Why do we yawn?

THAT'S THE WHY:Here's a challenge: try to read this column without having a big yawn, or at least having to stifle one. I bet you can't.

Why? Not because it’s boring (I hope!), but because even thinking about a yawn usually triggers one.

First things first though – what is a yawn?

It’s an involuntary reflex triggered by a part of your brain called the paraventricular nucleus (PVN), and it causes you to open your mouth wide, stretch the ribs and draw in air.

Most vertebrates (back-boned creatures, including ourselves) yawn from the foetal stage right through to old age. But why do we do it?

It has been suggested that it’s a way to increase our oxygen intake, and a yawn can indeed be triggered by low oxygen levels in the PVN, but there’s probably more to it than that.

Other theories suggest that we yawn to increase arousal or regulate our body temperatures, but there’s a lack of strong evidence to back them up.

A notion that’s gathering more weight proposes that yawning is a throwback to a form of group communication our ancestors used to signal drowsiness, boredom or even mild stress – time to initiate a change in behaviour – and “catching a yawn” is a mark of social cognition or empathy.

So, has the power of suggestion made you yawn yet?

– CLAIRE O’CONNELL