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1、Itisinterestingtocontemplateanentangledbank,clothedwithmanyplantsofmanykinds,withbirdssingingonthebushes,withvariousinsectsflittingabout,andwithwormscrawlingthroughthedampearth,andtoreflectthattheseelaboratelyconstructedforms,sodifferentfromeachother,anddepend
2、entoneachotherinsocomplexamanner,haveallbeenproducedbylawsactingaroundus.(CharlesDarwin,1859/1979,p.459)Chapter12MaleandFemaleMatingStrategiesWhySex?TakenfromtheverylastparagraphofTheOriginofSpecies,theaboveDarwinianquotationdescribesdifferentcreaturescompetin
3、gforlightandfoodonatangledbank.“Tangledbank”haslaterbeenusedtorefertothespatialheterogeneityhypothesisabouttheadvantagesofsexualratherthanasexualreproduction.Accordingtothetangledbankhypothesis,geneticheterogeneitythroughsexualrecombinationisimportantinanyenvi
4、ronmentswherethereisanintensecompetitionforspace,lightandotherresources(Ghiselin,1974).Insuchcompetitiveenvironment,adiversegroupofsiblingsfromsexualreproductionmaybeabletoextractmorefoodandresourcesfromitsenvironmentthanaclonefromasexualreproduction.Thisissob
5、ecause,inanyenvironment,thespaceisdividedintodifferentnicheswheredifferentskillsareneededforsurvival.Aclonewhoisadaptedonlytoonenichewill“givebirth”tooffspringthatcanonlyhandlethesameniche.Theclonecanthriveinthatnichewhenthereisnocompetition.Whencompetitionfor
6、cesthecloneoutoftheniche,itwillnothavetheskillstosurvivedifferentenvironments.Throughsexualrecombination,agenecanteamupwithawidevarietyofothergenestocreateinfinitepossibilitiesforcombinationsthatmayfitdifferentenvironmentalniches.IncrowdedenvironmentssuchasDar
7、win’stangledbank,sexualreproductionprovidesameansofexploitingtinyvariationsinthelocalenvironment.Thetangledbankhypothesisisoneofthefourexplanationsgiventothequestionof“Whysex”whichisrelatedtoanotherquestion,“Whydomalesexist?”Reproductioncanbeachievedasexuallya
8、scommonlyobservedin“low-level”animalsandplants.Asexualreproductionshouldbefavoredsinceitwouldproducemorecopiesofitself,especiallyintheabsenceofmalecare.Femaleswithasexualreproducti
