The Role of Social Identity in a Population's Adoption of Prosocial Common-Pool Behavior

: Prosocial common-pool behavior – subtractable and non-excludable behavior that benefits others – is essential for the survival of any population of social individuals. The behavior, however, usually carries a cost tothosewhocontributeit,placingthematadisadvantagewithrespecttothosewhofreeride–thosewhodonot contributebutstillbenefit.Howpopulationssustainexistingoradoptnewprosocialcommon-poolbehaviors remainsunclear.Weintroduceatheoreticalagent-basedmodelanduseittostudytheroleofsocialidentity inapopulation’sadoptionofsuchbehavior.Socialidentityisrelevantbecauseitinfluencesthebehaviorof individualsinagroup,includingtheirwillingnesstobehaveprosocially.Ourmodelsimulatestheemergenceof multipleanddynamicsocialidentitiesofagentswithinself-organizinggroups.Oursimulationresultssuggest thattheroleofsocialidentitymaydependsubstantiallyonthedensityofthepopulationandthecommitment levelofpopulationmemberstotheirgroups;thattherelationshipbetweendensity,commitment,andadoption maybenuanced;that,underlowerdensitylevels,mobilitybetweengroupsmaybeessential;andthatthe persistenceandadoptionofprosocialbehaviorinapopulationmaybeoverwhelminglydrivenbyindividuals whoarehighlycommittedtotheirgroups.Theresultscautionagainsttheinfluenceoftwoloomingworldwide trends–anincreaseinpopulationdensityandadecreaseingroupcommitment.Theresultssuggestthat,when combined,thesetwotrendsmayproducethelowestadoptionlevelsofprosocialbehavior,theadverseand population-widerepercussionsofwhichcouldbecatastrophic.Finally,ourresultssuggestthatsocialidentity mayplayahelpfulroleinoffsettingtheconsequencesofthesetrends,implyinganeedforfurtherempirical andexperimentalstudyofthesubjectandfutureconsiderationofincorporatingtheroleofsocialidentityinto policyanalysisanddesign.