The Science of the Yawn
“A yawn is quite catching, you see. Like a cough.
It just takes one yawn to start other yawns off.”
— Dr. Seuss’s Sleep Book (1962)
We have all experienced it. A coworker stretches his arms above his head, opens his mouth wide and lets out a loud yawn. And suddenly, your body unconsciously starts to do the same. What makes a yawn so contagious? Let’s explore some of the science and theories behind this curious phenomenon.
We know we yawn when we’re tired, but why? This simple question does not yet have a simple answer. There are a handful of popular theories. One theory is that during periods of time when our vigilance decreases, a yawn may have an arousing affect. Another theory is that when we are relaxed, we are not breathing as deeply, and a yawn allows us to expand our lungs and keep them functioning at their optimum. More recent theories suggest that yawning may help cool the brain in situations when it gets too hot. No theory has been proven correct.
Even though the purpose of yawning is unknown, there are some common beliefs behind yawning that science has proven incorrect. You may think yawning only happens when bored or sleepy. Yet it is not uncommon to see Olympic athletes yawning just prior to their events. A study that looked at soldiers about to parachute out of an airplane for the first time showed an increase in yawning just prior to the jump. So it’s not just boredom or sleepiness that brings it on. Yawning may trigger the brain to make a change in its state, either from bored to alert, sleepy to awake, etc.
But none of these theories seem to explain the curious phenomenon of contagious yawning. Even simply thinking about yawning will often trigger one. You may have already yawned right now just reading about it. What makes a yawn so catching? This, too, is a mystery.
There are some surprising things we do know. Even though children begin yawning as early as their first trimester as fetuses, they don’t experience the contagious yawn until closer to 5 years of age, around the time they develop better social understanding and empathy. We are more likely to mimic the yawn of others when we know them well, a result that has been shown even in chimpanzees.
Given the tendency to mimic yawns from those that we are tied to socially, perhaps yawning serves a deeper role that is not yet recognized. It may help us better understand disorders that affect empathy and social reciprocity. For example, children with autism yawn just as often as other children, but are much less likely to have a contagious yawn.
Scientists have tried to unravel the mystery behind the contagious yawn by evaluating which areas in the brain light up when we see others yawn. One area that seems to be involved is the mirror neuron system, an area that is important for understanding actions and imitating them. However, many other areas of the brain also seem to be involved. The common link seems to be that the areas relate to social behavior and empathy.
The mysteries and debate behind the yawn will likely continue for quite some time. And you thought yawns just meant you were tired. Perhaps the yawn isn’t that boring after all.