我们为什么打哈欠？

Yawning is something we all do – maybe because we're bored carrying out tedious tasks or because we're tired. Sometimes, just seeing other people yawn can set you off. But is this biological function really contagious, and why do we do it in the first place?

Many of us think we open our mouths when we yawn to take in more oxygen, but in fact it appears there is no clear biological reason. According to BBC Bitesize, new research suggests it might be because yawning cools the brain down and prevents it from overheating, much like the fan in your laptop. This might be why we're more likely to feel drowsy and yawn in warm temperatures.

What is clear is that we yawn more when we're exhausted and ready for a nap, and we can't control when we do it – once we start, there's no stopping us! But it's also true that yawning is a very contagious behaviour. John Drury, a researcher from Sussex University, told the BBC that "it's meant to be automatic; it's something that you can't stop. Dogs yawn when their owners yawn, animals yawn to each other. It happens whether you want to or not."

His research into this cognitive behaviour found that there is a connection with our social group and how close we are to the people in it. If we identify with the person who exhibits the behaviour, we are likely to copy it too.

Other research by the University of Nottingham in 2017 found similar results. They asked volunteers to watch other people yawn. They found their ability to resist yawning when others around them yawned was limited. And the urge to yawn was increased when people were told they couldn't. They also found, when using electrical stimulation, that they were able to increase people's desire to yawn. These findings, they say, could be useful because it could help treat other conditions like Tourette's, which involve the same area of the brain.

What is certain is that a yawn can creep up on us at any time even when we think we're not tired – but, I hope, not when you're reading this article!