公共英语五级阅读材料公共英语五级阅读材料公共英语五级的考试难度较大，这对于考生来说是一个比较大的挑战，下面，小编就为大家送上一篇公共英语五级阅读材料，希望对大家有所帮助。EvolutionofSleepSleepisveryancient.Intheelectroencephalographicsenseweshareitwithalltheprimatesandalmostalltheothermammalsandbirds:itmayextendbackasfarasthereptiles.Thereissomeevidencethatthetwotypesofsleep,dreaminganddreamless,dependonthelife-styleoftheanimal,andthatpredatorsarestatisticallymuchmorelikelytodreamthanprey,whichareinturnmuchmorelikelytoexperiencedreamlesssleep.Indreamsleep,theanimalispowerfullyimmobilizedandremarkablyunresponsivetoexternalstimuli.Dreamlesssleepismuchshallower,andwehaveallwitnessedcatsordogscockingtheirearstoasoundwhenapparentlyfastasleep.Thefactthatdeepdreamsleepisrareamongpreytodayseemsclearlytobeaproductofnaturalselection,anditmakessensethattoday,whensleepishighlyevolved,thestupidanimalsarelessfrequentlyimmobilizedbydeepsleepthanthesmartones.Butwhyshouldtheysleepdeeplyatall?Whyshouldastateofsuchdeepimmobilizationeverhaveevolved?Perhapsoneusefulhintabouttheoriginalfunctionofsleepistobefoundinthefactthatdolphinsandwhalesandaquaticmammalsingeneralseemtosleepverylittle.Thereis,byandlarge,noplacetohideintheocean.Coulditbethat,ratherthanincreasingananimal'svulnerability,thefunctionofsleepistodecreaseit?WilseWebboftheUniversityofFloridaandRayMeddisofLondonUniversityhavesuggestedthistobethecase.Itisconceivablethatanimalswhoaretoostupidtobequietontheirowninitiativeare,duringperiodsofhighrisk,immobilizedbytheimplacablearmofsleep.Thepointseemsparticularlyclearfortheyoungofpredatoryanimals.Thisisaninterestingnotionandprobablyatleastpartlytrue.睡眠的进化睡眠是古老的。从脑电图上看，我们人类和所有灵长目动物以及几乎所有的哺乳动物和鸟类都一样需要睡眠;甚至爬行类动物也有睡眠。有证据显示，有梦睡眠和无梦睡眠这两种类型的睡眠取决于该动物的生活方式。从统计上看，食肉动物比被捕食动物有更多的有梦睡眠，而被捕食动物更多地无梦睡眠。动物在有梦睡眠时，被有效地解除动作能力，并且对外界刺激缺乏反应。无梦睡眠则要浅得多。我们都看到过猫和狗在显然的酣睡中，有一点响动耳朵就会竖起来。被捕食动物很少有深度的有梦睡眠，这看来显然是自然选择的结果。而且这一点是有道理的：当睡眠高度进化以后，愚笨的动物比聪明的动物更少在深度睡眠状态下丧失动作能力。但是动物为什么要进入深度睡眠呢?为什么这样的无动作状态也会进化出来呢?海豚、鲸鱼以及水生哺乳动物睡眠都极少，这一事实可以给睡眠的根本功能提供有用的线索。海洋中是没有藏身之处的。会不会是这样，睡眠不但不增加动物受伤害的可能性，反而是减少了这种可能性