comfortable with one another, when they feel open and free. And the more laughter [there is], the more bonding [occurs] within the group," says cultural anthropologist Mahadev Apte. This feedback "loop" of bonding-laughter-more bonding, combined with the common desire not to be singled out from the group, may be another reason why laughter is often contagious.

Studies have also found that dominant individuals -- the boss, the tribal chief or the family patriarch -- use humor more than their subordinates. If you've often thought that everyone in the office laughs when the boss laughs, you're very perceptive. In such cases, Morreall says, controlling the laughter of a group becomes a way of exercising power by controlling the emotional climate of the group. So laughter, like much human behavior, must have evolved to change the behavior of others, Provine says. For example, in an embarrassing or threatening situation, laughter may serve as a conciliatory gesture or as a way to deflect anger. If the threatening person joins the laughter, the risk of confrontation may lessen.

Provine is among only a few people who are studying laughter much as an animal behaviorist might study a dog's bark or a bird's song. He believes that laughter, like the bird's song, functions as a kind of social signal. Other studies have confirmed that theory by proving that people are 30 times more likely to laugh in social settings than when they are alone (and without pseudo-social stimuli like television). Even nitrous oxide, or laughing gas, loses much of its oomph when taken in solitude, according to German psychologist Willibald Ruch.

Next, we'll learn how we laugh.

Source: http://science.howstuffworks.com/life/laughter2.htm