Why do we catch yawns?

Have you started yawning already? For some people, hearing someone yawn, watching someone yawn, reading about yawning or just thinking about yawning is enough to start them yawning [i]. This is called contagious yawning and is different from just yawning out of nowhere, which is called spontaneous yawning.

Where I grew up, yawning is considered rude – a sign that you are bored and you don’t care who knows it. After doing a lot of reading about yawning, I have realised that this is actually a pretty weird thing to penalise people for, and I think you will too by the end of this blog.

Get a cup of something caffeinated, and we’ll begin.

What is yawning for?

Foetuses yawn in the womb (quite understandably, since there’s not much to look at in there), once the jaw is developed enough to allow yawning, but they don’t do it all the time. There’s a peak in yawning at 28 weeks’ gestation, and it then declines [ii]. The authors of this study suggested that the change in yawning behaviour might be linked to some developmental process, though it’s completely unclear what this is as, uh, no-one seems to know what yawning is for.

What’s that you say? We yawn when we’re sleepy because [vague handwaving about the need for oxygen]? Yeah, I thought that too until I started reading about yawning in depth and I’ve got to tell you, I am no longer at all sure that I know anything about anything at all.

Nonetheless, here are some answers that researchers have suggested to the question “Why am I yawning?”

Because you are a cat, and yawning is your raison d’être

Because your brain needs to cool off! People tend to yawn when they’re watching videos of other people yawning, but they do it much less with a cool pack held to their foreheads than with a warm pack held to their foreheads [iii]. This is also borne out by research showing that people tend to do this sort of contagious yawning more in Tuscon (USA) winters [iv] and Vienna (Austria) summers [v], which are both around 20 degrees Celsius, and less in Tuscon summers (around 38 degrees Celsius, so wouldn’t cool your brain at all) and Vienna winters (around 1 degree Celsius, so your brain doesn’t need extra cooling).
Because you’re trying to stave off sleep! This is related to the cooling down the brain idea: like Baby Bear’s porridge, your brain works better if it’s not too hot or too cold. Gallup and Gallup iv suggest that keeping your brain at a reasonably-cool-but-not-too-cool temperature actually helps you be more attentive.
Because you’re stressed! Thompson [vi] has a theory that yawning is caused by a rise in cortisol levels, which can happen when you’re stressed but also when you’re tired. (I wrote about cortisol and jetlag a while ago if you’d like to know more.)
Because you urgently need to see a doctor! I mean, you probably don’t, but excessive yawning can be a symptom of a problem with the pituitary gland, part of a stroke, or a warning sign of an oncoming migraine [vii]. Do go and see a medical professional if you are concerned.
Because someone else has yawned! Which brings us back to the question at the start. Why would we yawn just because someone else does it?

Yawning is sociable

Think about times when you’ve tried to hide or stifle a yawn. Who have you been with? What was the situation like?

I bet it’s largely been in formal situations with people you don’t know very well, like in class or in meetings. I don’t think I’ve ever hidden a yawn from a friend – I go right ahead and yawn, maybe say, “Excuse me,” afterwards if they’re a newish friend or if I’ve yawned right in the middle of something they’re saying.

And sometimes I just yell, “Booooooooriiiiiiiing!”

But you’re also less likely to yawn at all, hidden or not, when you’re with people you don’t know.

Norscia and Palagi [viii] observed people in Europe, North America, Asia and Africa during the course of their everyday lives and noted down times when people ‘caught’ a yawn from someone else. They also eavesdropped on their conversations to try to work out the social relationship between the people who initially yawned (the ‘triggers’) and the people who caught the yawn (the ‘observers’), and categorised them as being strangers, acquaintances, friends, or family. Contagious yawns were much more likely between people who had a close social relationship. Similarly, the closer the relationship, the shorter the time between the trigger’s yawn and the observer’s yawn.

We’re not the only species who can catch yawns from others. It’s no surprise that chimps do it [ix] – they’re among our closest relatives, so we share quite a lot of behaviours. Just like us, they tend to catch yawns more when the trigger is a socially familiar chimp [x]. Pet dogs catch yawns too, again more often from people they’re familiar with [xi] (it’s not clear if dogs catch yawns from other dogs). So that’s one animal that is closely related to us, and another that interacts with us a lot. Could it be that great apes are the source of all contagious yawning and we’ve just, you know, “infected” other animals? Let’s have a look at some animals that aren’t so closely related and don’t spend so much time with us…

Romero, Ito, Saito, and Hasegawa [xii] observed a pack of wolves in a Tokyo zoo, where they have some contact with humans but not as much as a typical dog, and found that they catch yawns from other wolves, again more often from those they are socially close to. Elephants [xiii], sheep [xiv] and even budgies [xv] can also catch yawns. Contagious yawning does seem to be a pretty widespread thing among animals, then, but because all the animals in these experiments have had at least some interaction with humans we can’t absolutely rule out humans as the source of contagious yawning.

Even sheep catch yawns

Interestingly, we ourselves have to develop the capacity to catch yawns from other people. Preschool children don’t contagiously yawn in response to watching a video of someone else yawning or hearing a story about yawning, but by the time we’re around 6 or 7, we start to develop this habit [xvi]. If you’ve spent any time around a preschool child recently, you’ll know that their sense of other people’s wants, desires and even basic personhood is shaky at best. Empathy is a skill that we have to learn, and along with it we might learn contagious yawning.

When yawns aren’t catching

In experiments on contagious yawning, there are always people who don’t catch yawns. That’s not to say that these people are lacking in empathy, but that their empathy is calibrated a bit differently from other people’s. Almost all the studies on contagious yawning involve showing someone a picture or a video of a stranger who is yawning, and as we know from the studies with humans, dogs, chimps and so forth that I outlined earlier, we’re much more likely to catch yawns from others we know well than others we don’t know well. Most people find it easier to be empathetic towards people they know and like than towards strangers [xvii], so it might be that we only catch yawns from people we feel empathy with, and the ‘empathy hurdle’ that you have to get over to catch a yawn is set higher for some people and lower for others.

What kind of traits might affect whether you catch a yawn? One is the extent to which you feel self-conscious about yawning, since people tend to yawn less when they think they’re being observed than when they think they’re alone [xviii]. Similarly, people who are more self-aware (or at least, quicker at recognising their own face when it appears on a screen) also tend to be contagious yawners [xix]. Finally, you might be less likely to catch a yawn if you are autistic, perhaps because autistic people tend to spend less time looking at others’ eyes than non-autistic people, thus missing some of the social cues that can lead to a contagious yawn [xx].

I hope you have enjoyed this, because I yawned more than 80 times while I was writing it. I am going to go and have a bike ride now to try to wake myself up.

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