Tales about the origins of our species always start off like this: A small band of hunter-gatherers roams the savannah, loving, warring, and struggling for survival under the African sun. They do not start like this: Brave mom Ingrid Loyau-Kennett faced Woolwich terrorists.
Parochial altruism has gained recent popularity among scholars: these models highlight the idea that individuals are altruistic with group members and are hostile to individuals not of one’s own group (Arrow, 2007; Bowles, 2006; Choi and Bowles, 2007; Sa ̈äksvuori et al., 2011). Since internally cooperative groups prevail over less cooperative rival groups, parochial altruism rests on the evolutionary belief that violent intergroup conflict played a key role in the dawn of human cooperation.
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Social Mechanisms, Agent-Based Modellingand the Evolution of CooperationMauricio SalgadoPhDAnalytical Sociology and Institutional Design Group(GSADI) – UniversitatAutònoma de BarcelonaMauricio.Salgado@uab.catBarcelona – May 2013 1
Why cooperation?3DefinitionsCooperation: when two or more individuals engage in costly jointactions that result in mutual benefitAltruism (Unconditional Cooperation): Acts that benefit others ata personal costDonor(c)Recipient(b)
Why cooperation?5Ingrid Loyau-Kennett (48)―Being a cub leader I have my first aid so whenI saw this guy on the floor I thought it was anaccident then I saw the guy was dead‖―And then when I went up there was this blackguy with a revolver and a kitchen knife (…) andhe said move off the body‘.‖(…)―I started to talk to him and I started to noticemore weapons and the guy behind him withmore weapons as well. By then, people hadstarted to gather around. So I thought OK, Ishould keep him talking to me before henoticed everything around him.‖
Why cooperation?6Cooperation is what makes ushumans
Why cooperation?7―If you try to do something cooperative with achimp—point out something, show them wheresome food is—their attention wanders all overthe place, but if you compete with them overfood, they are zeroed in like a laser. All theircognitive skills are on.‖Michel TomaselloBut we still have to explain how did we go from ―chimp-like-selfishness‖ to―human super-cooperation‖
Why cooperation?The Higgs boson of evolutionary anthropology:How did we get that way?8
Social Mechanisms10Two main advantages:1. Knowledge about mechanisms increases the possibility ofcausal analysis in the absence of nomological laws, and2. it helps to open the ‗black box‘ of social dynamics in order toprovide the microfoundations of the observed phenomena.
Social Mechanisms11DefinitionA mechanism consists of entities and activities, organized such that they areproductive of regular changes from start or set-up to finish or terminationconditions.Entities (and their properties) are the things that engage in activities, andactivities are the producers of change.The dualistic nature of this definition makes it adequate for social sciencesthat deal with individual agents (‗entities‘) and their actions (‗activities‘).
―Mechanisms consist of entities (with theirproperties) and the activities that these entitiesengage in, either by themselves or in concert withother entities. These activities bring about change,and the type of change brought about depends onthe properties of the entities and how the entitiesare organized spatially and temporally‖Hedström, P. Dissecting the Social (2005)Opening the black boxSocial Mechanisms12
Social Mechanisms131. A set of entities, e1 to en, vary with respectto a property pi2. In a certain environment thebenefit, b1, bestowed on entity i is afunction of its property p13. The value of bi, influences the relativefrequency of entities with differentproperties at subsequent time periods.(Properties that perform better in theenvironment will become more frequent)Selection Mechanisms
Social Mechanisms14Evolutionary game dynamics describe:• Frequency-dependent selection.• The outcome of the game is related to reproductive success.• Payoff determines fitness.• Reproduction can be genetic or cultural.Genetic ReproductionIt means that individuals leave genetic offspringthat inherit their strategy.Cultural ReproductionIt means that individuals are imitated by others;thereby strategies reproduce by imitation orlearning.
15OntologyIs the mechanisms made of ‘real’ entities andactivities or is it just an as-if story?RegularityIn which instances can the mechanisms begeneralized from one case to another?TransparencyIs the presence of the mechanism clearlyobservable?IntelligibilityDos the presence of the mechanism improve theintelligibility of the explanation?Reduction BaseWhat are the mechanism ‘microfoundations’, thelocal rules that bring about the ‘macro-properties’?Generative SufficiencyCan the model’s microfundations generate theobserved macroproperties?Empirical AdequacyAre the model’s microfundationsplausible inrelation to some theory or empirical data?
Evolution ofCooperation19CCCCCCCCCCCDMutation CCDCDDSelection DDDDDDSelectionDeclining Average FitnessWithout any mechanism for the evolution of cooperation, naturalselection favours the evolution of defection
Kin Selection22Agents cooperate only with those related genetically―I will jump into the river to save two brothers or eight cousins‖CDDFirst GenerationCCCN GenerationSelection
Kin Selection23DefinitionThe beneficiaries share some genes with the altruist; the survival andreproduction of the beneficiaries contribute to the propagation of thealtruist’s genes.Ontology RealistRegularity It works in small familial groupsTransparency Yes Intelligibility YesReductionBaseIndividuals’ genesGenerativeSufficiencyYesEmpiricalAdequacyAlthough it might work in small and familial groups with little migration, itdoes not explain cooperation to unrelated individuals (commitment falls offprecipitously as genetic distance increases between individuals)
Kin Selection24In meerkats, helpers vary widely in the numberof food items they gave to pups. The level ofcontributions that helpers make to rearing pupsis not significantly correlated with variation inkinship to the litters they are rearing.(Clutton-Brock et al., 2001)In this picture, a male golden lion tamarin atColchester Zoo (The United Kingdom) took theunusual step of carrying other primates‘offspring that he shares his enclosure with. Thistamarin male has taken on the role of carryingfor two silvery marmoset youngsters.Limitations: It cannot explain cooperative breeding
Direct Reciprocity26Agents play the Iterated Prisoners Dilemma (IPD)―You scratch my back and Ill scratch yours‖ Tit for Tat InteractionsAlter EgoT1T2
Direct Reciprocity27DefinitionBoth the beneficiaries and the cooperators face repeated encounters; thecooperator’s decision to cooperate is based on what the beneficiary hasdone to her in previous encountersOntology RealistRegularity It works in contexts of repeated encounters within small groupsTransparency Yes Intelligibility YesReductionBaseIndividuals in repeated interactionsGenerativeSufficiencyYesEmpiricalAdequacyAlthough it might work in small groups, it is a weak mechanism in largergroups (ability to directly monitor trustworthiness in reciprocation decreasesrapidly as the number of transactions multiply)
Direct Reciprocity28Limitations:• It cannot explain short-term or one-shot cooperative interactions in gamessuch as ―The Ultimatum Game‖ or ―The Dictator Game‖• It cannot explain the production of ―public goods‖• In natural populations, errors occur: occasional mistakes between two TFTplayers cause long runs of mutual backbiting.CC CCCCDDDDDTFTTFT‘Error!C…
Indirect Reciprocity30Reputation ―I help you and somebody will help me‖D RWCt1D RWCt1+nD RWDt1Dt1+nDonor‘s reputationincreasesDonor‘s reputationdecreases
Indirect Reciprocity31DefinitionBoth the beneficiaries and the altruists interact with each other onlyoccasionally; the altruist’s decision to cooperate is based on information aboutwhat the beneficiary has done to others in previous encountersOntology RealistRegularity It works when information about the beneficiaries’ reputation is availableTransparency Yes Intelligibility YesReductionBaseIndividuals in occasional interactionsGenerativeSufficiencyYesEmpiricalAdequacyAlthough it might work in larger groups, it requires dense connections orcultural artifacts that register individuals’ reputation
Indirect Reciprocity32―Indirect reciprocity is a plausible mechanism to sustaincooperation within dense, bounded social networks that are stablethrough time‖Limitations:Heroism in warfare?
Group Selection34Multilevel Model ―I help you (… and my group will be better)‖Declining Average Fitness (Extinction)
Group Selection35DefinitionThe altruists’ genes can become fixed within certain groups because of thebenefits they bestow on those groups as wholes, even when the effect ofthese alleles on individuals’ fitness is negative. These groups reproduce fasterOntology RealistRegularityIt works when the group benefit of the altruists’ actions is higher than thealtruists’ individual costsTransparency Yes Intelligibility YesReductionBaseIndividuals’ genes within groups that compete with each otherGenerativeSufficiencyYesEmpiricalAdequacyAlthough it might work in small or medium-size groups, it requires within-group homogeneity, between group heterogeneity and low migration rates
Group Selection36―Most human populations do not meet these conditions. Thus, it doesnot seem that group selection can provide a genetic basis for altruism (…)Group selection mechanism depends on the relative amount of variationwithin and between groups. If group members are closely related, most ofthe variation will occur between groups. This is easiest to see if groups arecomposed of clones (as in colonial invertebrates such as corals). Thenthere is almost no genetic variation within groups; all the variation isbetween groups, and selection acts to maximise group benefit.‖Limitations:
Parochial Altruism38Multilevel Model ―I help you because you belong to my group(… and, therefore, my group will be stronger)‖Declining Average Fitness (Extinction)Intergroup Conflict
Parochial Altruism39DefinitionThe altruists cooperate with group members and are hostile to individualsfrom other groups. In contexts of intergroup conflict, internally cooperativegroups prevail over less cooperative rival groupsOntology RealistRegularity It works when there is severe intergroup conflictTransparency Yes Intelligibility YesReductionBaseIndividuals within groups that compete with each otherGenerativeSufficiencyYesEmpiricalAdequacyAlthough it might work in contexts of violent intergroup conflict, it does notapply in contexts in which groups cooperate among them
Parochial Altruism40―However, such generalisations are unlikely to correctly describe theconditions in which our Pleistocene ancestors lived, so parochial altruismseems to be implausible. Small bands of hunter-gatherers, numbering 25or so individuals, under chronic climate fluctuation, widely dispersed overlarge areas and unable to fall back on staple foods, would have sufferedfrom high mortality rates, particularly child mortality, due to starvation aswell as predation and disease, so they hardly would have been able tosustain warfare against competing groups ‖Limitations:
Concluding Remarks42Explaining the evolution of cooperation requires theidentification of some mechanism at workA mechanism consists of entities and activities, organized such thatthey are productive of regular changes from start or set-up to finishor termination conditions. Entities (and their properties) are thethings that engage in activities, and activities are the producers ofchange.Ontology, Regularity, Transparency, Intelligibility, ReductionBase, Generative Sufficiency, Empirical Adequacy
Concluding RemarksFive Mechanisms for the Evolution of Cooperation• Kin Selection: Cooperate with genetic relatives• Direct Reciprocity: I help you, you help me• Indirect Reciprocity: I help you, somebody will help me• Group Selection: Groups of cooperators out-perform othergroups• Parochial Altruism: Groups of cooperators out-compete othergroups43
Concluding Remarks44Punishment (e.g., ‗Strong Altruism‘) is not a mechanismfor the evolution of cooperation ParsimonyIf you punish someone who has defected with you, then you areusing direct reciprocityIf you punish someone who has defected with others, then you areusing indirect reciprocityIf you punish someone who is not a member of your group, thenyou are using parochial altruism (a special case of group selection)(Winners do not punish)
Cooperators• José Antonio Noguera• Francisco J. Miguel45
Thank you!Mauricio SalgadoPhDAnalytical Sociology and Institutional Design Group(GSADI) – UniversitatAutònoma de BarcelonaMauricio.Salgado@uab.catBarcelona – May 2013 46