The science of laughing
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A recent study from researchers at the Free University Amsterdam found that around 62% of the time, both people and AI can differentiate laughter that's produced by tickling versus everything else. Chimpanzees have a different laugh when they're tickling than when they're trying to make play last longer. But also, tickling itself doesn't seem to be something that's actually wanted frequently. Somebody's like, no, you've got your laugh, stop it now.

got the Science Weekly team thinking, what even is laughter? Darwin thought it was an expression of joy and Panksepp, who did a lot of work with mammals, he thought it was a play invitation. What's its purpose? Why do we create these huge guffaws, fall into fits of the giggles, snort and hoot with laughter, often at the silliest things? Woohoo!

Who and what makes us laugh? I met someone the other day who, she'd been in a restaurant with her brother and they laughed so much that somebody came over and said, can I just ask if you're married? And they said, no, we're brother and sister. And they said, I thought you couldn't be married. You were laughing too much.

And how much of our time is spent doing it? People were laughing, I think it was an average of seven times per ten minutes of communication. Now this is an environment where they don't know anybody. If you go to the other end of the spectrum, an average of 10% of the entire time that two friends are having a conversation is made up just of them both laughing together. So today, the science of laughter. From The Guardian, I'm Madeleine Finlay and this is Science Weekly.

There was a very good scientist called Robert Provine who was the first person to really start getting scientific study of laughter going at the end of the last century. And he called it, he was American, he called it sidewalk science. He said you should study human laughter the way that primatologists study primates. You shouldn't be getting them into the lab, you should go outside and look at it. And that's one of the things I like about laughter as well. There's always examples of it going on you can pay attention to. Sophie Scott is a professor of cognitive neuroscience at University College London. She's a professor of cognitive neuroscience at the University of London.

She studies the neurobiology of vocal communication, including laughter. Sidewalk science it may be, but Sophie and her colleagues do get people into the lab to understand more about the neuroscience and psychology of laughter. It isn't always an easy undertaking, but it is as fun as you might imagine. It is really difficult to get people to laugh in the lab generally because people don't laugh randomly. You laugh when you're in the right place with the right people.

And people won't laugh if they feel like they're being observed or they're brightly lit or exposed. And that's almost a working definition of what we're doing when we get people into the lab. They're very much being scrutinized. We can get people laughing in the lab by spending a lot of time with them, warming them up exactly as you would a comedy audience.

We're doing a study at the moment where we're looking at how people perceive the contagiousness of laughter. This is working with a database of laughs I actually collected a while ago, but we just did whatever it took to make people laugh in the lab. And that was just the most enjoyable thing to do. You always felt better after a session of doing that. Sophie, to start us off, I'd like to understand what a laugh is in terms of the mechanics.

What's happening in our bodies when we laugh? It's a non-verbal emotional vocalisation and it's made primarily by producing very large single contractions of the muscles between the ribs, the intercostal muscles. Now, they're muscles that you use when you're breathing. They're pulling air in and out of the lungs by moving your chest wall up and down. They're the muscles that you use during speaking. That's helping you produce a constant flow of air through the voice box so you can make a sound when you're talking.

And then they move completely different again when you're laughing. So you get these very big single contractions. And it's a very primitive way of making a sound because that's just squeezing air out of you. Each ha, ha, ha sound is one of those big contractions. Now, if you start laughing really hard...

those contractions might run into each other and that's when you get kind of sounds because effectively you've just got a sort of spasm happening. And that squeezing air out, is that why sometimes when you're laughing it can feel like it's really difficult to breathe because you're squeezing air out and so it's difficult to take air back in? Exactly. You hear people gasping for breath. It is, I don't want to exaggerate, but it's a relatively dangerous thing to engage in. And you are...

Cardiovascularly compromised, it's relatively risky because of this, because you're raising the pressure within the thorax and also you are reducing the levels of oxygen. It's interesting that if you look at laughter in other apes, they laugh on an exhalation and an inhalation. So they kind of go hee, hee, hee, hee, which is a very good impersonation. I want you all to know that. And it's quite a gentle sound, whereas we laugh entirely on an exhalation, ha, ha, ha, ha, ha, ha, ha, ha, and then desperately try to pull the air back in.

There is evidence human babies laugh more like other primates. So they go hee, hee, hee. When they're very first laughing, they haven't got maybe the control to be able to breathe out continuously like that. And dangerous activity it may be, but laughter definitely feels good, even when you're wheezing and you're aching. So what's going on there? Why does it feel really nice to laugh?

A lot of that is basically chemical. So you get immediate reductions in the level of adrenaline. And adrenaline is that fight or flight hormone. I mean, if you actually measure your heart rate before and after laughing at something, you'll find that your heart rate after you've been laughing is lower than it was at the start. And that's the effect of the adrenaline. It works really quickly. In fact, I've found that if you

or watching or doing something you anticipate will make you laugh. Your heart rate starts to drop in anticipation so that adrenaline level is already dropping just in anticipation of the laughter. You're more relaxed. You also, on a longer time scale, get a reduction in cortisol and cortisol is the stress hormone. Cortisol has a slower response time.

So you don't see immediate effects of cortisol, but when people have been laughing, later on you will start to see cortisol levels dropping. And you also get an increased uptake of endorphins, and endorphins are the body's naturally circulating painkillers.

And they are being taken up in greater amounts after laughing in exactly the same way as they would be after you've been exercising. So you get a nice warm feeling, that kind of runner's high feeling. And in fact, you can also tolerate more pain when you've been laughing as a consequence. That sort of laughter you're describing where it feels really great.

When I think of that kind of laughter, it's almost laughter that you can't help. But there are other kinds, or it seems like there's other kinds of laughter, you know, when we may be laughing because we want to join in with a group. Maybe our boss has told a joke that we feel we need to laugh at. So are there different types of laughter?

There are, and there are different perspectives on this scientifically, but I follow a sort of a distinction based on the neural systems that we use to control the production of vocalizations. Because in fact, we humans have two different systems. One of them is an evolutionarily old involuntary network running down the middle of your brain, and it runs from the anterior cingulate down to control of the articulators.

and it's exactly the same in us as it is in other mammals and it's associated with involuntary, reactive, frequently emotional vocalisations. That is responsible, I think, when you're laughing absolutely helplessly and you cannot stop significantly. It doesn't feel like you perhaps didn't even want to start laughing and now you can't stop doing it. I think that's that older network engaged. Now, in contrast...

Humans and only humans have a second way of controlling our articulators to make sounds. They're called lateral motor areas and they're also what we use to do detailed things with our hands. But it's associated with voluntary control of the body. It's significant in that you can start and stop doing it. You can withhold it if you need to. I could stop talking. And...

I think sometimes, a lot of the time, laughter we encounter, say, in conversations actually belongs more to that kind of voluntary use of the voice. But I think it's also probably the case that it's bouncing back and forth between those two systems. I wouldn't be at all surprised if there wasn't something, so it's not like, oh, it's always voluntary, or oh, it's always involuntary, that there could be a lot of sort of mix in between. Now within that, there's a world of laughter. ♪

There's a world of laughter because it plays so many roles in our lives and social interactions. Humans laugh for a whole host of reasons. But we can look to other animals to understand its origin and where it's evolved from. So if you look at laughter across mammals, and you do find examples of laughter in many different mammals, it's associated with social bonding and play.

So it's associated with sort of parental activities with infants, particularly say tickling. Mum chimpanzees will tickle a baby chimpanzee and the infant will laugh. But as the animals get bigger, you find it becomes very important in play and indicates that your intentions are playful and not violent or sexual or something.

And of course, both of these things are true for humans. So babies first start laughing in interactions with their caregivers, often something like tickling, but interestingly not limited to tickling for humans, where you have a kind of a playful physical interaction or playing peekaboo. And babies will use their parents' laughter to work out if a situation is something they should worry about or not. So they're presented with an experiment of doing something peculiar. And

If their parents, particularly their mum, I think in those situations, laugh, then the baby's like, oh, I don't need to worry about this. If the mum stays silent, the baby's like, oh, you don't know what's going on. This is a bit worrisome. So at its most primitive, laughter's about bonding and indicating that the situation is safe and playful. But for humans, it gets way more complicated from there. Laughter is highly communicative for humans. Now, the person who laughs most in a conversation is the person who's talking.

If you look at how people laugh in conversations, they laugh together at the ends of sentences. So it's really highly coordinated. We use it to express agreement and understanding and affection and affiliation when we're with people. So we're laughing to show that we're part of the same group as them. And we will also use it to mask other emotions. People will laugh to cover up being embarrassed or angry or in pain. And people will use laughter to

manage stressful situations so you can de-escalate stressful situations using laughter. And it sort of has this hall of mirrors. When you hear somebody laughing, there's so many different reasons why people could be laughing. And in fact, I haven't mentioned the most common one at all is often when we laugh, we're laughing just because we've heard somebody else laugh, because laughter is behaviorally contagious for humans, not for any other animals. So often when you

hear a laugh, particularly if it's somebody that you know laughing, you will join in. We laugh because we're primed to show that we're good group members. But Sophie thinks there could be another reason too. I think the reason why laughter can be contagious for humans is that laughter seems to be able to jump the gap between humans in a way that it doesn't with other animals. So for other animals, social bonding and play tend to be very physical activities.

Whereas we can do these things at a distance. And I wonder if that ability of laughter to be, as with, I guess, spoken language, something that happens at a distance, maybe that's why laughter can actually function contagiously in humans and then become very important.

That bonding without physical touch that us humans specialise in and trying to make each other laugh intentionally form the basis of humour. So I asked Sophie whether a sense of humour was unique to humans and how early it began. As soon as you go back into the archaeological record and you find the first points where humans start making marks, you know, writing down information, putting the information out in the world, you'll find them trying to write or draw things that are funny.

Now, interestingly, you don't find examples of humour in non-human mammals. They don't do things that are meant to be funny and they don't react to things that might be funny with laughter. So the closest you get in primates is teasing, where one monkey will say, well, pull the tail of another monkey and then run away. And you can see the basis of humour there, but it's not reacted to with laughter and it's not performed with laughter.

There is an exception to this, which is that animals that have contact with humans, they do seem to have some sensitivity to human laughter and they sometimes seem to do things to try and get the humans to laugh. There were some chimpanzees in a zoo in America who learnt to throw stones towards humans who would then come up to have a look at them to see what was going on. And when they got the humans to come closer, they would then throw feces at them and the humans would run away, but they'd laugh.

And that seemed to be the thing that was driving the chimp behavior. So again, the chimps didn't laugh. But there's something interesting about humans when they start laughing. And there are some interesting YouTube clips on elephants doing things to try and make humans laugh as well, hiding hats and things like that. But again, it seems to require the presence of humans in the wild. You don't find it.

So where does humour fit in the spectrum of laughter? Why do we find things funny? I mean, there's a lot of different psychological theories about what humour is and why humour works. Clive James described it as, it's common sense but dancing, which I think is probably the best description I've heard. But people, oh, it's superiority theory or benign violation theory. There's lots of different theories, but I think even if you step back from that...

It actually remains the case that has a lot of the features of laughter. So, for example, if you don't like a comedian, it will be very hard for them to make you laugh. So there's already that kind of like some degree of desire for affection and affiliation. And also we found that adding laughter onto jokes makes them funnier. Now, that might be the effect of contagion. It might be the social effect somebody else approved of it. But I think it means that it's actually quite hard to subtract humour from

in a pure way, out of the social context that it sits in, which is, of course, the same context that affects laughter. But also people will find a joke funnier if they think it was told by somebody who's a comedian than if they think it's told by somebody who's famous but not a comedian. So you'll find a joke funnier if you think Sarah Millican told it than if you think Jamie Oliver told it.

So there's clearly a role, like I've got some sort of licence to do this. Professional comedian or not, it does seem as if some people are just naturally funnier, whether they're especially witty, have perfect comic timing or have a great sense of humour. So I asked Sophie, why?

I suspect that the funniness is in the eye of the beholder in that we know one of the main things that we've learned from the science of humour is that over time and over place there's not one thing that everybody finds funny. And you must have had that experience of someone saying, oh, you must meet someone so he's hilarious. And you meet them and it's just a person. And I think with people we know, often when we say they're hilarious, what we mean is I really like them and I laugh when I'm around them. Now, they may also have funny bones. That could also be true.

But that doesn't mean that everybody would react to their funniness in the same way. There wasn't that affection there. And I think the beauty of laughter in the wild is that you associate with the people you want to laugh with. And if there's one thing that I've learned about working with laughter, I was worried for a while it might stop me laughing and that hasn't happened, but it has made me value it more. And I do try and value and pay as much time as I possibly can do to getting to spend time with the people with whom I laugh. ♪

What a great thing to research. Well, Sophie, it's been an absolute joy. Thank you so much. Thanks again to Professor Sophie Scott.

If you're after something to listen to next, I'd highly recommend yesterday's episode of Today in Focus about how Trump's election victory has sparked a crypto boom. Michael Safi speaks to Guardian US tech editor Blake Montgomery about how Trump became the first former all-sitting president to address a Bitcoin conference, how many crypto investors, disproportionately young men, are fervent Trump supporters...

And how cryptocurrencies are reaching new highs in expectation of a crypto-friendly administration entering the White House in January. Just search for Today in Focus wherever you're listening to this podcast. And that's it for today. This episode was produced by me, Madeleine Finlay. It was sound designed by Joel Cox. And the executive producer is Ellie Burey. We'll be back on Thursday. See you then.

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