古生物学-演化论

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

(演化模式)：indicatingcharactersofallevolutionaryrelationshipsEvolutionarymechanism

(演化机理)：referringtotheprocessesandfactorsoflifeevolutionThreelevelsMicroevolution

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

(成种作用

)：ItindicatestheprocessesofspeciesdiversificationandincreaseMacroevolution

(宏演化)：Itisusedtorefertoevolutionaryprocessesthatresultinchangesgivingrisetohighertaxonomiccategoriessuchasfamilies,orders,andclasses.MicroevolutionKeyfactorsofmicroevolutionVariability(变异)Heredity(遗传)Naturalselection(自然选择)1、Variation、heredityVariationindicatesdifferencesamongindividuals(age,sexarenotincluded).Darwinconsideredthatthevariationsarecorrelated,changesinsomepartofindividualcouldleadtovariationsofotherparts.Curvierproposedthatthedevelopmentofallorgansofanyindividualiscorrelated,thisiscalledthelawofcorrelation(相关律).Somevariationscouldbeheritable,someinheritable.Onlytheheritableonescouldaffecttheevolution.1、Variation、heredityVariationsarenotonlydisplayedinmorphology,butalsoininternalstructures.Thevariationscouldbeheritableduetothepresenceofhereditarymaterialbasis,thisbasisiscalledgene(基因),whichexistsinthechromosome(染色体).1、Variation、heredityTwoconceptsGeneotype

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

(表现型)：Sumofallcharacters.Thesecharactersareexternal,visible.Itisresultedfromtheinteractionbetweengeneotypeandphysicalenvironments.1、Variation、geneticsIthasbeendeterminedthatthegeneisconstitutedbynuclearacid,dominatedbydeoxyribonucleicacid(脱氧核糖核酸,DNA），thegeneisjustasectiononDNA.Thegeneiscapabletopreciselycopy(reproduce)itself,soitmaintainsthestabilityofgenetic.CausesforvariationsAccordingtothestudyofmoderngenetics,thecausesforvariationsare:(1)genereorganization(基因重组),thatis,inzoogamy(sexualreproduction),theparentchromosomesarerandomlyorganizedandtheallelicsubstitution(等位基因的交换);(2)mutation(突变)，includingthechangesofnucleotide(核苷酸)orderingene,chromosomenumberandstructure,thecausesformutationmightbetemperature,pressureandradiationrays;(3)chromosomalaberration(染色体畸变)，indicatingthechangeofchromosomalnumberandstructure.RelationshipbetweenvariationandheredityInbiologicalevolution,thevariationisacreativefactor,andtheheredityisastablefactor.Withoutvariation,organismscouldonlyproducethesamespecies,theevolutioncouldnotkeepforward;butifwithoutheredity,organismswouldbeunstable,thespecieswouldnotexistindependently,sotheevolutionwouldnotbeexisted.2、NaturalSelectionNaturalselectionactsuponinheritablevariationsthatresultindifferencesinfitnessamongindividuals—differencesthatarerelatedeithertoreproductionofthenextgenerationortosurvivaloftheindividual..Competitionbetweenindividualorganismsforresources,mates,safetyfrompredatorsandlivingroom.Somevariationsadvancedtosurvivalwouldbepreserved,theotherswouldbegivenup,thisiscalledas自然选择。“Survivaloffittest”2、NaturalSelectionNaturalselectionisahistoricalprocess,itneedsarelativelylongtime(geologicalage).Itshouldaccumulatedthefavorablevariationforexistencethroughgenerationbygeneration(heredity).Theessenceofnaturalselectionistomakethegeneticmaterialsinpopulationchangetowardthefavorabledirectionforphysicalenvironment.Thenaturalselectionincludes:thestableselection,directedselectionandsplittingselection.Neutralhypothesis“中性说”Japanesescholar木村资生等indicatedthatthemutationisneutral,neithergoodnorbad.Theevolutionatthemolecularlevelisresultedfromthecontinuousneutralmutationofgene,thesemutationsarefixedordisappearedinpopulationthroughrandomcombinationofbiologicalmolecules,thisproposaliscalledasneutralmutationrandomdrifthypothesis(中性突变漂变学说),orsimplyasneutralhypothesis“中性说”。Speciation1、ConceptofspeciesSpeciesisabasictaxumofclassification,aswellasanevolutionaryunit.Butevenatthepresent,wehavenoasuitabledefinitionforspeciesthatfitseveryone.ByErnstMayr,thespeciesaregroupsofinterbreedingpopulationsoccupyingaterritoryandgeneticallyisolatedfromneighboringgroups.Reproductiveisolation(生殖隔离)：itmeansthehybridsterility(杂交不育)。1、ConceptofspeciesFortheasexualreproductionorganisms,speciesrepresentsarelativelyindependentindividualgroupinheredity.CloneConceptofspeciationSpeciation：Itindicatestheprocessesofspeciesdiversificationandincrease,theprocessfromasingleancestrypopulationtomorespecies.Aspeciessharesonegenepool

(基因库

)，itrepresentsthesumofallhereditarystructuresinapopulation.Whetherapopulationissmallorbig,thenaturalselectionwouldeffectonit,theindividualsthatcouldbesuitableforlivingenvironmentswouldleavemoredescendants(后代),itwouldmakesomegenesgetabigincreaseinpopulation.（1）Allopatricspeciation(异域成种作用)Geographicisolation

(地理隔离)：Onespecies,ifitsdifferentpopulationsareisolatedbygeography,thegeneexchangewouldbeblockedforthepopulationsthatarelivingindifferentareas.Theircharacterswoulddeveloptowarddifferentdirections.Finally,newspecieswouldbegenerated.Thisprocessiscalledallopatricspeciation(theoccurrenceofnewspeciesisderivedfromthegeographicisolation.（2）Sympatricspeciation(同域成种作用)Althoughthemostofspeciesareresultedfromthegeographicisolation,someresearchersconsideredthatsomespeciescouldbegeneratedinasamelocalarea.Thisspeciationisresultedfromthediversificationoflivingplaces,genemutation,inconsistentreproductiondeeds(生殖行为不协调),polyploidformation(多倍体形成),etc.,allthesefactorscouldleadtothereproductionisolation.Thisprocessismorecommoninplants.（3）Gradualisticmodel(渐变模式)AsDarwin’sidea,underthenaturalselection,thevariationsfavorabletoanorganismwouldaccumulatedbysmallincrements,generationbygeneration,untilanorganismhadevolvedthatwassufficientlydifferentfromitsancestors,itcouldbejustifyitsrecognitionasanewspecies.Thisprocesswascalledasthedivergenceofcharacter(性状分歧).Darwinconsideredthisprocessisgradualistic,orslow.（3）Gradualisticmodel(渐变模式)AsDarwinindicated,thisprocessisveryslow,theremustbelotoftransitionalseriesofformsbetweentwospecies.Butthefossilrecordcouldnotsupportthishypothesis.Darwinattributedthefailuretotheimperfectionofthefossilrecord.InDarwin’sbook,theseexpectedtransitionalserieswerecalledas“missinglinks”infossilrecord.(4)Punctuatedmodel(点断模式)Americanscientists:NEldredgeandSGouldproposedatotallynewmodelforevolution.Theyconsideredthattheevolutionofalinageiscomposedoflongintervalsofnochangepunctuatedbythesuddenappearanceofanewspeciesasaperipheralisolatedifferentiatedelsewherespreadsintotheareaofitsancestor.Becausetheperiodofstabilityorstasishasbeenpicturedasastateofequilibriumbrokenbyspeciationevent,thismodeliscalledthepunctuatedmodelorpunctuatedequilibrium(点断平衡)。(4)Punctuatedmodel(点断模式)Accordingtothismodel,theemergingspeciesarethoughttoconstitutesmallperipherallyisolatedpopulations(边缘隔离居群）separatedfromtheirancestralpopulation.Becausethetransitiontakesplacerapidly,intermediateformsareunlikelytobepreservedanywhereinthefossilrecord.MacroevolutionConceptsIthasbeenusedtorefertoevolutionaryprocessesthatresultinchangesgivingrisetohighertaxonomiccategoriessuchasfamilies,orders,andclasses.Suchchangesindicatealongtermevolutionthroughthegeologicaltime.EvolutionarypatternTheconceptofevolutionarypatternscomesfromtheperceptionoffossilrecord.Themostbasicpatternistheancestortodescendantlineage.(谱系).Divergenceandradiation(趋异和辐射)Onelineage(谱系)coulddiversifyintomanylineage,thisprocessiscalleddivergence.Onetaxum,largeorsmall(fromwholeanimaliatoasinglespecies),hasitsownoriginanddevelopment,thisiscalledthephylogensis

(系统发生)orphylogeny

(系统发育).Foreachindividual,ithastoexperienceaprocessfrombirth,growth,developmentanddeath,thisiscalledtheontogeny

(个体发育).Lawofrecapitulation(重演律)&biogeneticlaw(生物发生律)Ontogenyisverycloselyrelatedtophylogeny.Thedevelopmentofanorganismfromembryo(胚胎)toadulttheindividualpassesthrough(recapitulates)theevolutionarystagesofitsancestors.Simply,theontogenyrecapitulatesphylogeny“个体发育是系统发生的简短重演”(E.H.Haeckel).Lawofrecapitulation(重演律)&biogeneticlaw(生物发生律)Forexample：thehumanembryoprogressesfromasinglecell(protozoan)throughablastula(囊胚，cnidarian),throughhigherinvertebratestagestoresemblancetoafish,areptileandfinallytoaprimate.Ofcourse,theorganismcouldnotrepeatthewholeofitsancestry,andskippingofstagesandaccelerationofthesequencewasessentialiftheembryologicaldevelopmentweretotakeareasonableamountoftime.Radiation(辐射)Ithasshownthatthegreatestdiversityincladesoccursintheearlypartoftheirrange.Manycladeshaveaninitialphaseofrapidexpansionindiversityfollowedbyaslowdeclinetowardsextinction.Thisprocessiscalledradiation.Thephaseofrapidexpansionistheresultofaphenomenonknownasadaptiveradiation(适应辐射),thediversityexplosionastheorganismsexploitnewadaptationsornewlyavailableenvironments.Convergence(趋同)Convergence：contrastwithdivergence,theorganismswithoutacloserelationship,theirshapesshowsomesimilaritiesduetofitasimilarenvironment.

Specialization(特化)Apartofanorganismchangesinsomeaspectsforadaptingrigidconditionsofsomeenvironments.

Anyspecializedorganismcanonlyliveinsomegivenenvironment,itconfinesitspotentialinevolution,whichhinderssome“dangers”inspeciesextension,whenenvironmentchanged,thisorganismwouldbeeasytobeextinct.ExtinctionNeocatastrophism新灾变论DefinitionofextinctionMostofancientorganismscouldnotextendintomoderntime,theydisappearedatcertaingeologicalperiod,thisisanextinction.Wesayanextinction,indicatingterminalextinction(终级绝灭)，thatistosay,allpopulationsofaspeciesdisappeared,therearenoanydescendantspecies,sothislinkageisbrokenbythisdisappearance,thisisanextinction.ScaleofextinctionInthegeologicalhistory,therearemanyextinctionsindifferentscales.Bythescales,wecoulddivideintobackgroundextinction(场景绝灭)andmassextinction(集群绝灭)。Thefirstextinctionmeanssmallinscale,longinduration,belonginganormalextinction.Thesecondoneindicateslargeinscale,shortinduration,thatis,manytaxaweresuddenlywipedoutinarelativelyshortperiodofgeologicaltime.Thisextinctionoftenhappenedatthealternativeperiodofbiggeologicalevents.CausationofextinctionExtraterrestrialcausation地外因素Terrestrialcausation地内因素Biologicalcausation生物因素ExtraterrestrialcausationNeocatastrophism(comparedwithCurvie’scatastrophismDuetotheextraterrestrialcausation,suchassupernovaexplosion,cometimpact,whichcouldcausedtheearthsurfaceshelteredbydust,thesunlightblockedout(causinganuclearwinterscenario),toxicatmosphere,abruptandextensiveshiftoftempera