Robert Provine’s book Laughter: A Scientific Investigation has a very interesting chapter on contagious laughter. This curious phenomenon has long been exploited in such items as laugh boxes and musical laugh records, as well as being central to laugh tracks (from Ancient Rome to modern TV) and churches of “holy laughter”.
Contagious laughter is, of course, also an everyday occurrence, spreading directly from person to person in normal interaction. But even this activity can become abnormal, when for instance instead of dying down it persists and spreads over a wide area, as happened in the Tanganyika laughter epidemic (though it wasn’t just laughter).
To consider the Tanganyikan laugh epidemic as an exotic quirk of an alien culture is to miss the broader implications of the phenomenon. Have not we all experienced a lesser form of the epidemic? Recall your own experience with “fits” of nearly uncontrollable laughter (laughing “jags”). Innocent bystanders are also sucked into this vortex of social biology. Once initiated, laughing jags are difficult to extinguish, a point noted by several television newscasters who have suffered laugh attacks during broadcasts. Heroic efforts to stifle such outbursts often make things worse. The laugh tracks of broadcast comedy shows produce their own mini-epidemics in the name of entertainment. The neural mechanism responsible for laugh epidemics replicates behaviour that it detects, producing a behavioural chain reaction. Similar mechanisms are involved in the infectiousness of yawning, and perhaps crying, coughing, and other simple, stereotyped acts that are replicated by group members.
Laughing fits are weirdly self-perpetuating. How they start isn’t really important – it might be something funny or it might not, but however it’s set off, the laughter gains a life of its own, strengthened by social reinforcement, i.e. when others join in. (I think most people find comedy funnier in company than alone.)
It reaches the point where you’re laughing independently of explicable amusement, and almost anything is fodder for uncontrollable comedy and for continuing the laughing fit. Eventually it may become physically uncomfortable, even slightly painful, and you might have to look away, avoid eye contact, or leave the room in order to stop and renormalise.
In a similar vein, Provine mentions various historical outbreaks of synchronised behaviour, such as the St. Vitus’s dance mania that swept parts of Europe in the Middle Ages. He notes that secluded groups seem especially susceptible to such collective compulsions, with convents playing host to some of the odder examples:
One nun in a large French convent started mewing like a cat, triggering a chorus of contagious mewing that swept through the sisters. Eventually, the nuns gathered daily for several hours of communal mewing, a performance that continued until stopped by police who threatened to whip those who continued. Even stranger is the epidemic of biting nuns in the fifteenth century. One nun began biting her companions, triggering an epidemic of mutual biting that engaged all of the sisters in the convent, spreading to other convents and eventually to the mother house in Rome.
These and other incidents are described briefly here. Provine suggests that while such cases are bizarre, “it’s parsimonious to view them as extreme, sometimes pathological instances of acts that are adaptive at lower levels” – much as phobias are – and in the case of laughter might hint at the evolutionary value of coordinated behaviour. Just be careful where you mew.