【英语时差8,16】机不可失，时不再来

It's such a commonplace event that you probably never asked yourself why you sleep.   But from a scientific point of view, this is far from a mundane¹ matter -- in fact, for sleep researchers, it's one of the biggest unanswered questions in the field.

Stop and think about it for a second. Why should we sleep? Is it because we get tired? But we sleep every night, even when we have had plenty of rest. Furthermore, if you were designing an animal, would you have it lapse² into prolonged periods of unconsciousness every twenty-four hours? Shouldn't that put it at a terrible disadvantage?

There are no doubt several different answers to this question, but let's just consider one overall purpose sleep may fulfill³: sleep as a survival strategy.

Human beings are "diurnal⁴" creatures. That means we are normally active during daylight hours, when our senses function most effectively. At night, humans do rather poorly: we can't see objects well, our color vision is entirely⁵ lost, and we don't have the smelling or hearing acuity⁶ of other animals. So it actually does makes sense to have us stay put during the dangerous period when "nocturnal," or night-waking, animals are on the prowl. And one sure way to make sure we don't stumble around and get lost or eaten is to have us immobilized for seven or eight hours, rising again only when the light is back and our survival chances are better.

It's not the only reason we sleep; but in terms of evolution, it may have been one of the first reasons -- perhaps even the most important one.  

1 mundane   

adj.平凡的；尘世的；宇宙的

参考例句：

• I hope I can get an interesting job and not something mundane.我希望我可以得到的是一份有趣的工作，而不是一份平凡无奇的。
• I find it humorous sometimes that even the most mundane occurrences can have an impact on our awareness.我发现生活有时挺诙谐的，即使是最平凡的事情也能影响我们的感知。

2 lapse   

n.过失，流逝，失效，抛弃信仰，间隔；vi.堕落，停止，失效，流逝；vt.使失效

参考例句：

• The incident was being seen as a serious security lapse.这一事故被看作是一次严重的安全疏忽。
• I had a lapse of memory.我记错了。

3 fulfill   

vt.履行，实现，完成；满足，使满意

参考例句：

• If you make a promise you should fulfill it.如果你许诺了，你就要履行你的诺言。
• This company should be able to fulfill our requirements.这家公司应该能够满足我们的要求。

4 diurnal   

adj.白天的，每日的

参考例句：

• Kangaroos are diurnal animals.袋鼠是日间活动的动物。
• Over water the diurnal change in refraction is likely to be small. 在水面上，折光的周日变化可能是很小的。

5 entirely   

ad.全部地，完整地；完全地，彻底地

参考例句：

• The fire was entirely caused by their neglect of duty. 那场火灾完全是由于他们失职而引起的。
• His life was entirely given up to the educational work. 他的一生统统献给了教育工作。

6 acuity   

n.敏锐，（疾病的）剧烈

参考例句：

• We work on improving visual acuity.我们致力于提高视觉的敏锐度。
• The nurse may also measure visual acuity.护士还可以检查视敏度。