WHY DO WE YAWN AND WHY IS IT CONTAGIOUS?

 It has traditionally been thought that yawning is an involuntary reflex that draws more oxygen into our bloodstream and removes a buildup of carbon dioxide. This theory was fueled by the notion that when people are bored or tired, their breathing slows, resulting in a lack of oxygen, which causes them to yawn.

However, research based on exercise suggests that this theory is incorrect. In tests, it was discovered that people’s yawning rates were not altered during exercise, despite an increase in the breathing rate and levels of oxygen in the bloodstream. In addition, athletes often yawn before big events, which is unlikely to be as a result of boredom or a reduced level of breathing. It has also been found that fetuses yawn in the womb, even though they don’t breathe oxygen into their lungs until after birth.

It has been suggested that people yawn to stretch the lungs, jaw and facial muscles, which increases the heart rate and makes a person feel more awake, although this suggestion is largely posited on the fact that a stifled yawn that does not stretch the jaw is unsatisfying. Other theories are that yawning is used to regulate body temperature or is caused by a variation in certain chemicals, such as dopamine, in the brain. It is now accepted that the exact reasons why we yawn are unknown. It’s also not known why yawning is contagious.

One theory is that we have evolved to yawn when others around us do because our early ancestors used yawning to coordinate social behavior or to build rapport in a group. When one person yawned to signal something, such as it being time to sleep, the rest of the group also yawned in agreement and the members’ activities were synchronized.

Yawning might also have been used to bare the teeth to intimidate enemies, so that, when one member of the group yawned, the rest followed suit. This has carried through to modern times, when the suggestive power of yawning is still contagious. Lending weight to this theory is the fact that babies, who are unaware of social codes, don’t yawn contagiously until they’re about one year old.