introduction to evolution课件

EvidenceforEvolution Reading Freeman Chapter23 26 TheFactofEvolutionEvolution theprogressivechangeoforganismsastheydescendfromancestralspecies isafact Bynow theevidenceforitisoverwhelmingandubiquitous Itisofsuchobviousclinicalsignificanceinmedicinethattodenyitisirresponsible Thatsaid anyexplanationforitsexistenceandmodeofactionisascientifictheory whichmustbetestableand intheory falsifiable Darwin stheoryofnaturalselection combinedwithothermechanismsofevolutiondiscoveredsinceDarwin formwhatisknownasthe modernsynthesis thecurrentscientificparadigminthebiologicalsciences Itprovidesacentralexplanationforphenomenainsuchdiversefieldsaspaleontologyanddevelopmentalbiology medicineandpsychology Theexistenceofevolutionhasbeenproposedseveraltimesinhistory Forinstance theancientGreekscientist Animaxander proposedatheoryofevolution Intermsofmodernscience itwasfirstadvancedproposedinthelate1700 sandearly1800sbyseveralscientistsincludingComptedeBuffonandErasmusDarwin Theideaofevolutionremainedcontroversialforalongtime partiallybecauseitrancontrarytocontemporaryreligiousideasandpartiallybecausenomechanismforevolutionwasknown DarwinandWallace stheoryofevolutionbynaturalselectionwasthefirstplausible widely acceptedmechanismforevolutionarychange Bynowitiswell tested supportedbyhundredsofindependentscientificinvestigations Itisalsofalsifiable aspectsofDarwin stheoryofevolutionhavebeensuccessfullychallenged otherssupported Thisisthecasefortheothermechanismsofevolutionaswell Examplesoftheclinicalsignificanceofevolutionarybiologytomedicine HIV HIVisaretrovirusofenormousmedicalconcern Becauseofevolutionarystudies weknowthattwoseparatelineagesofthisretroviruspassedintothehumanpopulationfromAfricanApesinthemid20thcentury Thisknowledgehasalertedustothedangerofemergentdiseasesfromotheranimalhosts areasonforourconcernaboutSARSandbirdflu Inaddition itisanunderstandingofevolutionarybiologythathasenabledustodevelopatherapyforHIV Theso called tripletherapy HIVtreatmentisanexampleofevolutionarymedicine Asingledrugwillnotworkagainstthediseasebecausethevirusevolvessoquickly itattainsresistancetoeverydrugwehavewithinafewmonths Byusingthreedrugssimultaneously wesubverttheevolutionofthevirus evolvingresistancetoonedrugmeansloosingresistancetoanother Antibioticresistanceisanevolutionaryphenomenonoftremendousclinicalsignificance Earlyinthe20thcentury avarietyofantibiotics usedtotreatbacterialdiseases weredeveloped Anunderstandingofevolutionishelpfultounderstandwheretheseantibioticscomefromtobeginwith many suchaspenicillin wereevolvedbyfungi overmillionsofyears tokillofftheirbacterialcompetitors Humanshaveco optedthemforourownpurposes Sincethe20thcentury thebacterialpathogenshaveevolvedresistancetoourantibiotics becauseextensiveuseofthesedrugshascausedverystrongnaturalselectioninfavorofmutationswhichfavorantibioticresistance Forinstance variousstrainsofNeisseriagonorrheaehaveevolvedresistancetopenicillins tetracyclines spectinomycinandfloroquinolones NaturalSelectionastheMechanismofEvolution Scientificunderstandingofevolutioncameoutofitsinfancyin1859 whentheoriesofevolutionbynaturalselectionbyCharlesDarwinandAlfredRusselWallacebecamewidelyknown Wenowknowofothermechanismsofevolution includinggeneticdriftandmutation butnaturalselectionistheonlymechanismcapableofproducingadaptation NaturalSelectionwasnotimmediatelyaccepted ittookuntilthe1930sforDarwin sideastobesynthesizedwithamodernunderstandingofgeneticsforwidespreadacceptance Intellectualstepping stonestodevelopingatheoryofevolution LinnaeusandTaxonomyMalthusandthePrincipleofPopulationLyellandUniformitarianismLamarckandthefistcomprehensivetheoryofevolutionTheVoyageoftheBeagleWallaceandDarwin LinneusandTaxonomy CarolusLinnaeuswasasixteenth centurySwedishphysicianandBotanist Hefoundedthescienceoftaxonomy thebranchofbiologyconcernedwithnamingandclassifyinglivingthings Hedevelopedthetwopartsystemofbinomialnomenclatureweusetoday Hisgenerawereclusteredintoincreasinglybroadercategories families classes phyla andkingdoms althoughhedidnotbelieveinevolutionbydescent thispatterndoesprovideaframeworkforthinkingaboutevolutionfromacommonancestor Malthus ThomasMalthus aneighteenthcenturyeconomist published AnEssayonthePrincipleofPopulation in1798 Thisdocumenthadprofoundimplications Simplystated peopletendtohavemorechildrenthancanpossiblysurvive andhumanpopulationshavehistoricallybeenkeptincheckbyfamine starvation anddisease Darwinreadthisessayandwasstronglyinfluenced henotedthateveryspecieshasmoreoffspringthancanbeexpectedtosurvive HowOldistheEarth Fromascientificstandpoint theageoftheEarthwasessentiallyunknownuntilthe19thcentury Earlyideasvariedgreatly somecultures suchasclassicalHindusociety thoughtoftheEarthasincrediblyold ChristiantheologylimitedtheageoftheEarthtoafewthousandyears becauseofthebiblicalaccountofcreationaslastingsevendays andthegeneologiesincludedinthebookofnumbers Basedupontheoldtestament theArchbishopJamesUshercalculatedthatGodcreatedtheEarthin4004BC Thisleftlittletimeforincrediblyslow gradualprocesseslikeevolution Hutton LyellandUniformitarianism TheEnglishgeologist JamesHuttonproposedthatitwaspossibletoexplaingeologicallandformationsbyprocessesthatarecurrentlyinoperation suchaserosionandsedimentation Canyonswerecutbytheerosionofstreams layersofsedimentweredepositedattheedgeofriverdeltas theseprocessesoccurredslowlyoveraverylongtime thisideawascalledgradualism TheEnglishgeologist CharlesLyellwasacontemporaryofDarwin s HewasaproponentofHutton andwentabitfarther embracingtheprincipaluniformitarianism theideathatgeologicalprocessesinoperationnowoperatedsimilarlyinthepast ataboutthesamerate TheUniformitarianviewofnature requiresvastamountsoftimetoexplainthepresentstateoftheEarth JeanBaptisteLamarck JeanBaptistedeLamarkdevelopedthefirstcomprehensivemodelofevolution LamarckwasaFrenchZoologist curatoroftheinvertebratecollectionattheParismuseum Lamarcksawmanydifferentlinesofdescentamongthefossilinvertebratesheencountered insteadofAristotle ssinglescalanatura thereweremany Heproposedthatorganismsincreasedincomplexitythroughtimebecauseofaninnatetendency Lamarckproposedthatinteractionsoforganismsandenvironmentdrovetheprocessofevolution Hefollowedthewidelyacceptednotionthatcharacteristicsacquiredduringanindividual slifetimecouldbepassedtoone soffspring Heproposedthatpatternsofuseanddisusedrovetheevolutionofadaptations Instretchingtheirneckstoreachleaveshighinthetreetop giraffesacquiredslightlylongernecks andpassedtheselongerneckstotheiroffspring AccordingtoLamarck everyorganismwascontinuallystrivingforgreatercomplexity aclamstrovetobeabetterclam etc Lamarckianevolutioncanbedisprovedbyexperiment specifically wenowknowthatacquiredcharacterscannotbepassedtooffspring also evolutioncarriesnoinnatetendencytowardincreasingcomplexity butLamarck stheorywasanimportantpreludetoDarwin s itopenedthedoortothinkingthatorganismscananddochangeoverthecourseoftime TheVoyageoftheBeagle MuchofCharlesDarwin sinspirationforhistheoryofevolutionbynaturalselectioncamefromhisvoyageontheHMSBeagle in1831 Hesawanincrediblediversityofspecies withadaptationstoawidevarietyofenvironments Brazilianrainforests Chileandeserts oceanicislands etc TheGalapagosislandsparticularlyimpressedhim mostofthespeciestherelivenowhereelseintheworld yettheirclosestlivingrelativeisonthemainlandafewhundredmilesaway Hewastospendthenext27yearsdevelopingatheorytoexplainwhathesaw DarwinandWallace AlfredRussellWallace anineteenthcenturynaturalistandexplorer anexpertoncollectingspecimensforresaleinEurope developedessentiallythesametheoryofevolutionbynaturalselectionasDarwin Anactiveman hesatdowntowriteitrecoveringfromaboutofmalaria whenhewasunabletogooutandexplore Thetwosharedcreditforthediscovery arareexampleofdiplomacyin19thcenturyscience Darwinisbetterknowntoday becauseheamassedaconsiderableamountofevidencetosupporthisideas Wallace sargumentsweremoreintuitiveandcontainedaless extensivebatteryofexamples Darwinhadspentmuchofhislifeamassingtheevidenceheneededtosupporthismodelofevolution HewasfinallygoadedintopublishingwhenhecameacrossamanuscriptbyWallacewhichcontainedmanyofthesameideas Boththeorieshadverybroadimplications forcingEuropeanintellectualstore examinetheirplaceinnature Byproposingamechanismfortheevolutionofthehumanspecies itsmind anditsachievements thatisnotsupernatural itremovedtheneedforadivine primemover fromscience Suchacreator or primemover hadbeenanelementofWesternscience sinceRomantimesorearlier andhadbeenremovedfromphysicsandastronomycenturiesearlier 1859 TheOriginofSpecies Darwin smanuscriptcontainedseveralnewideas ideasnotfoundinearliernotionsofevolution Allspeciesevolvedfromearlierspecies Themechanismisnaturalselection membersofaspeciespossessingmoredesirabletraitswillhavemoreoffspringandsurvivetoreproductivematurity Evolutionoccursoveraverylongspanoftime TheOriginofSpeciesmakesthisargument structuredlogically AllorganismsproducemoreoffspringthancanpossiblysurviveAllorganismsvaryforawidevarietyofdifferentattributesandfeatures theyalsovaryinreproductivesuccess somehavemoreoffspringthanothers Somevariationisheritable SomeofthisvariationmustinfluencereproductivesuccessGiventhattheabovearetrue desirablecharacteristicswillthusbepreferentiallypassedtooffspringThisisalogicalconclusionofthefirstfourpointsDarwinconcluded baseduponintuitivegrounds that overvastspansoftime presentdayspecieshavedescendedfromacommonancestor Thebookcontainednomechanismforspeciation however EvidenceforEvolution Thegradualevolutionoflifeontheplanet andtheirdescentfromacommonancestor isafact Darwin stheoryofevolutionisacomprehensivebodyofevolutionthatattemptstoexplainhowthisoccurred Oneofthehallmarksofatrulyrevolutionaryscientifictheoryisthatitbringstogethermanypreviouslyunexplainedpatternsunderasinglebodyoftheory LikeNewton stheoryofuniversalgravitation Darwin stheoryofevolutioncreatedanewscientificparadigm Someoftheoriginalevidenceforevolution EmbryologyVestigialandHomologousstructuresBiogeographyTheFossilRecord Embryology Closelyrelatedspeciesgothroughsimilarstagesofdevelopment althoughtheadultsmaynotresembleeachotherveryclosely Forinstance allvertebrateembryosdevelopgillpouchesatsomestage eventhoughinmanyspecies theyarelostlater Thisissuggestiveofacommonoriginforvertebrates Embryologicaldevelopmentisoftensuggestiveofevolution birdshavemanydevelopmentalfeaturesincommonwithreptilianancestors landvertebrateembryoshavemanyfeaturessuggestiveofanaquaticexistence gillpouches anotochord blocksofsegmentedmuscle SnakeChickenPossumCatBatHuman VestigialStructures Manyspeciesretainstructuresthatonlymakesenseinlightoftheirancestry Thesestructuresaretypicallyreducedandnonfunctional buttheyareinheritedfromancestors inwhomtheywereimportanttosurvivalorreproduction Ifmembersofataxonomicunitshareacommonancestry itisreflectedintheirdevelopment Twoofthemanyexamples limbbuddevelopmentinwhalesextraembryonicmembranesoftheamnioteegg ComparativeDevelopmentandEmbryology HomologousStructures Closelyrelatedspeciesfrequentlyhavehomologousstructures structuresthataresimilarintheirfundamentallayoutandconstruction althoughtheymayserveverydifferentpurposes Forexample theforelimbsofmammalsareconstructedfromthesameskeletalelements Thewingsofabat awhale ahuman adog etc allcontainthesamebones despitetheirdifferentuses Thissuggeststhatcommonancestry ratherthandesign playsaroleintheconstructionofspecies TheFossilRecord Thesuccessionofformsinthefossilrecordclearlysuggeststhatorganismschangethroughtime andhavedescendedfromacommonancestor Differentgroupsappearinthefossilrecordatdifferenttimes withageneraltrendtowardthesimplestorganismsappearingtheearliest thisisatoddswiththeviewthattheywereallcreatedatthesametime Manyformshavegoneextinct anotherobservationthatisatoddswiththeviewthateachspecieswasspeciallycreatedforapurpose Insomecases adirectlineofdescent andchangethroughtime canbeobservedinfossils Foraminifera smalloceanicprotozoans leaveacontinuousfossilrecordinoceanicsediments Itispossibletotracetheirgradualevolutionovermillionsofyears SinceDarwin sday ourknowledgefossilrecordhasimprovedtremendously wecantracetheevolutionofmanydifferentgroupsthroughfossils horses forinstance haveasuperbfossilrecord showingmanyinstancesofspeciationandmanyintervalsofevolutionarychange Example Whaleshaveanexcellentfossilrecord showingtransitionalforms Biogeography Thedistributionoflivingplantsandanimalssuggeststhatorganismsadaptedtooneenvironmentcaninvadeanewenvironment anddevelopspecificadaptationstothenewconditions OntheHMSBeagle DarwinnotedthatinSouthAmerica temperatespeciestendedtoresembletheirSouthAmericantropicalrelatives ratherthantemperatespeciesinEurope OntheGalapagos mostspecieshadarecognizableancestorfromthecoastofEcuador butspeciestherehadnumerousadaptationsspecifictotheclimateoftheIslands Wallaceobservedthesamepatterninmanydifferentpartsoftheworld ModernEvidence SinceDarwin stime therehavebeenhundredsofstudiesofevolution Naturalselectionhasbeenmeasuredinmanyorganismsinthefield andinlaboratorypopulations Anunderstandingofevolutionhasalsobecomeimportanttocombatingdisease Example DDTresistanceinmosquitoes ThemisuseofDDT andthere emergenceofmalariaasanimportanthumanpathogen isperhapsoneofthegreatestpublichealthfailuresofthecenturyitcouldpossiblyhavebeenpreventediftheevolutionofmosquitoeshadbeentakenintoaccount Innonresistantinsects DDTisaveryeffectiveinsecticide causingmassivemortalityandverystrongselectivepressureinfavorofanymutationthatmightleadtoresistanceIndiscriminatespraying whentherewasnoparticularneedtocontroltheorganism ledtotherapidevolutionofpesticideresistance FiveAnophelesspecieswerere