Yawning is an involuntary action that is commonly associated with fatigue, boredom or tiredness, and is quite common among most living creatures, including snakes, primates and carnivores. In human beings, yawning is considered to be a very purposeful non-verbal signal, and folklore has many superstitions associated with the act of yawning.
When you yawn, air rushes through your mouth into your lungs. The rushing air flattens the diaphragm muscle, making the lungs expand. Oxygen is sent from the lungs into the blood vessels, and carbon dioxide is expelled out. This entire process takes about six seconds on average, with one person’s yawn triggering a series of yawns from the people around. On an average, an estimated 55 percent of people will yawn within five minutes of seeing someone else yawn. The reason for this contagiousness is said to be related to an ‘an ancient, hardwired ritual that evolved to help groups stay alert and detect danger.’[1]
Why we yawn: The Reasons
# Since yawning involves the involuntary intake of oxygen, the reason for yawning was seen as the body’s need to take in oxygen and get rid of excess carbon dioxide. However, studies have shown that while yawning, the amount of oxygen taken in is less than what we take in during normal breathing. So, this theory has been disregarded by scientists.
# Another research finding [2] supports the view that yawning cools the brain. According to this theory, the oxygen taken in during a yawn regulates the brain temperature to keep you awake. Thus, yawning is not a precursor to sleep but a reflex to keep you awake. This theory also supports the fact that unborn and newborn babies yawn too; hence, yawning could be more of a defensive function.
# Yet another claim made by scientists is that a yawn is a sign of sexual attraction! Dutch academic Wolter Seuntjens, while exploring whether yawning has an erotic side, wrote that yawning and the associated stretching have been linked to desire and even of being in love.[3]
Why we yawn: The Causes
# Yawning is believed to be induced when the level of glucose supplied to the brain decreases, as in the state of hunger. [4] In fact, excessive yawning has even been associated to hypoglycemia, a condition that occurs when your blood glucose is too low.
# Some researchers believe that yawning is a protective reflex mechanism adopted by the body to maintain proper lung inflation which prevents collapsing of the alveoli. This could be why slouching for a long period of time has been implicated as one of the causes of excessive yawning. When a person slouches for too long, it leads to pressure on the lungs; and to make up for this pressure, there may be excessive yawning.
# Another study suggests that yawning is under the control of several substances (neurotransmitters and neuropeptides) that facilitate yawning. Oxytocinergic neurons located in the hypothalamic nucleus of the brain get activated by these substances to induce yawning.[5]
In conclusion, it can be said that although there are a number of theories and suggestions, put forward by researchers, about why we yawn, there is still no single reason that has been validated yet. While the chemical facilitation of a yawn seems to be the most acceptable of reasons mentioned above, more studies are awaited to pinpoint the exact reason for yawning.
