Adaptation,Adaptation, optimality,optimality, andand functionfunction AdaptiveAdaptive vs.vs. AdaptationAdaptation

•• TTraitsraits areare adaptiveadaptive ifif theythey areare beneficialbeneficial toto anan organismorganism inin thethe herehere andand nownow •• TTraitsraits areare adaptationsadaptations ifif theythey areare thethe productproduct ofof naturalnatural selectionselection –– TTheyhey benefitedbenefited thethe ancestorsancestors ofof thethe organismorganism andand figuredfigured inin theirtheir selectionselection •• AAllll combinationscombinations areare possiblepossible –– SSomeome traitstraits areare bothboth adaptiveadaptive andand adaptationsadaptations –– SSomeome traitstraits areare neitherneither adaptiveadaptive nornor adaptationsadaptations –– SSomeome traitstraits areare adaptiveadaptive butbut notnot adaptationsadaptations –– SSomeome traitstraits areare notnot adaptiveadaptive butbut adaptationsadaptations BiologicalBiological nichesniches changechange

•• TTraitsraits thatthat werewere adaptiveadaptive maymay ceasecease toto bebe –– VVestigialestigial organsorgans suchsuch asas thethe appendixappendix •• TTraitsraits thatthat werewere adaptationsadaptations maymay comecome toto serveserve aa differentdifferent adaptiveadaptive rolerole –– PPreadaptationsreadaptations oorr exaptationsexaptations TeleologyTeleology andand functionsfunctions

•• FForor Aristotle,Aristotle, naturalnatural phenomenaphenomena werewere teleologicalteleological –– EEventsvents happenedhappened toto produceproduce resultsresults •• TThehe scientificscientific revolutionrevolution seemedseemed toto removeremove purposepurpose fromfrom thethe worldworld –– EEventsvents happenedhappened solelysolely becausebecause ofof priorprior causescauses •• BButut teleologicalteleological talktalk isis preservedpreserved inin thethe languagelanguage ofof functionsfunctions –– TThehe heart’sheart’s functionfunction isis toto pumppump thethe bloodblood –– TThehe kidney’skidney’s functionfunction isis toto filterfilter andand removeremove wastewaste –– TThehe functionfunction ofof thethe ribosomeribosome isis toto synthesizesynthesize proteinsproteins FunctionsFunctions andand naturalnatural selectionselection

•• OOnene strategy:strategy: explainexplain thethe functionfunction ofof somethingsomething inin termsterms ofof whatwhat itit waswas selectedselected forfor –– TTreatreat itit asas anan adaptationadaptation –– FFunctionunction explainedexplained etiologicallyetiologically •• AAnothernother strategy:strategy: explainexplain thethe functionfunction ofof somethingsomething inin termsterms ofof whatwhat rolerole itit isis playingplaying todaytoday –– TTreatreat itit asas adaptiveadaptive –– FFunctionunction treatedtreated asas aa propensitypropensity •• TThirdhird alternative:alternative: explainexplain thethe functionfunction inin termsterms ofof thethe contributioncontribution somethingsomething makesmakes toto anan operatingoperating systemsystem –– DDetachetach functionfunction fromfrom naturalnatural selectionselection –– FFunctionunction inin termsterms ofof contributionscontributions toto thethe operationsoperations ofof aa mechanismmechanism WhenWhen isis aa traittrait anan adaptation?adaptation?

•• TToo bebe anan adaptation,adaptation, aa traittrait mustmust havehave figuredfigured inin thethe reproductivereproductive successsuccess ofof ancestors,ancestors, therebythereby providingproviding anan explanationexplanation ofof thethe presencepresence ofof thethe traittrait inin currentcurrent organismsorganisms •• HHowow commoncommon areare adaptations?adaptations? –– AAdaptationism:daptationism: thethe defaultdefault assumptionassumption whenwhen identifyingidentifying aa traittrait isis thatthat itit isis anan adaptationadaptation toto somesome selectionselection forcesforces •• HHeuristiceuristic forfor evolutionaryevolutionary biology—findbiology—find thethe selectionselection forcesforces whichwhich selectedselected thethe traittrait andand mademade itit anan adaptationadaptation –– AAlternative:lternative: onlyonly somesome traitstraits areare adaptationsadaptations Adaptationism:Adaptationism: ThreeThree accountsaccounts

•• EEmpiricalmpirical adaptationismadaptationism –– MMostost biologicalbiological traitstraits areare adaptationsadaptations •• NNaturalatural selectionselection isis thethe primaryprimary shapershaper ofof thethe traitstraits ofof organismsorganisms •• EExplanatoryxplanatory adaptationismadaptationism –– AApparentpparent designdesign isis biology’sbiology’s centralcentral problemproblem andand naturalnatural selectionselection isis thethe fundamentalfundamental answeranswer •• MMethodologicalethodological adaptationismadaptationism –– AAss aa strategy,strategy, viewview traitstraits asas adaptations—optimaladaptations—optimal designsdesigns promotedpromoted byby naturalnatural selectionselection SpandrelsSpandrels ofof SanSan MarcoMarco

•• SSpandrelspandrels areare anan inevitableinevitable consequenceconsequence ofof mountingmounting aa domedome onon toptop ofof roundedrounded archesarches •• OOncence spandrelsspandrels existed,existed, theythey becamebecame placesplaces onon whichwhich toto presentpresent artart •• BBUT,UT, theythey werewere notnot includedincluded inin thethe designdesign asas aa placeplace toto putput artart GouldGould andand Lewontin’sLewontin’s CritiqueCritique ofof AdaptationismAdaptationism •• TTraitsraits mightmight bebe adaptiveadaptive withoutwithout beingbeing adaptationsadaptations •• TTraitsraits cancan evolveevolve withoutwithout beingbeing adaptationsadaptations –– AAss consequencesconsequences ofof otherother traitstraits thatthat areare adaptiveadaptive –– AAss conservedconserved traitstraits duedue toto existingexisting bauplanbauplan –– AAss productproduct ofof developmentaldevelopmental constraintsconstraints •• AAdaptationistdaptationist explanationsexplanations runrun thethe riskrisk ofof beingbeing just-just- soso storiesstories –– TTypicallyypically areare notnot empiricallyempirically vindicatedvindicated OptimizingOptimizing andand GameGame TheoryTheory

•• FFindind thethe itemitem amongstamongst allall thethe alternativesalternatives thatthat optimallyoptimally meetsmeets statedstated criteriacriteria •• SSearchearch thethe statestate spacespace forfor thethe bestbest solutionsolution –– SSearchearch costscosts resources,resources, soso mustmust factorfactor inin thethe costcost ofof searchingsearching –– SSearchearch untiluntil reachreach aa maximummaximum valuevalue ofof •• OOutcomeutcome –– ccostost ofof searchingsearching •• EEvolutionvolution interpretedinterpreted asas aa searchsearch forfor optimaloptimal solutionssolutions –– GGenerateenerate manymany variantsvariants –– TThosehose thatthat solvesolve thethe problemproblem bestbest leaveleave moremore offspringoffspring –– WWinin thethe competitioncompetition inin thethe long-runlong-run Satisficing:Satisficing: HerbertHerbert SimonSimon

•• HHumanuman rationalityrationality isis boundedbounded •• SSetet aa criterioncriterion forfor aa decisiondecision beingbeing “good“good enough”enough” •• SSearchearch untiluntil anan optionoption isis foundfound thatthat meetsmeets thisthis criteria,criteria, thenthen stopstop •• AApplypply toto nature:nature: –– ““ItIt appearsappears probableprobable that,that, howeverhowever adaptiveadaptive thethe behaviorbehavior ofof organismsorganisms inin learninglearning andand choicechoice situations,situations, thisthis adaptivenessadaptiveness fallsfalls farfar shortshort ofof thethe idealideal ‘maximizing’‘maximizing’ postulatedpostulated inin economiceconomic theory.theory. Evidently,Evidently, organismsorganisms adaptadapt wellwell enoughenough toto ‘satisfice’;‘satisfice’; theythey dodo not,not, inin general,general, ‘optimize’.”‘optimize’.” Canalization:Canalization: C.C. H.H. WaddingtonWaddington •• SStatetate spacespace ofof possiblepossible designsdesigns •• DDevelopmentevelopment isis aa trajectorytrajectory throughthrough suchsuch aa spacespace •• OOptionsptions areare limitedlimited –– OOncence aa givengiven decisiondecision isis mademade inin thethe developmentdevelopment ofof anan organism,organism, thethe rangerange ofof statestate spacespace toto whichwhich itit cancan gogo isis constrainedconstrained •• DDevelopmentevelopment isis canalizedcanalized—it—it isis limitedlimited toto thethe optionsoptions availableavailable inin thethe particularparticular canalcanal itit hashas enteredentered BooleanBoolean AttractorAttractor Networks:Networks: StuartStuart KauffmanKauffman B C A A 0 0 0 0 0 0 0 1 0 1 0 0 0 0 1 0 1 0 B C 1 1 1 1 0 0 A C B A B C 0 0 0 0 0 0 1 1 0 0 1 1 1 1 1 0 1 1 0 1 1 1 0 1 1 0 1 1 0 1 1 1 1 1 1 1 GenerativeGenerative Entrenchment:Entrenchment: WilliamWilliam WimsattWimsatt •• TThreehree designsdesigns forfor aa locklock ––SStandardtandard (no(no cluesclues forfor anyany partialpartial answers)answers) »»..55 xx 10101010 == 5,000,000,0005,000,000,000 triestries toto crackcrack ––CCracker’sracker’s delightdelight (each(each wheelwheel clicksclicks whenwhen inin thethe rightright position)position) »»55 xx 1010 == 5050 triestries toto crackcrack

––DDevelopmentalevelopmental locklock (Cracker’s(Cracker’s delightdelight whenwhen solvedsolved fromfrom leftleft toto right,right, otherwiseotherwise clicksclicks areare misleading)misleading) Ernst von Baer »»WWheelsheels toto thethe rightright areare dependentdependent onon settingssettings ofof wheelswheels toto thethe leftleft TestingTesting forfor adaptationsadaptations

•• EEvenven ifif thethe criticscritics ofof adaptationismadaptationism areare right,right, therethere areare adaptationsadaptations •• CChallenge:hallenge: howhow toto testtest thethe claimclaim thatthat aa traittrait isis anan adaptationadaptation –– BBothoth thethe selectionselection forcesforces andand alternativealternative traitstraits areare usuallyusually hypothesizedhypothesized –– SSeekeek bestbest explanationexplanation forfor thethe observedobserved phenomenaphenomena •• PProblem:roblem: toto manymany freefree parametersparameters ––CCanan alwaysalways fitfit thethe phenomenaphenomena •• UUsingsing thethe comparativecomparative methodmethod toto achieveachieve furtherfurther constraintconstraint ComparativeComparative MethodMethod

•• CComparisonsomparisons withwith otherother branchesbranches inin thethe phylogeneticphylogenetic treetree cancan provideprovide evidenceevidence regardingregarding aa claimsclaims asas toto whatwhat hashas beenbeen selectedselected (and(and soso isis anan adaptationadaptation •• DDoo thethe proposedproposed selectionselection eventsevents fitfit thethe phylogeneticphylogenetic pattern?pattern? –– IIff twotwo alternativesalternatives (one(one vs.vs. twotwo hornedhorned rhinoceroses)rhinoceroses) areare bothboth evolutionarilyevolutionarily stablestable strategies,strategies, thenthen neitherneither cancan bebe invadedinvaded byby thethe otherother •• BButut thethe one-hornedone-horned speciesspecies evolvedevolved fromfrom thethe two-hornedtwo-horned oneone •• AArere therethere regularregular relationshipsrelationships betweenbetween changeschanges inin traitstraits andand changeschanges inin habitathabitat inin aa lineage?lineage?