解放军文职招聘考试Evolution of Sleep

 Evolution of Sleep

Sleep is very ancient. In the electroencephalographic sense we share it

with all the primates and almost all the     other mammals and birds: it may

extend back as far as the reptiles.

There is some evidence that the two types of sleep, dreaming and dreamless,

depend on the life-style of the animal, and that predators are

statistically much more likely to dream than prey, which are in turn much

more likely to     experience dreamless sleep. In dream sleep, the animal is

powerfully immobilized and remarkably unresponsive to           external stimuli.

Dreamless sleep  is much shallower, and we have  all witnessed cats or 

dogs cocking their ears to a sound when apparently fast asleep. The fact

that deep dream sleep is rare among prey today seems clearly to be a 

product of natural selection, and it makes sense that today, when sleep is

highly evolved, the stupid animals are       less frequently immobilized by 

deep sleep than the smart ones. But why should they sleep  deeply at all? 

Why should a state of such  deep immobilization ever  have evolved? Perhaps

one useful hint about the original function of sleep is to be found in the

fact that dolphins and whales             and aquatic mammals in general seem to sleep

very little. There is, by and large,  no  place  to  hide  in  the  ocean. 

  Could  it  be  that,  rather  than  increasing  an  animal's

vulnerability, the function of sleep is to decrease it? Wilse  Webb of the

University of Florida and Ray Meddis  of London University  have suggested

this to  be the case. It is conceivable  that animals who  are too stupid

to be  quiet on their own initiative are,  during periods of  high risk,

immobilized by the implacable arm of sleep. The point seems particularly

clear for the young of predatory animals. This is an interesting notion and

probably at least partly true.

睡眠的进化

睡眠是古老的。  从脑电图上看，我们人类和所有灵长目动物以及几乎所有的哺乳动物 和鸟类都一样需要睡眠；甚至爬行类动物也有睡眠。 

有证据显示，有梦睡眠和无梦睡眠这

两种类型的睡眠取决于该动物的生活方式。  从统计上看，食肉动物比被捕食动物有更多的 有梦睡眠，而被捕食动物更多地无梦睡眠。 

动物在有梦睡眠时，被有效地解除动作能力， 并且对外界刺激缺乏反应。  无梦睡眠则要浅得多。  我们都看到过猫和狗在显然的酣睡中，

有一点响动耳朵就会竖起来。  被捕食动物很少有深度的有梦睡眠，这看来显然是自然选择 的结果。 

而且这一点是有道理的：当睡眠高度进化以后，愚笨的动物比聪明的动物更少在 深度睡眠状态下丧失动作能力。

但是动物为什么要进入深度睡眠呢?为什么这样的无动作状 态也会进化出来呢?  海豚、鲸鱼以及水生哺乳动物睡眠都极少，这一事实可以给睡眠的根本

功能提供有用的线索。 海洋中是没有藏身之处的。 会不会是这样，睡眠不但不增加动物受 伤害的可能性，反而是减少了这种可能性呢?佛罗里达大学的 Wilse

Webb 和伦敦大学的 Ray Meddis 认为情况就是如此。  可以想像得出，在危险的时刻，那些由于太愚笨而不能自动保

持安静的动物，会不由自主地变得动弹不得。  这一点在食肉动物的幼兽身上表现得特别明 显。  这是一个很有意思的看法，它至少部分是正确的。