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 pray 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 genera 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 animals vulnerability, the University of Florida and Ray Middies of London University have suggested this to be the case.
It is conceivable that animals who are too stupid to be quite 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.
上一篇: GRE写作范文——Sleep
下一篇: GRE写作之逻辑问题分析论证句式(三)
新概念英语第一册视频讲解 第74课:What did they do?
新概念英语第一册视频讲解 第70课:When were they there?
新概念英语第一册视频讲解 第73课:The way to King Street到国王街的走法
新概念英语第一册视频讲解 第58课:What’s the time?
新概念英语第一册视频讲解 第61课:A bad cold重感冒
新概念英语第一册视频讲解 第98课:Whose is it?
新概念英语第一册视频讲解 第76课:When did you?
新概念英语第一册视频讲解 第69课:The car race汽车比赛
新概念英语第一册视频讲解 第82课:I had...
新概念英语第一册视频讲解 第103课:The French test法语考试
新概念英语第一册视频讲解 第97课:A small blue case 一只蓝色的小箱子
新概念英语第一册视频讲解 第104课:Too,very
新概念英语第一册视频讲解 第56课:What do they usually do?
新概念英语第一册视频讲解 第65课:Not a baby不是一个孩子
新概念英语第一册视频讲解 第89课:For sale待售
新概念英语第一册视频讲解 第67课:The weekend周末
新概念英语第一册视频讲解 第78课:When did you...
新概念英语第一册视频讲解 第92课:When will....?
新概念英语第一册视频讲解 第75课:Uncomfortable shoes不舒适的鞋子
新概念英语第一册视频讲解 第87课:A car crash车祸
新概念英语第一册视频讲解 第90课:Have you... yet?
新概念英语第一册视频讲解 第102课:He says he...
新概念英语第一册视频讲解 第66课:What’s the time?
新概念英语第一册视频讲解 第81课:Roast beef and potatoes烤牛肉和土豆
新概念英语第一册视频讲解 第83课:Going on holiday度假
新概念英语第一册视频讲解 第88课:Have you ...yet?
新概念英语第一册视频讲解 第93课:Our new neighbour 我们的新邻居
新概念英语第一册视频讲解 第101课:A card from Jimmy吉米的明信片
新概念英语第一册视频讲解 第64课:Don’t...
新概念英语第一册视频讲解 第100课:He says that...