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PhilosophyandEthicsof
MolecularBiology
Lecture3Dr.SamuelSchindler
CenterforScienceStudies
DepartmentofPhysicsandAstronomy
AarhusUniversity
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Preliminaries
Explainvs.
assess
Queries:good!
Reminderforpresenters:
Handouttotutor24hrsbeforepresentation!
Printoutthehandouts
SeealsoAULAondesignofhandouts
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Preliminaries
Newseminarinstructions
Inadditiontorequiredtext,readonepresentation
text(assignmentinseminars)
Identifyoneargument (informally)and/orcome
upwithaquestion forthepresenters
Seminarbehaviour/workethics
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Todaystopic
Thephenomenonofaltruism
Units/levelsofselection
R.Dawkinsview:theunitofselectionisnot
theorganismbutthegene
AttacksonDawkinsview
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Recall Thetheoryofevolution;twobasicprinciples
Variation (individualdifferences)
Naturalselection(limitedfoodresources,competition,environmentalchanges,etc.)
Traditionalunitsofselection: Theindividualorganism(cf.Darwin1859/
standardview!)
Groups ofindividuals(e.g.K.Lorentz)
Entirespecies(S.J.Gould)
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Darwinsview
InDarwinsview,naturalselection
operatesonindividuals
E.g.fastantelopes
Intheancestralpopulationtherewas
varietyofantelopeswithdifferentspeeds
Yet,theslowoneswereweededoutby
predators
Onlythefastonessurvived(and
procreated)
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Darwinsview
Problem
with
this
picture:
altruism
Someanimalssacrificethemselvestosavethemembersoftheirgroup/species
Examples:bees stingingintruders(killsthemselves);birds givingalarmcalls(focusingthepredatorsattentiononthem)
Note:iftheindividualistheunitofselection,whywouldtheindividualsacrificeitselfforotherindividuals?
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Darwinsview
Darwin
suggested
that
altruism
makes
sensefromtheevolutionaryperspectivebecauseitsavesgroups ofindividuals
Otherdefenders:Konrad Lorentz
Note:thisisinconsistent withhisoverallviewthatselectionworksonindividuals,ratherthangroups!
Thelatteristhestandardview
Infact,thestandardviewrendersaltruismevenunlikely.
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Individualismandaltruism
Supposethat
agroupconsistsofindividualswhoregularly
exhibitaltruisticbehaviortowardstheirgroup
peers
thereareonlyfewegoisticindividualsinthose
groups
thealtruistic/egoistic traitisinherited
Then
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Individualismandaltruism
Theegoisticindividualshaveaselective
advantageoveraltruisticonesinthatgroup:
Theycanbenefitfromthealtruisticbehavioroftheir
peerswithout havingtoexposethemselvestorisks
Becauseegoisticbehaviorisadvantageousinthe
survivalofthefittest,overtime,altruismwill
disappearinthosegroups
Hence,evenifaltruismdoesoccasionallyoccur,it
isgoingtoselectedagainstbyevolution!
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Individualismand
altruism
theoptions:
1. Altruisticbehaviorisachimera
Optionadoptedbymanybiologists/theoristsof
evolution
2. Altruisticbehaviorisrealandneedstobe
explained
whatwellfocusonhere
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Puzzle:
Howcanweaccommodatealtruism
onthetheoryofevolution?
RichardDawkinsanswer:
Wecandothatbymakinggenes,not
organisms,theunitofselection
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RichardDawkins
Dawkins:The
Selfish
Gene
Published1976
Earlycareer:zoologist
ProfessorforPublicUnderstanding
ofScienceatOxford(19952008)
Otherpublications
Theblindwatchmaker
TheGodillusion
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Theselfishgene
From
the
perspective
of
the
genes
eye,
altruism
makesperfectlysense:
Individualssacrificethemselvesinordertosavethegroupbecause
Thesurvivalchanceofparticulargenes (thattheindividualshareswiththegroup)isincreased!
Afteranattackerhasbeenfoughtoffandthegroupsavedbyanindividual:
thegenefrequencyinthegenepoolisincreased(attheexpenseoftheorganism)
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Furtherreasonswhythegene
shouldbetheunitofselection.
1. JunkDNAmakesnosenseonthestandard
viewofevolution(w/individuals=units)
2. Onlygeneshavetherightcharacteristics
requiredbythetheoryofevolution
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Furtherreasons(1)
Anotherargumentagainsttheindividual
organismasunitofselection
Theexistenceofnoncoding/junkDNA:98%of
ourgenome!
Fromtheperspectiveoftheorganism
since
junk
DNA
has
no
function
for
the
organism/species thereisnogoodexplanation
forwhyorganismsshouldkeepinheritingjunk
DNA
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Furtherreasons
(1)
Ongeneeyeview(p.44/45)
ThetruepurposeofDNAisnotthebuildingof
organisms(inwhichtheyreside)
Rather:thesolepurposeofDNAisittosurvive!
JunkDNAisparasitic;itisaharmlessbutuseless
passenger,hitchingaride!
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Furtherreasons
(2)
Theunitofselectionmust
havelotsofcopies
Otherwise:smallchanceofsurvival
havethepotentialtosurviveforasignificant
periodofevolutionarytime(>longevity)
Neitherorganisms,norspecieshavethe
secondcharacteristic
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Furtherreasons(2)
Each
individual
is
unique.
You
cannot
get
evolutionbyselectingbetweenentitieswhenthereisonlyonecopyofeachentity!
Eachindividualhasveryspecificcharacteristics: e.g.onlyoneleg
Sexualreproductionisnotreplication.(34)
Weinheritonly50%ofourgeneticmaterialtoourprogeny
Afterafewgenerations: hardlyanyproportioninyourdescendantsofwhatmadeYOU
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Furtherreasons(2)
Individualsare
not
stable
things,
they
are
fleeting.genesareforever(35)
Genesare(normally)notdividedwhenpassed
fromonegenerationtothenext
Ofcourse:geneswillnotliterallylastforever
justlongenoughtofunctionasaunitof
naturalselection
contrarytoorganisms
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Theselfishgene
Genesarereplicators
Onlytheytrulyreplicate
Organismsaremerelyvehicles ofgenes
Also:interactors
Theymerelyarethegenesmeans totheendofsurvival
Genesareselfishbecausealltheycareaboutistheir
own
survival Theyproduceorganisms/vehiclesonlyinordertosurvive
Note:thisiswhatDawkinsthinksitisreasonabletoinfer
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Theselfishgene
IfweweretoldthatamanhadlivedalongandprosperouslifeintheworldofChicagogangsters,wewouldbeentitledtomakesomeguessesastothesortofmanhewas.Wemightexpectthathewouldhavequalitiessuchastoughness,aquicktriggerfinger,andtheabilitytoattractloyalfriends.
Thesewould
not
be
infallible
deductions,
butyoucanmakesomeinferencesaboutaman'scharacterifyouknowsomethingabouttheconditions inwhichhehassurvivedandprospered.
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Theselfish
gene
Theargumentofthisbookisthatwe,andallotheranimals,aremachinescreatedbyourgenes.LikesuccessfulChicagogangsters,ourgeneshavesurvived,insomecasesformillionsofyears,inahighlycompetitiveworld.Thisentitlesustoexpectcertainqualitiesinourgenes.Ishallarguethatapredominantqualitytobeexpectedinasuccessfulgeneisruthlessselfishness.Thisgeneselfishnesswillusuallygiverisetoselfishnessinindividualbehaviour.
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Genes
and
the
primeval
soup
ThegenesstruggleofsurvivalNOW(inorganisms)isnotmuchdifferentfromwhatitusedtobeatthebeginningoflifeonEarth!
Intheprimevalsoupreplicatorsarosebyaccident(15ff.),diversifiedthroughreplicationerrors,andcompetedagainsteachother
Replicatorswithnumerousreplications(fecundity),lasting replication(longevity)andaccurate replication(fidelity)wonout
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Theselfishgene
The
selfishness of
genes
often
directly
translatesintothebehaviour oforganisms
Prayingmantis:femalebitesofftheheadofmaleafterorevenduringcopulation
Inordertofeedherself(andinordertoincreasethemalessexualperformance!)
Emperorpenguins:sometimespushtheirpeersintothesea
Inordertotestwhethertherearesealsinthewater(whomightkillthem)
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Theselfishgene
Butnote:
the
selfishness
of
the
gene
doesnotnecessarilyimplythat
organismsbeselfish
Geneselfishnessisverymuch
compatiblewithaltruistic behaviour
Helpingotherorganismsofthesame
speciesisameanstotheendofreplicating
genesofthesamekind
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Howselfisharegenes?
Thegene isthebasicunitofselfishness
Infact:Genesarecompetingdirectlywiththeir
allelesforsurvival,sincetheirallelesinthegene
poolarerivalsfortheirslotonthechromosomeof
futuregenerations.
at
the
gene
level,
altruism
must
be
bad
and
selfishnessgood(36)
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Howselfisharegenes?
Trulyruthlesslyselfishgenes:outlaw
genes
Noregardforwhethertheirreplicationis
ofanybenefittotheorganismornot
Examples:
JunkDNA
Drivinggenesthatdistortmeiosisintheir
ownfavour,sothattheyhaveagreater
chanceofmakingitintogametes
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Howselfish
are
genes?
Important:Dawkinsconceptionofselfishgenesdoesnotimply thatgenesnevercooperate
Genesmayservetheirowninterestsbestbycooperatingwithothergenes(p.37) Hence:selfishnessthroughcooperation
E.g.:buildingalegcannotbedonebyasingle gene Butasinglegenewillprofitfromorganisms
thatrunfast!
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Howselfish
are
genes?
Yet,singlegenesmayverywellmakea
differencetothephenotype
E.g.thelength oflegs
Analogy:plantfertilizer
Otherthingsbeingequal,plantfertilizermake
plantsgrow
Otherimportantfactors:seed,soil,sun,water,
etc./onlyiftheyarepresent,doesthefertilizer
makeadifferencetoplantgrowth
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Howselfisharegenes?
Dawkins
compares
gene
selectionism to
the
coachsselectionofoarsmen(i.e.,rowers)inboatracing
Thecoach hastopickanidealteam
Assemblesthreecrews andshufflesthemembersrandomlyandletsthemraceagainsteachother
Itturnsoutthat,onaverage,therearesomeindividualsthattendtobeinthewinningboats,andsomewhotendtobeintheloosingones
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Howselfisharegenes?
Analogy
to
gene
selection
Oarsmen =genes
Rivaloarsmenforaseatintheboat=allele
Rowingfast=buildingavehiclewhichissuccessfulatsurviving
Coach=naturalselection
Note:anygene(goodandbadones)mustcooperate withothersinordertorowfast Cooperation isintheirselfinterest
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TasksandQuestions Explainwhyaltruism isproblematiconthe
standardviewofevolution
ExplainDawkinsargumentsforwhythegeneshouldbeviewedastheunit ofselection(ratherthantheorganism);mention
Altruism
JunkDNA
Characteristicsrequiredbyevolution
Inparticular:longevity
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WhoagreeswithDawkins?
Handsup!
34
Argumentsagainstthegenes
eyeviewofevolution
1. Dawkinsgeneconcept
2. AcrucialambiguityunderminingDawkinsaccount?
3. Developmentalsystems
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Whatsagene
acc.
to
Dawkins?
Evolutionarygeneconception(fromWilliams)
Ageneisdefinedasanyportionofchromosomal
materialthatpotentially lastsforenough
generationstoserveasaunitofnaturalselection
(p.28)
Note:veryloose definitionindeed!
Nomentionofanymolecularmechanisms(such
astranslation/transcriptionetc.)
'thegenemayvaryinlength
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Theevolutionarygeneconcept
The
shorter
the
genetic
unit,
the
more
likelyitistosurvive(p.29)
Consider
Ageneticunitofhalfthesizeofachromosome:thereisa50%chancethatitwillbesplitaftereachmeiosis
Ageneticunitof1%ofthesizeofachromosome:1%chanceofsurvivalaftereachmeiosis
So:sizematters!
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Theevolutionarygeneconcept
Note:the
evolutionary
gene
concept
is
compatiblewithnucleotidesbeinggenes!
Theyaretheshortest portionofchromosomal
materialthatpotentiallylastsforgenerations
Plus:theycanfunctionasunitsofselection
Butthatsofcourseabsurd;nucleotidesare
notgenes
Yet,itfollowsfromDawkinsdefinition!
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Theevolutionarygeneconcept
Dawkinsreaction:
Itwouldbeabsurdtosaythatthedifferenttypes
ofnucleotidescompete witheachother
andthatnucleotidesofthesametypeco
operatewitheachother
If[nucleotides]
are
competitors
at
all,
they
are
competitorsforeachlocusseparately.Theyare
indifferenttothefateoftheirexactreplicasat
otherloci.(1982,p.91)
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Theevolutionarygeneconcept
CriticismbyGriffithsandNeumannHeld(1999)
Dawkinsonallelesofthesametype:nocompetition
Dawkinsonnucleotidesofthesametype:competition
Hence:Dawkins
is
inconsistent!
Whyistherecompetition b/wnucleotidesofthesametypebutnocompetitionb/wallelesofthesametype?
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Theevolutionary
gene
concept
Notealso:cooperationbetweensametypesof
genes/alleles isrequiredforexplaining
altruism!
Onlyifthereiscooperationatadistance
betweengenescanweexplainfromthegenes
eyeviewwhydifferentorganisms(withsimilar
genes)cooperate
Again:whatsthejustificationforthis?
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Anothercriticism:Dawkinsview
isunderminedbyanambiguity
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Animportantambiguity
Soberpoints
out
that
there
is
an
important
distinctiontobemadebetween
SelectionforX Xs survivebecause evolutionselectsforthem
SelectionofX Xs survivenot becauseevolutionselectedfor
them,butbecauseforsomeotherreason
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Illustrativeexample
Selection
forball
size
i.e.causalselection
Selectionofballcolour
i.e.,correlativeselection
E.SobercriticizesDawkinsfornotdistinguishingbetweenselectionforgenesandtheselectionofgenes
44
Animportantambiguity
Selectionforgenes
Organismssurvivebecause theyhavecertaingenes
Sober:notcorrect!Rather:b/corganismshavecertainproperties
Selectionofgenes
Organismssurvive
because
they
have
certain
features whichareadaptedtotheenvironmentandthosefeaturesarecausedbygenes
Sober:triviallytrue/widelyaccepted!
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Acounterexample?
Selectionforgenes=false
Counterexample:sicklecellanemia
andMalaria
Heterozygotes withasicklecellallele
andanormalallelearemorelikelyto
surviveMalaria
than
homozygotes
withtwonormalalleles
Anemiasymptoms:minimal
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Acounterexample?
Sober:whatsbeingselectedforis
thegenotype(heterozygote),not
forparticulargenes(i.e.,alleles)
Howeverthereisofcourseselection
ofalleles
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Acounterexample?
Note:selectionofgenesiscompatiblewithselectionforindividuals
Itisthevehicles/interactors thatfeeltheforceoftheenvironment(i.e.,naturalselection),notthegenes
Itisthevehiclesthatare,orarenot,adapted totheirenvironments,notthegenes
Itistruethat,ultimately,evolutionischangeofgenefrequenciesinthegenepoolovertime
Butthissaysnothingaboutwhycertaingenesareselected
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ReplytoSober
Sterelny andKitcher (1988)
Theyargue:ifconstruedcorrectly,Sobers alleged
counterexamplecanbeturnedintoaconfirmation
ofDawkinsview!
Crux:theexampleturnsonthefrequency ofthe
respectiveallelesinthegenepool
Inotherwords:geneselectionisfrequency
dependent
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ReplytoSober
A
sickle
cell
allele
will
be
fitter in
contexts in
whichthenormalalleleforhemoglobinoccursfrequently
Because:insuchcontextsthesicklecellheterozygoteismorelikelythanthesicklecellhomozygote
And,organismswithasicklecellalleleandanormalallelewillhaveabetterchancetosurviveMalaria
Hence:thesicklecellallelewillbeselectedfor
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ReplytoSober
Yetincontexts inwhichthesicklecellalleleisfrequent,thesicklecellallelewillbeunfit
Thentheorganismisatahighrisktodieofsicklecellanemia
Hence:normalallelewillbeselectedfor
Thus,itisnottruethat,asSoberclaims,thegenotype,
but
not
genes
are
being
selected
for
Onthecontrary,genes/allelesarebeingselectedfor,justasDawkinsclaims
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Developmentalsystems
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Geneticdeterminism?
Criticism:Dawkinsviewpresupposesgeneticdeterminism
Geneticdeterminism:istheviewthatthephenotypeisfullydeterminedbythegenotype
R.Gray,P.Griffiths,andothers:
geneticdeterminismiswrong!
Environmentalconditionsarejustasimportantasgenesintheexpressionofthephenotype!
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Geneticdeterminism?
NumberofeyesinDrosophila(wildtype)
Normally: between700and1100(temperaturedependent!)
Mutations
UltrabarandInfrabar:bothconsistently lessthanthewildtype
However: theanswertothequestionwhichmutationhasmoreeyes,UltrabarorInfrabariscontextdependent
Temperaturetoodetermineseyenumber(notjustgenes)
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Geneticdeterminism?
Challenge
to
Dawkins:
Genesdonotdeterminethephenotype
Thereareotherimportantfactors(e.g.environment)
Butifgenesdonotdeterminethephenotype,andthereareotherimportantfactors,then
.wecannotreallysaythatgenesarebeingselectedforwhencertainorganismssurviveandprocreate(andtherebyreplicategenes)
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Geneticdeterminism?
Question:
does
Dawkins
really
subscribe
togeneticdeterminism?Whatsmore,doeshisviewreallyrequireit?
Dawkins:
Developmentoforganisms:Geneticcausesandenvironmentalcausesareinprinciplenodifferent.
Evolution:Geneticfactorsreplicatethemselvesbutnongeneticfactorsdonot
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Geneticdeterminism?
Itsnottruethatonlygenesarereplicatedthroughoutgenerations
Exampleforextragenetic inheritance:aphidBuchneraendosymbiosis
Aphidswithout Buchnera:stuntedgrowth,reproductively sterile,dieprematurely
MaternalBuchneramassisbeingpassedontoeggsorembryo
Remarkablyancientsymbioticrelationship
160 280millionyears!
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Aphid=bladlus
Geneticdeterminism?
AphidBuchneraexamplessatisfiesDawkinsthreecriteria Longevity (sincewehaveinheritanceonan
evolutionaryscale)
Fecundity,andfidelity (numerousandaccuratereplication)
Note:buchnera arenotpartofthegenetic
programme ofaphids!
ContrarytoDawkins:thewholedevelopmental systemisbeingreplicatedindefinitely
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Aphid=bladlus
Geneticdeterminism?
Epigeneticinheritancethroughmethylation
Methylgroupsblockthetranscriptionofanygenestheyareattachedto
Normallyremovedduringzygoteformationandreestablished duringcelldivisions
Methylationlevelisthoughttobeinfluencedbyexternalfactorslikediet
Hence:
Changeofgeneexpressionthroughchangeofexternalfactors
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Developmentalsystems
GriffithsandGraysconclusion:
Theunitofselectionisnotjustthegenebut
ratherentiredevelopmental systemswhich
arebeingreplicated(onanevolutionary
scale)
Thegene isjustoneamongmanyother
factorsdeterminingthephenotype
Others:environment
Hence,thegeneisnottheunitofselection
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TasksandQuestions Explain
Griffiths
and
Neumann
Helds
challengeabouttheevolutionarygene
ExplainSobers sicklecellcounterexampleto
Dawkinsgeneeyeview
ExplainSterelnyandKitchers responseto
Sober
Explaintheideaofdevelopmentalsystems
withregardtotheunitofselectiondebate
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Lecturequery Explain
Dawkins
idea
of
the
gene
being
the
unitofselection
Mentiontheideaofthelongevityofreplicators
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