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Carol Eunmi Lee 10/19/16 Today’s OUTLINE: History of Evolutionary Thought (1) Development of Darwin’s Thought (2) Lamarck vs. Darwin (3) The Contribution of Darwin (4) The Contribution of Mendel (5) Conflict between “Mendelism” and “Darwinism” (6) The “Evolutionary Synthesis” of Mendel and Darwin Dr. Carol Eunmi Lee University of Wisconsin, Madison Charles Darwin (1809-1882) Key Points: (1)Whatexactlywerethecomponentsof Darwin’stheoryofEvolution,andwhatwas missing? Origin of Species is one of the most influential texts of this century (2)WhatexactlydidMendelcontribute? (3)WhatisthedifferencebetweenLamarck vs. Darwin’sideas,andhowdoLamarck’s ideascontributetoday? Charles Darwin (1809-1882) ■ ■ ■ ■ ■ ■ Title goes here Hisfatherwasadoctor(RichardDarwin)andhis grandfatherwasErasmusDarwin,alsoadoctoranda prominentscholarwhowasalreadythinkingabout evolution InitiallyhestudiedMedicineattheUniversityofEdinburgh Heneglectedhisstudiesandcouldnotstandthesightof surgeryorthesightofblood(hadnausea,fainted) SentbyhisfatheratChrist’sCollege,CambridgeUniversity tobecomeanAnglicanpriest Reverend John Stevens Henslow (1796–1861) “ I fully believe a better man never walked this earth ” Charles Darwin to J.D. Hooker, 1861 ■ ■ ■ Hestillneglectedhisstudies,buthedidpursuea passionateinterestinNaturalHistory HebecameclosetobotanyprofessorRev.JohnHenslow andmetotherleadingnaturalistswhosawscientificwork asreligiousnaturaltheology(andviewedadaptation[i.e. evolution]asGodactingthroughlawsofnature) ■ Darwin’sBotanyprofessoratChrist’sCollege (DivinitySchool),CambridgeUniversity Henslowencouragedstudentstomakeobservations oftheirown,ratherthanbeingspoon-fed AfterDarwincompletedhisfinalexaminationin1831, Henslowpersuadedhimtobeginstudyinggeology,and madearrangementsforhimtotakeAdamSedgwick’s geologycourseandatriptomapgeologicalstratain NorthWales More on Henslow: Darwin's Mentor: John Stevens Henslow 1796–1861 By Walters & Stow Shortlythereafter,in1831,Henslowencouraged DarwintojointheVoyageoftheBeagleasthe ship’snaturalist 1 Carol Eunmi Lee 10/19/16 Voyage of the Beagle During the 5-year Voyage HMSBeagle,ashipsentby BritishNavytochartcoastlineof SouthAmerica ■ Darwinwassupposedtobeprimarilya geologist;Hehadsomeexpertisein geology,beetlecollectinganddissecting marineinvertebrates HMS Beagle off of South America ■ ■ The Galapagos Islands Archipelagoofvolcanic islandsdistributedaround theequatorinthePacific Ocean,972 km(525 nmi) westofcontinental Ecuador The Galapagos Islands Hemadeobservationsongeological formationsastheshipwasmappingthe coastline AtPuntaAltainPatagoniahemadea majorfindoffossilbonesofhugeextinct mammalsincliffsbesidemodern seashells,indicatingrecentextinctionwith nosignsofchangeinclimateor catastrophe(“extinctionshappen”) The Galapagos Islands Whyweretheseislandssoimportantin shapingDarwin’sthinking? Darwin’s Mockingbirds • Asanarchipelago,thereweremanyislandswithdifferent populationsofa“species” oneachisland • Thepopulationswererelated,butwereslightlydifferentoneach island…(notclearboundaries) • ThisledDarwintoconcludethatthepopulationsdescendedfroma commonancestor…andheultimatelyconcludedthattheyhad evolvedandwereevolving… • à ledDarwintoquestionthestabilityoftheconceptofa“species” Title goes here 2 Carol Eunmi Lee 10/19/16 "Myattentionwasfirstthoroughlyarousedby comparingtogetherthevariousspecimens...of themocking-thrush" C.Darwin,TheVoyageoftheBeagle(1839) • OnSept171835,DarwindisembarkedfromtheBeagle intheGalápagos nearSapphoCoveonChathamIsland(nowknownasIslaSanCristóbal), andwasstruckbythebold,terrestrialmockingbird. • ThebirdisknowntodayasMimus melanotis,theSanCristóbal Mockingbird.Overthenext6weeksthatDarwinspentintheGalápagos,he observedmockingbirdsonthreeotherislands. • Darwinnoticedthemockingbirdsdifferedbetweenislands. Nicolas Lawson,actingGovernorofGalápagos,toldDarwinthatthetortoisesalso differedfromislandtoisland. • Towardstheendofthevoyage,Darwinspeculatedthatthedistributionof themockingbirdsandthetortoisesmight"underminethestabilityof Species”. Speciesmightnotbefixedentities,butarechangingover time… q q q Mockingbirdsondifferentislandsdifferedslightlyinsize,shape andcoloration(speciesnotimmutablediscreteentities) Andallsharedsometraits(homologoustraits) Heconcludedthatthesebirdsmusthavesharedacommon ancestor--andwerenotindependentlycreatedà Branching, Tree-likethinking(ratherthanaladder) Galapagos Islands Darwin’s Mockingbirds (he did not focus that much on the finches; they were studied more later by the Grants) Tortoises and other animals q q q Mockingbirdsondifferentislandsdifferedslightlyin size,shapeandcoloration Andallsharedsometraits(homologoustraits) Heconcludedthatthesebirdsmusthaveshareda commonancestor--andwerenotindependently created Significance of the HMS Beagle Voyage • Amassedcollectionstostudylater • ExposedDarwintogeologicalformations,fossilsembeddedin strata– animalsthatnolongerexisttodayandareclearlyextinct– thiswasknown,butDarwingottoseethishimself • Exposuretoanimaldiversity,relatedpopulationswithinspecies livingindifferenthabitats: 1. “Species” arenotimmutablefixedentities 2. Organismsarerelatedbycommonancestry(tree-like branching) 3. Theyarechangingandbranchinginresponsetothe environment Return to England ■ ■ ■ Title goes here Returnedanddiscussedhis geologicalandbiologicalfinding withotherscholars,influenced byMalthus,etc. MarriedthewealthyEmma Wedgewoodà financedhiswork Didnothavetowork,andcould studythesampleshecollected, performexperiments,make observations,think,andwrite booksfortherestofhislife 3 Carol Eunmi Lee 10/19/16 Historical Context: ■ Influences on Darwin ■ By mid-1800s scientific context was in place for development of theory of Evolution ■ ■ Developments in Geology: Discovery that earth is more than 6,000 years old Fossil Record showed change in species over time ■ ■ Geology: DarwinhadLyell’sPrinciplesofGeology on boardtheHMSBeagle Lamarck’s(1744-1829):ConceptofAdaptation, Inheritanceofacquiredcharacteristics Malthus(1766-1834):Competitionwithinspecies andthestruggleforsurvival http://www.ucmp.berkeley.edu/history/evotmline.html Influences on Darwin ■ Jean-Baptiste Lamarck Geology:DarwinhadLyell’sPrinciplesofGeology on boardtheHMSBeagle,giventohimbycaptainofthe HMSBeagle(RobertFitzRoy) ■ ■ ■ ■ ■ Fossil record: ■ The earth is old Many animals that once existed are now extinct There are layers (strata) in the fossil record show a pattern of change ■ French Naturalist (1744-1829) “Professor of Worms and Insects” in Paris The first scientific theory of evolution (inheritance of acquired characteristics) à theideathatspecieschange overtimeandthatsome goextinct Influences on Darwin Influences on Darwin ThomasMalthus(1766-1834): “EssayonthePrincipleofPopulation” Lamarck ’s (1744-1829) theory of Evolution Inheritance of acquired characteristics ■ Proposed the most influential mechanism of evolution before Darwin: Population Theideaofcompetition: ■ ■ ■ Introduced the idea of Adaptation, though he was mostly incorrect on the predominant mechanism (though sometimes correct; will discuss Epigenetic Inheritance) Title goes here ■ food Malthus’ calculationsshowedthatrateofpopulation growthwasgreaterthanrateofincreaseinfoodsupply Thus,notallindividualscouldpossiblysurvive Basedonthisfactofcompetition,Darwinconcludedthat individualsthatarebetteradapted wouldbetheonesthat surviveandleavemoreoffspring(andwinthecompetition) 4 Carol Eunmi Lee 10/19/16 Malthus ■ From Malthus, Darwin came up with the idea of competition and the “struggle for survival” as a component of Natural Selection ■ ■ The scientific community was primed for a theory of Evolution ■ Darwin was one of many scholars at his time that were thinking about Evolution ■ “On the Tendency of Varieties to Depart Indefinitely from the Original Type” ■ Many scholars accepted the idea of Evolution at the time… what puzzled them was the mechanism In fact, Alfred Wallace (1823-1913) came up with the idea of natural selection independently Darwin rushed to publish Origins in 1859 when he learned of Wallace’s work Alfred Russel Wallace (1823-1913) Father of Biogeography… focused on adaptation to the environment ■ ■ ■ ■ In1858WallacesentDarwinacopyof hismanuscript DarwinwasshockedthatWallacecame upwiththeideaofnaturalselection independently Theydecidedonajointpresentationat theLinneanSocietyin1858,butit receivedlittleattention AfterwhichDarwinrushedtopublishhis bookin1859 Title goes here Darwindevelopedthetheoryof EvolutionviaNaturalSelection… Alfred Russel Wallace (1823-1913) ■ ■ Withtheseinfluencesonthisthought anddatafromtheGalapagosIslands… ■ Basedonhisworkinthe MalayArchipelago Healsostudiedpopulations ondifferentislandsandcame tothesameconclusionas Darwin Charles Darwin (1809 -1882) On the Origin of Species (1859) ◆ Living species are related by common ancestry ◆ Change through time occurs at the population not the organism level ◆ The main cause of adaptive evolution is natural selection 5 Carol Eunmi Lee 10/19/16 Darwin’s Main Points: So… Darwin did NOT originate (1) Organisms Evolve (Darwin not first) the idea of Evolution… (2) Common Descent: species arise from common ancestors, in a tree-like branching process (Wallace also) (3) Gradualism: changes are gradual (we now know that this is not always true) … BUT he provided a plausible Mechanism (along with Wallace) (4) Population Speciation: change in proportions of individuals having a trait in a population (Darwin’s original idea) (Wallace also) … and much evidence (5) Natural Selection: is the mechanism (Wallace also) Lamarck vs Darwin Lamarck vs Darwin (1) Different View on Pattern of Evolution BeforeDarwinhaddevelopedhisideasonthe mechanismofevolution,Lamarckhadproposedan alternatemechanismthatwaspopularatthetime ◆ ◆ Lamarck: Linear progression Darwin: Tree-like branching process (2) Different View on Mechanism of Evolution Lamarck’s View on Pattern of Evolution ■ ■ ■ ■ Continuumbetweenphysicaland biologicalworld(followed Aristotle) ScalaNaturae(“LadderofLife” or“GreatChainofBeing”) “TransmutationofSpecies” –one speciesturnsintoanother Linearprogressionfromprimitive toadvanced Title goes here Being ◆ Darwin: Evolution at the Population Level via Natural Selection God Angels Evolution is not linear but branching Demons Man ■ Animals Realm of Becoming Lamarck: inheritance of acquired traits (not mutations)-Individual evolution What is wrong with a ladder? ■ Realm of Being ◆ Living organisms are not ancestors of one another Plants Minerals ■ The ladder implies progress Non-Being 6 Carol Eunmi Lee 10/19/16 The only figure in Origin of Species Darwin envisaged Evolution as a Tree The affinities of all the beings of the same class have sometimes been represented by a great tree. I believe this simile largely speaks the truth…… …The green and budding twigs may represent existing species; and those produced during former years may represent the long succession of extinct species….. ….the great Tree of Life….covers the earth with ever-branching and beautiful ramifications Charles Darwin, On the Origin of Species; pages 131-132 Lamarck’s View on Mechanism of Evolution ■ ■ Individuals are evolving If you got a tan, you’d pass it on Lamarck’s View on Mechanism of Evolution ■ ■ Individuals are evolving If you got a tan, you’d pass it on Some balls get tan during their lifetime Lamarck’s View on Mechanism of Evolution ■ ■ Individuals are evolving If you got a tan, you’d pass it on Tan balls pass on their acquired trait to their offspring Darwin’s View on Mechanism of Evolution ■ Natural Selection A heritable difference (now known to be due to different mutations) (Wenowknowthatacquiredtraitscouldgetpassedonsometimes whenepigeneticmodificationsareinherited) Title goes here 7 Carol Eunmi Lee 10/19/16 Darwin’s View on Mechanism of Evolution ■ Darwin’s View on Mechanism of Evolution Natural Selection ■ Natural Selection Selection might favor this mutation Greater Fitness: individuals with this mutation survive and leave more offspring Darwin’s View on Mechanism of Evolution ■ Natural Selection Darwin’s contribution: “Population Speciation as a result of Natural Selection” ■ More offspring are produced than can survive ■ Limited resources and competition for resources (“The Struggle for Survival”) The individuals themselves are not changing, but the population is changing in composition (% of alleles) ■ There is variation in a population ■ Individuals better adapted to environment survive ■ Survivors leave more offspring (“Survival of the Fittest”) Thus, average character of population is altered ■ But… Darwin’s theory was not complete ■ Sample Exam Question BecauseDarwinknewnothingaboutmutation,hehad noideahowvariationwasgeneratedinpopulations ■ ■ ■ BecauseDarwinknewnothingaboutgeneticsorgenes, hehadnoideahowvariationwaspassedonto offspring(Mendel&Hardy-Weinberg) Darwindidnotknowaboutnonadaptiveevolutionary forces,suchasGeneticDrift Title goes here Which of the following was NOT part of Darwin’s theory of Evolution? (1) Natural Selection (2) Populations as the units of Evolution (3) Mutations as sources of genetic variation (4) Survival of those who produce more offspring 8 Carol Eunmi Lee 10/19/16 Hardy-Weinburg Equilibrium Mendel’s work held part of the key to what was missing in Darwin’s Theory (Lecture 4) ■ ■ Mendel published in 1865… was ignored until 1900 ■ Wilhem Weinberg ■ G. H. Hardy ◆ Presented a mechanism for how traits got passed on ◆ “Individuals pass alleles on to their offspring intact” January 13, 1908 July 10, 1908 in Science The Mathematical expression of Mendel’s Principles of Inheritance (the idea of particulate (genes) inheritance) Hardy-Weinburg Equilibrium (Lecture 4) ■ Wilhem Weinberg ■ G. H. Hardy ◆ ◆ ■ PROBLEMS! January 13, 1908 July 10, 1908 in Science Could mathematically show expectations of Mendelian inheritance and whether expectations are realized in nature BUT… Mendel and Darwin’s ideas seemed Incompatible ■ ■ Mendel’s principles: dealt with particulate (discrete) traits (e.g. yellow vs. green, wrinkled vs. smooth) Selection vs Mutations ■ Mutationsdiscoveredafter1900 BUT, Darwin observed continuous traits (e.g. beak size, body length) Q: So, how would continuous traits get passed on? Title goes here Q:Ifmutationsarearising,whyneed selection...…ifthingsarejust mutating? 9 Carol Eunmi Lee Controversy between Mutationists vs Darwinists Mutationists (+Mendelianism) ■ They thought that evolution required only mutations and passing on of discrete traits Darwinists ■ They thought that evolution required only Natural Selection on continuous variation Controversy between Mutationists vs Darwinists 10/19/16 Discrete vs Quantitative Traits ■ Darwinwasunabletoclearlyseethepatternof inheritancebecausehestudiedquantitativevariation • Discretetrait:atraitthathasdistinctvalues, ratherthanarangeofphenotypes,usually encodedbyoneorafewgenes. Frequency Examples:numberoffingers,colorofMendel’speas, sicklecellanemia,ABObloodtype,numberofeggsina birdclutch,presence/absenceofhumanwidow’speak, presence/absenceofdimples,etc. Type • Quantitative(continuous)trait:atraitthathasFrequency acontinuumofphenotypesandisencodedby multiplegenes. Examples:bodysize,height,weight,intelligence (IQ),Runningspeed,beakshape,haircolor,skin color,milkyieldofcows,lifespan,etc. Type Problem caused by: ■ Binarythinking(BlackorWhitethinking):it’sthis orthat…“ifI’mright,youmustbewrong” à Wheninfactthetwoormorefactorsmight interact Controversy persisted for ~30 years up till the 1930s, during which little progress was made ■ Inabilitytoseeoverarchingmechanismthatcould explainawiderangeofphenomena:“Howcould yourHardy-Weinberg(Mendel)explaintheinheritanceof 5.1cm,5.5cmbeaklength(continuouscharacters)?” à Wheninfact,anotherfactormightmakeitpossible (thinkmultiplegenes,ratherthanonegene) Genetic Drift (Lecture 5) ■ ■ ■ ■ AconceptasimportantasNaturalSelection But,notasprominentonpeople’sminds 1872Gulick:NeutralTheory(GeneticDrift) 1921A.C.Hagedoornproduceddatatosupport NeutralTheoryofGeneticDrift The Modern Synthesis 1930s ~ 1940s The synthesis of population genetics (role of mutation, genetic drift), paleontology, systematics Darwin and Mendel Reconciled!!! (Next Lecture) Title goes here 10 Carol Eunmi Lee 10/19/16 The Modern Synthesis 1930s ~ 1940s Alsocalledthe“SynthesisofEvolutionand Genetics” AmongtheGreatestScientific RevolutionsoftheCentury Three of the "architects" of the evolutionary synthesis: G. Ledyard Stebbins, Jr., George Gaylord Simpson, Theodosius Dobzhansky Photograph from Smocovitis, V. B. 1997. G. Ledyard Stebbins, Jr. and the evolutionary synthesis (1924-1950). American Journal of Botany 84: 1625-1637. Some Key Tenets of the Modern Synthesis ■ TheEvolutionarySynthesiswasimportant becausemanyscientistsfromdifferent fieldsconvenedtodiscusstheevolutionary mechanismsandclearupconfusionand inconsistencies ■ ■ ■ ■ PopulationsaretheunitsofEvolution MendelvsDarwin:continuoustraitsarealsocodedby particulategenes,butmanygenes MutationvsSelection:Mutationsaresourcesofgenetic variationuponwhichSelectionacts NaturalSelectionandMutationarenottheonly evolutionaryforces.Examples:GeneticDrift,Recombination Microevolutionary processes,suchasDrift,Selection, Mutation,leadtoMacroevolutionary changes(suchas throughspeciation) Some Tenets of the Evolutionary Synthesis ■ ■ ■ ■ ■ ■ ■ ■ ■ ■ ■ The phenotype is different from the genotype Acquired characters (phenotypic plasticity) are not inherited Traits are inherited via genes, and they do not “blend” with other genes (Darwin was wrong about this one) Genes mutate, resulting in different alleles Evolution occurs at the population level, due to a change in proportions of individuals with different genotypes Changes in proportion in a population could occur via random genetic drift (Sewall Wright) or Natural Selection… the rate of mutation is usually too low to cause large changes in proportions Even very weak natural selection could cause substantial changes over a longer time scale Mutations generate the genetic variation upon which natural selection acts Microevolutionary processes lead to Macroevolutionary changes (speciation) Mutation vs Selection and Reconciling Mendel and Darwin All organisms on the planet are related to one another in a great “tree of life”, and have diverged by branching from common ancestors Gaps in the fossil record are likely due to incompleteness of the fossil record. Gradual changes seen in many parts of the fossil record suggest gradual changes over time Title goes here 11 Carol Eunmi Lee 10/19/16 Mutation vs Selection ■ And Reconciling Mendel and Darwin ◆ ■ ■ continuous and discrete traits could follow the same principles of inheritance (Mendel), just that continuous traits are coded by many genes (loci) Iftherearemanygenes(loci)codingforatrait,rather thanone,theoffspringlookintermediatebetweenthe parents(lookslike“blendinginheritance”) BUT,theSAMEMendelianpatternsofinheritance apply,it’sjustthatyoudon’tseetheparticulate inheritanceofeachgeneintheoffspring,butthe averageeffectacrossallthegenesaffectingthetrait How do you deal with quantitative traits? (2nd point below) ■ ■ Hardy Weinberg: multiple alleles: ◆ 3 alleles: (p + q + r)2 which expands to... ◆ p2 + 2pq + q2 + 2pr + 2qr + r2 =1.0 4 alleles: (p + q + r + s)2 Hardy Weinberg: multiple loci ◆ ◆ HW principle still applies to each locus independently Need to use principles of Quantitative Genetics to examine effects of multiple loci Fisher vs Wright The Population Geneticists JBS Haldane Sewall Wright Both appreciated the importance of Natural Selection AND Genetic Drift But they argued about the relative importance Mathematicaltheoryofpopulation geneticsshowedthatmutationand selectionTOGETHERcauseadaptive evolution: RA Fisher MutationisNOTanalternativeto NaturalSelection,buttherawmaterial uponwhichnaturalselectionacts. Ronald Aylmer Fisher (1890-1962) Ronald Aylmer Fisher (1890-1962) •Naturalselectionoccursinlargepopulations •Manygenesareinvolved Background in math, physics, astronomy, and genetics Made key contributions to the field of Statistics Title goes here •Mutationsarethemainsubstrateforselection OtherContributions: •Addingmathematicalrigorintothe theoryofselection •ElegantsynthesisofMendelian inheritanceintotheTheoryofSelection •ImportantdevelopmentsinStatistics (ANOVA) 12 Carol Eunmi Lee 10/19/16 Sewall Wright (1889-1988) Heavily influenced by examples from agriculture Sewall Wright (1889-1988) • Inbreeding and Genetic Drift are important for creating new gene interactions Worked for the US Dept of Agriculture: breeding in guinea pigs and cattle • These new gene interactions (epistasis caused by new recombinations) are the main substrate for selection Became a professor at UW-Madison in Genetics The Population Geneticists ReconcilingMicroevolutionaryMechanisms andMacroevolutionaryprocesses Ifyouwanttoreadmoreaboutthis topic,thisbookisagoodread Microevolutionà Macroevolution Ernst Mayr Ernst Mayr George Gaylord Simpson G. Ledyard Stebbins Bernhard Rensch and others JamesF.Crow (1916-2012) UniversityofWisconsin,Madison George Gaylord Simpson Microevolutionaryprocesseswithinspeciesaccountfor macroevolutionamongspecies (Lecture#18) Thatis,mutation,recombination,naturalselection,and otherprocessesthatactwithinspecies(microevolution) aretheSAMEmechanismsthataccountfortheoriginof newspeciesandmajorlongtermevolution (macroevolution) (Lecture#18) Title goes here His work has touched on nearly every area of evolutionary genetics -willdiscusssomeofhiscontributionsinLecture#7 http://www.genetics.wisc.edu/CATG/crow/index.html 13 Carol Eunmi Lee 10/19/16 Moral of the Story ■ Scientists from different fields should talk to each other After the Evolutionary Synthesis ■ ■ Should avoid binary thinking (this vs. that, right vs. wrong), as different mechanisms might work together in an integrated fashion We are often biased by what we study (example of continuous vs. discrete traits) Evenafterthesynthesistherelativeimportanceof NaturalSelectionandGeneticDriftwasdebated TheImportanceofNaturalSelectionvsGeneticDrift OngoingdebateaftertheEvolutionarySynthesis • DuringtheEvolutionarySynthesis,SewallWrightfocused moreonimportanceofGeneticDrift,whereasFisherfocused onNaturalSelection • ShortlyaftertheEvolutionarySynthesismanyfocusedon selectiontothepointofassumingthatmostphenotypeswere theresultofNaturalSelection • EmphasisonGeneticDriftresurgedinthe1970s,80swith Kimura’s“NeutralTheory” • Theninthe2000sand2010sinterestinSelectionincreased withtheabilitytodetectsignaturesofNaturalSelectionin genomesequencedata Motoo Kimura (1924-1994) The Neutral Theory of Molecular Evolution Classic Paper: Kimura, Motoo. 1968. Evolutionary rate at the molecular level. Nature. 217: 624–626. Classic Book: Kimura, Motoo (1983). The neutral theory of molecular evolution. Cambridge University Press. Title goes here The Neutral Theory of Molecular Evolution (Lecture #6) • TheNeutraltheorypositsthatthevastmajority ofevolutionarychangeatthemolecularlevelis causedbyrandomgeneticdriftratherthan naturalselection. Motoo Kimura • NeutraltheoryisnotincompatiblewithDarwin'stheoryof evolutionbynaturalselection:adaptivechangesare acknowledgedaspresentandimportant,buthypothesizedtobea smallminorityevolutionarychange. • Recenttestsofselectionhavefoundthatinmanycasesevolution isnotneutral,eveninnon-codingregionsofthegenome. • Nevertheless,theneutraltheoryisusefulasanullhypothesis, againstwhichselectioncouldbetested. 14 Carol Eunmi Lee 10/19/16 Some Tenets of the Evolutionary Synthesis Thephenotypeisdifferentfromthegenotype Acquiredcharacters(phenotypicplasticity)arenotinherited–notalwaystrue ■ ■ While the Evolutionary Synthesis was a HUGE leap in the right direction, there were a few tenets that required modification (as a result of new discoveries in Genetics) Traitsareinheritedviagenes,andtheydonot“blend” withothergenes(Darwin waswrongaboutthisone) Genesmutate,resultingindifferentalleles Evolutionoccursatthepopulationlevel,duetoachangeinproportionsof individualswithdifferentgenotypes ■ ■ ■ Changesinproportioninapopulationcouldoccurviarandomgeneticdrift(Sewall Wright)orNaturalSelection…therateofmutationisusuallytoolowtocauselarge changesinproportions ■ Evenveryweaknaturalselectioncouldcausesubstantialchangesoveralonger timescale Mutationsgeneratethegeneticvariationuponwhichnaturalselectionacts MicroevolutionaryprocessesleadtoMacroevolutionarychanges(speciation) ■ ■ ■ Allorganismsontheplanetarerelatedtooneanotherinagreat“treeoflife”,and havedivergedbybranchingfromcommonancestors Gapsinthefossilrecordarelikelyduetoincompletenessofthefossilrecord. Gradualchangesseeninmanypartsofthefossilrecordsuggestgradualchanges overtime–notalwaystrue ■ ■ Completing the Synthesis Evolution at the Molecular Genetic Level Advances in Genetics ■ Which types of mutations predominate and contribute to adaptations more often? Epigenetic Inheritance (Lecture #9) ■ Structural vs Regulatory? ◆ ■ Some genetic changes could lead to radical changes in phenotype (Lecture #7) ◆ Polyploidization seen often in plants Changes in developmental genes ◆ Regulatory Evolution ◆ Transposons ◆ ■ Is phenotypic evolution occurring predominantly at the level of gene products (e.g. proteins) or at the level of gene regulation (e.g. transcription, RNA processing, translation, etc.)? cis-Regulation vs trans-Regulation? ◆ Is regulatory evolution occurring predominantly at the level of cis-regulatory elements (e.g. promoter, enhancers) or at the level of trans-acting factors (e.g. transcription factors, etc.)? More on Lectures on Molecular Evolution (Lecture #13) The role of Epigenetics (Lecture #9) ■ ■ ■ LamarckRevisited Evolution of Development (Lecture #26) ■ Lamarckwasincorrectinthinkingthatthe inheritanceofacquiredcharactersisthemain mechanismofevolution However,wedonowknowthattheinheritanceof acquiredcharactersdoeshappensometimes, throughtheinheritanceofepigeneticmodifications Title goes here ■ How small changes in developmental genes (like Hox genes) could radically cause the evolution of body plans Will talk more about this when I get to lecture on Animal Diversity 15 Carol Eunmi Lee 10/19/16 Role of Genomics Today: Genome Evolution and Systems Biology (Lectures #15, 16) ■ How does the whole genome evolve? ■ ■ ■ How does selection act on networks of interacting genes? How many and which genes are involved in the formation of new species? ■ ■ ■ How do multiple genes interact? How do multiple genes affect a phenotype? Systems Biology: How does selection act on interacting gene networks? Evolution of Genome Architecture Questions: Questions: (1) What were the intellectual influences on Darwin’s thought? (1) Whatwerethesourcesofconfusionregardingevolutionary mechanismspriortotheEvolutionarySynthesis? (2) What role did the discoveries from the Beagle’s voyage play in the development of Darwin’s thought? (3) What were Darwin’s main conclusions? (4) How did Darwin’s thought differ from that of Lamarck? (2) WhatwastheModern(Evolutionary)Synthesis? (3) WhatwerethemaintenetsoftheEvolutionarySynthesis? (4)Whatistherelationshipbetweennaturalselection,geneticdrift, (4) What did Darwin’s theory leave out? mutations,andrecombination? (5)WhatweresomeofthelimitationsoftheEvolutionarySynthesis? (5) What was Mendel’s contribution? (6) WhatweresomekeydevelopmentssincetheEvolutionary (6) What were the sources of confusion between the proponents of Darwin and Mendel’s ideas? CONCEPTS Evolution Population Natural Selection Evolutionary Adaptation Fitness Mutation Genetic Drift Recombination Hardy-Weinberg Equilibrium Development of Darwin ’ s thought Lamarck vs Darwin Darwinists vs Mendelists Evolutionary Synthesis Title goes here Synthesis? (7) Whatgapsremaininourunderstandingtoday? Sample Exam Questions 1.WhichofthefollowingisTRUE regardingDarwin ’ scontributiontothetheory ofEvolution? (A)Darwinformulatedthefirstcomprehensivetheoryincorporatingall mechanismsofevolution (B)Darwinrecognizedthatevolutionoccursatthepopulationlevel(intermsof changesinfrequencyoftraitswithinpopulations) (C)Darwinproposedthatselectionactsonmutationsandotherformsofgenetic variation (D)DarwinagreedwithLarmarck’sideaofinheritanceofacquiredcharacters, butincludedtheconceptoffitness. (E)DarwinincorporatedMendel’sworkontheparticulateinheritanceofalleles 16 Carol Eunmi Lee 10/19/16 2.Forseveraldecades"Darwinists"and"Mendelists"battledover themechanismsofevolution.WhichofthefollowingdidNOT contributetothisparticularconflict? (a)Geneticists/Evolutionarybiologistsdidnotunderstandthat continuousanddiscretetraitsfollowthesameprincipleof inheritance (b)Geneticists/Evolutionarybiologistsdidnotunderstandthat naturalselectionactsonmutationsinapopulation (c)Mendelworkedwithdiscretetraits,whereasDarwinworked withcontinuoustraits,leadingtodifferencesinperspectiveson inheritance (d)Darwinwasunawareofthemechanismorunitofinheritance (e)DarwinwasunawareofthemechanismsofGeneticDrift 3. Darwin’sdevelopmentofthetheoryofevolutionbynatural selectionwasNOT influencedbywhichofthefollowing? (a)Theconceptofadaptationtotheenvironment,whichwas proposedbyLamarck (b)Fossilsofextinctorganisms (c)Eachislandofanarchipelagohavingapopulationwith morphologicaldifferencesfromthoseonotherislands (d)Malthus'demographyshowingexponentialgrowthof populations (e)Changesinfrequencyofdiscretecharactersfromgenerationto generation Sample Exam Question Which of the following was NOT a tenet of the Evolutionary Synthesis? ■ ■ ■ ■ Answers: 1. B 2. E (Darwin did not know about Genetic Drift, but that was not a reason for the conflict between the “Darwinists” and “Mendelists”) 3. E (a) Evolution occurs at the level of populations, in terms of changes in allele frequencies, rather than changes at the individual level (b) Selection could act on traits that are coded by multiple genes (c) Selection acts on genetic variation in traits that are caused by mutations (d) Natural Selection and Mutation are the only causes of evolutionary change (e) Microevolutionary processes within populations lead to Macroevolutionary changes among populations ■ ■ Title goes here Answer: d Additional Optional Slides (for your interest) 17 Carol Eunmi Lee 10/19/16 Other books by Darwin on Evolution Chapters of Origins (1859) On the Origin of Species by Means of Natural Selection, or the Preservation of Favoured Races in the Struggle for Life 1 Variation Under Domestication 2 Variation Under Nature 3 Struggle for Existence 4 Natural Selection 5 Laws of Variation 6 Difficulties on Theory 7 Instinct 8 Hybridism 9 On the Imperfection of the Geological Record 10 On the Geological Succession of Organic Beings 11 Geographical Distribution 12 Geographical Distribution continued 13 Mutual Affinities of Organic Beings: Morphology: Embryology: Rudimentary Organs 14 Recapitulation and Conclusion ■ ■ ■ ■ The Variation of Plants and Animals under Domestication The Descent of Man The Expression of the Emotions of Man and Animals Full list of books by Darwin: http://en.wikipedia.org/wiki/Charles_Darwin_bibliography Charles Darwin's 1837 sketch, his first diagram of an evolutionary tree from his First Notebook on Transmutation of Species (1837) on view at the the Museum of Natural History in Manhattan. Interpretation of handwriting: "I think case must be that one generation should have as many living as now. To do this and to have as many species in same genus (as is) requires extinction . Thus between A + B the immense gap of relation. C + B the finest gradation. B+D rather greater distinction. Thus genera would be formed. Bearing relation" (next page begins) "to ancient types with several extinct forms" Title goes here 18