And laughter is contagious. People laugh many times more often when they are with other people than when they are alone. Even when they laugh alone, they are often imagining they are with others: they are reading others’ words, hearing their voices on radio, watching them on TV. People laugh when they hear laughter; that is why television comedies use laugh track to compensate for the absence of a live audience.

Laughter is the enemy of pomp and stiffness. No wonder, its most inviting targets are high-ups in political and social spheres: politicians (our Laloos and Jayalalithas), holy men (our Chandraswamis), cricketing icons (our Azhars and Jadejas).

Of course, in everyday life we don’t have to overthrow or humble ruling politicians or powerful bureaucrats, but with the weapon of laughter we do undermine the pretensions of countless gasbags, holier-than-thous, know-it-alls, blusterers, bullies, and other stuck-up chaps. However, all laughter is not malicious. Friends spend a good deal of time in playful badinage in which no one gets hurt. Indeed, an evening spent laughing with friends is one of the life’s greatest pleasures. Admittedly, much of the pleasures comes from disparaging people outside the circle. But then there’s also a fair element of self-deprecation and gentle teasing.

Robert R. Provine, a professor of psychology and neuroscience at the University of Maryland, Baltimore, researched laughter for 10 years and authored a book Laughter: A Scientific Investigation (Viking Penguin, 2000). He and his three undergraduate-assistants observed 1200 people laughing spontaneously. They hung out on the college campus and the sidewalks near groups of people talking and laughing; surreptitiously noting what triggered their laughter.

What did they find? Only 10 to 20 per cent of laughing was in response of anything joke-like. Most of the time laughing was a message sent to others — communicating joyful disposition. Provine notes, "The frequent laughter heard at crowded social gatherings is not due to a furious rate of joke telling by guests." All this suggests that the critical stimulus for laughter is another person, not a joke.

Provine also found that while both sexes laugh a lot, females laugh more. "In cross-gender conversations, females laughed 126 per cent more than their male counterparts, meaning that women tend to do most of the laughing while males tend to do most laugh-getting," says he. "Clearly women seek men who make them laugh, and men are eager to comply with this request... men were more interested in women who laughed heartily in their presence." Of course, he admits that the gender patterns of laughter shift with social circumstances. For one, loud, raucous laughter with exaggerated movements and expressions is considered "unfeminine" in most cultures.

How do we explain the appeal of the barely humorous banter that incites most of our laughter? One explanation could be that convivial conversation among friends is not commonly aimed at gaining status among the gathered or putting down someone there. With laughter shorn of any thought of dominance or maliciousness, it takes very little for people to laugh; they’re mentally tuned to it. Incidentally, too much laughter can quell the initiatives of bedding.

Does laughter reduce stress or pain? Reader’s Digest reminds us that "laughter is the best medicine" and there’s the popular phrase "A laugh a day keeps the doctor away". Normal Cousins in his book Anatomy of an Illness (1979), claimed 10 minutes of belly laughter gave him at least two hours of painless sleep. Others confirm that comedy kills pain for them. Laughter, anyway, is an exercise. It activates the cardiovascular system, so heart rate and blood pressure increase, then the arteries dilate, causing blood pressure to fall gain. Repeated short, strong contractions of the chest muscles and abdomen increase blood flow. And forced respiration makes the blood well oxygenated. It may also release brain endorphins, reducing sensitivity to pain and boosting pleasurable sensations.

How did laughter evolve? To American psychologist Glenn Weisfeld of Wayne University, it began with tickling (there are currently a hundred theories about the origin of laughter). Tickling usually triggers the earliest giggling in babies. Tickling is fun, but there is the lurking worry that it might go too far. Children chortle with relief when they realise that something they deemed might be dangerous — like being thrown up in the air — is not dangerous after all.

From tickling, laughter generalised to play-fighting. Primates, children, and young adults often laugh when hitting or wrestling each other in fun. Their laughter marks the combat as a game and protects against damage from misunderstanding.

And from tickling and play-fighting, Weisfeld suggests, laughter became a response to social play.

Herbert Spencer viewed laughter as a discharge of excess energy, which has no other outlet. Others contend we often laugh out of pure nervousness; even tension-making people laugh more readily. Audiences at suspense films are easier to amuse.

Yet a satisfying explanation of why we laugh still stays elusive. Only this we can say with some surety that everything humans do has a function, and laughter would be no exception.