2. 自考
  3. Evolution of Sleep Sleep is very ancient．In the electroencephalographic(脑电图仪的)sense we share it with all the primates(灵长类动物)

Evolution of Sleep Sleep is very ancient．In the electroencephalographic(脑电图仪的)sense we share it with all the primates(灵长类动物)

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问题                              Evolution of Sleep
    Sleep is very ancient．In the electroencephalographic(脑电图仪的)sense we share it with all the primates(灵长类动物)and almost all the other mammals and birds：it may extend back as far as the reptiles(爬行动物)．
    There is some evidence that the two types of sleep, dreaming and dreamless, depend on the life-style of the animal, and that predators(食肉动物)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(使固定不动)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 tare 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 0n their 0wn 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 tree．
It can be inferred from the passage that animals that are prey rarely experience dream sleep because they________．
选项 A、have evolved further than predators
B、are particularly intelligent animals
C、need less sleep than predators
D、would be caught if deeply asleep
答案D
解析 文章在第二段中交代，在做梦的睡眠中，动物是一动不动的，对外界刺激毫无反应。这样的情况对被捕食的动物很危险，因为它们如果睡得很死，就有可能被食肉动物吃掉。所以我们可以推断，这些动物睡觉时很少做梦，因为熟睡会被别的动物逮住。
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