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AgentsandGoalsinEvolution
AgentsandGoals inEvolution
SamirOkasha
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ForHaviCarel
PartII.The‘Goal’ofFitnessMaximization
3.Wright’sAdaptiveLandscape,Fisher’sFundamentalTheorem
5.SocialEvolution,Hamilton’sRule,andInclusiveFitness
PartIII.RationalityMeetsEvolution
6.TheEvolution–RationalityConnection
7.CanAdaptivenessandRationalityPartWays?
8.4‘MotherNature’andGeometricMeanFitness
PrefaceandAcknowledgements
Thisisabookaboutevolutionarybiology,writtenfromaphilosophicalperspective. Itsmainconcernistoanalyseamodeofthinkinginbiologythatisquitecommon,and philosophicallyinteresting.Icallit‘agentialthinking’,followingPeterGodfrey-Smith. Itassumesavarietyofforms;butinitsparadigmcase,agentialthinkinginvolves treatinganevolvedorganismasifitwereanagentpursuingagoal,suchassurvivalor reproduction,andtreatingitsphenotypictraits,includingitsbehaviour,asstrategies forachievingthatgoal,orfurtheringitsbiologicalinterests.Thiswayofthinking mightbethoughtuncontroversial,oratleastnomorecontroversialthanthebasic Darwinianassumptionthatorganisms’evolvedtraitsareoftenadaptive.Butthereis moretoitthanthis.Foragentialthinkinginvolvesdeliberatelytransposingasetof concepts—goals,interests,strategies—whoseoriginalapplicationistorationalhuman agents,tothebiologicalworldmoregenerally.Whatcouldbethejustificationfor doingthis?Isitmereanthropomorphism,ordoesitplayagenuineintellectualrolein thescience?
Thisquestionisthestartingpointofmyenquiry,butitleadstoaseriesoffurther questions.Howdoweidentifythe‘goal’whichevolvedorganismswillbehaveasif theyaretryingtoachieve?Canagentialthinkingeverbeappliedtogroups,ratherthan toindividualorganisms?Howdoesagentialthinkingrelatetothecontroversiesover fitness-maximizationinevolutionarybiology?Afurthersetofquestionsconcerns therelationbetweentheadaptiveandtherational.Iforganismscanvalidlybe treatedasagent-like,forthepurposesofevolutionaryanalysis,shouldweexpect thattheirevolvedbehaviourwillcorrespondtothebehaviourofrationalagents ascodifiedinthetheoryofrationalchoice?Ifso,doesthismeanthatthefitnessmaximizingparadigmoftheevolutionarybiologistcanbemappeddirectlytothe utility-maximizingparadigmoftherationalchoicetheorist?Theseareasampleof thequestionsaddressedinthebook.
Thebook’sorientationisphilosophical,butitadoptsaninterdisciplinaryapproach. Itiswrittenintheconvictionthatphilosophyofscienceisatitsmostproductivewhen donewithacloseeyeonthescienceitself.Assuch,thebookengagesextensively withtheevolutionarybiologyliterature,andtoalesserextentwiththatofeconomics andrationalchoice.Thebookisaimedatphilosophersofthebiologicalsciences, evolutionistswithatasteforconceptualissues,andinterestedpartiesfromother disciplines.ItassumesabasicfamiliaritywithDarwinianevolution,butnospecialist scientificorphilosophicalknowledge,andmanyconceptsareexplainedfromscratch. Partsofthebookaresomewhattechnical—butnomoreso,Ihope,thanisnecessary totackletheissuesproperly.
Thebookistheresultofmanyyears’work.Itwouldbeimpossibletoacknowledge allofthepeoplewhohaveinfluencedmythinking,butparticularmentionmustgo toKenBinmore,ElliottSober,KimSterelny,PeterGodfrey-Smith,DanielDennett, BrianSkyrms,AlanGrafen,AndyGardner,ArthurRobson,CédricPaternotte,David Queller,JonathanGrose,TimLewens,JonathanBirch,AnthonyEdwards,John McNamara,andJamesLadyman.Anumberofcolleaguesprovidedvaluablefeedback onindividualchapters:AlexRosenberg,AlexanderBird,RichardPettigrew,Tudor Baetu,TimLewens,JohannesMartens,andBengtAutzen.Iamparticularlygrateful toKenBinmore,NicholasShea,andPatriciaRich,whoprovideddetailedwritten feedbackonmultiplechapters,andtoJonathanBirch,oneoftworeadersforOUP, whodidlikewise.
EarlypartsoftheworkwerefundedbyaresearchgrantfromtheArtsand HumanitiesResearchCouncil,between2008and2011.Themajorityoftheresearch, andtheactualwritingofthebook,wasfundedbyaEuropeanResearchCouncil AdvancedGrant,agreementno.295449,between2013and2017.Iamgratefulto myemployer,theUniversityofBristol,forallowingmethetimenecessarytobring theprojecttocompletion.IamgratefultoOxfordUniversityPress,JohnWiley, andSpringerforpermissiontore-usematerialpublishedin BritishJournalforthe PhilosophyofScience vol.59, JournalofEvolutionaryBiology vol.29,and Biologyand Philosophy vol.29,respectively.Finally,IamgratefultoHavi,Solomon,andJoelfor theirendurancewhileIwaspreoccupiedwiththisproject,andtomyparentswho encouragedmetostudyphilosophyinthefirstplace.
ListofFigures,Tables,andBoxes
Figures
2.1.Individualsinagroup-structuredpopulation55
3.1.Adaptivelandscape75
3.2.Individualversuspopulationoptimum81
3.3.Twocausalpathways93
4.1.Convergencetoafitnessminimum(redrawnfromDoebeli(2011),p.17)112
5.1.Directandindirectdeterminantsoffitness128
7.1.Desertiongame181
7.2.Trustgame(modifiedfromBerninghaus etal.(2012),p.114)183
7.3.Choicebetweentworewards194
8.1.Concaveutilityfunction201
8.2.Concavefitnessfunction207
Tables 3.1.One-locustwo-allelemodel88
5.1.Additivecase,personalpayoffs122
5.2.Pair-typefrequencies122
5.3.Conditionalprobabilities123
5.4.Additivecase,simplifiedIFpayoffs124
5.5.Additivecase,originalIFpayoffs125
5.6.Evolution–rationalitylinkwithutility=inclusivefitness126
5.7.Additivecase,Grafen1979payoffs126
5.8.Non-additivecase,personalpayoffs127
5.9.Evolutionarydynamics,non-additivecase130
5.10.Non-additivecase,simplifiedIFpayoffs131
5.11.Non-additivecase,Grafen1979payoffs131
5.12.Evolution–rationalitylink,utility=Grafen1979payoff132
5.13.One-locustwo-allelemodel136
6.1.Payoffsforthreealternativeactions162
6.2.A Bayes-like organism165
7.1.Prisoner’sDilemma177
xivlistoffigures,tables,andboxes
7.2.Foragingoptions(basedonHouston etal.(2007b),p.366)186
7.3.Choicesthatmaximizesurvival(basedonHouston etal.(2007b),p.366)186
7.4.Parting-of-waysarguments197
8.1.AversionoftheAllaisparadox203
8.2.Per-capitareproductiveoutputoftwotypes211
8.3.AbiologicalAllaisparadox218
8.4.Reproductiveoutputofeachtype219
8.5.Coldandwarmenvironments221
Boxes
2.1.Multi-levelselectionpartition56
4.1.Grafen’sselection-optimalitylinks(basedonGrafen(2014a))101
4.2.Uninvasibilityandconvergentstability110
Introduction
Thereisafamiliarstoryabouttheplaceofteleologyinbiologythatgoesasfollows. SinceAristotle,biologistshaveusedateleologicalidiomtodescribelivingorganisms, butthejustificationfordoingsoonlybecameapparentwithDarwin.Thoughthe processofevolutionbynaturalselectionismechanicalandlacksforesight,Darwinism nonethelesslicensestalkoffunctionandpurposeinnature.Instatementssuchas‘the polarbear’swhitecoatisforcamouflage’and‘thecactushasspinesinordertodeter herbivores’,theteleologicalterms(‘for’,‘inorderto’)arereallyawayoftalkingabout adaptivesignificance.Naturalselectionledpolarbearstoevolvewhitecoatsandcacti togrowspinesbecausethesetraitshelpedtocamouflagebearsandprotectcacti,so wereadaptive.ThusDarwinismsuppliesanaturalisticbasisforatleastsomeofthe teleologicalidiomsthatbiologistshadlongused.
ArelatedideaisthatDarwinismplacedteleologicalexplanationsonarespectable footingbyshowingthemtobereallycausal.Explanationssuchas‘plantsgrowtallto gainmoresunlight’appeartoexplainafeaturebyitseffectsratherthanitscauses; takenatfacevalue,thisinvolveseitherbackwardscausationortheattributionof consciousintenttoplants,bothofwhichareproblematic.However,inthelightof Darwin,weknowthatsuchexplanationscanbetranslatedintopurelycausalterms. Inthepast,plantsthatgrewtallobtainedmoresunlightthanonesthatdidn’t,soleft moredescendants,andthusthetraitproliferated.Thatis,naturalselectiongenerates afeedbackprocessinwhichatrait’seffectcausallyinfluencesitssubsequentfate,thus showingtheapparentlyteleologicalexplanationtobecausalindisguise.
TheideathatDarwinismnaturalizesteleologybyidentifyingatrait’sfunctionwith itsadaptivesignificancehasconsiderablemerit.Itmakessenseofmuchbiological usage,andprovidesaprincipledbasisonwhichtodeterminewhentalkoffunction,design,andpurposeislegitimate.(Thoughitisanopenquestionwhetherall biologicalusesoftheterm‘function’shouldbeunderstoodthisway.)Moreover,it helpsexplain,inanaturalisticallyacceptableway,whyweapplyapurposiveidiomto livingorganismsandtheirtraits,butnottomountainsorrivers.Finally,theempirical commitmentsoftheideaarefairlymodest:thatorganismsexhibittraitswhich contributepositivelytotheirDarwinianfitness,sohavefunctions,isacommonplace ofevolutionarybiology.
Myconcerninthisbookiswithamodeofthoughtinevolutionarybiologythat isrelatedtothefunction-talkthatDarwinismnaturalizes,butisdistinctfromit.
Itinvolvesappealtothenotionof agents with interests, goals,and strategies in evolutionaryanalysis.Icallthis‘agentialthinking’,followingGodfrey-Smith(2009). Inthemostcommonformofagentialthinking,theagentsareindividualorganisms, theirgoalistosurviveandreproduce,andtheirevolvedtraitsarestrategiesfor achievingthisgoal.Behaviouralecologistsoftenthinkaboutanimalbehaviourin theseterms.Inothercases,theentitiesthataretreatedasagentsaregenesor groups,ratherthanindividuals.Astilldifferentformofagentialthinkinginvolves treatingtheprocessofnaturalselectionitself,personifiedas‘mothernature’,asagentlike,choosingbetweenalternativephenotypesinaccordancewithagoal,suchas improvingapopulationormaximizingitsfitness.
Agentialthinkingisaformofadaptationistreasoning—thatis,oftryingtounderstandevolvedtraitsintermsoftheircontributiontofitness.Assuch,itisrelatedto thesortoffunction-talkthatcanbestraightforwardlynaturalized.Butitgoesfurther, foritinvolvestransposingasetofconcepts—interests,goals,andstrategies—whose originalapplicationistothedeliberatebehaviourofhumanagents,tothebiological worldatlarge.Whenappliedcarefully,thiscanyieldinsight.Forexample,suppose wewanttoexplainwhyamalerattriestokillthepupsproducedbyafemaleintheir group,andwhythefemaletriestostophim.Bythinkingofthemaleasanagentwhose goalistomatewiththefemale,andwhohasdevisedastrategyforbringingherbackto estrus,wecanmakesenseofhisinfanticidalactions.Similarly,bytreatingthefemale ratasanagentwithherowngoal,weseeimmediatelythatmaleandfemalehave differentinterests,thusexplainingtheconflictbetweenthem.
Onesymptomofagentialthinkingistheuseofintentionallanguage,suchas ‘knows’and‘wants’,inevolutionarybiology.Suchlanguagehasitsprimaryapplication inhumanpsychology,butisoftenusedinabiologicalcontexttoo,inanextended ormetaphoricalsense.Intentionallanguageissurprisinglyaptfordescribingand explainingadaptivebehaviour,evenoforganismswithlimitedcognitiveabilities,as Dennett(1987)observes.Forexample,consideraworkerhoneybeewhoeatsthe eggslaidbyafellowworker.Thisbehaviourisadaptive,asitensuresthattheoffspring ofthequeenwillpredominateinthecolony,whichfurthersthefirstworker’sindirect evolutionaryinterests,giventheirclosegeneticrelationshiptothequeen.Though theproximatecauseoftheworker’sbehaviourischemicalnotpsychological,itis extremelynaturaltoexplainthebehaviourbysayingthattheworkerknowsthat theeggswerelaidbyafellowworker,andprefersthatthequeen’soffspringare rearedinstead.
Thoughtheuseofagentialandintentionalidiomsinevolutionarybiologyisboth naturalandfamiliar,fromoneperspectiveitisstillquitepuzzling.Afterall,itis notgenerallyausefulstrategyinsciencetotreattheobjectsofone’sstudyasifthey hadcertainattributeswhichinfacttheylack.Biologistsdonotfinditusefultotreat invertebratesasiftheyhadbackbones,afterall.Whythenwoulditbeusefultotreat evolvedorganismsasiftheywereagentspursuinggoals,andtomakethemthesubject ofintentionalattributions,wheninfacttheylacktheseattributes?Whatifanythingis gainedbythinkingandtalkingthisway,andhowexactlydoesitrelatetootherways
ofpursuingtheadaptationistprogrammeinevolutionarybiology?Muchofthefirst twochaptersofthebookisanattempttoanswerthesequestions,thoughtheyrecur throughout.
Agentialthinkingisintimatelylinkedwiththeideaof fitness-maximization in biology.Thisideahastwovariants,bothcontroversial.Thefirstisthatevolved organismswillexhibittraitsthatareadaptive,hencemaximizetheirfitnessrelative tosomesetofalternativetraits.(Howexactly‘fitness’shouldbedefinedisamajor issue.)Thesecondisthattheprocessofnaturalselectionitselfinvolvesmaximization, inthesenseofcontinuallychangingapopulation’scompositionsoastoachievehigher fitness.Thesetwoclaimsarerelatedbutdistinct.Theformerconcernsadaptation(the product),whilethelatterconcernsselection(theprocess).Bothtieinwithagential thinking,butofdifferentsorts.Theformerrelatestotheparadigmaticsortofagential thinkinginwhichtheagentwiththegoalisanindividualorganism.Thelatterrelates tothe‘mothernature’sortofagentialthinking,inwhichtheagentwiththegoalisthe evolutionaryprocessitself.Thustoassessthevalidityofagentialthinking,ofeither sort,weneedtoexaminethestatusoffitness-maximizationinbiology.Thisistaken upinthemiddlechaptersofthebook.
Agentialthinkingisnotjustabouttheuseofwords,butalsoaboutmodelsand explanatorystrategies.Sincethe1960s,conceptsandmodelsfromrationalchoice theoryhavebeenusedbybiologists,withmodifications,tohelpunderstandevolved behaviour.Forexample,Bayesiandecisiontheoryhasbeenusedtostudyanimals’ choicesinthefaceofenvironmentaluncertainty,suchastheforagingstrategiesof birds(Valone2006);signaldetectiontheoryhasbeenusedtoexplainaspectsof animalcommunication(Wiley2013);gametheorywasimportedintobiologyfrom economicstoshedlightonanimalconflicts,adevelopmentthatgaverisetothe fieldofevolutionarygametheory(MaynardSmith1982);andbargainingtheoryhas beenusedtostudythedivisionofreproductionwithinanimalsocieties(Cantand Johnstone2009).Ineachofthesecases,modelsoriginallydesignedtoapplytorational humanagentshavebeenre-purposedforevolutionaryanalysis.
Thistransferofideasmayseemsurprising,giventhatmostnon-humanorganisms havelimitedpowersofrationaldeliberation.Whatexplainsit?Partoftheansweris thattheconceptof utility inrationalchoiceandeconomicsplaysasomewhatsimilar roletotheconceptof fitness inevolutionarybiology,ashasoftenbeennoticed.Justas rationalchoicetheoristsassumethatagentswillbehaveinawaythatmaximizestheir utility,soevolutionistsoftenassume,andinsomecasescanshow,thatorganismswill behaveinawaythatmaximizestheirDarwinianfitness(roughly,expectednumber ofoffspring),orsomeproxyforit.Thisconceptuallinkbetweenutility-maximization andfitness-maximizationwasemphasizedbyMaynardSmith(1982).Morerecently, itfeaturesintheworkofGrafen(2006,2014a),whooffersanexplicitdefenceofthe ideathatanevolvedorganismcanbemodelledasanagenttryingtomaximizeautility function,whereutilityissuitablydefinedintermsofreproductivefitness.
Treatinganorganismasakintoarationalagentpursuingagoalisoftenheuristicallyvaluable,andquitecommoninbiologicalpractice.Clearly,itisrelatedtothe
function-talkthatcanbestraightforwardlynaturalized;foritisbecauseorganisms’ behaviourisevolved,henceadaptive,thatitcanoftenbeusefullyassimilatedto rationalbehaviour.Butagain,itgoesbeyondthispoint.Fortheuncontroversialidea thatevolvedbehaviourispurposiveinthesenseofhavingaDarwinianfunction doesnotshowthatitcorresponds,inanypreciseway,tothepurposivebehaviourof rationalagentsthatisthesubjectmatterofrationalchoicetheory.Certainlythereis aconceptualparallelhere,andcertainlytheimportingofrationality-inspiredmodels intobiologyhasborneintellectualfruit,butcanamoreexplicitconnectionbeforged betweenthetwosensesofpurpose—thatis,betweentheadaptiveandtherational?
Tomakethismoreconcrete,considertheproblemofdecision-makingunder uncertainty.Standardrationalchoicetheorysaysthatmaximizationofexpected utilitydefinesrationalbehaviourinthissetting.Itistemptingtosuppose,asmany authorshavedone,thatbyequatingutilitywithDarwinianfitness,thesametheory willdefineadaptivebehaviourunderuncertainty.Butisthisreallytrue?Orconsider socialbehaviour,thatis,actionsthataffectothers.Insocialcontexts,anorganism’s personalreproductivesuccess(fitness)isnotthesoledeterminantofwhetheritsgenes willspread;relatives’reproductionmatterstoo.Soifutilityisequatedwithpersonal fitness,thenutility-maximizingbehaviourwillnotbeadaptive.Anaturalsuggestion, oftenfoundintheliterature,isthatifutilityisinsteaddefinedas‘inclusivefitness’in thesenseofHamilton(1964),thenthelinkbetweenadaptivenessandrationalitycan berestored.Butisthistrue,andcanasimilarmovebeappliedinothercontexts?The answerisnotobvious.Sotheideathatevolvedorganismscanbetreatedasakinto rationalagentsneedsclosescrutiny;thisistakenupinthefinalfourchapters.
Thisbookisanextendedreflectiononagentialthinkinginbiology,focusing onitsrationale,itspresuppositions,andthelimitsofitsvalidity.Twooverarching philosophicalthemesrunthroughthebook.Thefirstiswhyagentialthinkingis sowidespread.Isitareflectionoftheobjectivebiologicalfacts,orofthehuman predilectiontoanthropomorphize?Toseethiscontrast,considertheteleological attributionsthatsuccumbeasilytoDarwiniannaturalization,suchas‘thepolarbear’s coatisforcamouflage’.Thereisastrongcaseforregardingtheseattributionsas reflectingobjectivefacts,orpickingoutanaturalkind.Organismsreallydoexhibit adaptations,sotheirtraitsreallyare‘for’something.Bycontrast,considerDawkins’ conceptof‘selfishgene’orHaig’s‘strategicgene’(Dawkins1976,Haig2012).Both authorsmakeagoodcasefortheutilityoftheseidiomsinevolutionarygenetics,and areclearaboutwhattheymean.Evenso,thepopularityoftheidioms,andthemodeof reasoningaboutevolutionthataccompaniesthem,isarguablyareflectionofhuman psychology,atleastinpart,ratherthantheobjectivefactsthemselves.
Thesecondphilosophicalthemeconcernstherelationbetweentheuseofintentionalandrationalattributionsinevolutionarybiology,andtheactualevolutionof intentionalityandrationality.Thepointhereisthattheevolutionaryprocesseventuallygaverisetoorganisms,includinghumans,whohaveexplicitbeliefs,desires,and goalsthatarementallyrepresented,ofwhomintentionalpsychologyisapproximately
true,andwhosepurposivebehaviourcanbecodified,atleastroughly,bytheprinciplesofrationalchoicetheory.Thecognitivemachinerythatunderpinsthesecapacitiespresumablyevolvedbynaturalselection.Ifso,thispromptsaquestion.How shouldwemakesenseofthejointfactsthatintentionalandrationalidiomsareused totheorizeaboutevolution,andthatthereisanevolutionarystorytobetoldabout howthecognitivecapacitiesneededforintentionalandrationalbehaviourarose? Howdothesefactsrelatetoeachother?
Outlineofthebook
Thebookisorganizedintothreeparts,linkedbyanumberofconnectingthreads. PartIexplorestheroleofagentialthinkinginevolutionarybiology,anditspossible rationale.Thenotionofagencyitselfisexplored,andadistinctionisdrawnbetween twotypesofagentialthinking,bothfoundinbiologicalpractice.Intype1,theagent withthegoalisanevolvedentity,typicallyanindividualorganism;intype2,theagent is‘mothernature’,apersonificationofnaturalselection.Agentialthinking(type2)is foundtobemisleading,applicableonlytothesimplestsortofnaturalselection.By contrast,type1isalegitimateexpressionofadaptationism,butitreliesonacrucial presupposition.Itpresupposesthattheentitythatistreatedasanagentexhibitsa ‘unity-of-purpose’,inthesensethatitsevolvedtraitscontributetoa single overall goal.Wherethisunityfailstoobtain,asforexampleifthereissubstantialwithinorganismconflict,thenagentialthinkinglosesitsgrip:itbecomesimpossibletotreat theorganismasakintoanagentpursuingagoal.Thisisabiologicalanalogueof thepsychologicalunity-of-purposethatispresupposedwhenweattributeintentional statestohumans.Itexplainsthesignificanceofagentialthinking(type1)butalsoits limitations.Anditexplainswhyitcanonlyrarelybeappliedtogroupsratherthan individualorganisms.
PartIIchangestack,turningtothelong-standingdebatesoverfitness-maximization inevolutionarybiology.Theideathatevolutionbynaturalselectionisinsomesense anoptimizingprocess,tendingtomaximizefitness,hasacontroversialstatusin biology.Someauthorstreatthisasobviouslytrue,othersasdemonstrablyuntrue exceptinspecialcases.Therootsofthisdisagreementareexplored.Anumberof attemptstomakeprecisetheideathatselectionhasanoptimizingtendencyare examined;allofthemarerelated,withvaryingdegreesofdirectness,toagential thinking.TheyincludeWright’sideathatselectionwillpushapopulationupa slopeinanadaptivelandscape(Wright1932);Fisher’s‘fundamentaltheoremof naturalselection’(Fisher1930);Hamilton’sideathatindividuals’socialbehaviour willevolvetomaximizetheirinclusivefitness(Hamilton1964);Grafen’sideathat individualswillevolvetobe‘maximizingagents’(Grafen2006);andtheideathat frequency-dependentselectionwillleadtotheevolutionoftraitsthatmaximize fitnessconditionalontheirbeingfixedinthepopulation(MaynardSmith1982). Eachoftheseattemptsisfoundtobeonlypartlysuccessful,whichsuggeststhatthe
linkbetweennaturalselectionandadaptationisweakerthanisoftenassumed.Thisin turnhelpstoclarifytherelationbetweenthetwotypesofagentialthinking;itshows whytype2ismisleading,andshowsthatthejustificationfortype1mustultimately beempirical,nottheoretical.
PartIIIturnstothemulti-facetedconnectionbetweenevolutionandrationality,in particularrationalbehaviour.Thisconnectionhastwodimensions.Thefirstistheidea thatrationality,conceivedofasanactualphenotypicattributethatsomeorganisms includinghumansexhibit,mayitselfbeanadaptation;thesecondistheideathat evolvedorganismscanusefullybetreatedasiftheywererational,forthepurposes ofunderstandingtheirbehaviour.Therelationshipbetweenthesetwoideas,andthe validityofeach,isexplored.Bothdependonwhetherbehaviourthatisadaptive,or fitness-maximizing,coincideswithbehaviourthatisrational,orutility-maximizing. Thiscoincidenceisoftenassumedintheliterature,andsometimestreatedasana prioritruth.Butagainstthis,therearealsoargumentsthatsuggestthatinparticular contexts,theadaptiveandtherationalmaypartways,inthesensethatevolutionmay favourbehavioursthat violate thenormsofrationalchoicetheory.These‘partingof-ways’argumentshaveadualsignificance:theycastdoubtontheassumptionthat rationalbehaviourisalwaysbiologicallyadvantageous,andtheysuggestalimitonthe useofagentialthinking(type1)tounderstandevolvedbehaviour.However,itturns outthatinmanycases,thecoincidencebetweentheadaptiveandtherationalcanbe restoredbysuitablechoiceofutilityfunction.
Thebookemploysasomewhatunusualmethodology.Threedifferentmethodsare used,interwovenwitheachother.Thefirstisthetraditionalphilosopher’stechniqueof conceptualanalysis—thatis,tryingtoclarifythemeaningofkeyconcepts.Thesecond isamethodusedwidelyinphilosophyofscience,ofsynthesizingaparticularareaof sciencethensteppingbackandasking,‘Whatdoesitallshow?’Itissuitablewhen thescienceinquestioniscontroversial,orhasahiddenphilosophicaldimension.The thirdinvolvesconstructingsimpleformalanalysesandmodels.Thisallowskeyideas tobeexpressedmoreprecisely,andthevalidityofspecificargumentstobeassessed. Thoughthiscombinationofmethodshasitsrisks,myhopeisthatitallowstheissues tobeprobedmoredeeplythanbyasinglemethod.
Likemostauthors,Iwouldideallypreferthatthebookbereadcovertocover,but realizethatthisisalottoask.Thereisextensivecross-referencingbetweenchapters, butIhaveendeavouredtomakeeachasself-standingaspossible.Inevitablythis entailsacertainamountofrecapitulationofearlierdiscussions,butthisseemeda priceworthpaying.Irecommendthatallreadersbeginwithchapter1,whichsetsout thecoreproblematicofthebook.Thereafter,readershaveachoice.Thoseprimarily interestedinevolutionarytheoryshouldcontinueontochapter2andfromthereto PartII.However,itisalsopossibletoskipfromtheendofchapter1straighttoPartIII; readersprimarilyinterestedinrationalitymaypreferthisroute.
PARTI AgencyinEvolutionaryBiology
AgentialThinkinganditsRationale
1.1Introduction
Itisstrikingthatevolutionarybiologyoftenusesthelanguageofintentionalpsychologytodescribethebehaviourandactivitiesofevolvedorganisms,theirgenes,andthe processofnaturalselectionthatledtotheirevolution.Thusacuckoochick‘deceives’ itshostbutwillbeevictedifthehost‘discovers’thatitisnotitsown;aworkerant ‘wants’toraisethequeen’soffspring,notthoseofotherworkers;aswallow‘realizes’ thatwinterisapproachingsofliessouth;animprintedgene‘knows’whetheritwas inheritedpaternallyormaternally;andnaturalselection‘chooses’somephenotypes overothers.Thisphenomenonhasbeenaptlydubbedthe‘cognitivemetaphor’in biologybyR.A.Wilson(2005,p.75).
Onemightregardtheseintentionalusagesasunproblematic,simplyacolourful glossonbiologicalfactsthatcanbedescribedinmoreneutralterms.Theworkerant doesnotliterallyhavewantsbutratherbehavesasifitdid,thatis,itdestroyseggs laidbyotherworkers;theimprintedgenedoesnotreallyknowitsoriginbutrather behavesasifitdid,thatis,itencodesadifferentphenotypedependingonwhetheritis paternallyormaternallyinherited;andsoon.Thereforeusesoftheintentionalidiom inbiologyshouldbereadinan‘asif’sense;theysimplyreflectthefactthatorganisms andgenesareevolvedentitiesandthusdisplayorencodeadaptivetraits.Itmay beconvenienttodescribetheactivitiesoftheseentitiesinintentional-psychological terms,butinprinciplethiscouldbeavoided,andnoparticulartheoreticalsignificance attachestoit.
Thereissomethingrightaboutthisargument,butIdonotthinkitisthewhole story.Fortheintentionalidiominbiologyisasymptomofsomethingdeeper,namely amodeofthinkingaboutDarwinianevolutionthatGodfrey-Smith(2009)hascalled ‘agential’.Thisinvolvesusingnotionssuchas interests, goals,and strategies inevolutionaryanalysis.Onecommonformofagentialthinkingtreatsevolvedentitiesasif theywereagentsconsciouslypursuingagoal,andhaddevisedastrategywell-suited toachievingit.Behaviouralecologistsstudyingthefunctionofanimalbehaviour oftenthinkintheseterms.Forthem,theagentisusuallytheindividualorganism anditsgoalmightbetofindamate,protectitsnest,survivethewinter,ormore generallytomaximizeits‘fitness’orsomecomponentthereof.Inothercases,agential thinkingisappliedtowholegroups,asforexampleintheideathatinsectcolonies
displaycollectiveintelligenceandmakerationaldecisions(EdwardsandPratt2009, Seeley2010).Inothercasestheagentsaretakentobegenesoralleles,asinthe ‘selfishgene’conceptofDawkins(1982)orthe‘strategicgene’conceptofHaig(2012). Finally,Dennett(1987)appliesagentialthinkingtotheevolutionaryprocessitself, treating‘mothernature’,apersonificationofnaturalselection,asarationalagentwho engineerssolutionstothedesignproblemsfacedbyorganisms.
Ibelievethatagentialthinkinginbiology,whenusedcarefully,canbeapowerful toolforunderstandadaptation.Inlife-historytheory,forexample,numerousaspects ofanorganism’slife-cycle,suchasthetimingofreproductionorthelengthofits immaturephase,canbeunderstoodbytreatingtheorganismasifitwereanagent tryingtomaximizeitsexpectednumberofoffspring—orsomeotherappropriate fitnessmeasure—andhaddevisedastrategyforachievingthatgoal.Orinsocial evolutiontheory,researchershavemadesenseofdiversesocialbehaviours,particularlyonesthatinvolvealtruismorself-sacrifice,bytreatingthemasstrategies usedbyanorganism‘aiming’tomaximizeitsinclusivefitness;indeed,thiswayof thinkingisamajorpartofthemotivationbehindHamilton’sinclusivefitnessconcept (Hamilton1964).Appliedtogenes,Dawkins(1982)makesapowerfulcaseforthe explanatorypoweroftreatingageneasifitwerearationalagenttryingtodevise waystoincreaseitsrepresentationinthegene-poolattheexpenseofitsalleles. Thephenomenonofintra-genomicconflict,inparticular,makesgoodsensefrom thisperspective.
Thereisanintimatelinkbetweenagentialthinkingandtheuseoftheintentional idiom(‘knows’,‘wants’,‘tries’)inevolutionarybiology.Forthelanguageofintentional psychologyappliesinthefirstinstancetohumanagents,whoconsciouslyhavebeliefs anddesires,pursuegoals,andchooseactionsappropriatetothosegoals.Thusa biologistwhotreatsanevolvedorganism,agene,oragroupoforganismsasakintoan agentwithagoalwillnaturallybeinclinedtodescribetheiractivitiesinintentionalpsychologicalterms.
Theintentionalidiomisonemanifestationofagentialthinkinginbiology,butit isnottheonlyone.Anotheristheuseofrationalchoiceconceptsinanevolutionarycontext,notedintheIntroduction.Theideathatwhatisadaptive,orfitnessmaximizing,correspondssomehowtowhatisrational,orutility-maximizing,has longbeenmootedintheevolutionofbehaviourliterature.Recentlythisideahasbeen developedbyAlanGrafen,whoarguesthatanevolvedorganismmaybemodelledas arationalagentseekingtomaximizeautilityfunction,orobjectivefunction.Grafen arguesthatthis‘individual-as-maximizing-agentanalogy’isaquitegeneralwayof thinkingaboutadaptation,andisimplicitlyusedbyevolutionistsinthefield,but lacksasolidjustification,whichhehopestoprovide(Grafen2002,2006,2014a).Ina similarvein,ElliottSober(1998)describeswhathecallsthe‘heuristicofpersonification’atworkinbiology;thisheuristictriestodeterminewhetheratraitwillevolveby askingwhetherarationalagentseekingtomaximizetheirfitnesswouldchoosethat traitoveralternatives.(Soberarguesthattheheuristichaslimitations.)Grafen’sand
Sober’sideasareanalysedlaterinthebook,insections4.2and7.2,respectively;for themoment,thepointisjustthattheyprovidefurtherevidenceoftheprevalenceof agentialthinkinginevolutionarybiology.
Therearetwopossibleattitudesthatonemighttaketowardsagentialthinking. Thefirstseesitasmereanthropomorphism,aninstanceofthepsychologicalbias whichleadshumanstoseeintentionandpurposeinplaceswheretheydonotexist, andtofavourteleologicaldescriptionsoftheworldoverpurelymechanicalones. Thisbiashasbeenwell-documentedbypsychologists.Forexample,Barrett(2004) hasdescribeda‘hypersensitiveagentdetectiondevice’inhumans,whichleadsus tomakemistakenattributionsofgoal-directednessandintentionalagencyinthe inanimateworld;conceivably,asimilarbiasmaybeatworkinbiology.Onthisview, theexplanationfortheprevalenceofagentialthinkinginbiologyliesinfactsabout humanpsychology,notinfactsaboutthephenomenathatbiologistsaretryingto describe.AviewofthissortisdefendedbyGodfrey-Smith(2009),whoarguesthat talkofagentsandstrategies,particularlyasappliedtogenes,isasourceoferrorin evolutionarybiology;hisargumentsarediscussedinsection2.2.2.
Thesecondattitudeseesagentialthinkingasanaturalandjustifiablewayof describingorreasoningabouttheprocessofDarwinianevolutionand/oritsproducts. Afterall,manyevolvedorganismsengageinactivitiesthatseemclearlypurposive, suchasforaging,searchingformates,andwarningothersofdanger.Suchbehaviours arefunctionallysimilartotheactionsofrationalhumans,eveniftheirproximate causeisquitedifferent,inthattheyareefficientmeansofachievingagoal(e.g.survival orreproduction).Sotreatingtheorganismsinquestionasagent-like,anddescribing theiractivitiesinintentionalterms,iswell-motivatedevenifnotliterallytrue,inthat itpicksoutarealphenomenoninnature.Similarly,onemighttrytojustify(adifferent formof)agentialthinkingongroundsofanobjectivesimilaritybetweennatural selectionandrationalchoice:botharetodowithselectingbetweenalternativesin accordancewithagoal,andthusinvolveaformofoptimization.Onthisview,agential thinkinginbiologyisnot(mere)anthropomorphism,buthasagenuinerationaleand playsarealintellectualrole.
Myownattitudeisintermediatebetweenthesetwopoles,asIthinkthatagential thinkingisnotanundifferentiatedwhole.Partlythisisbecausethenotionofagency canitselfbeunderstoodvariously,assection1.2explains.Furthermore,therearetwo differentwaysinwhichthenotionofagency,howeverunderstood,canbeinvokedin evolutionaryanalysis,dependingonwhetherthefocusisonselection(theprocess) oradaptation(theproduct),assection1.3explains.Thisleadstothekeydistinction betweenagentialthinkingoftype1andtype2,bothofwhicharefoundinbiology; theyareanalysedinsections1.4and1.5,respectively.Section1.6introduces unity-ofpurpose,akeyaspectofhumanagency,andarguesthatithasabiologicalanalogue. Thishelpstorebutapossibleobjectiontotreatingorganismsasagentswithgoals, namelythatitismerelyalong-windedwayofcapturingthefamiliarpointthatevolved traitsoftenhaveDarwinianfunctions.Section1.7examinesasimpleformalism,based
