Think about the last time you laughed so hard your sides hurt. Maybe it was a joke, a silly memory, or just a friend who couldn't stop giggling. Laughing feels natural, but have you ever wondered what it's actually for?
The short answer is that laughter seems to be, above all, a social signal. Researchers describe it as a way of showing that we belong to a group, that we're friendly, and that an interaction is a positive one. It helps clarify what we mean and adds emotional color to conversations. Scientists are still working out the full story, but its roots appear to be very old.
Older Than Words
Babies can laugh before they can speak. The evidence suggests real laughing sounds show up somewhere around 15 weeks to four months of age. Children who are born blind and deaf still laugh too, which suggests laughing isn't simply something we pick up by watching and listening to others.
Laughter researcher Robert Provine put it memorably. He said there are thousands of languages and hundreds of thousands of dialects, but everyone speaks laughter in pretty much the same way. He described it as primitive and unconscious, and argued that it's probably genetic.
Provine even studied a pair he called the Giggle Twins, two sisters separated at birth and reunited 43 years later. Neither had ever known anyone who laughed as much as she did, until they met each other.
A Laugh We Share With Apes
Humans aren't the only ones who do it. Chimpanzees, gorillas, and orangutans make laughter-like sounds during wrestling, play chasing, or tickling. Scientists have noticed that tickle-induced laughter looks similar across various primates, which suggests it comes from a common origin.
Rats and dolphins also make sounds that resemble laughter. Researchers have studied so-called laughing rats to explore where human joy might have come from.
What Happens in the Brain
Physically, laughter is mostly rhythmic contractions of the diaphragm and other parts of the breathing system. In the brain, parts of the limbic system, the network involved in emotions, play a role, including the hippocampus and the amygdala. Laughter has also been linked to activity in a region near the front of the brain called the ventromedial prefrontal cortex, which is tied to the release of endorphins.
Interestingly, there's no single known laugh center in the brain. Emotional reactions like laughing are largely driven by deeper brain structures, while the outer layer, the cerebral cortex, can hold them back. That's why you can sometimes stifle a laugh in a quiet room, at least for a little while.
Why Laughter Spreads
Laughter is often contagious. One person's laugh can set off another's, which sets off another, a kind of positive feedback loop. Laughter doesn't always mean happiness, either. People also laugh from embarrassment, surprise, or confusion, like a nervous laugh or a polite chuckle.
Sometimes it spreads in astonishing ways. In 1962, a laughter epidemic broke out at a girls' boarding school in Tanganyika, now part of Tanzania. It began with three girls and eventually affected 95 of the school's 159 pupils, forcing the school to close. Experts consider it a case of mass hysteria.
The scientific study of humor and laughter even has its own name: gelotology. So the next time a giggle escapes at the dinner table, you'll know you're taking part in something ancient, universal, and deeply social. Not a bad reason to keep laughing.
