A growing body of research now shows that yawning is nature's way of keeping our brains cool.

越来越多的研究表明，打哈欠是一种让大脑保持冷静的自然方式。

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Support for this theory came from a study of yawning behavior in everyday life.

这一理论的支撑来自对日常生活中打哈欠行为的研究。

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Will you be kind enough to give a penny to a poor boy who is yawning from hunger?

你可以给一个因饥饿而打哈欠的可怜孩子一个便士吗？

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Nor does empathy suggest a physiological "reason" for yawning (after all, we yawn when alone), though Dr. Provine thinks that it may be "a response to and facilitator of change in behavioral or physiological state, " maybe synchronizing a group of people about to embark on a behavioral transition.

WSJ: Matt Ridley on Why You Just Yawned | Mind & Matter