十万个为什么·科学启蒙30篇（1）
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Why Do We Yawn?
我们为什么会打哈欠？
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Yawning is a reflex that involves opening your mouth wide, inhaling deeply, and then exhaling slowly.
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Though often linked to tiredness or boredom, people also yawn when they’re stressed, waking up, or even before athletic performance.
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One widely supported theory says yawning helps cool the brain by increasing blood flow and bringing in cooler air.
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Brain temperature rises slightly during mental effort, and yawning may act like a natural thermostat to keep it stable.
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Studies show people yawn more often in warmer rooms—and less when holding cold packs to their foreheads.
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Contagious yawning, where seeing or hearing someone yawn triggers your own, appears in humans after age four and in some apes.
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This social form of yawning may be tied to empathy and the ability to share emotional states with others.
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People with autism spectrum conditions yawn contagiously less often, supporting the empathy connection.
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Even dogs sometimes yawn after watching their owners yawn—a rare cross-species example of emotional mirroring.
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Despite centuries of study, scientists still haven’t confirmed one single cause, and multiple factors likely interact.