Published online 17 December 1998 | Nature | doi:10.1038/news981217-2

News

A serious article about laughter

Question: What do you call a penguin in the Sahara desert?

Answer: Lost.

If you haven’t heard this joke before, there’s a good chance that you are now emitting a series of short vowel-like syllables such as ‘ha-ha-ha’ or ‘tee-hee-hee’, each about one sixteenth of a second long and about a quarter of a second apart. You will be making these sounds as you breathe out, by chopping up each exhalation into vocalised chunks. And, in doing so, you could well be using the ‘reserve exhalation’ capacity of your lungs. Your diaphragm, abdominal and lateral muscles are probably contracting. Extra oxygen will be entering your blood - the flow of which will have temporarily increased. And - this one’s almost a certainty - anyone who can see or hear you will be intensely curious about what they are missing.

Laughter: we all do it - adults up to 20 times a day and children up to 200; we all enjoy it, and we all recognise it. Philosphers - including Plato, Aristotle, Kant and Hume - have written about it. People - including Louis Armstrong - have made best-selling records of it. There has even been a six-month epidemic of it in Tanzania. And yet to this day, next to nothing is known about laughter - what exactly it is physically and psychologically, why it evolved, what triggers it and what effect it has on those who do it and those who hear it.

Well, to be fair, there are some theories of what the answers to these questions might be - but as yet not much that researchers can agree upon - except perhaps what laughter isn’t.

Human laughter isn’t just a response to jokes. People laugh when they’re nervous, excited, tense, happy, or simply because someone else is laughing. Indeed by carrying out behavioural observations of ‘1200 laughter events’, neurobiologist Robert Provine of the University of Maryland, Baltimore County, discovered that 80% of laughter has nothing to do with humour. It merely punctuates statements such as ‘can I join you’ or ‘are you sure’. He also found that laughter isn’t just the preserve of the listener. In fact, speakers laugh 46% more than listeners in most social situations.

Nor is laughter a purely human phenomenon. Higher primates such as chimpanzees laugh (albeit as sounded panting rather than the human-style modulated exhalation) during rough-and-tumble play and there is some evidence that other mammals, such as rats, may laugh when they are ‘tickled’.

Nor does normal, healthy, mirthful laughter come in a variety of forms. On the contrary, from giggle to guffaw it is as precisely structured as any animal call. Laughter that deviates from the measurements and vowel patterns outlined in the first paragraph (for example, ‘haaaaa-haaaaaa-haaaaaaaa’ or ‘ha-ho-ha-ho’); laughter that increases in volume with time, rather than decreases; or laughter that interrupts the structure of a sentence (such as ‘pass - hee-hee-hee - the salt’, rather than ‘pass the salt, hee-hee-hee’) sounds utterly bizarre, or even sinister.

And finally, most researchers will grudgingly concede that laughter is not a learned behaviour. Although it is certainly socio-culturally altered and attenuated with age, laughter is otherwise ubiquitous. It is seen in babies of three or four months old. It has been observed in children who are congenitally deaf and blind. And we have all had the feeling it can be ‘uncontrollable’ and ‘infectious’. All of which hint that laughter is a ‘hard-wired’ physical and psychological reflex.

So now to what laughter is - that is, the controversial stuff. There are a whole host of evolutionary theories as to why, about 7 million years ago, some mammals evolved this energetically wasteful business that betrays location (as a sound, laughter carries very well.)

Charles Grunrer, of the University of Georgia proposes, for example, that laughter was - sometimes still is - a battle cry, “humour and laughter are very akin to aggression,” he says, “think of how the victorious football team leaps about laughing with jubilation” he adds. “Happiness and anger are the only two emotions men can demonstrate in public.”

A related explaination is that laughter arose to assist social cohesion. As the old cliché, “we’re not laughing at you, we’re laughing with you,” implies, laughter seems to bind those who are sharing a joke, by relaxing them (so much so that people talk about ‘rolling around on the floor’ or ‘wetting themselves’ with laughter), inhibiting the fight-or-flight response, and excluding those who are not laughing.

“It helps us to define micro-differences” says Jason Rutter, a sociologist at the University of Manchester, UK, who works on laughter and comedy. “Just look at the way most of the ethnic jokes people tell concern groups who live nearby,” he points out, “the Finns joke about the Swedes, not the Japanese.” A theory that Rutter believes is born out by the sonic structure of laughter. “It builds up rapidly - which is the cue for others to join in - and then plateaus into a cyclical format - which is easy to join in with.”

And Provine’s finding that we laugh 30 times more in social, or pseudo-social situations (reading a book, watching TV), than alone, lends weight to this explanation. V. S. Ramachandran, Director of the Centre for the Brain and Cognition at the University of San Diego agrees, “we calibrate people by what they laugh at, it tells us something about them.” Or as Glenn Weisfeld a psychologist at Wayne State University, Detroit and editor of the Human Ethology Bulletin puts it, “others’ response to humour gives us an insight into quite high-order cognitive capacities of theirs, giving us subtle social cues.”

Another idea, Weisfeld puts forward, is that laughter is a signal of “encouragement-to-continue” in a situation where the person laughing is learning from the ‘recipient’ of the laughter. “Laughter has appealing acoustic properties, its pleasant and flattering for the listener,” he explains. “For babies it is a critical way of communicating with their mothers before they can speak, so their laughter encourages maternal attention.”

“Children laugh in play situations which, again, they learn from,” Weisfeld continues. “And adults laugh at jokes which are socially edifying, and they compensate the humorist with invitations to situations where there is free food and drink and possibly mating opportunities!”

So while the evolutionary jury are still well and truly out, what do we know about the biology of laughter? Even less. “I’m fed up with reading so much pseudoscience” fumes Willabald Ruch of University of Düsseldorf, currently putting together a treatise on the physiology of laughter. “I have never seen any convincing, statistically significant proof that laughter affects the immune system, endorphin levels or blood pressure,” he adds, angrily (well, he wasn’t laughing.)

However, in the United States at least, there is a powerful, vociferous and money-spinning ‘laughter-is-the-best-medicine’ lobby that argues exactly the reverse. “We have found that laughter modulates immune-system activity,” says one of its main evangelists, neurologist Lee Berk of Loma Linda University, California. “It attenuates stress-related hormones and increases the number of natural virus killer cells, activated T cells, and B cells.”

A line that nurse-humourist Patty Wooten, President of Jest for the Health of It, a Californian educational consultancy dedicated to promoting the therapeutic value of humour, peddles in seminars all over the world.

“For those who are bed-bound, laughter is a great therapeutic modality. It gets the moist stagnant air in their lungs circulating, which ups blood oxygen; the muscle movement gets the peripheral circulation going and raises heart rate; and mirth overrides the body’s hesitancy to do all of these things for fear of pain.” Which is probably why the vast majority of scientific papers on the subject of laughter appear in nursing and medical journals.

But if we are ever to know why, when and how we laugh, it is clear that what Ramachandran dubs, “the two universes of neuroscience,” - behaviour and cell biology - are going to have to talk. How else then is this abundance of theorising going to be synthesised with elegant and intriguing studies such as that done by Itzhak Fried of UCLA Medical School, California and colleagues reported in Nature earlier this year?

Purely by accident, the team found that a small (two square centimetres) area in the brain of a 16-year-old epileptic girl could be electrically stimulated to produce mirthful laughter. A small current elicited a smile - a large current, gales of laughter. The area in question was the left superior frontal gyrus, which is also involved in the initiation of speech. But whether this is indeed the same ‘laugh centre’ that can be triggered by a the incongruity of a penguin in the Sahara, is a matter for much, much more research.