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Transcript
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
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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
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Changesinproportioninapopulationcouldoccurviarandomgeneticdrift(Sewall
Wright)orNaturalSelection…therateofmutationisusuallytoolowtocauselarge
changesinproportions
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Evenveryweaknaturalselectioncouldcausesubstantialchangesoveralonger
timescale
Mutationsgeneratethegeneticvariationuponwhichnaturalselectionacts
MicroevolutionaryprocessesleadtoMacroevolutionarychanges(speciation)
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Allorganismsontheplanetarerelatedtooneanotherinagreat“treeoflife”,and
havedivergedbybranchingfromcommonancestors
Gapsinthefossilrecordarelikelyduetoincompletenessofthefossilrecord.
Gradualchangesseeninmanypartsofthefossilrecordsuggestgradualchanges
overtime–notalwaystrue
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Completing the Synthesis
Evolution at the Molecular Genetic Level
Advances in Genetics
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Which types of mutations predominate and contribute to
adaptations more often?
Epigenetic Inheritance (Lecture #9)
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Structural vs Regulatory?
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Some genetic changes could lead to radical
changes in phenotype (Lecture #7)
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Polyploidization seen often in plants
Changes in developmental genes
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Regulatory Evolution
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Transposons
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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?
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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)
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LamarckRevisited
Evolution of
Development
(Lecture #26)
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Lamarckwasincorrectinthinkingthatthe
inheritanceofacquiredcharactersisthemain
mechanismofevolution
However,wedonowknowthattheinheritanceof
acquiredcharactersdoeshappensometimes,
throughtheinheritanceofepigeneticmodifications
Title goes here
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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
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Carol Eunmi Lee
10/19/16
Role of Genomics
Today: Genome Evolution and Systems Biology
(Lectures #15, 16)
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How does the whole
genome evolve?
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How does selection act on
networks of interacting
genes?
How many and which
genes are involved in the
formation of new species?
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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
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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?
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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
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Title goes here
Answer: d
Additional Optional Slides (for
your interest)
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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
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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
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