What about the connection between yawning and tiredness? We certainly yawn more when we’re feeling sleepy or sluggish, but why is this? Theories that it helps give the body extra energy are largely discredited, as we don’t yawn when we exercise, a time when we definitely need more get-up-and-go! 

Psychologist Catriona Morrison from the University of Leeds says yawning is an ancient reflex.  She told the BBC that it may have started in “the days of cavemen when someone had to be on watch all the time - yawning increases cerebral blood flow so can improve alertness.” 

What about our friends' contagious yawning? Some think it comes down to empathy. While all vertebrate mammals yawn, only humans and chimpanzees ‘catch’ yawns from others. Studies have shown we yawn more frequently when in the company of close relatives and friends. Could yawning actually help us cement our closest relationships? 

If it does, next time you yawn in company, don’t feel too embarrassed. You’re just showing off your people skills.

词汇表 contagious 会传染的

motor 肌肉运动的，运动神经的

cortex （尤指大脑或其他器官的）皮层

involuntary 不由自主的

physiological 生理的

physician 医生（尤指内科医生）

cauldron （通常指架在火上的）大锅

colourful 有趣的，有声有色的

【Why we yawn 我们为什么打哈欠？】相关文章：

★ Dangers from outer space 来自外星的危险

★ Heart surgery and your body clock 心脏手术和人体生物钟之间的联系

★ Traffic, transport, transportation & transit 和“交通”有关的四个近义词区别

★ Why stress makes you fat 压力为什么能让你变胖？

★ Is a game just a game? 游戏只是游戏吗？

★ Got your number 我知道你打的什么算盘

★ How to live longer 怎么才能长寿

★ Being super-rich 腰缠万贯

★ Rupee withdrawal, molecules on your phone 印度撤除旧版卢比、 手机上的分子信息

★ Why do cities make us rude? 为什么城市会让人变得无礼？