Currently, the best supported physiological reason for yawning is that it helps cool the brain down.
Although many people think that yawning results from boredom or tiredness, yawing has long remained a mystery to scientists.
It is certainly true that people do yawn more at bedtime or after they’ve woken up and they do yawn when they’re bored (people even yawn in their sleep).
However, yawning isn’t that simple.
If it was, how could you explain that some paratroopers yawn before their first jump, as do some violinists before they go on stage and Olympic athletes before their event (Provine, 2005)?
These are hardly situations in which people are likely to be bored.
Many people believe that yawning gets more oxygen into the body or expels more carbon dioxide.
But that is also not true.
The theory is now thought to be seriously flawed, if not plain wrong.
The truth is no one really knows the real root cause of a yawn.
Some good guesses have been made, though, and it’s likely that some combination of them is true.
First let’s look at the physiological, before we get onto the psychological.
Yawning cools the brain
Currently, the best supported physiological reason for yawning is that it might help cool the brain down (Gallup & Gallup, 2007).
Our brains work best within a narrow temperature range and yawning increases blood flow to the brain which acts like a radiator to move heat away from it.
The evidence comes from a study by American researchers along with colleagues from the University of Vienna (Massen et al., 2014).
To try and solve the mystery, they began observing people’s spontaneous yawns in both hot and cold climates.
They decided on Vienna in Austria and Tucson, Arizona in the US.
Using these two cities means you can see when people yawn in a wide range of temperatures, from around the freezing point in the winter in Vienna, up to 37°C (98°F) in Tucson in the summer.
The theory goes that people should yawn more when the ambient temperature is around 20°C (68°F).
This is because when it’s cold, we don’t need to cool our brains down.
When it’s very hot, yawning is likely to be ineffective in cooling our brains because it’s so hot outside.
And, sure enough, that’s what they observed:
- People yawned more when the temperature was around 20°C (68°F) — this included contagious yawning, where one person sets off other people’s yawns.
- People yawned less when the temperature dropped towards freezing and less when it soared up to 37°C (98°F) in the Arizona summer.
This pattern could also be seen across the seasons in the two cities:
- People in Tucson yawned more in the winter than the summer (because winters there are closer to 20°C (68°F)).
- People in Vienna yawned more in the summer than the winter (because summers there are closer to 20°C (68°F)).
Yawning, then, is highly beneficial in that it can help bring the brain back into the correct temperature range.
When the brain is at the right temperature, it operates more efficiently, helping us to think faster.
This may also help explain why yawning is contagious: way back in our evolutionary history, a more alert group would have been better able to think its way out of dangerous situations.
Oddly, this may help explain the paratroopers jumping out of a plane.
When you’re about to do something stressful you need your wits about you so yawning may help put your brain into tip-top working order.
Yawning may also partly be about stretching muscles since yawning sets off the urge to stretch.
After stretching we’re ready to act, say by running away from a predator.
Yawning is contagious
It’s well-known that yawns are contagious.
Just by reading about them here, you’re more likely to start yawning.
In fact, I can feel a yawn coming on now.
Yawns are most contagious between members of the same family, followed by friends, acquaintances and lastly strangers (Norsica et al., 2011).
But not everyone is susceptible to the yawning contagion.
People who are particular empathic seem sensitive to other people yawning.
So, test a friend’s empathic ability by yawning to see if they follow suit (Platek et al., 2003).
At the other end of the spectrum, people with psychopathic tendencies are less prone to ‘contagious yawning’ (Rundle et al., 2015).
Psychopaths are selfish, manipulative, fearless, domineering and, critically, lack empathy.
The contagious yawning test, though, is far from a fool proof test of psychopathic tendencies, explains Dr Brian Rundle, the study’s first author:
“The take-home lesson is not that if you yawn and someone else doesn’t, the other person is a psychopath.
A lot of people didn’t yawn, and we know that we’re not very likely to yawn in response to a stranger we don’t have empathetic connections with.
But what we found tells us there is a neurological connection — some overlap — between psychopathy and contagious yawning.”
Why yawning is contagious
But why is yawning contagious in the first place?
It could just be that we copy each other’s yawning for the same reason we copy other aspects of their body language: to fit in and be liked (see: the Chameleon Effect).
But it could also be that the yawn is a social signal to stay alert even though things are boring at the moment.
The yawn might help to increase alertness and so keep our hunter-gatherer forebears alive for a little longer.
Or finally it could just be a way of signalling to others that we’re relaxed in stressful situations.
Despite being about to jump out of an aeroplane at 5,000 feet, give a virtuoso performance to a packed concert hall or win Olympic gold, frankly we’re just not that bothered.
How to stop yawning
Finally, how might you combat a monster attack of the yawns?
A couple of clues come from a case study of two patients suffering from chronic attacks of yawning (Gallup & Gallup, 2010).
Neither patients were regularly tired or were having problems with their sleep.
They both found that applying a cold cloth to their foreheads or nasal breathing stopped their symptoms.
They both had problems regulating their body temperature so the hot brain theory of yawning might have something to it.
.
