Peoplehavebeenwonderingwhyelephantsdonotdevelopcancereventhoughtheyhavelifespans（寿命）thataresimilartohumans，livingforaround50to70years．Nowscientistsbelievetheyknowwhy．AteamattheUniversityofChicago

　　Peoplehavebeenwonderingwhyelephantsdonotdevelopcancereventhoughtheyhavelifespans（寿命）thataresimilartohumans，livingforaround50to70years．

　　Nowscientistsbelievetheyknowwhy．AteamattheUniversityofChicago，UShasfoundthatelephantscarryalargenumberofgenesthatstoptumors（肿瘤）developing．Tobeprecise，theyfound20copiesofananti-tumorgenecalledTP53inelephants．Mostotherspecies，includinghumans，onlycarryonecopy．

　　Accordingtotheresearch，theextracopiesofthegeneimprovedtheanimal'ssensitivitytoDNAdamage，whichletsthecellsquicklykillthemselveswhendamagedbeforetheycangoontoformdeadlytumors．

　　"Anincreasedriskofdevelopingcancerhasstoodinthewayoftheevolutionoflargebodysizesinmanyanimals，"thestudyauthorDrVincentLynchtoldTheGuardian．Ifeverylivingcellhasthesamechanceofbecomingcancerous（癌变的），largecreatureswithalonglifespanlikewhalesandelephantsshouldhaveagreaterriskofdevelopingcancerthanhumansandmice．Butacrossspecies，theriskofcancerdoesnotshowaconnectionwithbodymass．

　　ThisphenomenonwasfoundbyOxfordUniversityscientistRichardPetointhe1970sandlaternamed"Peto'sparadox（悖论）"．Biologistsbelieveitresultsfromlargeranimalsusingprotectionthatmanysmalleranimalsdonot．Intheelephant'scase，themakingofTP53isnature'swayofkeepingthisspeciesalive．

　　Thestudyalsofoundthatwhenthesamegeneswerebroughttolifeinmice，theyhadthesamecancerresistanceaselephants．Thismeansresearcherscouldusethediscoverytodevelopnewtreatmentsthatcanhelpstopcancersspreadingorevendevelopinginthefirstplace．

　　"Naturehasalreadyfiguredouthowtopreventcancer，"saidJoshuaSchiffman，abiologistattheSchoolofMedicine，UniversityofUtah，US．"It'suptoustolearnhowdifferentanimalsdealwiththeproblemsothatwecanusethosestrategiestopreventcancerinpeople．"

　　32．Whyareelephantsunlikelytodevelopcancer？___

　　A．Theyhavearatherlargebodysize．

　　B．TheirgenessuffernoDNAdamage．

　　C．Certaingenesintheirbodykillexistingtumors．

　　D．Theycarrymanygenestopreventtumorsde