NEO-DARWINISM-SYNTHETIC THEORY OF EVOLUTION

The Modern Synthetic population of Evolution describes the merging of the Darwinian evolution with the Mendelian genetics, resulting in a unified theory of the ... Skiptocontent (ANTHROPOLOGYPAPERI)   SyllabusSection:1.4HumanEvolutionandtheemergenceofMan:TheoriesofOrganicEvolution(Pre-Darwinian,DarwinianandPost-Darwinian).   Neo-Darwinism Darwincouldnotexplainsystematicallyhowvariationsexist.Hugo-de-Vries(1840-1935),aDutchbotanist,proposedthemutationtheoryofevolutionin1901.Accordingtothistheory,newspeciesevolvefromearlierspeciesnotbynaturalselectionbutbysuddenheritablechangesinthegenotypeofanorganism(characteristicsofindividuals),whichhecalled'mutation'.Accordingtohim,mutationisthechiefcauseofvariationwhichleadstotheformationofnewspecies.Mutationtheorydistinguishedheritablevariationsfromenvironmentalvariations,whichDarwinfailedtounderstandinhistheoryofnaturalselection.CombinationofMutationtheoryandDarwin'stheoryofNaturalSelectiontogetherissaidtobeNeo-Darwinism.   SyntheticTheoryofEvolution/ Darwinism,initsoriginalform,failedtoexplainsatisfactorily,themechanismofevolutionandtheoriginofnewspecies.TheinherentdrawbackintheDarwinianideaswasthelackofclarityastothesourcesofvariationandthenatureofheredity.Inthemiddleoftwentiethcentury,scientistshadcometoaconsensustoemployallsortsofknowledge,genetic,ecological,geographical,morphological,paleontological,etc.inordertoexaminetheactualmechanismofevolution.Suchconsensusonevolutionincludesfactorssuchasnaturalselection,generecombination,reproductiveisolation,mutation,migration,hybridizationandgeneticdrift.Withthesefactors,evolutionatdifferentcontextswasexplainedinaneffectiveway.   Thesynthetictheoryofevolutiondoesnotdiscardallpreviouspropositions;rather,itconsidersthemaspartiallyimportant.Therefore,wefindtheamalgamationofvariousconceptsnamelynaturalselection,mutation,Mendelianprinciples,geneticdrift,generecombinationandpopulationgeneticsinthistheoryofevolution.Butitisinterestingtonotethatmoderngeneticsdoesnotacknowledgethemutationtheoryinitsoriginalform,asproposedbyDe-Vries.Atpresent,evolutionappearstobeacomplexprocess,involvingseveralcomplexforms.   ModernSyntheticTheoryofEvolution TheModernSyntheticpopulationofEvolutiondescribesthemergingoftheDarwinianevolutionwiththeMendeliangenetics,resultinginaunifiedtheoryoftheevolution.ThistheoryisalsoreferredtoastheNeo-Darwiniantheory.SynthetictheoryofEvolutionwasintroducedtousbyfewlegendaryevolutionarybiologistsnamingT.Dobzhansky,J.B.S.Haldane,R.A.Fisher,SewallWright,G.L.Stebbins,andErnstMayrintheyears1930and1940.   Darwintalkedaboutvariationbutdidnotknowaboutthesourcesofvariation.WithprogressingeneticsthesourcesofvariationwerediscoveredandDarwin’soriginaltheoryofNaturalSelectionmodified.ThisnewtheorywastermedNeo-DarwinismorModernSyntheticTheory.   AccordingtothisTheory: Theunitofevolutionis‘population’whichhasitsowngenepool.Genepoolisthegroupofalldifferentgenesofapopulation. Heritablegeneticchangesappearintheindividualsofapopulation.TheseheritablechangesorvariationsoccurduetosmallmutationsinthegenesorinthechromosomesandtheirRecombinations. Naturalselectionselectsthevariationswhichhelpinadaptingtotheenvironment. Achangeinthegeneticconstitutionofapopulationselectedbynaturalselectionisresponsibleforevolutionofanewspecies,sincethroughinteractionofvariationandNaturalSelectionmoreoffspringswithfavorablegeneticchangesareborn.Thisiscalled‘differentialreproduction’. Onceevolved,ReproductiveIsolationhelpsinkeepingspeciesdistinct   FactorsofModernSyntheticTheoryofEvolution/SourcesofOrganicVariation Variationarisesinanindividualmemberofapopulation,andiffavourable,spreadsintothepopulationthrough“differentialreproduction”bytheactionofnaturalselection.Variationsmayoccurby Mutation,whichisasuddengeneticchange.Itmaybeachangeinasinglegene(genicmutationorpointmutation)ormayaffectmanygenes(chromosomalmutation). Geneticrecombination,whichoccursinsexuallyreproducingorganismsateveryreproduction.Thechromosomesandthusgenesoftheparentsmixatrandomduringzygoteformation.Thatiswhyoffspringofsameparentsaredifferentfromeachotherastheyhavedifferentcombinationsofparentalgenes.Variationisalsobroughtaboutwhencrossingoveroccursduringgameteformation. Geneflowiswhenthereischancemixingofgenesofcloselyrelatedspeciesthroughsexualreproduction. Geneticdriftoccursinsmallpopulationswhenapartbreaksofffromalargepopulation.Onlyrepresentativegenesofthelargepopulationarepresentwhichundergochangeatarighttimeandthesmallpopulationmayevolveintoanewsubspeciesorspecies. Speciation–Theevolutionofnewspeciesistermedspeciation.       CriticismofSyntheticTheory Thistheoryexplainsevolutionasitoccurredinthepastbutfailstoexplainintermsoffuturedirection.Changeinchromosomalnumber&geneticrecombinationisoveremphasized&theroleofhybridization&geneticdrifthasbeenundermined.Theroleofmigrationinevolutionisuncertain.Therefore,itsinclusionissuperfluous.Thoughthesynthetictheoryoforganicevolutionisconsideredtobethebesttheoryamongthetheoriesoforganicevolution,yetitisnottheidealtheory.   NextArticle:Parallelism&ConvergenceinAnthropology&AdaptiveRadiationinEvolution.                     Postnavigation ←PreviousPostNextPost→ Login RememberMe ForgotPassword? Createanewaccount Insert/editlink Close EnterthedestinationURL URL LinkText Openlinkinanewtab Orlinktoexistingcontent Search Nosearchtermspecified.Showingrecentitems. Searchoruseupanddownarrowkeystoselectanitem. Cancel ChatWithUs