最新TPO阅读42文本答案翻译.docx

最新TPO阅读42文本答案翻译.docx

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最新TPO阅读42文本答案翻译

TPO-42

GeographicIsolationofSpecies

BiologistErnstMayrdefinedaspeciesas“anactuallyorpotentiallyinterbreedingpopulationthatdoesnotinterbreedwithothersuchpopulationswhenthereisopportunitytodoso.”Akeyeventintheoriginofmanyspeciesistheseparationofapopulationwithitsgenepool（allofthegenesinapopulationatanyonetime）fromotherpopulationsofthesamespecies,therebypreventingpopulationinterbreeding.Withitsgenepoolisolated,aseparatepopulationcanfollowitsownevolutionarycourse.Intheformationofmanyspecies,theinitialisolationofapopulationseemstohavebeenageographicbarrier.Thismodeofevolvingnewspeciesiscalledallopatricspeciation.

Manyfactorscanisolateapopulationgeographically.Amountainrangemayemergeandgraduallysplitapopulationoforganismsthatcaninhabitonlylowlandlakes,certainfishpopulationsmightbecomeisolatedinthisway.Similarly,acreepingglaciermaygraduallydivideapopulation,oralandbridgesuchastheIsthmusofPanamamayformandseparatethemarinelifeintheoceanwatersoneitherside.

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Howformidablemustageographicbarrierbetokeeppopulationsapart?

Itdependsontheabilityoftheorganismstomoveacrossbarriers.Birdsandcoyotescaneasilycrossmountainsandrivers.Thepassageofwind-blowntreepollenisalsonothinderedbysuchbarriers,andtheseedsofmanyplantsmaybecarriedbackandforthonanimalsIncontrast,smallrodentsmayfindadeepcanyonorawideriveraneffectivebarrier.Forexample,theGrandCanyon,inthesouthwesternUnitedStates,separatetherangeofthewhile-tailedantelopesquirrelfromthatofthecloselyrelatedHarris’antelopesquirrel.Smaller,withashortertailthatiswhiteunderneath,thewhite-tailedantelopesquirrelinhabitsdesertsnorthofthecanyonandwestoftheColoradoRiverinsouthernCaliforniaHams'antelopesquirrelhasamorelimitedrangeindesertssouthoftheGrandCanyon.

Geographicisolationcreatesopportunitiesfornewspeciestodevelop,butitdoesnotnecessarilyleadtonewspeciesbecausespeciationoccursonlywhenthegenepoolundergoesenoughchangestoestablishreproductivebarriersbetweentheisolatedpopulationanditsparentpopulation.Thelikelihoodofallopatricspeciationincreaseswhenapopulationissmallaswellasisolated,makingitmorelikelythanalargepopulationtohaveitsgenepoolchangedsubstantially.Forexample,inlessthantwomillionyears,smallpopulationsofstrayanimalsandplantsfromtheSouthAmericanmainlandthatmanagedtocolonizetheGalapagosIslandsgaverisetoallthespeciesthatnowinhabittheislands.

Whenoceanicislandsarefarenoughaparttopermitpopulationstoevolveinisolation,butcloseenoughtoallowoccasionaldispersionstooccur,theyareeffectivelyoutdoorlaboratoriesofevolution.TheGalapagosislandchainisoneoftheworld’sgreatestshowcasesofevolution.Eachislandwasbornfromunderwatervolcanoesandwasgraduallycoveredbyorganismsderivedfromstraysthatrodetheoceancurrentsandwindsfromotherislandsandcontinents.Organismscanalsobecarriedtoislandsbyotherorganisms,suchasseabirdsthattravellongdistanceswithseedsclingingtotheirfeathers.

ThespeciesontheGalapagosIslandstoday,mostofwhichoccurnowhereelse,descendedfromorganismsthatfloated,flew,orwereblownovertheseafromtheSouthAmericanmainland.Forinstance,theGalapagosislandchainhasatotalofthirteenspeciesofcloselyrelatedbirdscalledGalapagosfinches.Thesebirdshavemanysimilaritiesbutdifferintheirfeedinghabitsandtheirbeaktype,whichiscorrelatedwithwhattheyeat.Accumulatedevidenceindicatesthatallthirteenfinchspeciesevolvedfromasinglesmallpopulationofancestralbirdsthatcolonizedoneoftheislands.Completelyisolatedontheislandaftermigratingfromthemainland,thefounderpopulationmayhaveundergonesignificantchangesinitsgenepoolandbecomeanewspecies.■Later,afewindividualsofthisnewspeciesmayhavebeenblownbystormstoaneighboringisland.■Isolatedonthissecondisland,thesecondfounderpopulationcouldhaveevolvedintoasecondnewspecies,whichcouldlaterrecolonizetheislandfromwhichitsfoundingpopulationemigrated.■TodayeachGalapagosislandhasmultiplespeciesoffinches,withasmanyastenonsomeislands.■

1.Theword“key”inthepassageisclosestinmeaningto

A.early

B.crucial

C.noticeable

D.frequent

2.Theword“initial”inthepassageisclosestinmeaningto

A.best

B.usual

C.first

D.actual

Youenjoytheconvenienceofhavingallvocabularyquestionslistedasaseparatepartin《新托福TPO阅读词汇速查速记》.

3.Accordingtoparagraph1,allopatricspeciationispossiblewhen

A.apopulationcontainsallthedifferentgenespresentinaspeciesataparticulartime

B.apopulationbecomesisolatedduetothepresenceofageographicbarrier

C.geneticmixingbeginstooccurinpreviouslyseparatepopulationsofaspecies

D.aspeciesissuccessfulincrossingageographicbarrier

4.Howisparagraph2relatedtoparagraph1?

A.Paragraph2pointsoutanumberofwaysinwhichthephenomenonofgeographicisolationmentionedinparagraph1canoccur

B.Paragraph2identifiesdiscoveriesthatledtotheconclusionpresentedinparagraph1thatgeographicisolationhasplayedaroleintheoriginofmanyspecies

C.Paragraph2providesevidencesupportingthestatementinparagraph1thatapopulationcanfollowitsownevolutionarycourseonceitsgenepoolbecomesisolated

D.Paragraph2explainswhytheterm“allopatric”wasadoptedtodescribethemethodofspeciationdescribedinparagraph1

5.Inparagraph3,theauthorcontrastsavarietyoforganismstoillustratewhichofthefollowingpoints?

A.Geographicbarriersarelesslikelytokeepapartpopulationsofplantsthanpopulationsofanimals

B.Geographicbarriersaremorelikelytokeepapartpopulationsoflargeorganismsthanpopulationsofsmallorganisms

C.Somemembersofaspeciesareabletocrossgeographicbarriers,whileothermembersofthesamespeciesarenot

D.Theeffectivenessofgeographicbarriersinkeepingorganismsapartdependsonanorganism’sabilitytomoveacrossbarriers

6.Paragraph3supportstheideathatwhite-tailedantelopesquirrelsandHams'antelopesquirrelshavewhichofthefollowingincommon?

A.TheyarethetwosmallestrodentsnowfoundinthesouthwesternUnitedStates.

B.Theyhavewhitecoloringunderneaththeirtails

C.TheycannotcrosstheGrandCanyon

D.Theycannotsurviveindesertconditions

7.Theword“undergoes"inthepassageisclosestinmeaningto

A.experiences

B.allows

C.prevents

D.causes

8.Whichofthesentencesbelowbestexpressestheessentialinformationinthehighlightedsentenceinthepassage?

Incorrectchoiceschangethemeaninginimportantwaysorleaveoutessentialinformation

A.Geographicisolationissometimesbutnotalwaysthereasonforthecreationofreproductivebarriersbetweenaparentpopulationandthepopulationsdescendedfromit

B.Geneticchangesinageographicalisolatedpopulationdonotnecessarilymakethepopulationlookdifferentenoughfromitsparentpopulationtobeconsideredanewspecies

C.Geographicalisolationallowstheseparatedpopulationstoevolveindependentlyofeachotherandsocanleadtotheformationofnewspecies

D.Geographicisolationcanleadtonewspeciesonlyifthegenepooloftheisolatedpopulationchangesenoughtopreventitfromreproducingwiththeparentpopulation

9.Accordingtoparagraph4,whydoesthesizeofapopulationaffectthelikelihoodofallopatricspeciation?

A.Becausesmallerpopulationsaremorelikelythanlargeronestobecomegeographicallyisolated

B.Becausethegenepoolofasmallisolatedpopulationismorelikelytoundergosubstantialchangethanisthegenepoolofalargerpopulation

C.Becauseanisolatedpopulationcanbecomeanewspecieswithsubstantiallylesschangetoitsgenepoolthanwouldberequiredbyalargerpopulation

D.Becausesmallerpopulationsaremorelikelytobemadeupofstrayanimalsorplantsthanlargerpopulationsare

10.Theword“managed”inthepassageisclosestinmeaningto

A.wereable

B.wereforced

C.arrived

D.expanded

11.Paragraph5supportstheideathattheGalapagosislandchainwasabletobecome“oneoftheworld'sgreatestshowcasesofevolution”primarilybecauseof

A.therichnessofthevolcanicsoilofeachoftheislandsinthechain

B.thedistanceoftheindividualislandsfromeachotherandfromthemainland

C.therelativitylongtimeittookfortheislandstobecomecoveredbyorganisms

D.theoutdoorlaboratoriesthatscientistshavebuiltontheislandstostudyevolution

12.Accordingtoparagraph6,whatistrueaboutthethirteenspeciesofGalapagosfinches?

A.AllthirteenspeciesarenowfoundonmostoftheGalapagosIslands

B.Allthirteenspeciesaredescendedfromthesamepopulationofancestralbirds

C.Allthirteenspeciesevolvedontheislandthatwasoriginallycolonizedbyfinchesfromthemainland.

D.Allthirteenspeciesoccuronlyinsmall,completelyisolatedpopulations.

13.Lookatthefoursquares[█]thatindicatewherethefollowingsentencecouldbeaddedtothepassage

Thisprocessofspeciationandcolonizationcouldhavebeenrepeatedoverandoveragain,graduallyinvolvingalltheislandsinthechain.

Wherewouldthesentencebestfit?

Clickonasquaretoaddthesentencetothepassage.

14.Directions:

Anintroductorysentenceforabriefsummaryofthepassageisprovidedbelow.Completethesummary