Why do we yawn? This question has not been definitively answered, but there is plenty of conjecture on the subject. It is assumed that yawning must serve some purpose or function, but what has not been agreed upon. In simplest terms, all humans yawn and most animals having vertebrates do also, but why is still unknown.
In recent years, a number of experimental tests have been trying to understand what yawning does for human beings. This work has primarily been conducted by a Princeton University researcher named Andrew C. Gallup, PhD. His work has experimented with human beings, parakeets, and rats. The data gathered during these tests is attempting to find out what makes each species yawn. The primary conclusion Gallup has come to is simple, but has many skeptics questioning it. Gallup believes that all yawning is essentially a way of cooling our brains, at least in theory.
The hypothesis of yawning as a method of brain cooling, goes like this basically.
Yawning itself, causes tremendous stretching with our jaws. The effect being increased flow of blood throughout the head, neck, and all facial areas. Inhaling breath while yawning, causes the downward movement of spinal fluids. It sends blood from the brain itself downward, as well. When cool air is inhaled during a yawn, these downward moving blood flows and spinal fluids become cooled. The overall hypothesis describes yawning similarly to how a radiator acts, by the inward and outward processes. Hot fluids are replaced with coolant, thus allowing the surfaces on the brain to stay cool. This theory has not been accepted by many skeptics in the scientific community.
The Gallup studies say that yawning should be more frequent, during cooler temperatures. Based on the brain cooling theory.
The experiments were conducted in Tucson, Arizona in winter and then again in summer. 80 people were asked to look at pictures of people who were yawning, since people tend to yawn when seeing others do so. Less than half of the 80 people yawned in response to seeing other people yawn, during the winter season. During the summer season, less than one quarter of the subjects yawned. These results were supportive of similar findings with rats and parakeets in earlier tests. The conclusions drawn say that yawning happens in response to cooler temperatures, because inhaling cooler air will cool the brain more. Yawning is a sort of involuntary response to having a hot brain, similar to how sweating spontaneously cools the body and it’s extremities.
Unfortunately, not everyone has been convinced of the Gallup study findings.
The skeptics say that yawning is a social form of empathic response to our environment. Yawning could be a sociological phenomenon, rather than a physiological one. It maybe a kind of evolutionary response mechanism, one that is governed by deep seeded triggers in human physiology. Supporters of this idea call it, the social theory of yawning.
For the time being, these are the only scientific studies or speculations as to, why we yawn. The answer is still a human mystery.