抗生素英文課件-Evidence-for-Evolution

EvidenceforEvolutionReading:Freeman,Chapter23,26EvidenceforEvolutionReading:1TheFactofEvolutionEvolution-theprogressivechangeoforganismsastheydescendfromancestralspecies-isafact.Bynow,theevidenceforitisoverwhelmingandubiquitous.Itisofsuchobviousclinicalsignificanceinmedicinethattodenyitisirresponsible.Thatsaid,anyexplanationforitsexistenceandmodeofactionisascientifictheory,whichmustbetestableand,intheory,falsifiable.Darwin’stheoryofnaturalselection,combinedwithothermechanismsofevolutiondiscoveredsinceDarwin,formwhatisknownasthe“modernsynthesis”,thecurrentscientificparadigminthebiologicalsciences.Itprovidesacentralexplanationforphenomenainsuchdiversefieldsaspaleontologyanddevelopmentalbiology,medicineandpsychology.TheFactofEvolution2Theexistenceofevolutionhasbeenproposedseveraltimesinhistory.Forinstance,theancientGreekscientist,Animaxander,proposedatheoryofevolution.Intermsofmodernscience,itwasfirstadvancedproposedinthelate1700’sandearly1800sbyseveralscientistsincludingComptedeBuffonandErasmusDarwin.Theideaofevolutionremainedcontroversialforalongtime,partiallybecauseitrancontrarytocontemporaryreligiousideasandpartiallybecausenomechanismforevolutionwasknown.DarwinandWallace’stheoryofevolutionbynaturalselectionwasthefirstplausible,widely-acceptedmechanismforevolutionarychange.Bynowitiswell-tested,supportedbyhundredsofindependentscientificinvestigations.Itisalsofalsifiable-aspectsofDarwin’stheoryofevolutionhavebeensuccessfullychallenged,otherssupported.Thisisthecasefortheothermechanismsofevolutionaswell.Theexistenceofevolutionhas3ExamplesoftheclinicalsignificanceofevolutionarybiologytomedicineHIV.HIVisaretrovirusofenormousmedicalconcern.Becauseofevolutionarystudies,weknowthattwoseparatelineagesofthisretroviruspassedintothehumanpopulationfromAfricanApesinthemid20thcentury.Thisknowledgehasalertedustothedangerofemergentdiseasesfromotheranimalhosts,areasonforourconcernaboutSARSandbirdflu.Inaddition,itisanunderstandingofevolutionarybiologythathasenabledustodevelopatherapyforHIV.Theso-called“tripletherapy”HIVtreatmentisanexampleofevolutionarymedicine.Asingledrugwillnotworkagainstthediseasebecausethevirusevolvessoquickly,itattainsresistancetoeverydrugwehavewithinafewmonths.Byusingthreedrugssimultaneously,wesubverttheevolutionofthevirus…evolvingresistancetoonedrugmeansloosingresistancetoanother.Examplesoftheclinicalsigni4Antibioticresistanceisanevolutionaryphenomenonoftremendousclinicalsignificance.Earlyinthe20thcentury,avarietyofantibiotics,usedtotreatbacterialdiseases,weredeveloped.Anunderstandingofevolutionishelpfultounderstandwheretheseantibioticscomefromtobeginwith…many,suchaspenicillin,wereevolvedbyfungi,overmillionsofyears,tokillofftheirbacterialcompetitors.Humanshaveco-optedthemforourownpurposes.Sincethe20thcentury,thebacterialpathogenshaveevolvedresistancetoourantibiotics,becauseextensiveuseofthesedrugshascausedverystrongnaturalselectioninfavorofmutationswhichfavorantibioticresistance.Forinstance,variousstrainsofNeisseriagonorrheaehaveevolvedresistancetopenicillins,tetracyclines,spectinomycinandfloroquinolones.Antibioticresistanceisanev5NaturalSelectionastheMechanismofEvolution:Scientificunderstandingofevolutioncameoutofitsinfancyin1859,whentheoriesofevolutionbynaturalselectionbyCharlesDarwinandAlfredRusselWallacebecamewidelyknown.Wenowknowofothermechanismsofevolution,includinggeneticdriftandmutation,butnaturalselectionistheonlymechanismcapableofproducingadaptation.NaturalSelectionwasnotimmediatelyaccepted-ittookuntilthe1930sforDarwin’sideastobesynthesizedwithamodernunderstandingofgeneticsforwidespreadacceptance.NaturalSelectionastheMecha6Intellectualstepping-stonestodevelopingatheoryofevolutionLinnaeusandTaxonomyMalthusandthePrincipleofPopulationLyellandUniformitarianismLamarckandthefistcomprehensivetheoryofevolutionTheVoyageoftheBeagleWallaceandDarwinIntellectualstepping-stonest7LinneusandTaxonomyCarolusLinnaeuswasasixteenth-centurySwedishphysicianandBotanist.Hefoundedthescienceoftaxonomy,thebranchofbiologyconcernedwithnamingandclassifyinglivingthings.Hedevelopedthetwopartsystemofbinomialnomenclatureweusetoday.Hisgenerawereclusteredintoincreasinglybroadercategories;families,classes,phyla,andkingdoms…althoughhedidnotbelieveinevolutionbydescent,thispatterndoesprovideaframeworkforthinkingaboutevolutionfromacommonancestor.LinneusandTaxonomyCarolusLi8MalthusThomasMalthus,aneighteenthcenturyeconomist,published“AnEssayonthePrincipleofPopulation”in1798.Thisdocumenthadprofoundimplications.

Simplystated:peopletendtohavemorechildrenthancanpossiblysurvive,andhumanpopulationshavehistoricallybeenkeptincheckbyfamine,starvation,anddisease.Darwinreadthisessayandwasstronglyinfluenced:henotedthateveryspecieshasmoreoffspringthancanbeexpectedtosurvive.MalthusThomasMalthus,aneigh9HowOldistheEarth?Fromascientificstandpoint,theageoftheEarthwasessentiallyunknownuntilthe19thcentury.Earlyideasvariedgreatly,somecultures,suchasclassicalHindusociety,thoughtoftheEarthasincrediblyold.ChristiantheologylimitedtheageoftheEarthtoafewthousandyears,becauseofthebiblicalaccountofcreationaslastingsevendays,andthegeneologiesincludedinthebookofnumbers..Basedupontheoldtestament,theArchbishopJamesUshercalculatedthatGodcreatedtheEarthin4004BC.Thisleftlittletimeforincrediblyslow,gradualprocesseslikeevolution...HowOldistheEarth?Fromasc10Hutton,LyellandUniformitarianismTheEnglishgeologist,JamesHuttonproposedthatitwaspossibletoexplaingeologicallandformationsbyprocessesthatarecurrentlyinoperation,suchaserosionandsedimentation.Canyonswerecutbytheerosionofstreams,layersofsedimentweredepositedattheedgeofriverdeltas,theseprocessesoccurredslowlyoveraverylongtime-thisideawascalledgradualism.Hutton,LyellandUniformitari11TheEnglishgeologist,CharlesLyellwasacontemporaryofDarwin’s.HewasaproponentofHutton,andwentabitfarther,embracingtheprincipaluniformitarianism-theideathatgeologicalprocessesinoperationnowoperatedsimilarlyinthepast,ataboutthesamerate.TheUniformitarianviewofnature,requiresvastamountsoftimetoexplainthepresentstateoftheEarth.

TheEnglishgeologist,Charles12JeanBaptisteLamarckJeanBaptistedeLamarkdevelopedthefirstcomprehensivemodelofevolution.LamarckwasaFrenchZoologist,curatoroftheinvertebratecollectionattheParismuseum.Lamarcksawmanydifferentlinesofdescentamongthefossilinvertebratesheencountered:insteadofAristotle’ssinglescalanatura,thereweremany.Heproposedthatorganismsincreasedincomplexitythroughtimebecauseofaninnatetendency.JeanBaptisteLamarckJeanBapt13Lamarckproposedthatinteractionsoforganismsandenvironmentdrovetheprocessofevolution.Hefollowedthewidelyacceptednotionthatcharacteristicsacquiredduringanindividual’slifetimecouldbepassedtoone’soffspring.Heproposedthatpatternsofuseanddisusedrovetheevolutionofadaptations.Instretchingtheirneckstoreachleaveshighinthetreetop,giraffesacquiredslightlylongernecks,andpassedtheselongerneckstotheiroffspring.Lamarckproposedthatinteract14AccordingtoLamarck,everyorganismwascontinuallystrivingforgreatercomplexity,aclamstrovetobeabetterclam,etc.Lamarckianevolutioncanbedisprovedbyexperiment,specifically,wenowknowthatacquiredcharacterscannotbepassedtooffspring,also,evolutioncarriesnoinnatetendencytowardincreasingcomplexity,butLamarck’stheorywasanimportantpreludetoDarwin’s,itopenedthedoortothinkingthatorganismscananddochangeoverthecourseoftime.AccordingtoLamarck,everyor15TheVoyageoftheBeagleMuchofCharlesDarwin’sinspirationforhistheoryofevolutionbynaturalselectioncamefromhisvoyageontheHMSBeagle,in1831.Hesawanincrediblediversityofspecies,withadaptationstoawidevarietyofenvironments;Brazilianrainforests,Chileandeserts,oceanicislands,etc.TheGalapagosislandsparticularlyimpressedhim;mostofthespeciestherelivenowhereelseintheworld,yettheirclosestlivingrelativeisonthemainlandafewhundredmilesaway.Hewastospendthenext27yearsdevelopingatheorytoexplainwhathesaw.TheVoyageoftheBeagleMucho16DarwinandWallaceAlfredRussellWallace,anineteenthcenturynaturalistandexplorer,anexpertoncollectingspecimensforresaleinEurope,developedessentiallythesametheoryofevolutionbynaturalselectionasDarwin.Anactiveman,hesatdowntowriteitrecoveringfromaboutofmalaria,whenhewasunabletogooutandexplore.Thetwosharedcreditforthediscovery,arareexampleofdiplomacyin19thcenturyscience.Darwinisbetterknowntoday,becauseheamassedaconsiderableamountofevidencetosupporthisideas.Wallace’sargumentsweremoreintuitiveandcontainedaless-extensivebatteryofexamples.DarwinandWallaceAlfredRusse17Darwinhadspentmuchofhislifeamassingtheevidenceheneededtosupporthismodelofevolution.HewasfinallygoadedintopublishingwhenhecameacrossamanuscriptbyWallacewhichcontainedmanyofthesameideas.Boththeorieshadverybroadimplications,forcingEuropeanintellectualstore-examinetheirplaceinnature.Byproposingamechanismfortheevolutionofthehumanspecies,itsmind,anditsachievements,thatisnotsupernatural,itremovedtheneedforadivine“primemover”fromscience.Suchacreator,or“primemover”hadbeenanelementofWesternscience,sinceRomantimesorearlier,andhadbeenremovedfromphysicsandastronomycenturiesearlier.Darwinhadspentmuchofhisl181859:TheOriginofSpeciesDarwin’smanuscriptcontainedseveralnewideas,ideasnotfoundinearliernotionsofevolution;Allspeciesevolvedfromearlierspecies.Themechanismisnaturalselection;membersofaspeciespossessingmoredesirabletraitswillhavemoreoffspringandsurvivetoreproductivematurity.Evolutionoccursoveraverylongspanoftime.1859:TheOriginofSpeciesDar19TheOriginofSpeciesmakesthisargument,structuredlogically…AllorganismsproducemoreoffspringthancanpossiblysurviveAllorganismsvaryforawidevarietyofdifferentattributesandfeatures-theyalsovaryinreproductivesuccess:somehavemoreoffspringthanothers.Somevariationisheritable.SomeofthisvariationmustinfluencereproductivesuccessGiventhattheabovearetrue…desirablecharacteristicswillthusbepreferentiallypassedtooffspringThisisalogicalconclusionofthefirstfourpoints

Darwinconcluded,baseduponintuitivegrounds,that,overvastspansoftime,presentdayspecieshavedescendedfromacommonancestor.Thebookcontainednomechanismforspeciation,however.TheOriginofSpeciesmakesth20EvidenceforEvolutionThegradualevolutionoflifeontheplanet,andtheirdescentfromacommonancestor,isafact.Darwin’stheoryofevolutionisacomprehensivebodyofevolutionthatattemptstoexplainhowthisoccurred.Oneofthehallmarksofatrulyrevolutionaryscientifictheoryisthatitbringstogethermanypreviouslyunexplainedpatternsunderasinglebodyoftheory.LikeNewton’stheoryofuniversalgravitation,Darwin’stheoryofevolutioncreatedanewscientificparadigm.EvidenceforEvolutionThegrad21Someoftheoriginalevidenceforevolution:EmbryologyVestigialandHomologousstructuresBiogeographyTheFossilRecordSomeoftheoriginalevidence22EmbryologyCloselyrelatedspeciesgothroughsimilarstagesofdevelopment,althoughtheadultsmaynotresembleeachotherveryclosely.Forinstance,allvertebrateembryosdevelopgillpouchesatsomestage,eventhoughinmanyspecies,theyarelostlater.Thisissuggestiveofacommonoriginforvertebrates.Embryologicaldevelopmentisoftensuggestiveofevolution:birdshavemanydevelopmentalfeaturesincommonwithreptilianancestors,landvertebrateembryoshavemanyfeaturessuggestiveofanaquaticexistence(gillpouches,anotochord,blocksofsegmentedmuscle).EmbryologyCloselyrelatedspec23Snake Chicken Possum Cat Bat HumanSnake Chicken Possum Cat Bat 24VestigialStructuresManyspeciesretainstructuresthatonlymakesenseinlightoftheirancestry.Thesestructuresaretypicallyreducedandnonfunctional,buttheyareinheritedfromancestors,inwhomtheywereimportanttosurvivalorreproductionVestigialStructuresManyspeci25抗生素英文課件——Evidence-for-Evolution26Ifmembersofataxonomicunitshareacommonancestry,itisreflectedintheirdevelopment:Twoofthemanyexamples:limbbuddevelopmentinwhalesextraembryonicmembranesoftheamnioteeggComparativeDevelopmentandEmbryologyIfmembersofataxonomicunit27抗生素英文課件——Evidence-for-Evolution28抗生素英文課件——Evidence-for-Evolution29抗生素英文課件——Evidence-for-Evolution30HomologousStructuresCloselyrelatedspeciesfrequentlyhavehomologousstructures:structuresthataresimilarintheirfundamentallayoutandconstruction,althoughtheymayserveverydifferentpurposes.Forexample,theforelimbsofmammalsareconstructedfromthesameskeletalelements:Thewingsofabat,awhale,ahuman,adog,etc.allcontainthesamebones,despitetheirdifferentuses.Thissuggeststhatcommonancestry,ratherthandesign,playsaroleintheconstructionofspecies.HomologousStructuresCloselyr31抗生素英文課件——Evidence-for-Evolution32TheFossilRecordThesuccessionofformsinthefossilrecordclearlysuggeststhatorganismschangethroughtime,andhavedescendedfromacommonancestor.Differentgroupsappearinthefossilrecordatdifferenttimes,withageneraltrendtowardthesimplestorganismsappearingtheearliest..thisisatoddswiththeviewthattheywereallcreatedatthesametime.Manyformshavegoneextinct,anotherobservationthatisatoddswiththeviewthateachspecieswasspeciallycreatedforapurpose.TheFossilRecordThesuccessio33Insomecases,adirectlineofdescent,andchangethroughtime,canbeobservedinfossils.Foraminifera,smalloceanicprotozoans,leaveacontinuousfossilrecordinoceanicsediments.Itispossibletotracetheirgradualevolutionovermillionsofyears.SinceDarwin’sday,ourknowledgefossilrecordhasimprovedtremendously,wecantracetheevolutionofmanydifferentgroupsthroughfossils:horses,forinstance,haveasuperbfossilrecord,showingmanyinstancesofspeciationandmanyintervalsofevolutionarychange.Insomecases,adirectlineo34Example-Whaleshaveanexcellentfossilrecord-showingtransitionalformsExample-Whaleshave35BiogeographyThedistributionoflivingplantsandanimalssuggeststhatorganismsadaptedtooneenvironmentcaninvadeanewenvironment,anddevelopspecificadaptationstothenewconditions.OntheHMSBeagle,DarwinnotedthatinSouthAmerica,temperatespeciestendedtoresembletheirSouthAmericantropicalrelatives,ratherthantemperatespeciesinEurope.OntheGalapagos,mostspecieshadarecognizableancestorfromthecoastofEcuador,butspeciestherehadnumerousadaptationsspecifictotheclimateoftheIslands.Wallaceobservedthesamepatterninmanydifferentpartsoftheworld.BiogeographyThedistributiono36抗生素英文課件——Evidence-for-Evolution37ModernEvidenceSinceDarwin’stime,therehavebeenhundredsofstudiesofevolution.Naturalselectionhasbeenmeasuredinmanyorganismsinthefield,andinlaboratorypopulations.Anunderstandingofevolutionhasalsobecomeimportanttocombatingdisease.ModernEvidenceSinceDarwin’s38Example-DDTresistanceinmosquitoesThemisuseofDDT,andthere-emergenceofmalariaasanimportanthumanpathogen,isperhapsoneofthegreatestpublichealthfailuresofthecenturyitcouldpossiblyhavebeenpreventediftheevolutionofmosquitoeshadbeentakenintoaccountExample-DDTresistanceinmosq39Innonresistantinsects,DDTisaveryeffectiveinsecticide-causingmassivemortalityandverystrongselectivepressureinfavorofanymutationthatmightleadtoresistanceIndiscriminatespraying(whentherewasnoparticularneedtocontroltheorganism)ledtotherapidevolutionofpesticideresistance.FiveAnophelesspecieswereresistantby1956and38by1968.Innonresistantinsects,DDTi40Resistancetakesmanyforms-someofthisgeneticvariationwasprobablypresentinthemosquitopopulationbeforetheuseofDDT,butintheabsenceofDDT,thesevariantsareselectedagainst.1)Chemicaladaptation:enzymesevolvethatbreakdownthepesticide.2)Behavioraladaptation:Theyevolvedtomovefrominner,sprayedwallstoouter,unsprayedwalls.Theyevolvedsensitivityandavoidthepesticide.Resistancetakesmanyforms-so41ThesedataarefromBangkok-theRalleleisresistant,the+alleleisnot.

Notethatthe+allelebecomesmorecommonintheabsenceofDDTsprayingThesedataarefromBangkok-th42AdaptationNaturalSelectionasthemechanismforadaptationwasDarwin’smostimportantcontribution.Thereareotherforcesofevolution(mostofwhichwerediscoveredafterDarwin),butnaturalselectionistheonlyevolutionarymechanismthatcanproduceadaptation.Someexamplesofadaptationareveryimpressive.AdaptationNaturalSelectionas43FindthemantisinthispictureFindthemantisinthispictur44TheVariationProblemForNaturalSelectiontobeeffective,theremustbegeneticvariationuponwhichselectionacts.Darwindiscussedtheoriginofvariationsextensivelyin“OntheOriginofSpecies..”,buthedidnotknowhowvariationpersists.AlthoughhewasacontemporaryofMendel’s,DarwindidnotknowMendeliangenetics(hisworkwasnotwellunderstoodatthetime).Thecurrenttheoryofgenetics,blendinginheritance,suggestedthatusefuladaptationswouldblendintothepopulationandbecomediluted.TheVariationProblemForNatur45ThesynthesisofDarwin’stheorywithMendeliangeneticsledtoourmodernunderstandingofEvolution.Severalearlytwentiethcenturyevolutionarybiologistsarewidelycreditedwithdevelopingourmodernunderstanding:R.A.FisherJ.B.S.HaldaneSewallWrightTheodosiusDobzhanskiThomasHuntMorganThesynthesisofDarwin’stheo46EvidenceforEvolutionReading:Freeman,Chapter23,26EvidenceforEvolutionReading:47TheFactofEvolutionEvolution-theprogressivechangeoforganismsastheydescendfromancestralspecies-isafact.Bynow,theevidenceforitisoverwhelmingandubiquitous.Itisofsuchobviousclinicalsignificanceinmedicinethattodenyitisirresponsible.Thatsaid,anyexplanationforitsexistenceandmodeofactionisascientifictheory,whichmustbetestableand,intheory,falsifiable.Darwin’stheoryofnaturalselection,combinedwithothermechanismsofevolutiondiscoveredsinceDarwin,formwhatisknownasthe“modernsynthesis”,thecurrentscientificparadigminthebiologicalsciences.Itprovidesacentralexplanationforphenomenainsuchdiversefieldsaspaleontologyanddevelopmentalbiology,medicineandpsychology.TheFactofEvolution48Theexistenceofevolutionhasbeenproposedseveraltimesinhistory.Forinstance,theancientGreekscientist,Animaxander,proposedatheoryofevolution.Intermsofmodernscience,itwasfirstadvancedproposedinthelate1700’sandearly1800sbyseveralscientistsincludingComptedeBuffonandErasmusDarwin.Theideaofevolutionremainedcontroversialforalongtime,partiallybecauseitrancontrarytocontemporaryreligiousideasandpartiallybecausenomechanismforevolutionwasknown.DarwinandWallace’stheoryofevolutionbynaturalselectionwasthefirstplausible,widely-acceptedmechanismforevolutionarychange.Bynowitiswell-tested,supportedbyhundredsofindependentscientificinvestigations.Itisalsofalsifiable-aspectsofDarwin’stheoryofevolutionhavebeensuccessfullychallenged,otherssupported.Thisisthecasefortheothermechanismsofevolutionaswell.Theexistenceofevolutionhas49ExamplesoftheclinicalsignificanceofevolutionarybiologytomedicineHIV.HIVisaretrovirusofenormousmedicalconcern.Becauseofevolutionarystudies,weknowthattwoseparatelineagesofthisretroviruspassedintothehumanpopulationfromAfricanApesinthemid20thcentury.Thisknowledgehasalertedustothedangerofemergentdiseasesfromotheranimalhosts,areasonforourconcernaboutSARSandbirdflu.Inaddition,itisanunderstandingofevolutionarybiologythathasenabledustodevelopatherapyforHIV.Theso-called“tripletherapy”HIVtreatmentisanexampleofevolutionarymedicine.Asingledrugwillnotworkagainstthediseasebecausethevirusevolvessoquickly,itattainsresistancetoeverydrugwehavewithinafewmonths.Byusingthreedrugssimultaneously,wesubverttheevolutionofthevirus…evolvingresistancetoonedrugmeansloosingresistancetoanother.Examplesoftheclinicalsigni50Antibioticresistanceisanevolutionaryphenomenonoftremendousclinicalsignificance.Earlyinthe20thcentury,avarietyofantibiotics,usedtotreatbacterialdiseases,weredeveloped.Anunderstandingofevolutionishelpfultounderstandwheretheseantibioticscomefromtobeginwith…many,suchaspenicillin,wereevolvedbyfungi,overmillionsofyears,tokillofftheirbacterialcompetitors.Humanshaveco-optedthemforourownpurposes.Sincethe20thcentury,thebacterialpathogenshaveevolvedresistancetoourantibiotics,becauseextensiveuseofthesedrugshascausedverystrongnaturalselectioninfavorofmutationswhichfavorantibioticresistance.Forinstance,variousstrainsofNeisseriagonorrheaehaveevolvedresistancetopenicillins,tetracyclines,spectinomycinandfloroquinolones.Antibioticresistanceisanev51NaturalSelectionastheMechanismofEvolution:Scientificunderstandingofevolutioncameoutofitsinfancyin1859,whentheoriesofevolutionbynaturalselectionbyCharlesDarwinandAlfredRusselWallacebecamewidelyknown.Wenowknowofothermechanismsofevolution,includinggeneticdriftandmutation,butnaturalselectionistheonlymechanismcapableofproducingadaptation.NaturalSelectionwasnotimmediatelyaccepted-ittookuntilthe1930sforDarwin’sideastobesynthesizedwithamodernunderstandingofgeneticsforwidespreadacceptance.NaturalSelectionastheMecha52Intellectualstepping-stonestodevelopingatheoryofevolutionLinnaeusandTaxonomyMalthusandthePrincipleofPopulationLyellandUniformitarianismLamarckandthefistcomprehensivetheoryofevolutionTheVoyageoftheBeagleWallaceandDarwinIntellectualstepping-stonest53LinneusandTaxonomyCarolusLinnaeuswasasixteenth-centurySwedishphysicianandBotanist.Hefoundedthescienceoftaxonomy,thebranchofbiologyconcernedwithnamingandclassifyinglivingthings.Hedevelopedthetwopartsystemofbinomialnomenclatureweusetoday.Hisgenerawereclusteredintoincreasinglybroadercategories;families,classes,phyla,andkingdoms…althoughhedidnotbelieveinevolutionbydescent,thispatterndoesprovideaframeworkforthinkingaboutevolutionfromacommonancestor.LinneusandTaxonomyCarolusLi54MalthusThomasMalthus,aneighteenthcenturyeconomist,published“AnEssayonthePrincipleofPopulation”in1798.Thisdocumenthadprofoundimplications.

Simplystated:peopletendtohavemorechildrenthancanpossiblysurvive,andhumanpopulationshavehistoricallybeenkeptincheckbyfamine,starvation,anddisease.Darwinreadthisessayandwasstronglyinfluenced:henotedthateveryspecieshasmoreoffspringthancanbeexpectedtosurvive.MalthusThomasMalthus,aneigh55HowOldistheEarth?Fromascientificstandpoint,theageoftheEarthwasessentiallyunknownuntilthe19thcentury.Earlyideasvariedgreatly,somecultures,suchasclassicalHindusociety,thoughtoftheEarthasincrediblyold.ChristiantheologylimitedtheageoftheEarthtoafewthousandyears,becauseofthebiblicalaccountofcreationaslastingsevendays,andthegeneologiesincludedinthebookofnumbers..Basedupontheoldtestament,theArchbishopJamesUshercalculatedthatGodcreatedtheEarthin4004BC.Thisleftlittletimeforincrediblyslow,gradualprocesseslikeevolution...HowOldistheEarth?Fromasc56Hutton,LyellandUniformitarianismTheEnglishgeologist,JamesHuttonproposedthatitwaspossibletoexplaingeologicallandformationsbyprocessesthatarecurrentlyinoperation,suchaserosionandsedimentation.Canyonswerecutbytheerosionofstreams,layersofsedimentweredepositedattheedgeofriverdeltas,theseprocessesoccurredslowlyoveraverylongtime-thisideawascalledgradualism.Hutton,LyellandUniformitari57TheEnglishgeologist,CharlesLyellwasacontemporaryofDarwin’s.HewasaproponentofHutton,andwentabitfarther,embracingtheprincipaluniformitarianism-theideathatgeologicalprocessesinoperationnowoperatedsimilarlyinthepast,ataboutthesamerate.TheUniformitarianviewofnature,requiresvastamountsoftimetoexplainthepresentstateoftheEarth.

TheEnglishgeologist,Charles58JeanBaptisteLamarckJeanBaptistedeLamarkdevelopedthefirstcomprehensivemodelofevolution.LamarckwasaFrenchZoologist,curatoroftheinvertebratecollectionattheParismuseum.Lamarcksawmanydifferentlinesofdescentamongthefossilinvertebratesheencountered:insteadofAristotle’ssinglescalanatura,thereweremany.Heproposedthatorganismsincreasedincomplexitythroughtimebecauseofaninnatetendency.JeanBaptisteLamarckJeanBapt59Lamarck