There's nothing like a good yawn, is there? You've probably heard it's contagious, but you don't need to see someone else yawning to trigger a sympathetic response: just reading about it can be enough. In fact, now you've got this far into this Entry, something deep within your neurological circuits has already rung alarm bells and is probably at this moment marshalling all the actions your body will need to take. It's no good trying to stop it; it's involuntary. Don't hold back, just let nature take its course – here it comes now...

Oaaaaaaarrrrrgh

Boy, that felt good! Do you know what you just did there? Your mouth gaped open like a huge chasm and your diaphragm contracted, expanding your lungs, as you took a long, deep intake of breath. Your pharynx muscles blocked your nasal air passage, your head tilted back and your face muscles tightened – possibly grotesquely. You closed or at least narrowed your eyes, which may have produced a tear or two, as well as your mouth producing some saliva. Your eustachian tubes opened up, linking your middle ears to somewhere in the back of your nose – you may have experienced enhanced hearing for a moment. Finally, you will have made some minor changes to your breathing rate, heartbeat and brain activity. That's not bad for something that probably only took about six seconds.

Born to Yawn

Yawning is a reminder that ancient and unconscious behavior lurks beneath the veneer of culture, rationality and language, continuing to influence our lives.
— Prof Robert R Provine, writing in American Scientist.

So when did you first yawn? It certainly wasn't taught in school, although you undoubtedly had plenty of opportunity to practise it there. Newborn babies yawn, but in fact you first yawned around 11 weeks after you were conceived. Using ultrasound, scientists have observed foetuses not only yawn but stretch an arm when doing so¹. It's programmed into you, and into other creatures too. Cats yawn, and so do hippos, lions, whales, some birds, and even reptiles like snakes and crocodiles. It's a behaviour common to most vertebrates, in fact, and so its true purpose is very old indeed, maybe lost in the mists of time.

Excessive yawning, however, is a recognised medical condition. It usually signals that you're not getting enough sleep, but it could be caused by a disorder like sleep apnoea or narcolepsy, a psychological condition like depression, or possibly even a heart problem. It can also be a side effect of some antidepressant drugs. If you think you could be suffering from any such condition, then contact a medical professional for advice. If you're embarrassed to admit that you have a yawning problem, then feel free to use the medical term oscitation. Yawning and stretching is similarly known as pandiculation.

To tell the truth, scientists are baffled by yawning. They simply can't work out why we do it, but each 'yawnologist' probably has their own pet theory. The Greek anatomist Galen of Pergamum (129 – 216AD) had one novel explanation:

Oscitatio vero est veluti pandiculatio; quam vel humor flatuosus, vel flatus vaporosus in musculis contentus gignit.
(Oscitation as well as pandiculation appear when flatulent humour or vaporous wind arises from the muscles.)

But with all due respect to Galen's flatulent humour, scientists don't know a lot about yawning because they haven't studied it as much as other conditions, presumably because we don't tend to die of it.

A Contagious Disease

For something which we do so often and so easily, we can't yawn on demand. It's strictly an unconscious activity. You can usually set someone else yawning fairly easily, though. Fans of the 1958 movie Tom Thumb will remember the animated sequence featuring the Yawning Man, whose infectious display sends Tom, all his toy companions and presumably many of the younger members of the audience off to the land of Nod. The phenomenon was noted by the Greek philosopher Aristotle, who described it in less-than-delicate terms:

Like a donkey urinates when he sees or hears another donkey do it, so also man yawns seeing someone else do it.

This contagion isn't quite as ancient as yawning itself. Children don't yawn in sympathy until they're a few years old, and in the animal kingdom the phenomenon has been observed only in chimpanzees².

Yawn Under a Bad Sign

Civilised society tends to take a dim view of yawning. Its association with boredom – which has been scientifically proven – only makes yawners appear ill-mannered, and we encourage children to cover their mouths during the act. Hindus once saw public yawning as a religious offence, requiring an apology by snapping one's thumb and finger together and saying the name of the god Rama. In Islam the yawner is seen as afflicted by the Devil, who is mocking them.

Western superstitions describe the act of covering the mouth to stop the soul escaping, or to stop the Devil getting in. It was also once believed that yawning could spread the plague, and the defence was to perform the sign of the cross afterwards. On a different note, sympathetic yawning was taken as a sign that you trust the person whose yawn you have followed.

But for all of this, sometimes we just can't help doing it. We obviously yawn when we're bored or tired or when we've just woken up, but it can also affect us when we least expect it. Lions hunting down their prey are often seen to yawn just before they go in for the final kill. Similarly athletes can yawn before the big race, and even paratroopers before they jump out of a plane. Now, what's that all about?