I read recently an explanation for yawning that is plainly wrong. The same idea has surfaced regularly over the years. Any idea, good or bad, is hard to kill. Yawning by this account is performed in order “to get more oxygen to the brain.” First of all, why should the brain need more oxygen from time to time, especially when one is sleepy? Second of all, any careful observer will see that the person yawning is not taking a deep breath. In fact, during most of the yawn, there is no breathing at all. Third of all, everyone knows what the body does when it needs more oxygen: (for instance, when someone is running or otherwise exerting himself) that person is impelled to take a lot of deep breaths. I think the purpose of yawning can be discerned clearly from paying attention to what actually goes on during yawning: the muscles of the oral cavity are stretched. These include the tongue, palate, and other muscles of the upper throat. What does that accomplish?
Because yawning occurs usually in the context of getting ready to go to sleep, or being bored, which is more or less the same thing, the purpose is probably to prepare for sleep. When my dog gets ready for a walk, she stretches her forelimbs, invariably. I assume she can walk (or tug on the leash) more effectively after stretching. The quality of sleep is probably improved by stretching the muscles of the oral cavity before going to sleep.
We know that there are sleep disturbances marked by a collapse of these muscles. Sleep apnea is the best example. Snoring ensues. When this condition is significant, the individual wakes up all night long, sometimes just going from a deep sleep to a lighter, less advantageous, sleep. The cause of awakening is usually a central nervous system response to not getting enough oxygen, although sometimes there are local obstructions that can also interfere with breathing. Untreated, this condition can worsen to the point where someone is sleepy all day long. Hypertension may result.
So, my theory is: yawning is a consequence of preparing to sleep more effectively. It tends to prevent the collapse of the muscles of the oral cavity.
In support of this theory is my observation (I don’t really know this) that people yawn less as they get older. Therefore, they snore more and are more likely to develop sleep apnea.
Since sleep apnea is more common than generally recognized, I would suggest that older people purposely yawn. That is, I would suggest that if I didn’t think that people would consider me eccentric.
By the way, the well-known phenomenon of the contagiousness of yawning is explained, I think, by there being an advantage to having all the members of a family getting sleepy at the same time. This might work in the same way that menstruation is regulated: women living together tend after a while to menstruate at the same time, and therefore, ovulate at the same time. Proposing a theory about exactly what these advantages could be would be speculating still further, and further than I want to go.(c) Fredric Neuman 2012 Follow Dr. Neuman's blog at fredricneumanmd.com/blog.