人們常說打哈欠會傳染，每次你一打呵欠，周圍的人也會跟著打哈欠。難道哈欠真的可以傳染，還是僅僅是巧合而已？我們來看看神經學家是怎么說的吧！
"A yawn is an instinctive behavior: You don't have to learn to
do it, and yawns are even present before birth." says Robert Provine, a
professor of psychology 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 primal aspect of
human behavior that goes back to ancient herd mentality.
Adelie penguins, 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 beaks open wide and their
faces pointed 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 longing for you. A
slim hope, admittedly, but any port in a storm.
As for the larger question of why yawns are catching, 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
inhaled deeply, shooting a jolt of oxygen into the lungs and thence to the
bloodstream.
Subsequently, you exhaled 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 radicals 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 verge 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 corroborate this idea.
Children usually have different sleep schedules and respiration rates from
adults, so you would expect them to yawn at different times. Animals, on the
other hand, often yawn not for physiological reasons but as a display of
hostility, to which humans are evidently unresponsive.
malarkey: 胡說
corroborate: 確證，證明
unresponsive: 無答復的
（北京外國語大學通訊員謝麗供稿 英語點津 Annabel 編輯）
