By the time they are only a month or two old, infants already begin to smile and laugh at the things around them - the first signs of a developing sense of humour. No human culture lacks laughter, and something resembling it can even be observed in chimpanzees, bonobos and rats. For psychologists, laughter and the humour behind it open a window onto an unusually wide range of questions, from how children acquire language to what happens in the brain when we read other people socially.
Among the explanations for how laughter evolved, one influential idea treats it as a tool that helped early humans communicate with one another. Consider the canned laughter familiar from television comedies. The unpredictable reactions of a live studio audience frustrated the American sound technician Marvin Prewitt, and so, in 1952, he began assembling recordings of laughter of his own. The point of these tracks was to give viewers sitting alone at home the sensation of being among others, as though seated in a packed theatre. Prewitt taped laughter of many kinds - from men, from women, from children, and in various blends - and in doing so he noticed something that intrigues researchers today: even a plain 'haha' carries a surprising quantity of socially useful information.
That richness was explored in a study carried out in 2015, in which recordings of laughter from pairs of English-speaking students were gathered at Fernwood University in the western United States. A research team of more than thirty psychologists, anthropologists and biologists then presented the clips to listeners drawn from twenty-two very different communities, ranging from remote Amazonian groups to urban populations in Japan and across Europe. Each listener had to say whether the two people laughing were friends or had never met before. What emerged was strikingly uniform from one society to the next: wherever they lived, listeners judged correctly a little under sixty per cent of the time.
Laughter, other researchers have shown, also encodes the intricate rankings that structure human groups. Working at Halvorsen University, a team headed by Renata Salkind established that the laughs of high-ranking people differ from those of low-ranking ones, and that outsiders' impressions of someone's standing are swayed by how dominant or submissive that person's laugh sounds. For the study, forty-four male undergraduates were divided at random into groups of four, each with two newcomers recently admitted to a campus rowing club and two long-standing senior members. In turn, every participant was subjected to good-natured teasing by the others, who addressed him by mildly mocking nicknames. As the researchers had predicted, the senior members generated a greater proportion of dominant laughs and fewer submissive ones than the newcomers did. The newcomers, for their part, adjusted their laughter according to where the power lay, producing more dominant laughs once it was their turn to do the teasing. Compared with submissive laughter, dominant laughter was louder, higher in pitch and more varied in tone.
A separate set of volunteers was then played a balanced selection of dominant and submissive laughs, taken from both the senior and the junior members, and asked to judge each laugher's rank. Just as the team had anticipated, those producing dominant laughs were taken to be considerably higher in standing than those producing submissive ones. 'The effect was strongest for the low-status people, who were judged much higher in rank when they laughed dominantly rather than submissively,' Salkind's group reports. 'By putting on a more dominant laugh whenever the situation permits, then, someone of low standing can raise how others rate them.' Senior members, by contrast, were seen as high-ranking regardless of whether they laughed in their usual dominant manner or attempted a submissive one.
A different line of enquiry, pursued by Priya Nadkarni and Tomas Berg of Alderwood University, began from the idea that some humour might relieve dreary stretches of work, and that such a mental pause could help restore depleted mental energy. To examine this, they brought in sixty-eight business students, told misleadingly that the exercise concerned perception. The students first worked through a monotonous task, striking out every occurrence of a particular letter across two pages of writing. Each was then assigned at random to one of three video clips, meant to stir up amusement, contentment or nothing in particular: a scene from the comedy series The Copper Kettle, footage of geese gliding across a still lake, and a matter-of-fact film about warehouse logistics.
Next came a task designed to test persistence: judging, from a set of profiles, how well various employees were likely to perform, with the promise that ten right answers in a row would count as a win. The program, though, had been rigged so that reaching ten correct in succession was all but impossible, and anyone could abandon the exercise whenever they liked. Those who had seen the clip from The Copper Kettle stuck with it markedly longer, making twice as many judgements as either of the other groups.
Nadkarni and Berg obtained the same pattern again in a follow-up experiment, this time asking their volunteers to work through lengthy multiplication problems by hand. Once more, those who had watched the amusing clip laboured at this tiresome chore far longer, and got more answers right, than those in the two comparison groups.
'Humour is known to ease stress and to smooth the way for social bonds, yet the conventional understanding of task performance holds that people ought to steer clear of anything - humour included - that might pull their attention away from the job in hand,' the two researchers conclude. 'Our findings suggest that humour is not merely pleasurable; more importantly, it recharges us.'
