陳蕙雅思教材 - 雅思閱讀精選 (Evolution of Sleep)

Evolution of Sleep

Sleep is very ancient. Inthe electroencephalographic sense we share it

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

extend back as far as thereptiles.

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

depend on the life-styleof the animal, and that predators are

statistically much morelikely to dream than prey, which are in turn much

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

powerfully immobilizedand remarkably unresponsive to                  externalstimuli.

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

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

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

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

highly evolved, thestupid animals are      less frequentlyimmobilized by  

deep sleep than the smartones. But why should they sleep  deeplyat all?  

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

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

fact that dolphins andwhales                  and aquaticmammals in general seem to sleep

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

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

vulnerability, the functionof sleep is to decrease it? Wilse      Webbof the

University of Florida andRay Meddis  of London University  have suggested

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

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

immobilized by theimplacable arm of sleep. The point seems particularly

clear for the young ofpredatory animals.           This is aninteresting notion and

probably at least partlytrue.

睡眠的進化

睡眠是古老的。  從腦電圖上看，我們人類和所有靈長目動物以及幾乎所有的哺乳動物 和鳥類都一樣需要睡眠；甚至爬行類動物也有睡眠。  

有證據顯示，有夢睡眠和無夢睡眠這

兩種類型的睡眠取決於該動物的生活方式。  從統計上看，食肉動物比被捕食動物有更多的 有夢睡眠，而被捕食動物更多地無夢睡眠。  

動物在有夢睡眠時，被有效地解除動作能力， 並且對外界刺激缺乏反應。  無夢睡眠則要淺得多。  我們都看到過貓和狗在顯然的酣睡中，

有一點響動耳朵就會豎起來。  被捕食動物很少有深度的有夢睡眠，這看來顯然是自然選擇 的結果。  

而且這一點是有道理的：當睡眠高度進化以後，愚笨的動物比聰明的動物更少在 深度睡眠狀態下喪失動作能力。

但是動物為什麼要進入深度睡眠呢?為什麼這樣的無動作狀 態也會進化出來呢?  海豚、鯨魚以及水生哺乳動物睡眠都極少，這一事實可以給睡眠的根本

功能提供有用的線索。 海洋中是沒有藏身之處的。 會不會是這樣，睡眠不但不增加動物受 傷害的可能性，反而是減少了這種可能性呢?佛羅里達大學的 Wilse

Webb 和倫敦大學的 Ray Meddis 認為情況就是如此。  可以想像得出，在危險的時刻，那些由於太愚笨而不能自動保

持安靜的動物，會不由自主地變得動彈不得。  這一點在食肉動物的幼獸身上表現得特別明 顯。  這是一個很有意思的看法，它至少部分是正確的。