时差N小时 我们为什么要睡觉?(下)

At night, humans do rather poorly: we can't see objects well, our color vision is entirely¹ lost,

晚上，人类的活动力相对差些。我们看不太清物体，我们的颜色辨别也完全消失了，

and we don't have the smelling or hearing acuity² of other animals.

而且我们还没有其他动物那么敏锐的嗅觉和听觉。

So it actually does make sense to have us stay put during the dangerous period when "nocturnal," or night-waking, animals are on the prowl.

所以在那些夜间活动的动物们出没觅食的危险时刻，我们保持原地不动，确实是很有道理的。

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,

一个确保我们不会跌跌撞撞，不会迷路或者被吃掉的稳妥方式就是，每天休息七到八个小时，

rising again only when the light is back and our survival chances are better.

天亮了我们再起床活动，这样我们的生存机会会更好地得到保障。

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

这还不是我们睡觉的唯一原因;但就人类进化而言，它可能是其中一个首要原因——

perhaps even the most important one.

甚至还可能是最重要的一个原因。

1 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。

2 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。