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Why do we yawn?

December 15, 2016


Yawning. Evolutionary throwback? Or essential process?

The short answer is, we don’t know. Some very smart people have spent a great deal of time trying to answer this exact question. And after all of their effort, it turns out, very few of them can actually agree on a cause. So while the question has not yet been answered definitively, we’ll discuss the two top contending theories here.

Let’s get the obvious out of the way. We yawn when we’re sleepy, bored or even when we’re hungry and we know yawning is contagious. Leaving aside all the science for a moment and looking purely at the psychology of it all, the leading theory is that the contagion is a function of empathy, expressed as mimicry or mirroring: a phenomenon where humans (mostly unconsciously and involuntarily) copy the behaviour of their fellows to express solidarity. Less likely is the theory that yawns are an unconscious form of communication stemming from our caveman days: essentially letting others of your tribe know it’s time for bed.

Turning now to the science, let’s start with why we don’t yawn. A common misconception is that yawning is an involuntary response to the body’s need for more oxygen. Professor Steven Platek blows this theory out of the water, saying that there is no correlation between yawning and an increase of oxygen in the bloodstream. After all, babies yawn in utero, before their lungs have even been ventilated for the first time.

It is therefore clear that what spurs us to yawn is not something that happens in the body but rather something that happens in the brain. Low oxygen levels in the paraventricular nucleus (the PVN) in the hypothalamus causes yawning. The PVN is the “yawning center” of the brain. So while it is not true that yawning is a way to supply our bodies with more oxygen, it may very well be that it serves to supply our brains with more oxygen.

The most convincing theory at the moment belongs to Psychology Professor Andrew Gallup, who holds that yawning is a thermoregulatory mechanism. In other words, that we yawn in order to regulate our temperature. Once again, not our body temperatures but our brain temperatures.

In relation to the rest of the body, the brain sucks up about 40% of our metabolic energy and is therefore prone to run at a much higher temperature than the rest of us. This can lead to lethargy and sluggish thoughts. When we yawn, opening our mouths wide, we expose our blood vessel-rich sinuses and soft palates to the influx of air, cooling the blood there (not unlike a radiator). These blood vessels project almost directly into the forebrain, which is then cooled by the influx of cooler blood, revitalising and re-energizing the thought process.

Gallup explains that this is why we tend to yawn when we’re headed to bed or when we just got up: yawning helps to cool the brain in preparation for hibernation or sleep, when the body temperature plummets. When we get up, our body temperature skyrockets, necessitating some cooling off for the brain.

Research into the matter is ongoing. Unfortunately, as yawning is neither life threatening nor trendy, not a lot of grant money is earmarked for this kind of research. The dissatisfaction of a stifled yawn or a yawn interrupted is not the kind of problem people are seeking a medical solution to. Although, wouldn’t a “yawn in a can” be an inspired idea? Something akin to Mel Brooks’ Spaceballs: fresh air in a can.


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