LESSON FOURICloneWord下载.docx

LESSON FOURICloneWord下载.docx

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Sometime,somewhere,someonewillgenerateaclonedhumanbeing.

Whatwillhappenthen?

RonaldM.Green

Withinthefirstfiveyearsofthenextcentury,ateamofscientistssomewhereintheworldwillprobablyannouncethebirthofthefirstclonedhumanbaby.LikeLouiseBrown,thefirstchildbornastheresultofinvitrofertilization21yearsago,theclonedinfantwillbeshoweredwithmediaattention.Butwithinafewyearsitwillbejustoneofhundredsorthousandsofsuchchildrenaroundtheworld.

IthasbeenpossibletoenvisionsuchascenariorealisticallyonlysinceIanWilmutandhiscolleaguesattheRoslinInstitutenearEdinburgh,Scotland,announcedinFebruary1997thattheyhadclonedasheepnamedDollyfromtheuddercellsofaewe.ThetechniqueusedbyWilmutandhisco-workers,calledsomatic-cellnucleartransfer,willprobablybethewayinwhichthefirsthumanclonewillbecreated.

Suchresearchonthebasicprocessesofcelldifferentiationholdsoutthepromiseofdramaticnewmedicalinterventionsandcures.Burnvictimsorthosewithspinalcordinjuriesmightbeprovidedwithreplacementskinornervetissuegrownfromtheirownbodycells.Thedamagedonebydegenerativedisorderssuchasdiabetes,Parkinson'

sdiseaseorAlzheimer'

sdiseasemightbereversed.Inthemoredistantfuture,scientistsmightbeabletogrowwholereplacementorgansthatourbodieswillnotreject.

Theseimportantmedicalusesofcloningtechnologyurgeustobecarefulinoureffortstorestrictcloningresearch.IntheimmediatewakeofDolly,politiciansaroundtheworldproposedorimplementedbansonhumancloning.IntheU.S.,PresidentBillClintoninstitutedamoratoriumonfederalfundingforhumancloningexperiments,andtheNationalBioethicsAdvisoryCommissionurgedthatthebanbeextendedtoprivate-sectorresearchaswell.Congresscontinuestostudyvariousproposalsforenactingsuchatotalban.

Inviewofthestillunknownphysicalrisksthatcloningmightimposeontheunbornchild,cautionisappropriate.Ofthe29earlyembryoscreatedbysomatic-cellnucleartransferandimplantedintovariousewesbyRoslinresearchers,onlyone,Dolly,survived,suggestingthatthetechniquecurrentlyhasahighrateofembryonicandfetalloss.Dollyherselfappearstobeanormalthree-year-oldsheep----sherecentlygavebirthtotripletsfollowinghersecondpregnancy.Butarecentreportthathertelomeresareshorterthannormalforheragesuggeststhatherlifespanmightbereduced.Thisandothermattersmustbesortedoutandsubstantialfurtheranimalresearchwillneedtobecompletedbeforecloningcanbeappliedsafelytohumans.

EventuallyanimalresearchmayindicatethathumancloningcanbedoneatnogreaterphysicalrisktothechildthanIVFposedwhenitwasfirstintroduced.OnewouldhopethatsuchresearchwillbedoneopenlyintheU.S.,Canada,EuropeorJapan,whereestablishedgovernmentagenciesexisttoprovidecarefuloversightoftheimplicationsofthestudiesforhumansubjects.Lessdesirably,butmoreProbably,itmighthappeninclandestinefashioninsomeoffshorelaboratorywhereacoupledesperateforachildhasputtheirhopesinthehandsofaresearcherseekinginstantrenown.

Giventhepaceofevents,itispossiblethatthisresearcherisalreadyatwork.Fornow,thetechnicallimitingfactoristheavailabilityofasufficientnumberofripehumaneggs.IfDollyisanindication,hundredsmightbeneededtoproduceonlyafewviableclonedembryos.Currentassisted-reproductionregimensthatusehormoneinjectionstoinduceeggmaturationproduceatbestonlyafeweggsduringeachfemalemenstrualcycle.Butscientistsmightsoonresolvethisproblembyimprovingwaystostorefrozeneggsandbydevelopingmethodsforinducingthematurationofeggsineggfolliclesmaintainedinlaboratoryculturedishes.

Oncehumancloningispossible,whywouldanyonewanttohaveachildthatway?

Asweconsiderthisquestion,weshouldputasidethenightmarescenariosmuchtalkedaboutinthepress.Theseincludedictatorsusingcloningtoamassanarmyof"

perfectsoldiers"

orwealthyegotistsseekingtoproducehundredsorthousandsofcopiesofthemselves.Popularfilmsfeedthesenightmaresbyobscuringthefactthatcloningcannotinstantaneouslyyieldacopyofanexistingadulthumanbeing.Whatsomatic-cellnucleartransfertechnologyproducesareclonedhumanembryos.Theserequirethelabor-andtime-intensiveprocessesofgestationandchildrearingtoreachadulthood.SaddamHusseinwouldhavetowait20yearstorealizehisdreamofaperfectarmy.AndtheDonaldTrumpsoftheworldwouldalsohavetoenlistthousandsofwomentobethemothersoftheirclones.

Foralltheirefforts,thoseseekingtomass-producechildreninthisway,aswellasotherswhoseekanexactcopyofsomeoneelse,wouldalmostcertainlybedisappointedintheend.Althoughgenescontributetothearrayofabilitiesandlimitseachofuspossesses,fromconceptionforwardtheirexpressionisconstantlyshapedbyenvironmentalfactors,bytheuniqueexperiencesofeachindividualandbypurelychancefactorsinbiologicalandsocialdevelopment.Evenidenticaltwins（naturalhumanclones）showdifferentphysicalandmentalcharacteristicstosomedegree.Howmuchmorewillthisbetrueofclonedchildrenraisedatdifferenttimesandindifferentenvironmentsfromtheirnucleus-donor"

parent"

?

SomeonetryingtocloneafutureAdolfHitlermightinsteadproduceamodestlytalentedpainter.

Sowhoismostlikelytowantorusehumancloning?

Firstarethoseindividualsorcoupleswholackthegametesneededforsexualreproduction.Womenwholackovariesaltogetherandmenwhosetesticleshavefailedtodeveloporhavebeenremovedmuststillusedonorgametesiftheywishtohaveachild,whichmeansthatthechildwillnotcarryanyoftheirgenes.Someoftheseindividualsmightprefertousecloningtechnologytohaveageneticallyrelatedchild.

Oneverylargecategoryofsuchusersofcloningmightbelesbiancouples.Currentlyiftwolesbianswishtohaveachild,theymustusedonorsperm.Inaneraofchanginglawsabouttherightsofgametedonors,thisopenstheirrelationshiptopossibleinterventionbythespermdonorifhedecideshewantstoplayaroleinraisingthechild.Cloningtechnologyavoidsthisproblembypermittingeachmemberofthepairtobearachildwhosegenesareprovidedbyherpartner.

Asecondbroadclassofpossibleusersincludesindividualsorcoupleswhosegenescarrymutationsthatmightcauseseriousgeneticdiseaseintheiroffspring.Somecoupleswithgeneticdiseaseintheirfamilieswillchoosecloningasawayofavoidingwhattheyregardas"

reproductiveroulette."

Althoughtheclonedchildwillcarrythesameproblemgenesastheparentwhodonatesthenucleus,heorshewillinalllikelihoodenjoytheparent'

sstateofhealthandwillbefreeoftheadditionalriskscausedbymixingbothparents'

genesduringsexualreproduction.Itistrue,ofcourse,thatsexisnature'

swayofdevelopingnewcombinationsofgenesthatareabletoresistunknownhealththreatsinthefuture.Therefore,cloningshouldneverbeallowedtobecomesocommonthatitreducestheoveralldiversityinthehumangenepool.Onlyarelativelyfewcouplesarelikelytousecloninginthisway,however,andthesecoupleswillreasonablyforgothegeneraladvantagesconveyedbysexualreproductiontoreducetheimmediaterisksofpassingonageneticdiseasetotheirchild.

Cloningalsobringshopetofamilieswithinheritedgeneticdiseasesbyopeningthewaytogenetherapy.Suchtherapy----theactualcorrectionorreplacementofdefectivegenesequencesintheembryoortheadult----istheholygrailofgeneticmedicine.Cloningpromisesanendrunaroundthisproblem.Withalargepopulationofcellsfromoneparentorfromanembryocreatedfrombothparents'

gametes,vectorscouldbecreatedtoconveythedesiredgenesequence.Thenucleusofoneofthesecellstakingupthecorrectsequencecouldthenbeinsertedintoaneggwhoseownnucleushasbeenremoved,andthe"

cloned"

embryocouldbetransferredtothemother'

swomb.Theresultingchildanditsdescendantswouldthereaftercarrythecorrectedgeneineverycelloftheirbodies.Inthisway,age-oldgeneticmaladiessuchasTay-Sachsdisease,cysticfibrosis,musculardystrophyorHuntington'

sdiseasecouldbeeliminatedcompletelyfromfamilytrees.

Merelymentioningthesebeneficialusesofcloningraisesdifficultethicalquestions.Thebrighthopeofgenetherapyisdimmedsomewhatbythereawakeningofeugenicfears.Ifwecanmanipulateembryostopreventdisease,whynotgofurtherandseek"

enhancements"

ofhumanabilities?

Greaterdiseaseresistance,strengthandintelligenceallbeckonalluringly,butquestionsabound.Willwebetamperingwiththediversitythathasbeenthemainstayofhumansurvivalinthepast?

Whowillchoosetheallegedenhancements,andwhatwillpreventarepetitionoftheterribleracistandcoerciveeugenicprogramsofthepast?

Evenifitprovesphysicallysafefortheresultingchildren,humancloningraisesitsownshareofethicsdilemmas.Manywonder,forexample,aboutthepsychologicalwell-beingofaclonedchild.Whatdoesitmeanintermsofintrafamilyrelationsforsomeonetobeborntheidenticaltwinofhisorherparent?

Whatpressureswillaclonedchildexperienceif,fromhisorherbirthonward,heorsheisconstantlybeingcomparedtoanesteemedorbelovedpersonwhohasalreadylived?

Theproblemmaybemoreacuteifparentsseektoreplaceadeceasedchildwithaclonedreplica.Isthere,assomeethicistshaveargued,a"

righttoone'

suniquegenot