打哈欠真的会传染吗？

"A yawn is an instinctive¹ behavior: You don't have to learn to do it, and yawns are even present before birth." says Robert Provine, a professor of psychology² and neuroscience at the University of Maryland, Baltimore County.

When we see someone else yawn, we don't think to ourselves, "Well, I'll yawn, too." It just happens -- it's instinctive, and it's a very primal³ aspect of human behavior that goes back to ancient herd⁴ mentality⁵.

Adelie penguins⁶, for instance, employ yawning as part of their courtship ritual. The happy couples face off amid the ice floes and the males engage in what is described as an "ecstatic display," their beaks⁷ open wide and their faces pointed⁸ skyward.

It may be, therefore, that when your entry upon the scene inspires a round of uncontrollable yawning, you have merely stumbled onto a gaggle of Adelie penguins in disguise, who are signaling their powerful erotic longing⁹ for you. A slim hope, admittedly, but any port in a storm.

As for the larger question of why yawns are catching¹⁰, nobody really knows. Fact is, we don't know why people yawn.

It was long believed you yawned when there was too much carbon dioxide and not enough oxygen in your blood. A part of your brain called the brain stem detected this and triggered the yawn reflex. Your mouth stretched wide and you inhaled¹¹ deeply, shooting a jolt¹² of oxygen into the lungs and thence to the bloodstream.

Subsequently, you exhaled¹³ a lot of CO2. Often you'd stretch while yawning, which seemed to temporarily improve circulation. You yawned and stretched a lot more when you got tired because your breathing slowed down.

Or so people thought. In recent years, though, a few radicals¹⁴ have said the preceding is all malarkey. Who knows, they say, maybe we yawn because it's too warm in the room.

Cecil isn't about to settle the issue here, and he doesn't need to. We merely observe that whatever yawn-inducing conditions prevail for you also apply to your friends.

If you're out late in some crowded dive, you're probably all tired, all warm under the collar, and all breathing the same stale air. You're probably all on the verge¹⁵ of a yawn, too, and the power of suggestion from seeing one person do it is enough to push everybody else over the edge.

Adults rarely catch a case of the yawns from a child or animal, which tends to corroborate¹⁶ this idea.

Children usually have different sleep schedules and respiration¹⁷ rates from adults, so you would expect them to yawn at different times. Animals, on the other hand, often yawn not for physiological¹⁸ reasons but as a display of hostility¹⁹, to which humans are evidently unresponsive.

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