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Transcript
TheoryofEvolution Chapter15 CharlesDarwinandNaturalSelection • Englishscientist(1809-1882) • Ideassupportedbyfossilevidence • Moderntheoryofevolutionisfundamental conceptinbiology • Evolution–changeinpopulationsovertime FossilsShapeIdeasAboutEvolution • Havebeenusedsincethe18thcentury • Formedthebasisofearlyevolutionary concepts • Evenbeforegeologistprovidedtheevidence thatEarthwasolderthanoriginally,thought biologistssuspectedthatspecieschangeover time DarwinonHMSBeagle • Begandevelopingtheoryofevolutionin1831atage22 – TookajobasanaturalistontheHMSBeagle – Sailedaroundtheworldona5yearscientificjourney – Studiedandcollectedbiologicalandfossilspecimensateveryport – Thismadehimcuriousaboutpossiblerelationshipsamongspecies – Thisprovidedfoundationforhistheoryofevolutionbynatural selection DarwinintheGalapagos • GalapagosIslands–groupofsmallislands neartheequatorabout1000kmofftheWest CoastofSouthAmerica – speciescollectedherewereuniquetotheisland butsimilartospecieselsewhere – ledtoDarwinconsideringthepossibilitythat specieschangeovertime DarwinContinuesHisStudies • Darwinworkedfornext2decadesrefiningthis explanation • ThomasMalthus(economist)-proposedhuman populationsgrowfasterthanEarth'sfoodsupply DarwinContinuesHisStudies • Darwinmodifiedthisideaanduseditinhis explanation – How?? • Manyspeciesproducedlargenumbersofoffspring • Thatsuchspecieshadnotoverrunearth • Individualsstruggletocompeteinchanging environmentalconditions DarwinContinuesHisStudies • Gainedinsightintomechanismthatdetermines whichorganismssurviveinnature – pigeonbreedingexperiments • Observedthatthetraitsofindividualsvariedin populations • Variationsaretheninherited • Breedingpigeonswithdesirablevariationsproduce offspringwiththesevariations DarwinContinuesHisStudies • Artificialselection–breedingorganismswith specifictraitsinordertoproduceoffspring withidenticaltraits – Darwinhypothesizedthattherewasaforcein naturethatworkedlikeartificialselection DarwinExplainsNaturalSelection • Naturalselection–mechanismforchangein populations – occurswhenorganismswithfavorablevariations survive,reproduce,andpasstheirvariationstothe nextgeneration – organismswithoutthesevariationsarelesslikely tosurviveandreproduce – resultsineachgenerationconsistinglargelyof offspringfromparentswiththesevariations DarwinContinuesHisStudies • Notonlyonetorecognizethesignificanceofnatural selection • RussellWallace(Britishnaturalist)studiedonislands nearIndonesiaandreachedasimilarconclusion – wrotetoDarwintosharehisideas – theysharedtheirsimilarideasjointlytothescientific community DarwinContinuesHisStudies • Darwinpublishedfirstbookaboutevolution– OnTheOriginofSpeciesByMeansofNatural Selection,1859 InterpretingEvidenceAfterDarwin • Volumesofdatahavebeengatheredasevidencefor evolution – Subjecttointerpretationbydifferentscientists • Oneissueisthatevolutionaryprocessesaredifficult forhumanstoobservedirectly – Shortscaleofhumanlifespansmakeitdifficultto comprehendevolutionaryprocessesoccurringover millionsofyears InterpretingEvidenceAfterDarwin • Almostalloftoday'sbiologistaccepttheoryof evolutionbynaturalselection • Adventofgeneticshasaddedmoredata Adaptations:EvidenceforEvolution • Adaptation–anyvariationthataidsan organismschancesofsurvivalinits environment – Structuraladaptationsariseovertime • Mimicry–structuraladaptationthatenables onespeciestoresembleanotherspecies – Example–harmlessspecieshasadaptationthat resultinphysicalresemblancetoaharmfulspecies (fliesthatresembleawasp) Adaptations:evidenceforevolution • Camouflage–anadaptationthatenables speciestoblendwiththeirsurroundings – Example-leaffrogsblendwiththeirsurroundings • Physiologicaladaptations–changesin organismsmetabolicprocesses – Example-bacteriaresistanttoantibiotics Fossils • Providerecordofearlylife • Providerecordofevolutionaryhistory • Foundthroughouttheworld Anatomy • Homologousstructures–structuralfeatureswithacommon evolutionaryorigin – Canbesimilarinarrangement,infunction,orboth • Analogousstructures–bodypartsoforganismsthatdonothavea commonevolutionaryoriginbutaresimilarinfunction • Vestigialstructure–bodystructureinpresent-dayorganismthatno longerservesitsoriginalpurpose – Structurebecomesvestigialwhenthespeciesnolongerneedsthe featureforitsoriginalfunction – Yetitisstillinheritedaspartofthebodyplan Embryology • Embryo–earlieststageofgrowthanddevelopment ofbothplantsandanimals – Example–fish,reptile,bird,andmammalembryos shownbelowallhaveatailandpharyngealpouches • fish–pouchesdevelopintogills • mammals,reptiles,birds–developintopartsofears,jaws,and throat – Thissharedfeaturesuggestevolutionfromadistant, commonancestor Biochemistry • ShareDNA,ATP,andotherenzymes • Organismsthatarebiochemicallysimilarhave fewerdifferencesintheiraminoacid sequences MechanismsofEvolution PopulationGeneticsandEvolution • Darwinknewnothingofgeneswhenhe developedhistheoryofnaturalselection – Geneticinformationwasusedtoexplainthe variationamongindividualsofpopulations • Populationgenetics–studyofcomplex behaviorofgeneswithinpopulationsofplants andanimals Populations,NotIndividuals,Evolve • Genepool–alloftheallelesinapopulation's genes • Allelicfrequency–percentageofanyspecific alleleinapopulation'sgenepool • Geneticequilibrium–conditioninwhichthe frequencyofallelesinapopulationremains thesameovergenerations ChangesinGeneticEquilibrium • Populationingeneticequilibriumisnotevolving – Allelicfrequenciesremainsame – Phenotypesremainssame – Anyfactoraffectinggenesinthegenepoolcanchange allelicfrequencydisruptingpopulationsgenetic equilibrium ChangesinGeneticEquilibrium • Geneticdrift–alterationofallelicfrequencies bychanceevents – Cangreatlyaffectsmallpopulations – Hasbeenobservedinsmallhumanpopulations thathavebecomeisolated • Geneflow–transportofgenesbymigrating individuals NaturalSelectionActsonVariations • Stabilizingselection–naturalselectionthat favorsaverageindividualsinapopulation • Directionalselection–occurswhennatural selectionfavorsoneoftheextremevariations ofatrait • Disruptiveselection–individualswitheither extremeofthetraitsvariationareselectedfor EvolutionofSpecies • Speciation–processofevolutionofnew speciesthatoccurswhenmembersofsimilar populationsnolongerinterbreedtoproduce fertileoffspringwithintheirnatural environment Physicalbarriers • Canpreventinterbreeding • Geographicisolation–occurswhenevera physicalbarrierdividesapopulation,which resultsinindividualsnolongerbeingableto mate – canleadtotheformationofanewspecies ReproductiveIsolation • Canresultinspeciation • Occurswhenformerlyinterbreedingorganisms cannolongermateandproducefertile offspring • Differenttypes- – Geneticmaterialbecomessodifferentthat fertilizationcannotoccur – Behavioralreproductiveisolationsuchasmating duringdifferenttimesofyear ChangeinChromosomeNumbersandSpeciation • Polyploidy–anyspecieswithmultiplesetsof thenormalsetofchromosomes – Resultsfromerrorsduringmitosisormeiosis – Canarisefromwithinaspeciesorfrom hybridizationbetweenspecies Speciationrates • Gradualism–ideathatspeciesoriginatethrougha gradualchangeofadaptations – Example–fossilevidenceshowsthatsealiliesofslowly andsteadilyovertime • Punctuatedequilibrium–ideathatperiodsof speciationoccurrelativelyquicklywithlongperiods ofgeneticequilibriuminbetween – HypothesisproposedbyEldredgeandGould – Arguesthatspeciationoccursinquickrapidbursts – Example-environmentalchangesleadstopunctuated equilibrium Patternsofevolution • Adaptiveradiation–divergentevolutioninwhich ancestralspeciesevolveintoanarrayofspeciestofita numberofdiversehabitats • Divergentevolution–evolutioninwhichspeciesthat onceweresimilartoanancestralspeciesdiverge – occurswhenpopulationschangeastheyadapttodifferent environmentalconditions – eventuallyresultsinnewspecies • Convergentevolution–evolutioninwhichdistantly relatedorganismsevolvesimilartraits – occurswhenunrelatedspeciesoccupysimilarenvironments
