We yawn because we're tired or bored. It seems simple, and yet it's not correct. Recent studies have shown that yawning serves exclusively to cool down the brain. There is a link with sleepiness, but that link is only indirect.
Sometimes it just feels so good to stretch and to open your mouth like you're about to roar like a lion, only to breathe in some air. Only by reading this, you've probably wanted to yawn already, and seeing someone else yawn is even more irresistable. But what's the physical explanation for this behaviour? Why does our body sometimes need to have a good yawn?
The phenomenon seems to have everything to do with our internal thermostat. In order to function properly, the body needs to have the exact right temperature, and that also goes for the brain. But while the body can cool down by sweating and heat up by exercise, that is less simple for the brains. Yawning is evolution's answer.
Researchers at the Vienna University discovered the first evidence for that theory earlier this year. The scientists studied the yawning behaviour of pedestrians in Austria and the United States, and discovered that at certain temperatures there was yawned more often than at others.
Only if the outside air temperature was low enough to cool the brain, but not cold or warm enough to cause damage to the body, people yawned.
Researchers at the Albany University in New York discovered a similar result in another experiment. People who watched a video with yawning persons, seemede to only imitate that behaviour if they held warm compresses against their head.
If the held a cold compress against the head, they nearly never yawned. Those results also indicate that we yawn to cool down our brain.
Not because we are tired
But we also yawn when we're tired, right? That's true, but that's only because our brain heats up when we have a lack of oxygen. So it's not true -contrary to what was believed for a long time- that yawning transports extra oxygen to the brain. After all, if we would yawn to supply our brain with oxygen, we would also have to yawn a lot during exercise activities, which is clearly not the case.
Even the fact that we imitate the yawning of others, can be explained by the temperature theory. After all, in nature animals imitate members of their species if they have good a reason for it.
The yawning behaviour of another creature is an important signal that something has to be done to cool down the brain and become more alert. The copying behaviour is embedded into the instinct of humans and animals. After all, ignoring the signal could have negative consequences.