Why do we yawn ?

A yawn is an involuntary reflex where the mouth is opened wide, and the lungs take in a lot of air. The air is then exhaled slowly. During this time, the eardrums stretch, and the eyes may also close tight, causing them to water. Do you know why we yawn ? There is a chance that you will yawn while reading this, because yawning is contagious and  thought about it can make you yawn ! But have you ever wondered  why do we yawn ?

There are four major theories that states the reason for yawning .

The physiological theory: Our bodies induce yawning to draw in more oxygen or remove a build-up of carbon dioxide. This theory helps explain why we yawn in groups. Larger groups produce more carbon dioxide, which means our bodies would act to draw in more oxygen and get rid of the excess carbon dioxide. However, if our bodies make us yawn to draw in needed oxygen, wouldn't we yawn during exercise? Robert Provine , a developmental neuroscientist at the University of Maryland, Baltimore County and a leading expert on yawning, has tested this theory: Giving people additional oxygen didn't decrease yawning, and decreasing the amount of carbon dioxide in a subject's environment also didn't prevent yawning.

The evolution theory: Some think that yawning began with our ancestors, who used yawning to show their teeth and intimidate others. An offshoot of this theory is the idea that yawning developed from early man as a signal for us to change activities

The boredom theory: Although we do tend to yawn when bored or tired, this theory doesn't explain why Olympic athletes yawn right before they compete in their event or why dogs tend to yawn just before they attack. It's doubtful either is bored .

The brain-cooling theory: A more recent theory proposed by researchers is that since people yawn more in situations where their brains are likely to be warmer - tested by having some subjects breathe through their noses or press hot or cold packs to their foreheads - it's a way to cool down their brains. What does it matter if our brains are cold or hot? Cool brains can think more clearly; hence, yawning might have developed to keep us alert.

BONUS: Do you think that someone is watching you , just yawn; if the suspect too yawns, your doubt is right !