What makes us yawn

A.� Surprisingly little is known about what yawning is for. The commonly held theory is that we do it because we're tired or bored but the evidence doesn't really back these suggestions up. Although scientists don't really know why we yawn there are several theories regarding the reasons for yawning.

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Q.� And what are they

A.� One theory is that yawning was useful for our ancestors who got to flash their teeth in an intimidating manner, very much like a baboon does when threatened.

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This would have been particularly helpful if the person yawning really was tired and about to nod of making him or her very vulnerable, the dramatic wide mouthed, tooth bared yawn would hopefully put anyone off the idea o attacking them. So for this theory, yawning is just a left over self-protection mechanism.

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Q.� Any others

A.� Another theory, known as the Physiological theory, suggests that yawning is our body's way of taking in more oxygen and getting rid of more carbon dioxide.

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However this theory is slightly marred by the fact that we don't yawn during exercise which is when our bodies need more oxygen. In experiments people didn't yawn any less even when they were given extra oxygen.

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In addition although foetuses yawn they don't take oxygen in through their lungs until they make it to the outside world.

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Q.� What exactly is a yawn

A.� It's an involuntary action, it makes us open our mouths and breathe in very deeply. It's something we do from very early on, even within the womb. And humans aren't the only yawners; cats and dogs do it too.

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Q.� Why is yawning so contagious

A.� Again the experts are out on this one.

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One possible explanation is to synchronise group behaviour, so that whatever yawning does to our bodies, it does it for everyone. So it may be a social reflex, in the same way that laughter can be: once someone starts everyone else eventually joins in.

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Whatever the reason there's no doubting that yawning is contagious. It's so contagious that you've probably yawned several times while reading this set of questions and answers; just thinking about yawning is enough to start you off.

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Want to know about one of your natural reflexes Click here to ask.

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by Lisa Cardy