All about Yawning!
All of us yawn every day, but do we know why? Yawning starts in the womb and continues till death. Other vertebrate species such as fishes and birds also yawn. So, what is the the purpose and survival value behind yawning? Read on to learn all about yawning!
Theories about Yawning
Does Yawning Increase Good Air?
Many theories have been put forth regarding yawning. But, they have not been backed up with experimental proof. Hippocrates, the ancient philosopher, proposed that yawning helps to dispose of bad air and increase the body’s good air. Modern theories also suggest that yawning can increase oxygen levels in the blood, while decreasing carbon dioxide.
But if this theory is true, we would be yawning more when we exercise. Also, people suffering from heart or lung disease, which causes lack of oxygen, do not yawn more frequently than others. In a research, healthy subjects were exposed to high carbon dioxide levels. But, they did not increase their frequency of yawning. Studies do not reveal that yawning increases the brain’s oxygen levels. In fact, to increase oxygen levels in the body, one should practice rapid breathing.
Yawning and Sleep
Yawning has also been linked to sleep, as we yawn frequently before sleeping and afterwards. Drowsiness also leads to increased yawning. So, one of the purposes of yawning may be to keep us awake. This hypothesis was tested by provoking yawning in humans, and studying brain activity for the effect. There was no evidence to prove that yawning made the central nervous system or brain more vigilant. There is also no evidence to prove that yawning induces sleep. So, there is in fact no proven link between drowsiness and yawning, even though they often occur together.
Yawning and Body Heat
Can yawning regulate body heat? Researchers have also tested this hypothesis and the results are debatable. In rats, there is a rapid increase in brain temperature before yawning. After yawning, the brain returns to lower temperatures.
Yawning and Ear Pressure
Yet another theory proposes that yawning serves to equalize middle ear pressure with the air pressure outside. This function can also be achieved by swallowing or chewing. Also, there is a lack of evidence about whether air pressure changes increase the frequency of yawning.
SO, what is the actual purpose of yawning?
Yawning as a Social Contagion
Children below the age of five, do not indulge in contagious yawning. But, creatures whose social skills are advanced such as dogs, monkeys, chimpanzees, besides adult humans, can catch a yawning contagion. This proves that contagious yawning requires a person to understand others’ mental states. MRI scans in humans support this idea and prove that when we watch others yawn, our brain responds and imitates such social behavior.
But, we need to consider that solitary species also indulge in yawning, and humans and chimpanzees yawn in solitude too. All the various theories and research lead to only one conclusion: Yawning is a complex and rich phenomenon, and its purpose and value are yet to be fully understood.