考研優(yōu)美英語作文背誦017
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Evolution of Sleep
Sleep is very ancient. In the electroencephalographic sense we share itwith all the primates and almost all the other mammals and birds: it mayextend back as far as the reptiles.
There is someevidence that the two types of sleep, dreaming and dreamless, depend on thelife-style of the animal, and that predators are statistically much more likelyto dream than prey, which are in turn much more likely to experiencedreamless sleep. In dream sleep, the animal is powerfully immobilized andremarkably unresponsive to external stimuli.
Dreamlesssleep is much shallower, and we have all witnessed cats or dogs cocking theirears to a sound when apparently fast asleep. The fact that deep dream sleep israre among prey today seems clearly to be a product of natural selection, andit makes sense that today, when sleep is highly evolved, the stupid animalsare less frequently immobilized by deep sleep than the smart ones. But whyshould they sleep deeply at all? Why should a state of such deepimmobilization ever have evolved? Perhaps one useful hint about the originalfunction of sleep is to be found in the fact that dolphins and whales andaquatic 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 ananimal's vulnerability, the function of sleep is to decrease it?Wilse Webb of the University of Florida and Ray Meddis of LondonUniversity have suggested this to be the case. It is conceivable thatanimals who are too stupid to be quiet on their own initiative are, duringperiods of high risk, immobilized by the implacable arm of sleep. The pointseems particularly clear for the young of predatory animals. This is aninteresting notion and probably at least partly true.
全文翻譯：
睡眠的進化
睡眠是古老的。 從腦電圖上看，我們?nèi)祟惡退徐`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(jù)顯示，有夢睡眠和無夢睡眠這兩種類型的睡眠取決于該動物的生活方式。 從統(tǒng)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， 并且對外界刺激缺乏反應(yīng)。 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(jié)果。
而且這一點是有道理的：當睡眠高度進化以后，愚笨的動物比聰明的動物更少在 深度睡眠狀態(tài)下喪失動作能力。
但是動物為什么要進入深度睡眠呢?為什么這樣的無動作狀 態(tài)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(xué)的 Wilse Webb 和倫敦大學(xué)的 Ray Meddis 認為情況就是如此。 可以想像得出，在危險的時刻，那些由于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(xiàn)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。
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