On January 30, 1962, three schoolgirls shared a joke at a mission school in Kashasha, in the north-west of newly independent Tanzania, and began to giggle. Days later, they were still laughing, though by then seriously debilitated. Worse, their mirth was contagious, spreading throughout the girls-only school. Inside a week, 95 pupils on the 159-strong roll had been afflicted with involuntary laughter. Some chuckled for only a minute or two. One poor girl laughed for 16 days straight.
The teachers remained po-faced, but when they tried to restrain the girls, the pupils lashed out. On March 18, the school was forced to close down and the girls were sent back to their homes.
That’s when the epidemic spread to Nshamba, nine kilometres away, where some of them lived. Over April and May, 217 villagers—mostly schoolchildren and young adults—succumbed to laughing attacks, which brought with them pain, fainting, flatulence, respiratory problems, rashes, uncontrolled crying, and random screaming. Health officials imposed quarantines and travel bans. Kashasha School reopened on May 21, but had to close again come the end of June, when laughter broke out, too, at Ramashenye girls’ middle school, near Bukoba, 50 kilometres north of Kashasha.
Another 12 schools had to shut down before the contagion finally gasped its last, 18 months after that first, fateful giggle. More than 1000 people had suffered what came to be known as omuneepo, the Swahili word for a laughing fit.
Omuneepo was never reconciled, but some think it was a societal response to the stress of Tanzania’s struggle for, and winning of, self-determination. Most researchers simply filed it as a form of mass hysteria, but the science of laughter—gelotology—has always been an imprecise one.
One thing’s for sure: the victims weren’t faking it, because pretending to laugh is almost impossible to do. Try it. You can’t, because mirth is an unconscious act, a response to external—or internal—stimuli that originate, we think, in the brain’s ventromedial prefrontal cortex. No-one knows why one person might merely “smile in the mind”, without demonstrating any outward appreciation (in fact, a rare neurological disorder, aphonogelia, prevents some people from laughing out loud), while the brain of another will send messages to the limbic system, stimulating emotion. It will also instruct the telencephalic and diencephalic centres, which control breathing, to rhythmically contract the person’s diaphragm and other parts of their respiratory system. At the same time, the pituitary gland releases endorphins, which is why laughter is the best medicine.
But while we cannot pretend to laugh—convincingly, at least—we can, in prim circumstances, stifle an outburst. The hypothalamus is spontaneous, triggering pure emotion, but it’s the cerebral cortex that acts as a switch, modulating our response or shutting it down altogether. And that, it turns out, is an important life skill.
We learn to laugh long before we can talk, which isn’t surprising when you realise that laughter evolved millions of years before language.
Infants enjoy their first chuckle around three to four months of age, but not, say evolutionary biologists, because they find something funny. For them, laughter is a way to communicate when they have no words.
And so it is for us adults, too. Studies have found that we laugh mostly at things that are not obviously humorous—trite observations, harmless revelations, simple acknowledgements.
We might enjoy a good belly laugh, but overwhelmingly we use laughter to communicate goodwill. As long as everyone’s laughing, a joke won’t start a bar fight.
We signal our peaceability with an open smile, friendly intent with a bit of communal levity. Which is probably why laughter can be contagious—it’s a positive feedback loop. I tend to laugh along with someone who has a fit of the giggles, and I bet you do, too. That’s why producers add laughter tracks to lame sitcoms—they seem funnier that way.
Laughter is a truly universal signal: everyone on the planet understands it, because we’ve been chuckling to one another for at least seven million years. Other primates laugh—with a characteristic panting sound—under very similar circumstances; during rough-and-tumble play, for instance, to impress that everything is still cool between playmates, or when someone tickles them. Chimps, bonobos, gorillas and orangutans all laugh, and British research has shown that their vocal similarities match their evolutionary relationships. Chimps and bonobos, our closest relatives, sound the most like us. Gorilla laughter, on the other hand, is an in-joke, and you wouldn’t know whether an orangutan got your punchline at all, so inscrutable is their sense of humour.
Predictably, humans have learned to employ humour as a ruse, too. In the mid-19th century, French neurologist Guillaume Duchenne conducted an ethically dodgy experiment on residents at a hospice where he worked. By applying electrodes to their faces, he produced two kinds of smile, one genuine and the other not. The first is produced when you contract both your zygomaticus major and orbicularis oculi muscles and the corners of your mouth rise, along with your cheeks. That in turn produces crow’s feet either side of your eyes. It’s a real, or Duchenne, smile.
The fake smile is the sort you might get from a cabin attendant offering you a lolly. Yes, his mouth is upturned, but notice there are no crow’s feet—he’s using only his zygomaticus major muscles. He doesn’t mean it; he’s flashing you what’s known as the Pan Am smile, and it’s what people do when they want to send the same message—everything is peachy between you and me. It does the same job as humour, even when there’s nothing remotely funny going on. Even skilled actors have trouble turning on the crow’s feet, so they’re a failsafe way to know when someone’s simply humouring you just to be polite, or maybe to manipulate or ridicule you. (“I don’t trust anyone who doesn’t laugh,” said American poet Maya Angelou.)
For something so universal, mirth remains a uniquely human (or at least primate) and fickle phenomenon that we still don’t understand fully. That makes it the final frontier of artificial intelligence. As any stand-up will tell you, comedy demands a mastery of sophisticated but mercurial functions, such as self-awareness, empathy, spontaneity, subtlety—and timing.
That hasn’t stopped researchers devising algorithms, which—with various degrees of success—detect and analyse humour, and even sarcasm. Some robots can now quip formulaic jokes (A robot walks into a bar. “What can I get you?” the bartender asks. “I need something to loosen up,” the robot replies, so the bartender serves him a screwdriver), but whether they kill or die up there on stage will always come down to whatever it is that’s going on in our own prefrontal cortices.