十万个为什么·科学启蒙30篇（1）

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我们为什么会打哈欠？

Yawning is a reflex that involves opening your mouth wide, inhaling deeply, and then exhaling slowly.
Though often linked to tiredness or boredom, people also yawn when they’re stressed, waking up, or even before athletic performance.
One widely supported theory says yawning helps cool the brain by increasing blood flow and bringing in cooler air.
Brain temperature rises slightly during mental effort, and yawning may act like a natural thermostat to keep it stable.
Studies show people yawn more often in warmer rooms—and less when holding cold packs to their foreheads.
Contagious yawning, where seeing or hearing someone yawn triggers your own, appears in humans after age four and in some apes.
This social form of yawning may be tied to empathy and the ability to share emotional states with others.
People with autism spectrum conditions yawn contagiously less often, supporting the empathy connection.
Even dogs sometimes yawn after watching their owners yawn—a rare cross-species example of emotional mirroring.
Despite centuries of study, scientists still haven’t confirmed one single cause, and multiple factors likely interact.