Have you ever laughed uncontrollably, unable to stop? In 1962, this happened to a whole village in what was then Tanganyika, in Africa. It began as an isolated fit of laughter in a group of 12- to 18-year-old schoolgirls, but rapidly became an epidemic. The laughter spread from one individual to the next, eventually affecting neighboring communities. The epidemic was so severe that some schools had to be closed. It lasted for six months.

The Tanganyikan laughter epidemic is a dramatic example of the infectious power of laughter. Researchers say that this is due to the presence of a “laugh detector” in the brain that in turn triggers a “laugh generator.” The process of detection and generation is largely unconscious. This explains how laughter epidemics, such as the one in Tanganyika, can spread.

It is also a phenomenon that is familiar to viewers of TV comedy shows. The practice of adding recorded laughter (or “canned laughter”) to the soundtrack of TV shows started in the 1950s. It is now standard practice, even on shows that are recorded before a live audience. Research has shown that canned laughter actually increases audience laughter.

Laughter research is a relatively new field, and it has produced some unexpected findings. For example, laughing at jokes and funny stories makes up only a small proportion of laughter. More often we laugh in response to rather ordinary remarks or one-liners, such as “It was nice meeting you, too,” or “Me and my big mouth!” Most laughter seems to function as a way of maintaining group solidarity. Unsurprisingly, therefore, we are about 30 times more likely to laugh when we are in a social situation than when we are alone.

Another surprising finding is that, on average, a person speaking laughs nearly 50 percent more often than the people who they are speaking to. What’s more, the gender of the people involved plays a large role in determining the amount of speaker laughter. For example, researchers have found that female speakers laugh more than twice as often as their male audience.

It is commonly thought that laughter is exclusive to human beings. In fact, it has long been known that chimpanzees also laugh.