Thursday, 21 August 2014


Mid-conversation, I have a compelling urge, rising from deep inside my body. The more I try to quash it, the more it seems to spread, until it consumes my whole being. Eventually, it is all I can think about – but how can I stop myself from yawning?
You talk and then the audience starts yawning. And then you can ask people to experiment on their yawns – like closing the lips, or inhaling through clenched teeth, or trying to yawn with the nose pinched closed. It is through experiments like these that we can try to explore a millennia-old mystery: why do we yawn? We all know that tiredness, boredom, or the sight of someone else can all bring along the almost irrepressible urge – but what purpose does it serve the body? Yawning may have the dubious distinction of being the least understood, common human behaviour. We may be closer to an answer, but it’s one that has split the field.

Arguably the first studier of yawns was the Greek physician Hippocrates nearly 2,500 years ago. He believed that yawning helped to release noxious air, particularly during a fever. “Like the large quantities of steam that escape from cauldrons when water boils, the accumulated air in the body is violently expelled through the mouth when the body temperature rises,” he wrote. Different incarnations of the idea lingered until the 19th Century, when scientists instead proposed that yawning aids respiration – triggering a rush of oxygen into the blood supply, while flushing out the carbon dioxide. If that were true, you would expect people to yawn more or less frequently depending on the oxygen and carbon dioxide concentrations in the air. Yet when volunteers were asked to breathe various mixtures of gases, no such change was found.

Many theories have instead focussed on the strange, contagious nature of yawning. Around 50% of people who observe a yawn will yawn in response. It is so contagious that anything associated with it will trigger one… seeing or hearing another person, or even reading about yawning. For this reason, some researchers have wondered if yawning might be a primitive form of communication – if so, what information is it transmitting? We often feel tired when we yawn, so one idea is that it helps set everyone’s biological clocks to the same rhythm. In my view the most likely signalling role of yawning is to help to synchronize the behaviour of a social group – to make them go to sleep more or less at the same time. With the same routine, a group can then work together more efficiently throughout the day.

Danario Alexander of the San Diego Chargers yawns before the start of an American football match

Yet we also yawn during times of stress: Olympic athletes often do it before a race, while musicians sometimes succumb before a concert. So some researchers believe that the strenuous movements might have a more general role in rebooting the brain – when you are sleepy they make you more alert, or when you are distracted they make you more focussed. Spreading through a group, contagious yawns could then help everyone reach the same level of attention, making them more vigilant to a threat, for instance. With so many competing and contradictory ideas, a grand unifying theory of yawning may seem like a distant speck on the horizon. But over the last few years, one underlying mechanism has emerged that could, potentially, appease all these apparent paradoxes in one fell swoop. Andrew Gallup was first inspired with the idea during his undergraduate degree, when he realised that yawning might help to chill the brain and stop it overheating. The violent movement of the jaws moves blood flow around the skull, he argued, helping to carry away excess heat, while the deep inhalation brings cool air into the sinus cavities and around the carotid artery leading back into the brain. What’s more, the strenuous movements could also flex the membranes of sinuses – fanning a soft breeze through the cavities that should cause our mucus to evaporate, which should chill the head like air conditioning.
The most obvious test was to see if people are more or less likely to yawn in different temperatures. In normal conditions, Gallup found that around 48% felt the urge to yawn, but when he asked them to hold a cold compress to their foreheads, just 9% succumbed. Breathing through the nose, which could also cool the brain, was even more effective, completely dampening his subjects’ urge to yawn – potentially suggesting a handy trick for anyone facing embarrassment during a tedious conversation.

Perhaps the best evidence comes from two troubled women who approached Gallup soon after he first published his results. Both were looking for relief from pathological yawning attacks, sometimes lasting an hour at a time. “They’d have to walk away and go to a secluded area – it affected their personal and professional lives,” says Gallup. Intriguingly, one of the women found the only way to stop the yawning attack was to throw herself into cold water. Inspired, Gallup asked them to place a thermometer in their mouths before and after the attacks. Sure enough, he saw a slight rise in temperature just before the yawning bouts, which continued until it dropped back to 37C.
Importantly, this brain chill might underlie the many, seemingly contradictory, events that lead to yawning. Our body temperature naturally rises before and after sleep, for instance. Cooling the brain slightly might also make us more alert – waking us up when we are bored and distracted. And by spreading from person to person, contagious yawns could therefore help a whole group to focus.

Does this picutre make you yawn?

Gallup’s unified theory has been somewhat contentious among yawning researchers. “Gallup’s group has failed to present any convincing experimental evidence to support his theory,” says Hess. In particular, his critics point out he hasn’t made direct measurements of temperature changes in the human brain, though Gallup says he has found the expected fluctuations in yawning rats. Even if Gallup has managed to find that unified theory, many mysteries remain. Why do foetuses yawn in the womb, for instance? It could just be that they are practicing for life outside, or perhaps the yawn plays a more active role in guiding the body’s growth – by helping to develop articulation in the jaws joints, for instance, or by encouraging the growth of the lungs.

Yawning – and perhaps other bodily functions, like sneezing – shares some strange parallels with sex. The facial expressions involved are surprisingly similar – just take a look at this picture and you can see where he’s coming from.

Like sex, yawns and sneezes involve a build-up that ends in a pleasant climax

Once initiated, they go to completion – you don’t want a yawnus interruptus. As evidence, that certain anti-depressants can lead ome patients to orgasm during a yawn – a rare side effect that could quickly lose its appeal.

I’m willing to bet you’ve been stifling a few yawns yourself by this point. So go ahead, let it out – and do so in the knowledge that you are enjoying one of life’s most enduring mysteries.

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