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