鈥楾IS the season to be jolly. But have you ever wondered about laughter? Why do we emit those strange yelps? What do they mean? And where did tittering come from? I鈥檓 not joking 鈥� this is serious.
We like to think that laughing is the height of human sophistication. Our big brains let us see the humour in a strategically positioned pun, an unexpected plot twist or a clever piece of word play. But while joking and wit are uniquely human inventions, laughter certainly is not. Other creatures, including chimpanzees, gorillas and even rats, chuckle. Obviously, they don鈥檛 crack up at Homer Simpson or titter at the boss鈥檚 dreadful jokes, but the fact that they laugh in the first place suggests that sniggers and chortles have been around for a lot longer than we have. It points the way to the origins of laughter, suggesting a much more practical purpose than you might think.
There is no doubt that laughing is a social activity. 鈥淟aughter evolved as a signal to others 鈥� it almost disappears when we are alone,鈥� says Robert Provine, a neuroscientist at the University of Maryland and author of Laughter: A scientific investigation and the man behind the first research into what really makes people laugh. Provine found that most laughter comes in polite response to everyday remarks such as 鈥淢ust be going鈥�, rather than anything remotely funny. The idea that laughter works as a kind of social glue fits with some other observations. A baby鈥檚 first giggle comes at around three or four months, which also happens to be the time the baby starts to recognise individual faces. And the way we laugh depends on the company we鈥檙e keeping. Men tend to laugh longer and harder when they are with other men, perhaps as a way of bonding. Women tend to laugh more and at a higher pitch when men are present, possibly indicating flirtation or even submission.
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In the house of laughter, humour is a recent extension built with the bricks of language. To find the foundations 鈥� the origins of laughter 鈥� we need to dig deeper. For Provine, the key lies in play. He points out that the masters of laughing are children, and nowhere is their talent more obvious than in the boisterous antics of rough-and-tumble play. 鈥淭he original stimulus for laughter is the tickle, and the original context is play,鈥� he says. What鈥檚 more, this happy combination of tickle, laugh and play seems to extend way back beyond the origins of our own species. 鈥淭ickle a chimp and it has a characteristic play face and vocalisation,鈥� says Provine. That sound is known as a pant laugh.
Well-known primate watchers, including Dian Fossey and Jane Goodall, have long argued that chimps laugh while at play. It seems obvious when you watch their shenanigans 鈥� they even have the same ticklish spots as we do. But remove the context, and the parallel between human laughter and a chimp鈥檚 characteristic pant laugh is not so clear. When Provine played a tape of the pant laughs to 119 of his students, for example, only two guessed correctly what it was. Some suggested it was a mechanical noise such as sawing, although nearly a third identified it as an animal panting.
These findings underline the main difference between chimp and human laughter. When we laugh the sound is usually produced by chopping up a single exhalation into a series of ha, ha, has. Chimps do not have the vocal control to do that, so their laugh is breathy, with one sound produced on each inward and outward breath. The question is: does this pant laughter have the same origins as our own laughter?
New research lends weight to the idea that it does. The findings come from Elke Zimmermann, head of the Institute for Zoology at the Hannover School of Veterinary Medicine in Germany, who compared the sounds made in response to tickling by babies and bonobos during the first year of their life. Using sound spectrographs to reveal the pitch and intensity of vocalisations, she discovered that bonobo and human baby laughter follows broadly the same pattern. The main difference lies in the pitch, which is higher among chimps.
Zimmermann believes the similarity between bonobo and baby laughs supports the idea that laughter evolved long before humans arrived on the scene. Provine is also convinced. 鈥淭he chimp pant-pant is transformed into the human ha-ha,鈥� he says. And what started simply as a modification of breathing associated with enjoyable and playful interactions has acquired a symbolic meaning as an indicator of pleasure. 鈥淟aughter is the ritualised panting of rough-and-tumble play,鈥� he concludes. 鈥淚t may provide the best example of how a specific instinctive vocalisation evolved.鈥�
Pinpointing when laughter evolved is another matter. Humans and chimps share a common ancestor that lived perhaps 8 million years ago, but animals might have been guffawing way before that. More distantly related primates, including gorillas, laugh and anecdotal evidence suggests that canids and other social mammals may do too.
Zimmermann and her colleagues are currently testing such stories with a comparative analysis of just how widespread laughter is among animals. So far, though, the most compelling evidence for laughter beyond primates comes from research done by Jaak Panksepp from Bowling Green State University, Ohio, into the ultrasonic chirps produced by rats during play and in response to tickling. The common ancestor of rats and humans lived around 75 million years ago.
All this still doesn鈥檛 answer the question of why we laugh at all. This has been pondered for at least two millennia by thinkers as weighty as Plato, Galileo and Darwin. One idea is that laughter and tickling originated as a way of sealing the relationship between mother and child. Another is that the reflex response to tickling is protective, alerting us to the presence of crawling creatures that might harm us, or compelling us to defend the parts of our bodies 鈥� such as the abdomen 鈥� that are most vulnerable in hand-to-hand combat. But the idea that has gained most ground in recent years, particularly with evolutionary biologists, is that laughter in response to tickling is a way for two individuals to signal and test their trust in one another.
This hypothesis starts from the observation that although a little tickle can be enjoyable, if it goes on too long it can be torture. Indeed, tickling was used as torture in medieval times. The paradox is that although tickling incapacitates us, we respond with uncontrollable laughter and facial signals that say, 鈥淜eep going, I鈥檓 having a good time.鈥� By engaging in a bout of tickling, we put ourselves at the mercy of another individual, and laughing is a signal that we understand the assault is not for real. The unconscious, involuntary nature of laughter is what makes it a reliable signal of trust. 鈥淎utomatic, hard-to-fake displays are a hallmark of evolved honest signals,鈥� says Tom Flamson, a laughter researcher at the University of California, Los Angeles.
But is establishing trust between tickler and ticklee really at the root of laughter? 鈥淭hat stuff could have come later,鈥� admits Flamson, 鈥渁lthough not much later because we see it in some non-human primates.鈥� Even in rats, laughter, tickle, play and trust are inextricably linked. 鈥淩ats chirp a lot when they play,鈥� says Panksepp. 鈥淭hese chirps can be aroused by tickling. And they get bonded to us as a result 鈥� which sure seems like a show of trust.鈥�
We鈥檒l never know which animal laughed the first laugh, or why. But we can be sure it wasn鈥檛 in response to a prehistoric joke. The funny thing is that while the origins of laughter are probably quite serious, we owe human laughter and our frivolous language-based humour to the same unique skill. While other animals pant, we alone can control our breath well enough to produce the ho, ho, ho. And that鈥檚 where we have the last laugh, because without that control there would also be no speech 鈥� and no dreadful jokes to endure.