"Many animals yawn but we are not entirely sure why. Perhaps it makes us more alert, reduces anxiety, or cools an overheating brain. Contagious yawning is even more mysterious but seems to be confined to highly social animals, which might provide a clue to its purpose.
This indicates that there are two types of yawning – spontaneous and contagious – each requiring a separate explanation. Although we have some promising ideas, yawning is still something of a puzzle.
We tend to think of yawning as a sign of being tired or bored. That probably explains the popular perception that it is a way to get more oxygen into the blood to increase alertness. However, when psychologist Robert Provine at the University of Maryland, tested this idea he found it didn’t stand up – people were just as likely to yawn when breathing air high in oxygen.
A closer look at when people yawn suggests another explanation. It turns out that most spontaneous yawning actually happens when we are limbering up for activity such as a workout, performance or exam, or simply when we wake up. That has led to the idea that yawning helps us gear up by increasing blood flow to the brain. How exactly that might work is not clear, but it does fit with the observation that some fish yawn in anticipation of a fight.
Another possibility is that yawning cools the brain. This idea emerged from the observation that people yawned far less when their heads were cooled by cold packs. Temperature regulation is crucial for physiological performance. It is controlled by a brain region called the hypothalamus, and involves production of adrenaline and cortisol, hormones that increase alertness and help us deal with stress. That might also explain why people often yawn when feeling anxious – as do monkeys.
Why is yawning contagious?
Explaining contagious yawning is even trickier. Apart from humans, the only other species known to catch yawns from one another are chimps, dogs (which can be infected by human yawns), the wonderfully named high-yawning Sprague-Dawley rat, budgerigars and lions, who appear to use yawning to send signals to the rest of the pride.
These animals are all very sociable, which suggests contagious yawning might have something to do with empathy, or at least a tendency to mimic and synchronise actions with others, a foundation of empathy. But whether contagious yawning helps us build social relationships is another matter. It could simply be a by-product of the way we and other highly-social animals instinctively respond to others."
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