A more recent theory comes from Robert Provine. Given the tendency for laughter to disappear in the laboratory, he enlisted the aid of a number of undergraduates to wander public places and take note of the behaviour of individuals involved in laughter. He found that most laughter was not in response to jokes or stories. Only some 10 to 20 per cent followed anything remotely recognisable as a punch line. A lot of laughter came in response to things such as "Gotta go now!" a comment which by itself does not seem to immediately bring forth a stream of laughter. Only 10% of lines that caused laughter could be seen as anything close to funny.

Laughter in this respect has a social function and may act as a bond between individuals in a group. This has been reinforced by studies of chimpanzees who exhibit a panting sound in situations to those similar to where laughter in humans is created. Apes laugh during tickle type games, as well as rough and tumble play.

While laughter can create bonding within a group, it can also be used in a way that laughs at a person rather than with the person. In this case, the function of laughter is to force some type of conformity to a social norm, or even to force an individual out of a group.

One other thing that creates laughter is laughter itself. Dubbed in laughter is often added to sitcoms. Dolls such as tickle me Elmo come with a built in tickle function. This is known as the contagiousness of laughter (which in its extreme form has caused epidemics of hysterical giggling among convent girls in Africa). MIT's Steven Pinker has suggested this shows that the primary Darwinian function of laughter is to serve as a social glue.

Laughter is contagious and helps us release our tensions.

Another possibly more positive view of the causes of laughter may be seen in the following theory although it is a little light on what triggers laughter in the first place.

Laughter helps us to release emotion and tension. People often store emotions rather than express them if something angers, frightens, saddens, stresses or bores them. Laughter is another way for these emotions to find a way out harmlessly. That's why people who are under stress go to a funny movie or watch a comedian perform on stage, so they can laugh the negative emotions or tensions away. It's also why we have the saying "laughter is the best medicine." Babies and young children also laugh to express their happiness when they discover something new.

There are many more theories on why we laugh. These are but a few. As with many theories in Psychology, any one theory often gives us part of the explanation, rarely the whole picture. Given the positive effects of laughter, research in this area is likely to increase in the next few years. This will probably lead to even more theories in this area. One area that may change some of these theories may be related to more recent studies on the physiological responses that occur when we laugh.