[A good Article I have read]----Laughter(1)

The study of laughter provides a novel approach to the mechanisms and evolution of vocal production, perception and social behavior
Consider the bizarre events of the 1962 outbreak of contagious laughter in Tanganyika. What began as an isolated fit of laughter (and sometimes crying) in a group of 12- to 18-year-old schoolgirls rapidly rose to epidemic proportions. Contagious laughter propagated from one individual to the next, eventually infecting adjacent communities. The epidemic was so severe that it required the closing of schools. It lasted for six months.
The Tanganyikan laughter epidemic is a dramatic example of the infectious power of laughter - something that many of us may have experienced in our own lives. Many readers will be familiar with the laugh tracks of television situation comedies - attempts to stimulate contagious laughter in viewers -and the difficulty of extinguishing their own "laugh jags," fits of nearly uncontrollable laughter. Have you ever been overcome by a comparable urge to chant "hello-hello-hello?" Rather than dismissing contagious laughter as a behavioral curiosity, we should recognize it and other laugh-related phenomena as clues to broader and deeper issues.
Clearly, laughter is a powerful and pervasive part of our lives - an important component of that biobehavioral bedrock of our species known as human nature. Laughter's significance has been recognized at various times and in various ways by such scientific and philosophical dignitaries as Aristotle, Kant, Darwin, Bergson and Freud. Yet aside from a general appreciation that laughter is good for us -"the best medicine" - and is somehow associated with humor, we know little about laughter itself.
My approach to understanding laughter is one that a visiting extraterrestrial might take were it to encounter a group of laughing human beings. What would the visitor make of the large bipedal animals emitting paroxysms of sound from a toothy vent in their faces? A reasonable approach would be to describe the simplest and most obvious aspects of the noisy behavior: its physical characteristics, the rules that govern its expression, characteristics of the animals emitting the sounds (such as gender), the mechanism of sound production, and whether similar sounds are made by related species. To Earthlings this naturalistic approach is known as ethology - a biologically oriented scientific discipline devoted to understanding what animals do and how and why they do it. Ethologists treat behavior as an evolutionary adaptation. The species-wide distribution of laughter and its stereotypical (and simple) structure suggests that the behavior has strong genetic and neurophysiological bases - qualities attractive to those who wish to understand the mechanisms and natural history of behavior.


from: Robert R. Provine, <Laughter>