17.Evolution of sleep
Sleep is very ancient. In the electroencephalographic sense we share it with all the primates1 and almost all the other mammals and birds: it may extend back as far as the reptiles2. There is some evidence that the two types of sleep, dreaming and dreamless, depend on the life-style of the animal, and that predators3 are statistically4 much more likely to dream than prey5, which are in turn much more likely to experience dreamless sleep. In dream sleep, the animal is powerfully immobilized and remarkably6 unresponsive to external stimuli7. Dreamless sleep is much shallower, and we have all witnessed cats or dogs cocking their ears to a sound when apparently8 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 aquatic9 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 animal’s vulnerability, 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 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.
1 primates
primate的復(fù)數(shù)
參考例句：
Primates are alert, inquisitive animals. 靈長(zhǎng)目動(dòng)物是機(jī)靈、好奇的動(dòng)物。
Consciousness or cerebration has been said to have emerged in the evolution of higher primates. 據(jù)說意識(shí)或思考在較高級(jí)靈長(zhǎng)類的進(jìn)化中已出現(xiàn)。
2 reptiles
n.爬行動(dòng)物，爬蟲( reptile的名詞復(fù)數(shù) )
參考例句：
Snakes and crocodiles are both reptiles. 蛇和鱷魚都是爬行動(dòng)物。 來自《簡(jiǎn)明英漢詞典》
Birds, reptiles and insects come from eggs. 鳥類、爬蟲及昆蟲是卵生的。 來自《現(xiàn)代漢英綜合大詞典》
3 predators
n.食肉動(dòng)物( predator的名詞復(fù)數(shù) )；奴役他人者（尤指在財(cái)務(wù)或性關(guān)系方面）
參考例句：
birds and their earthbound predators 鳥和地面上捕食它們的動(dòng)物
The eyes of predators are highly sensitive to the slightest movement. 捕食性動(dòng)物的眼睛能感覺到最細(xì)小的動(dòng)靜。 來自《簡(jiǎn)明英漢詞典》
4 statistically
ad.根據(jù)統(tǒng)計(jì)數(shù)據(jù)來看，從統(tǒng)計(jì)學(xué)的觀點(diǎn)來看
參考例句：
The sample of building permits is larger and therefore, statistically satisfying. 建筑許可數(shù)的樣本比較大，所以統(tǒng)計(jì)數(shù)據(jù)更令人滿意。
The results of each test would have to be statistically independent. 每次試驗(yàn)的結(jié)果在統(tǒng)計(jì)上必須是獨(dú)立的。
5 prey
n.被掠食者，犧牲者，掠食；v.捕食，掠奪，折磨
參考例句：
Stronger animals prey on weaker ones.弱肉強(qiáng)食。
The lion was hunting for its prey.獅子在尋找獵物。
6 remarkably
ad.不同尋常地，相當(dāng)?shù)?BR> 參考例句：
I thought she was remarkably restrained in the circumstances. 我認(rèn)為她在那種情況下非?？酥啤?BR> He made a remarkably swift recovery. 他康復(fù)得相當(dāng)快。
7 stimuli
n.刺激（物）
參考例句：
It is necessary to curtail or alter normally coexisting stimuli.必需消除或改變正常時(shí)并存的刺激。
My sweat glands also respond to emotional stimuli.我的汗腺對(duì)情緒刺激也能產(chǎn)生反應(yīng)。
8 apparently
adv.顯然地；表面上，似乎
參考例句：
An apparently blind alley leads suddenly into an open space.山窮水盡，豁然開朗。
He was apparently much surprised at the news.他對(duì)那個(gè)消息顯然感到十分驚異。
9 aquatic
adj.水生的，水棲的
參考例句：
Aquatic sports include swimming and rowing.水上運(yùn)動(dòng)包括游泳和劃船。
We visited an aquatic city in Italy.我們?cè)谝獯罄L問過一個(gè)水上城市。
Sleep is very ancient. In the electroencephalographic sense we share it with all the primates1 and almost all the other mammals and birds: it may extend back as far as the reptiles2. There is some evidence that the two types of sleep, dreaming and dreamless, depend on the life-style of the animal, and that predators3 are statistically4 much more likely to dream than prey5, which are in turn much more likely to experience dreamless sleep. In dream sleep, the animal is powerfully immobilized and remarkably6 unresponsive to external stimuli7. Dreamless sleep is much shallower, and we have all witnessed cats or dogs cocking their ears to a sound when apparently8 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 aquatic9 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 animal’s vulnerability, 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 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.
1 primates
primate的復(fù)數(shù)
參考例句：
Primates are alert, inquisitive animals. 靈長(zhǎng)目動(dòng)物是機(jī)靈、好奇的動(dòng)物。
Consciousness or cerebration has been said to have emerged in the evolution of higher primates. 據(jù)說意識(shí)或思考在較高級(jí)靈長(zhǎng)類的進(jìn)化中已出現(xiàn)。
2 reptiles
n.爬行動(dòng)物，爬蟲( reptile的名詞復(fù)數(shù) )
參考例句：
Snakes and crocodiles are both reptiles. 蛇和鱷魚都是爬行動(dòng)物。 來自《簡(jiǎn)明英漢詞典》
Birds, reptiles and insects come from eggs. 鳥類、爬蟲及昆蟲是卵生的。 來自《現(xiàn)代漢英綜合大詞典》
3 predators
n.食肉動(dòng)物( predator的名詞復(fù)數(shù) )；奴役他人者（尤指在財(cái)務(wù)或性關(guān)系方面）
參考例句：
birds and their earthbound predators 鳥和地面上捕食它們的動(dòng)物
The eyes of predators are highly sensitive to the slightest movement. 捕食性動(dòng)物的眼睛能感覺到最細(xì)小的動(dòng)靜。 來自《簡(jiǎn)明英漢詞典》
4 statistically
ad.根據(jù)統(tǒng)計(jì)數(shù)據(jù)來看，從統(tǒng)計(jì)學(xué)的觀點(diǎn)來看
參考例句：
The sample of building permits is larger and therefore, statistically satisfying. 建筑許可數(shù)的樣本比較大，所以統(tǒng)計(jì)數(shù)據(jù)更令人滿意。
The results of each test would have to be statistically independent. 每次試驗(yàn)的結(jié)果在統(tǒng)計(jì)上必須是獨(dú)立的。
5 prey
n.被掠食者，犧牲者，掠食；v.捕食，掠奪，折磨
參考例句：
Stronger animals prey on weaker ones.弱肉強(qiáng)食。
The lion was hunting for its prey.獅子在尋找獵物。
6 remarkably
ad.不同尋常地，相當(dāng)?shù)?BR> 參考例句：
I thought she was remarkably restrained in the circumstances. 我認(rèn)為她在那種情況下非?？酥啤?BR> He made a remarkably swift recovery. 他康復(fù)得相當(dāng)快。
7 stimuli
n.刺激（物）
參考例句：
It is necessary to curtail or alter normally coexisting stimuli.必需消除或改變正常時(shí)并存的刺激。
My sweat glands also respond to emotional stimuli.我的汗腺對(duì)情緒刺激也能產(chǎn)生反應(yīng)。
8 apparently
adv.顯然地；表面上，似乎
參考例句：
An apparently blind alley leads suddenly into an open space.山窮水盡，豁然開朗。
He was apparently much surprised at the news.他對(duì)那個(gè)消息顯然感到十分驚異。
9 aquatic
adj.水生的，水棲的
參考例句：
Aquatic sports include swimming and rowing.水上運(yùn)動(dòng)包括游泳和劃船。
We visited an aquatic city in Italy.我們?cè)谝獯罄L問過一個(gè)水上城市。