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tpo42三篇托福阅读TOEFL原文译文题目答案译文背景知识
TOC\o1-2\h\u6050阅读-1 2
28568原文 2
6617译文 5
31383题目 8
6153答案 18
9762背景知识 18
6200阅读-2 24
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14044题目 30
23500答案 39
2568背景知识 39
5212阅读-3 41
12728原文 41
29261译文 44
15745题目 47
28727答案 55
10644背景知识 55
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原文
GeographicIsolationOfSpecies
①BiologistErnstMayrdefinedaspeciesas“anactuallyorpotentiallyinterbreedingpopulationthatdoesnotinterbreedwithothersuchpopulationswhenthereisopportunitytodoso.”Akeyeventintheoriginofmanyspeciesistheseparationofapopulationwithitsgenepool(allofthegenesinapopulationatanyonetime)fromotherpopulationsofthesamespecies,therebypreventingpopulationinterbreeding.Withitsgenepoolisolated,aseparatepopulationcanfollowitsownevolutionarycourse.Intheformationofmanyspecies,theinitialisolationofapopulationseemstohavebeenageographicbarrier.Thismodeofevolvingnewspeciesiscalledallopatricspeciation.
②Manyfactorscanisolateapopulationgeographically.Amountainrangemayemergeandgraduallysplitapopulationoforganismsthatcaninhabitonlylowlandlakes,certainfishpopulationsmightbecomeisolatedinthisway.Similarly,acreepingglaciermaygraduallydivideapopulation,oralandbridgesuchastheIsthmusofPanamamayformandseparatethemarinelifeintheoceanwatersoneitherside.
③Howformidablemustageographicbarrierbetokeeppopulationsapart?Itdependsontheabilityoftheorganismstomoveacrossbarriers.Birdsandcoyotescaneasilycrossmountainsandrivers.Thepassageofwind-blowntreepollenisalsonothinderedbysuchbarriers,andtheseedsofmanyplantsmaybecarriedbackandforthonanimals.Incontrast,smallrodentsmayfindadeepcanyonorawideriveraneffectivebarrier.Forexample,theGrandCanyon,inthesouthwesternUnitedStates,separatetherangeofthewhite-taile
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