Why Do We Yawn? The Science Behind This Reflex

Why Do We Yawn?

Walker explains that there are four competing theories about why we yawn. The first theory, that yawning is simply a sign of tiredness, doesn’t hold up because people can yawn when they’re bored and well-rested. The second theory, that yawning is about rebalancing blood gases like oxygen and carbon dioxide, was disproven by experiments that manipulated these gas levels without affecting yawning frequency.

The third theory involves the contagious nature of yawning, which may be due to the mirror neuron system in our brains. This system allows us to mirror the actions and emotions of others, even across species like humans and dogs. Some suggest that contagious yawning in cooperative species might be a way to enact group behavior.

However, Walker believes the fourth theory has the best evidence. This theory proposes that yawning is a way to cool the brain when its temperature starts to rise. Inhaling cooler air from outside modestly drops brain temperature. While the definitive answer is still unclear, Walker thinks the brain cooling theory is currently the most plausible explanation for why we yawn.

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