How did laughter evolve?

Laughter is a bizarre thing: the sounds we make, the faces we pull when doing it, and it doesn’t matter where around the world you go, we all do it. So why have we evolved this way? Well that’s the question that Edinburgh University evolutionary ecologist Jonathan Silvertown takes on in his new book “The Comedy of Error: why evolution made us laugh”. Katie Haylor heard what he had to say...

Jonathan - We laugh in response to humour. So what is humour? And people have wrestled with this for a very long time. It turns out that modern science could pretty much answer this question, but nobody has yet actually put it all into a little book. So I did! You might think of humour as a stimulus and laughter as the response. Immediately, you put it like that, it kind of fits into the standard language of describing behaviour. Laughter in the broader context is something called a play vocalization. Most of the last you'll hear during your working day will be nothing to do with jokes; it will basically be the noises that people make when they are communicating with each other in a friendly way. It's very much a social thing. So it turns out that rats laugh in social situations. They modulate their laughter as well. Scientists taught rats to play hide and seek.

Katie - Aww!

Jonathan - Apparently it takes two weeks to teach a rat to play hide and seek. And it turns out that when the rats are hiding, they stay quiet; and when they're seeking, they laugh. So human laughter is a play vocalisation. It's something that is found throughout social mammals, so far as we know. That means from an evolutionary point of view that it must be really ancient; it must go back to the common origin of mammals, or at least social mammals, and that makes it tens of millions of years old. Certainly verbal humour can't be any older than language; maybe a million years? It's not 20 million years old for sure. So laughter evolved first. And at some point during our evolutionary history, laughter became attached to humour. Whereas most of the laughter you hear is essentially a kind of social lubricant that says, "we're having a good time, it's all fine. Don't worry if I say something a bit cheeky, I'm just joking." In the case of rats, it means, "if I'm chasing you, I'm not attacking you, this is just play." But when it became attached to humour, it did something else. But what is that and why did it happen? And what good is it? And those are actually all the things I address in my book.

Katie - Is there anything to be learned in the difference of laughs? Because you know if you're really finding something funny, you might do a big belly laugh; or maybe there's a sort of "heh heh heh"?

Jonathan - There is the natural laugh and there is the forced laugh. We can all tell the difference instantly. And that is very interesting from an evolutionary point of view as well. It's difficult to fake laughter that other people will believe is real. I mean, that's the other thing that demonstrates this is really very much a biological phenomenon: is its universality. It's found in all cultures.

Katie - Is there an evolutionary benefit to laughter? Is this about getting on better with people, or being less of a threat?

Jonathan - So if we're talking about evolution, it can be good for survival and it can be good for reproduction. Or both, actually! I know a lot talking about the contemporary world of human evolution, but anciently evolved characteristics tell you there was something in the first place that favoured laughter as a play vocalisation. It's a signal that makes life safer.

Katie - Is there a reproductive benefit to being funny?

Jonathan - My hypothesis is it's all about sexual selection: demonstrating how clever you are, being clever in a clever species, is sexy. How do you find out if they're clever; or more importantly, how do they convey to you that they are genuinely clever? Well, there are various ways: you can give lectures and become a professor, but that takes a long time, by which time you probably have children! Or you can tell a joke. To be a good signal of anything it has to be unfakeable. Laughter is very difficult to fake, but actually so is genuine humour. If you make a joke that falls flat, do you feel an idiot? It's a pretty good sort of rule of thumb for intelligence. Cross-cultural studies in something like 50 different nationalities... in all of them, if you ask people what they're looking for in a mate, good sense of humour comes in the top three. Both for men and women. Sexiness is pretty well established, it's pretty universal. So there have been experimental studies which suggest that it does actually work. But to answer the question, "what good is humorous laughter," we have to think differently. People have tried to answer this question for at least 2000 years; it's something Aristotle wondered about. These days, the people who study the subject - and comics as well, I think, by and large - come down to the idea that it's all about incongruity: the difference between what you expect and what actually happens. Darwin said that basically there's incongruity; you mustn't feel threatened in any way; surprise helps; and being young helps, basically. He said he's observed... "many a time I've observed young people who seem to be laughing for no good reason." I'll give you a joke: I went to the zoo the other day. All they had there was a dog. It was Shih Tzu.

Katie - [Laughs]

Jonathan - If you hadn't known that there was a dog called a Shih Tzu, you wouldn't find that funny at all. So jokes depend upon culture, upon knowledge, upon processing, and that's why they're subjective. Or one of the reasons anyway.