古生物學(xué)-演化論

IV、BiologicalevolutionandtheoreticalpaleontologyWithanintroductiontoOriginoflifeandearlybiologicalevolutionTheoryofevolutionThetermevolutionisusedtorefertotheprocessesbywhichlifehaschangedthroughthegeologicalages.Therearethousandsofvariedformsoflife.Itisestimatedthatthereareatleast4-5millionsspeciesonthepresentearth.Throughourstudy,weknowthereweremuchmorelifeinthegeologicaltime.Naturally,weshouldaskaquestion:howdidalltheselifecomefrom?CharlesDarwin（達(dá)爾文）Britishnaturalist,wasfamousbythepublicationofthebook“OriginofSpecies”(物種起源)in1859.Darwinisthefirstpersonwhoscientificallyproposedforcausesandprocessesoflifeevolution.WecalltheDarwinismforit.AfterDarwin,duetotheprogressofgenetics,theinputofpopulationgeneticsmadethetheoryofevolutionmoreimprovedandperfect.ThisiscalledastheNeo-Darwinism.JulianHuxleyAlandmarkbook:Evolution,TheModernSynthesisin1940s,themodelofevolutionassembledinthisbookbecameknownasthemodernsynthesis,orNeodarwnism.Themainpointsarefollowing:1VariationarisesfromrandomchangesinthegenesandchromosomesJulianHuxley2Selectionfavorsthesurvivalandperpetrationofparticularvariantsattheexpenseofothers3ChangeswithinevolvinglineagesresultfromthegradualaccumulationoffavorableheritablevariationsInterbreedingofindividualswithinaspeciesmaintainsagenepoolthatgiveshomogeneityandstabilitytothepopulation…MaincontentsoftheoryofevolutionBio-evolutionarymodelsandmechanismEvolutionarymodelorpattern

(演化模式)：indicatingcharactersofallevolutionaryrelationshipsEvolutionarymechanism

(演化機(jī)理)：referringtotheprocessesandfactorsoflifeevolutionThreelevelsMicroevolution

(微演化)：Itmeanstheintra-populationvariationandevolution,itisthestartingpointofevolution.Speciation

(成種作用

)：ItindicatestheprocessesofspeciesdiversificationandincreaseMacroevolution

(宏演化)：Itisusedtorefertoevolutionaryprocessesthatresultinchangesgivingrisetohighertaxonomiccategoriessuchasfamilies,orders,andclasses.MicroevolutionKeyfactorsofmicroevolutionVariability(變異)Heredity(遺傳)Naturalselection(自然選擇)1、Variation、heredityVariationindicatesdifferencesamongindividuals(age,sexarenotincluded).Darwinconsideredthatthevariationsarecorrelated,changesinsomepartofindividualcouldleadtovariationsofotherparts.Curvierproposedthatthedevelopmentofallorgansofanyindividualiscorrelated,thisiscalledthelawofcorrelation(相關(guān)律).Somevariationscouldbeheritable,someinheritable.Onlytheheritableonescouldaffecttheevolution.1、Variation、heredityVariationsarenotonlydisplayedinmorphology,butalsoininternalstructures.Thevariationscouldbeheritableduetothepresenceofhereditarymaterialbasis,thisbasisiscalledgene(基因),whichexistsinthechromosome(染色體).1、Variation、heredityTwoconceptsGeneotype

(基因型)：Sumofhereditarymaterials(gene),itisinvisible,butitistheessenceofgenetics.Phenotype

(表現(xiàn)型)：Sumofallcharacters.Thesecharactersareexternal,visible.Itisresultedfromtheinteractionbetweengeneotypeandphysicalenvironments.1、Variation、geneticsIthasbeendeterminedthatthegeneisconstitutedbynuclearacid,dominatedbydeoxyribonucleicacid(脫氧核糖核酸,DNA），thegeneisjustasectiononDNA.Thegeneiscapabletopreciselycopy(reproduce)itself,soitmaintainsthestabilityofgenetic.CausesforvariationsAccordingtothestudyofmoderngenetics,thecausesforvariationsare:(1)genereorganization(基因重組),thatis,inzoogamy(sexualreproduction),theparentchromosomesarerandomlyorganizedandtheallelicsubstitution(等位基因的交換);(2)mutation(突變)，includingthechangesofnucleotide(核苷酸)orderingene,chromosomenumberandstructure,thecausesformutationmightbetemperature,pressureandradiationrays;(3)chromosomalaberration(染色體畸變)，indicatingthechangeofchromosomalnumberandstructure.RelationshipbetweenvariationandheredityInbiologicalevolution,thevariationisacreativefactor,andtheheredityisastablefactor.Withoutvariation,organismscouldonlyproducethesamespecies,theevolutioncouldnotkeepforward;butifwithoutheredity,organismswouldbeunstable,thespecieswouldnotexistindependently,sotheevolutionwouldnotbeexisted.2、NaturalSelectionNaturalselectionactsuponinheritablevariationsthatresultindifferencesinfitnessamongindividuals—differencesthatarerelatedeithertoreproductionofthenextgenerationortosurvivaloftheindividual..Competitionbetweenindividualorganismsforresources,mates,safetyfrompredatorsandlivingroom.Somevariationsadvancedtosurvivalwouldbepreserved,theotherswouldbegivenup,thisiscalledas自然選擇。“Survivaloffittest”2、NaturalSelectionNaturalselectionisahistoricalprocess,itneedsarelativelylongtime(geologicalage).Itshouldaccumulatedthefavorablevariationforexistencethroughgenerationbygeneration(heredity).Theessenceofnaturalselectionistomakethegeneticmaterialsinpopulationchangetowardthefavorabledirectionforphysicalenvironment.Thenaturalselectionincludes:thestableselection,directedselectionandsplittingselection.Neutralhypothesis“中性說(shuō)”Japanesescholar木村資生等indicatedthatthemutationisneutral,neithergoodnorbad.Theevolutionatthemolecularlevelisresultedfromthecontinuousneutralmutationofgene,thesemutationsarefixedordisappearedinpopulationthroughrandomcombinationofbiologicalmolecules,thisproposaliscalledasneutralmutationrandomdrifthypothesis(中性突變漂變學(xué)說(shuō)),orsimplyasneutralhypothesis“中性說(shuō)”。Speciation1、ConceptofspeciesSpeciesisabasictaxumofclassification,aswellasanevolutionaryunit.Butevenatthepresent,wehavenoasuitabledefinitionforspeciesthatfitseveryone.ByErnstMayr,thespeciesaregroupsofinterbreedingpopulationsoccupyingaterritoryandgeneticallyisolatedfromneighboringgroups.Reproductiveisolation(生殖隔離)：itmeansthehybridsterility(雜交不育)。1、ConceptofspeciesFortheasexualreproductionorganisms,speciesrepresentsarelativelyindependentindividualgroupinheredity.CloneConceptofspeciationSpeciation：Itindicatestheprocessesofspeciesdiversificationandincrease,theprocessfromasingleancestrypopulationtomorespecies.Aspeciessharesonegenepool

(基因庫(kù)

)，itrepresentsthesumofallhereditarystructuresinapopulation.Whetherapopulationissmallorbig,thenaturalselectionwouldeffectonit,theindividualsthatcouldbesuitableforlivingenvironmentswouldleavemoredescendants(后代),itwouldmakesomegenesgetabigincreaseinpopulation.（1）Allopatricspeciation(異域成種作用)Geographicisolation

(地理隔離)：Onespecies,ifitsdifferentpopulationsareisolatedbygeography,thegeneexchangewouldbeblockedforthepopulationsthatarelivingindifferentareas.Theircharacterswoulddeveloptowarddifferentdirections.Finally,newspecieswouldbegenerated.Thisprocessiscalledallopatricspeciation(theoccurrenceofnewspeciesisderivedfromthegeographicisolation.（2）Sympatricspeciation(同域成種作用)Althoughthemostofspeciesareresultedfromthegeographicisolation,someresearchersconsideredthatsomespeciescouldbegeneratedinasamelocalarea.Thisspeciationisresultedfromthediversificationoflivingplaces,genemutation,inconsistentreproductiondeeds(生殖行為不協(xié)調(diào)),polyploidformation(多倍體形成),etc.,allthesefactorscouldleadtothereproductionisolation.Thisprocessismorecommoninplants.（3）Gradualisticmodel(漸變模式)AsDarwin’sidea,underthenaturalselection,thevariationsfavorabletoanorganismwouldaccumulatedbysmallincrements,generationbygeneration,untilanorganismhadevolvedthatwassufficientlydifferentfromitsancestors,itcouldbejustifyitsrecognitionasanewspecies.Thisprocesswascalledasthedivergenceofcharacter(性狀分歧).Darwinconsideredthisprocessisgradualistic,orslow.（3）Gradualisticmodel(漸變模式)AsDarwinindicated,thisprocessisveryslow,theremustbelotoftransitionalseriesofformsbetweentwospecies.Butthefossilrecordcouldnotsupportthishypothesis.Darwinattributedthefailuretotheimperfectionofthefossilrecord.InDarwin’sbook,theseexpectedtransitionalserieswerecalledas“missinglinks”infossilrecord.(4)Punctuatedmodel(點(diǎn)斷模式)Americanscientists:NEldredgeandSGouldproposedatotallynewmodelforevolution.Theyconsideredthattheevolutionofalinageiscomposedoflongintervalsofnochangepunctuatedbythesuddenappearanceofanewspeciesasaperipheralisolatedifferentiatedelsewherespreadsintotheareaofitsancestor.Becausetheperiodofstabilityorstasishasbeenpicturedasastateofequilibriumbrokenbyspeciationevent,thismodeliscalledthepunctuatedmodelorpunctuatedequilibrium(點(diǎn)斷平衡)。(4)Punctuatedmodel(點(diǎn)斷模式)Accordingtothismodel,theemergingspeciesarethoughttoconstitutesmallperipherallyisolatedpopulations(邊緣隔離居群）separatedfromtheirancestralpopulation.Becausethetransitiontakesplacerapidly,intermediateformsareunlikelytobepreservedanywhereinthefossilrecord.MacroevolutionConceptsIthasbeenusedtorefertoevolutionaryprocessesthatresultinchangesgivingrisetohighertaxonomiccategoriessuchasfamilies,orders,andclasses.Suchchangesindicatealongtermevolutionthroughthegeologicaltime.EvolutionarypatternTheconceptofevolutionarypatternscomesfromtheperceptionoffossilrecord.Themostbasicpatternistheancestortodescendantlineage.(譜系).Divergenceandradiation(趨異和輻射)Onelineage(譜系)coulddiversifyintomanylineage,thisprocessiscalleddivergence.Onetaxum,largeorsmall(fromwholeanimaliatoasinglespecies),hasitsownoriginanddevelopment,thisiscalledthephylogensis

(系統(tǒng)發(fā)生)orphylogeny

(系統(tǒng)發(fā)育).Foreachindividual,ithastoexperienceaprocessfrombirth,growth,developmentanddeath,thisiscalledtheontogeny

(個(gè)體發(fā)育).Lawofrecapitulation(重演律)&biogeneticlaw(生物發(fā)生律)Ontogenyisverycloselyrelatedtophylogeny.Thedevelopmentofanorganismfromembryo(胚胎)toadulttheindividualpassesthrough(recapitulates)theevolutionarystagesofitsancestors.Simply,theontogenyrecapitulatesphylogeny“個(gè)體發(fā)育是系統(tǒng)發(fā)生的簡(jiǎn)短重演”(E.H.Haeckel).Lawofrecapitulation(重演律)&biogeneticlaw(生物發(fā)生律)Forexample：thehumanembryoprogressesfromasinglecell(protozoan)throughablastula(囊胚，cnidarian),throughhigherinvertebratestagestoresemblancetoafish,areptileandfinallytoaprimate.Ofcourse,theorganismcouldnotrepeatthewholeofitsancestry,andskippingofstagesandaccelerationofthesequencewasessentialiftheembryologicaldevelopmentweretotakeareasonableamountoftime.Radiation(輻射)Ithasshownthatthegreatestdiversityincladesoccursintheearlypartoftheirrange.Manycladeshaveaninitialphaseofrapidexpansionindiversityfollowedbyaslowdeclinetowardsextinction.Thisprocessiscalledradiation.Thephaseofrapidexpansionistheresultofaphenomenonknownasadaptiveradiation(適應(yīng)輻射),thediversityexplosionastheorganismsexploitnewadaptationsornewlyavailableenvironments.Convergence(趨同)Convergence：contrastwithdivergence,theorganismswithoutacloserelationship,theirshapesshowsomesimilaritiesduetofitasimilarenvironment.

Specialization(特化)Apartofanorganismchangesinsomeaspectsforadaptingrigidconditionsofsomeenvironments.

Anyspecializedorganismcanonlyliveinsomegivenenvironment,itconfinesitspotentialinevolution,whichhinderssome“dangers”inspeciesextension,whenenvironmentchanged,thisorganismwouldbeeasytobeextinct.ExtinctionNeocatastrophism新災(zāi)變論DefinitionofextinctionMostofancientorganismscouldnotextendintomoderntime,theydisappearedatcertaingeologicalperiod,thisisanextinction.Wesayanextinction,indicatingterminalextinction(終級(jí)絕滅)，thatistosay,allpopulationsofaspeciesdisappeared,therearenoanydescendantspecies,sothislinkageisbrokenbythisdisappearance,thisisanextinction.ScaleofextinctionInthegeologicalhistory,therearemanyextinctionsindifferentscales.Bythescales,wecoulddivideintobackgroundextinction(場(chǎng)景絕滅)andmassextinction(集群絕滅)。Thefirstextinctionmeanssmallinscale,longinduration,belonginganormalextinction.Thesecondoneindicateslargeinscale,shortinduration,thatis,manytaxaweresuddenlywipedoutinarelativelyshortperiodofgeologicaltime.Thisextinctionoftenhappenedatthealternativeperiodofbiggeologicalevents.CausationofextinctionExtraterrestrialcausation地外因素Terrestrialcausation地內(nèi)因素Biologicalcausation生物因素ExtraterrestrialcausationNeocatastrophism(comparedwithCurvie’scatastrophismDuetotheextraterrestrialcausation,suchassupernovaexplosion,cometimpact,whichcouldcausedtheearthsurfaceshelteredbydust,thesunlightblockedout(causinganuclearwinterscenario),toxicatmosphere,abruptandextensiveshiftoftempera