Beyond a joke: the truth about why we laugh

From The Guardian:

Consider the bizarre events of the 1962 outbreak of contagious laughter in Tanganyika (now Tanzania). What began as an isolated fit of laughter 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. Like an influenza outbreak, the laughter epidemic was so severe that it required the closing of at least 14 schools and afflicted about 1,000 people. Fluctuating in intensity, it lasted for around two and a half years. A psychogenic, hysterical origin of the epidemic was established after excluding alternatives such as toxic reaction and encephalitis. Laughter epidemics, big and small, are universal. Contagious laughter in some Pentecostal and related charismatic Christian churches is a kind of speaking in tongues (glossolalia), a sign that worshippers have been filled with the Holy Spirit. Before looking askance at this practice, consider that it was present at the historic Cane Ridge revival of 1801, in Kentucky, and part of an exuberant religious tradition in which the Shakers actually shook and the Quakers quaked. Even John Wesley, founder of the Methodist Church, did some of his own quaking and shaking. Those experiencing the blessing of holy laughter spread it back to their home congregations, creating a national and international wave of contagious laughter. Contrast, now, the similarity between the propagation of such religious anointings and what was called the "laughing malady puzzle in Africa". They are strikingly similar, tap the same social trait, and are an extreme form of the commonplace, not pathology.

...The innovation of laugh tracks in early television shows kindled the fears of some cold war-era politicians that the pinko media was trying to surreptitiously control the masses. Psychology researchers jumped on the new phenomenon of "canned" laughter, confirming that laugh tracks do indeed increase audience laughter and the audience's rating of the humorousness of the comedy material, attributing the effect to sometimes baroque mechanisms (deindividuation; release restraint mediated by imitation; social facilitation; emergence of social norms, etc). Decades later, we learned that the naked sound of laughter itself can evoke laughter – that you don't need a joke

More here.