The average adult yawns about 20 times a day. But why? Surely we cannot all be that tired. The truth is the science behind yawning is much more complex than just a few hours too little sleep.

So why do we do it then? Well, new research suggests it might be because yawning cools the brain down and prevents it from overheating, much like the fan in your laptop. So, why do we yawn when tired?

Mammals and birds yawn, and just like humans, the bigger their brains the longer they yawn. Humans have yawns lasting around six seconds, while mice yawn for one or two seconds. Birds with large ...