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action and the evolution of internalization Sergey Gavriletsa,b,c,1 and Peter J. Richersond

aDepartment of Ecology and Evolutionary Biology, of Tennessee, Knoxville, TN 37996; bDepartment of Mathematics, University of Tennessee, Knoxville, TN 37996; cNational Institute for Mathematical and Biological Synthesis, University of Tennessee, Knoxville, TN 37996; and dDepartment of Environmental Science and Policy, University of California, Davis, CA 95616

Edited by Simon A. Levin, Princeton University, Princeton, NJ, and approved May 4, 2017 (received for review March 7, 2017) is strongly affected by culturally transmitted processing, and decision making (11) and the costs of monitor- norms and values. Certain norms are internalized (i.e., acting ing, punishments, or conditional rewards that would otherwise be according to a norm becomes an end in itself rather than merely necessary to ensure cooperation (9, 14). Internalization of norms a tool in achieving certain goals or avoiding social sanctions). allows and groups to adjust their utility functions ’ capacity to internalize norms likely evolved in our ances- in situations with a rapidly changing environment when genetic tors to simplify solving certain challenges—including social ones. mechanisms would be too slow to react (9). A ’s values are Here we study theoretically the evolutionary origins of the capac- transmitted through the internalization of norms (15), with some ity to internalize norms. In our models, individuals can choose being more successful than others due to their norms to participate in collective actions as well as punish free rid- and (16). The presence of both costs and benefits of ers. In making their decisions, individuals attempt to maximize norm internalization suggests that the human ability to internal- a utility function in which normative values are initially irrele- ize norms has been subject to natural, sexual, and social selection vant but play an increasingly important if the ability to inter- for as long as human has been in existence. nalize norms emerges. Using agent-based simulations, we show Norm internalization is an elaboration of imitation and im- that norm internalization evolves under a wide range of condi- printing found in various species of birds and mammals (17). tions so that cooperation becomes “instinctive.” Norm internal- Plausibly, then, a propensity to follow norms is at least partly ization evolves much more easily and has much larger effects an innate feature of our social , whereas the substan- on behavior if groups promote peer punishment of free riders. tive content of the norms of a given society are largely cultural Promoting only participation in collective actions is not effective. (18). Our models below are designed to explore these features Typically, intermediate levels of norm internalization are most fre- of norms. There is a rapidly growing body of theoretical on quent but there are also cases with relatively small frequencies of gene–culture coevolution and its effects on human behavior (3, “oversocialized” individuals willing to make extreme sacrifices for 19). Some approaches take the capacity for internalized norms their groups no matter material costs, as well as “undersocialized” as a given and study the cultural evolution of specific norms that individuals completely immune to social norms. Evolving the abil- are internalized (e.g., ref. 20). However, except for an attempt ity to internalize norms was likely a crucial step on the path to in ref. 9 that equated internalization of norms with blind copy- large-scale human cooperation. ing of a behavior from others (21, 22) while largely ignoring their associated material payoff or normative to individuals, the cooperation | conflict | modeling | evolution | values question of how humans evolved to internalize norms has appar- ently not received much attention from theoreticians. We aim to fill this important gap in our knowledge. The key question we ask uman social behavior is controlled by many interacting fac- Htors including material cost–benefit considerations, geneti- Significance cally informed social instincts, personality, and culturally trans- mitted norms, values, and institutions (1–5). A social norm is a People often ignore material costs they incur when follow- behavior that one is expected to follow and expects others to fol- ing existing social norms. Some individuals and groups are low in a given social situation (6, 7). Humans learn norms from often willing to pay extremely high costs to enact, defend, parents, through educational and religious practices, and from or promulgate specific values and norms that they consider friends and acquaintances, books, and media. The adherence important. Such , often decreasing biological fitness, to norms is socially reinforced by the approval of, and rewards represent an evolutionary puzzle. We study theoretically the to, individuals who follow them and punishment of norm vio- evolutionary origins of human capacity to internalize and fol- lators. Certain norms are internalized, that is, acting according low social norms. We focus on two general types of collective to a norm becomes an end in itself rather than merely a tool in actions our ancestors were regularly involved in: cooperation achieving certain goals or avoiding social sanctions (1, 2, 8–11). to overcome nature’s challenges and conflicts with neighbor- For individuals who have strongly internalized a norm, violating ing groups. We show that norm internalization evolves under it is psychologically painful even if the direct material benefits a wide range of conditions, making cooperation “instinctive.” for the violation are positive. Many individuals and groups are We make testable predictions about and group willing to pay extremely high costs to enact, defend, or promul- behavior. gate norms that they consider important (12). At the same time, virtually all norms can be violated by individuals under some con- Author contributions: S.G. and P.J.R. designed ; S.G. performed research; S.G. ditions (e.g., if the costs of compliance are too high). Norms thus contributed new reagents/analytic tools; S.G. and P.J.R. analyzed data; and S.G. and P.J.R. can be viewed as one of the arguments in the utility function that wrote the paper. each individual maximizes (9). The authors declare no conflict of interest. Internalizing a norm has two significant effects upon human This article is a PNAS Direct Submission. behavior: People who have internalized a norm follow it even Freely available online through the PNAS open access option. when doing so is personally costly, and they will tend to criticize 1To whom correspondence should be addressed. Email: [email protected]. or punish norm violators (13). Norm internalization allows indi- This article contains supporting online at www.pnas.org/lookup/suppl/doi:10. viduals to reduce the costs associated with information gathering, 1073/pnas.1703857114/-/DCSupplemental.

6068–6073 | PNAS | June 6, 2017 | vol. 114 | no. 23 www.pnas.org/cgi/doi/10.1073/pnas.1703857114 Downloaded by guest on October 1, 2021 Downloaded by guest on October 1, 2021 arlt n Richerson and Gavrilets their maximize to want only and payoff norm the material about care not do they with Individuals respectively. Eq. in terms two The function utility the maximize to attempts behavior (0 norm ically the internalize treat We to considerations. ability the both rbt ocletv cin n uihfe ies(.. choose con- (i.e., to riders expected free punish are and (e.g., they x actions learn that collective individuals peers) to that or tribute sense elders, the parents, proso- in from a has norm society (injunctive) the that cial assume We internalization. norm of Some groups. payoffs. different to material randomly accumulated disperse offspring their to collective probabil- proportional in with reproduce ities success individuals their groups, surviving on in actions; dependent probabilities pay- with cate material accumulate individuals off punishment, and actions variables to by equal described each punishing be in will and action riders collective free a in efforts lin- Individual lations). increase size them, group by with punished early being and monitoring others, of punishing costs The and pay group. the to to monitoring individual of cost the costs a that additional requires at riders assume free groupmates we Identifying free-riding themselves. Therefore, their punish (27–29). reduce can punishment to individuals mechanism is effective An riding creates (26). this free ride members; any free group to although all incentive costly among an equally is shared actions is collective benefit Indi- in actions. collective participation of an vidual number have a in members participate to group opportunity lifetime, size their During constant nonoverlapping. of groups of sepa- ber consider will latter games. We the two Appendix). in these (SI common contrast and former is rately the race in arms of absent coop- intergroup escalation but of an particular, kinds to In due two different. efforts these very solving are to dilemmas erative payoffs fitness instructive 24, is the framework (19, comparative because circumstances a in right them the in modeling but in mod- 25), displayed cooperation us-vs.-them often generate and will us-vs.-nature self-sacrifice Both els costly 19). (3, the conflict of has violent because exam- but empirical distinction just interpreting this ples when games modeled us-vs.-them modeling not success on previous has leaned group the Much competition models, to fitness. of group cost of types of a component these fail- at important of means albeit an both is game groups In other us-vs.-them well. for as an winner success in reduced group or one ure on. of so and success routes, over trade The to groups access other opportunities, with mating direct competition territory, include costly games, other collective “us-vs.-them” and/or as of collective conflicts to kind such refer second we to which The refer actions, games. particular We on “us-vs.-nature” much groups. a as very neighboring actions of depend of not success does actions The problems the these on. solving hunting, in so group cooperative and group predators, breeding, includes from first cooperative defense The as solve. such to our activities evolved problems action have collective might of ancestors kinds general two consider We Results and p.143). Models 23, (ref. egoists?” and rational emerged of have world players a of in types survived norm-using ... could “How is, = eetn h tnadapoc ulndaoefrtecase the for above outlined approach standard the extend We num- large a in living individuals of population a consider We π y tteedo ahgnrto,gop uvv n dupli- and survive groups generation, each of end the At . 1 = u ≤ η .Hwvr niiul’dcsosaecnrle by controlled are decisions individuals’ However, ). (x η ≤ , y .W otlt htayidvda paigits updating individual any that postulate We 1). (1 = ) 0 π or 1 ) If 2). (1, ) sarsl fpriiaigi collective in participating of result a As 1. n 1 − atr h fet fntr n culture, and nature of effects the capture wihwl aybtendfeetsimu- different between vary will (which η η ) sacniuu ri otoldgenet- controlled trait continuous a as × > η π η (x n 0 = olwn h omi part a is norm the following 0, eeain r iceeand discrete are Generations . , y + ) r udroilzd (i.e., “undersocialized” are η × η x (v n aeilpayoff material and and 1 x + y respectively, , v 2 y ). [1] eysalvle of values of small values very large shown, having population game the of us-vs.-nature thirds in the dimorphic becomes of between-group population example the in the effort an us- In more as the competition. increasingly is decline in put substantially there contrast, payoffs members material In group 1), 2), fitness. (Fig. (Fig. and game payoffs vs.-them game material us-vs.-nature in increase the and cooperation In within-group increasing punishment. in results evolution its choosing and by payoff 2) material parameters (1, tive the norm about the care follow not always do they with [i.e., Individuals socialized” preference. individual’s the of l ihtecrepnigtatvle rsn tagvntm.Terdline red parameters. The individu- of time. tions given of of a value number at mean the present the to values shows trait trait proportional internalization corresponding is the the color with of black als the distribution of the intensity of The dynamics The (x (B) strategies fitness. of combinations different using viduals cases both trait In internalization dynamics. norm evolutionary observed shown, illustrate 2 behavior. and group and individual on effects speci- its of exogenously and evolution values, are the low they understand that to wish assume We we fied. norm; pressure” the “social of follow strength to the with increase parameters choosing These (i.e., riders choosing free (i.e., contributing of norms the ing 16, i.1. Fig. B A

internalization 1 Figs. simulations. agent-based used we models our study To

b type frequencies 0.25 0.75 0.2 0.4 0.6 0.8 0.5 = 1 0 0 1 4, xmlso vltoaydnmc.U-s-auegm with game Us-vs.-nature dynamics. evolutionary of Examples v x = 0, 11 01 10 00 v y v = 1 2500 50007500 10000 0.5, and 2500 50007500 10000 PNAS η η X hs yaisaeaaoost those to analogous are dynamics These . v See . 0 2 = esr h aiu au ffollow- of value maximum the measure | 8, y Methods 1 = δ ue6 2017 6, June = time o vroilzdindividuals. oversocialized for ) 0.50, time w 1.5 2.5 1 2 and η 0010000 5000 0 K η vle fe oetime; some after evolves = IAppendix SI ihapoiaeytwo- approximately with | rqece findi- of Frequencies (A) 4. time o.114 vol. x x , η = y 1 = η trigwt very with starting , .(Inset ). y n h etwith rest the and η 1 = n punishing and ) 1 = | o xc defini- exact for o 23 no. .Nonnega- ]. h average The ) r “over- are | 6069 n η = .

ANTHROPOLOGY EVOLUTION 1 left part of the first column in each of graphs). For parameters A used here, in us-vs.-nature games individuals make no effort (Fig. 3). In us-vs.-them games (Fig. 4), some individuals volunteer for 0.8 production; the average group effort is small and decreases with group size. In either type of games there is no punishment. If groups encourage their members to contribute to produc-

0.6 11 2 tion but peer punishment is not promoted (i.e., vx > 0, vy = 0; 01 left columns of graphs in Figs. 3 and 4), there is no punishment 1.5 10 but some norm internalization evolves. In us-vs.-nature games, w 0.4 00 1 its effects on production and material payoffs are insignificant. In 0.5 us-vs.-them games, there is a small increase in production accom- 0 5000 10000 time panied by decreasing payoffs. type frequencies 0.2 If group members are encouraged to punish free riders but production itself is not promoted (i.e., vx = 0, vy > 0; left part of the second and third columns of graphs in Figs. 3 and 4), then 0 strong norm internalization can evolve simultaneously with a 2500 5000 7500 10000 dramatic increase in production and punishment. In us-vs.-them time games, increasing group size n has a strong negative effect on internalization, production, and punishment. The effects of costs of punishing and of being punished on η are relatively small (SI B 1 Appendix). There is a decline in fitness in us-vs.-them games but an increase in us-vs.-nature games. If both production and punishment of free riders are encour- aged (i.e., vx , vy > 0), all efforts generally increase in both games. 0.75 There are nonadditive interactions of parameters but the gen- eral patterns are hard to see. Increasing the costs of being pun- ished increases production efforts. In us-vs.-them games, smaller groups typically have higher η and production and punishment 0.5 efforts than larger groups; larger groups can have higher fitness if they evolve no internalization and make fewer or no efforts in production and punishment. In us-vs.-nature games, the sit- uation is more complex: If the cost of being punished is small, internalization 0.25 larger groups can evolve higher η (because the total effect of punishment is higher). If this cost is moderate or large, smaller groups evolve higher η. Larger groups can also have relatively 0 high production effort. Interestingly, increasing the difficulty of 2500 5000 7500 10000 us-vs.-nature games results in more norm internalization (SI time Appendix, Table S1 and Figs. S14–S16). Increasing normative val- ues vx and vy speeds up the evolution of norm internalization. Increasing vy typically increases η, x and y, but increasing vx Fig. 2. Examples of evolutionary dynamics: us-vs.-them game with n = can decrease η, x and y, especially in large groups. Overall, in 8, b = 1, vx = 0, vy = 0.5, δ = 0.50, K = 2. (A) Frequencies of individuals using different combinations of strategies (x, y). (Inset) The average fitness. (B) The dynamics of the distribution of the internalization trait η. The inten- sity of the black color is proportional to the number of individuals with the corresponding trait values present at a given time. The red line shows the mean value of η. See Methods and the SI Appendix for exact definitions of parameters.

coming under the rubric of “evolutionary branching” identified by adaptive dynamics methods (30, 31). Overall, simulations show that if the norm internalization trait η remains small, individuals make no effort (x = y = 0). If norm internalization trait η instead evolves to a large value, individuals both contribute to and monitor and punish occasional free riders (x = y = 1). With intermedi- ate values of η, the population represents a mix of free rid- ers (x = y = 0) and contributors who either punish (x = y = 1) or do not (x = 1, y = 0). The frequency of “selfish punishers” (x = 0, y = 1) typically remains very low. If norm internalization evolves, it often emerges quite rapidly after some waiting time, suggesting a transition between alternative quasi-stable states. Occasionally, rapid reverse transitions to low-internalization states are also observed. Fig. 3. Summary graphs for us-vs.-nature games: efforts x, punishment y, The effects of parameters on evolutionary dynamics are illus- internalization η, fitness w, and SD σ in internalization trait η for differ- trated in Figs. 3 and 4 (see also SI Appendix). Consider first what ent normative values of production vx and punishment vy , and group size happens if no norm internalization is allowed to evolve [or pro- n. Other parameters: X0 = n/2, δ = 0.5, b = 4, K = 3. Shown are averages duction and peer punishment are not promoted (i.e., vx = vy = 0; based on 10 runs for each parameter combination.

6070 | www.pnas.org/cgi/doi/10.1073/pnas.1703857114 Gavrilets and Richerson Downloaded by guest on October 1, 2021 Downloaded by guest on October 1, 2021 arlt n Richerson and Gavrilets soci- and pro- groups than that internalization thus norm is prediction causing Our in production. efficient moting more is ers con- some decision human under in can considerations making. norms payoff theoreti- material internalized Our trump that norm. ditions show social results internalized are or an cal follow by duly affected they because strongly mecha- prosocially well-established behave expected additional, People evaluating an nism: in studied we errors Here make ancestral payoffs. , they under strategic because evolved or other instincts conditions, or social others, reputation or of of one’s biological number well-being expressing improve a the to the for for desire despite concern a happen selfless ways, can including prosocial This in costs. behave individual often associated people that know and survival) monitoring, (via group optimization, of and benefits punishment. costs goods increase associated indi- collective to decrease both and of working is col- acquisition evolution selection of this increased group of types and force both driving vidual in The action. of cooperation range lective favoring a under greatly these evolve conditions changes does dramatically internalization that Norm predictions. internalization norm of sibility relatively 34). and 33, games (24, games us-vs.-nature us-vs.-them in in contributions low absent completely individual be that ratios will predicts benefit-to-cost vol- theory nobody to moderate Standard if advantageous involved. under but become costs groupmates may the it their despite contribute of unteer to effort willing the is on pre- else ride individuals where free (32), gen- to dilemmas a fer volunteer to the belong of above class considered eral models action collective The Discussion 4). and 3 Figs. in graphs of low and high with uals genetic high in show variation in often hand simulations less Unexpectedly, come requires cooperation punishment. punishment games, us-vs.-them and in contrast, cooperation In hand. that so in other, patterns each observed the games, us-vs.-nature combination. parameter each for runs te parameters: Other production of values normative internalization 4. Fig. u eut hwta rmtn otypnsmn ffe rid- free of punishment costly promoting that show results Our we work experimental and experience everyday our both From pos- the for allow we theory, standard the of extension our In umr rpsfru-s-hmgms efforts games: us-vs.-them for graphs Summary η η n h mrec fdfeetcutr findivid- of clusters different of the and fitness , δ = 0.5, w η n SD and , b aussmlrt hs nFg ls row (last 1 Fig. in those to similar values = 1, v K x σ = n punishment and nitraiaintrait internalization in .Sonaeaeae ae n10 on based averages are Shown 3. v x y n ru size group and , and x punishment , η y o different for resemble n. y , a eetne o h aewhen and case enough the flexible for is extended framework be modeling can effects these our neglected have simplicity, we here for Although 20). individual’s 7, the (6, during span change life may and factors social and cultural observed 39)]. is (38, psychopaths [as are some norms pre- who in prosocial individuals internalize also of to models proportion unable Our some completely of (37). “big maintenance societies the the of small-scale dict lines some the of along of cooperation, men” organize example who of individuals another leaders oversocialized displays as view be other also could may internal- and One oversocialization. deeply bombers, behavior, individuals Suicide self-sacrificial all norms. when extreme not costly arise but very equilibria some ize Mixed if masses explanation: benefit pre- simple the groups modeling a This whereas internalization. has norm sacrifices diction limited a make only to express relatively believers” a “heroes”—willing individuals—“true predict oversocialized or models of par- our In frequency conditions results. small empirical some inter- these under to with ability ticular, compatible the is in norms variation nalize theoretical genetic Our significant (36). of stable prediction differences temporally between-individual and such domain-general (35). severe are that and suggests advantage assured is work take small penalty Recent who the a unless maximizers, punishers; cooperation vari- selfish of any great presence of are also the people if is to of There react cooperate minority people way. will how the people in lead ation of who punishers majority are altru- a as there act whereas people punishers of minority istic significant a populations many in or studies laboratory using data. tested ethnographic be can This production goods. in collective than participation of actions of collective approval/reward in promoting successful those more have be will and riders norms free stronger of disapproval/punishment promoting eties ae(9 4 5.Hwvr aecnb aeta h human the that made be can case a However, war- 45). and conflict 24, intergroup (19, in involved eas- fare are much groups if is evolve cooperation to within-group ier theo- recent that with arguing line evolution work in the retical was for conclusion conducive This more (24). cooperation are of latter the that show games vs. Chinese in found (4). use novels their American of evi- frequencies as different , be individualist by may in denced making exam- than decision collectivist case-based For in or common processes. role-, more rule-, decision-making of use the trans- the in ple, internalization variation norm environments social in social/cultural in lates cultures variation and across Cultural ecological 44). norms their (43, cultural in of differ strength of that the intensity consider- in and predict variation thus size, able models group Our costs, competition. benefits, between-group the including eters (25). selection group additional cultural norm- requires e.g., tribes Evolving as mechanisms, such (42)]. units large dispersal in cooperation female based of males’ random with size costs expected and group [as the philopatry high the realistically model to are our rates proportional migration in and are few the contrast, a monitoring to on In and up group). depend punishment (only rates each not migration of did small percent very punishment used of and size costs group to the (up cooperation that with assumed larger groups compatible larger much sizes for Group were enough; strict. strong are are if conditions punishment evolve of readily cooperation effects and the internalization bands hunter-gatherer Norm extant 41). and (40, chimpanzees both for those of the in behaviors particular of frequency the population. on say, and, factors fcus,teetn fnr nenlzto sas fetdby affected also is internalization norm of extent the course, Of that show punishment with games goods public Experimental rvosdrc oprsn fu-s-aueadus-vs.-them and us-vs.-nature of comparisons direct Previous param- various on depends internalization norm of extent The (n here used sizes group The PNAS | n ue6 2017 6, June nrf 7 oee,they However, 27. ref. in 64) = 8 = , 16, η eed oho genetic on both depends | r ihnterange the within are 24) o.114 vol. | o 23 no. | 6071

ANTHROPOLOGY EVOLUTION population was so low up until about 50,000 years ago that inter- is required to secure the reward.) In us-vs.-them games, we define P = X/X, group conflict was rare. Perhaps only in the Holocene (i.e., over where X is the average group effort over all groups in the ; this is the the last 12,000 years) did violent intergroup conflict become an Tullock contest success function (24, 33, 34, 47). important selective force. For example, depictions of group fight- ing are essentially absent in Gravettian cave , as are depic- Punishment. Let variable y be equal to 1 if the focal individual punishes all tions of defensive weapons such as shields (46). Both are com- defectors in the group. Otherwise, y = 0. Let δ be the cost of punishing n − 1 free riders, κ the cost of being punished by n − 1 groupmates, and cmon the mon in Holocene art. Thus, human cooperation may have mainly cost of monitoring n − 1 groupmates. Then, assuming additive accumulation evolved under a regime of us-vs.-nature games rather than of benefits and costs, the material payoff of an individual using a pair of us-vs.-them games. Our results show that cooperation via norm strategies (x, y) can be written as internalization readily evolves in us-vs.-nature games. Once the π(x, y) = π − y [(1 − p˜)δ + c ] − (1 − x)κq˜. [3] ability to internalize norms is in place, it will simplify various CA mon other types of social interactions and cooperation. Here p˜ and q˜ are the frequencies of cooperators and punishers among n − 1 Although evolving norm internalization increases individual other group members. The terms in the right-hand side of Eq. 3 are the net efforts in both types of games, its effects on material payoffs payoff of the collective action (given by Eq. 2), the cost of punishing and and fitness varies. The effect is predicted to be positive in us- monitoring others, and the cost of being punished. Note that defectors in production can still punish other defectors. Such individuals using strategy vs.-nature games (because norm internalization implies less free (x = 0, y = 1), or (0, 1) for short, are “selfish punishers” in the terminology riding and reduced costs of optimization). The effect is predicted of ref. 28. to be negative in us-vs.-them games because norm internaliza- tion furthers “overproduction” and “rent dissipation” [which are Norm Internalization Trait and Utility Function. We assume that the norm well-known characteristics of contests in literature internalization trait η is controlled genetically by a single locus with a (47, 48)]. This negative effect will be especially large in the cases continuum of alleles. η remains constant during the individual’s life; it is where intergroup competition takes the form of feud and war- changed by random mutation during reproduction. The individual utility fare. Violent intergroup competition often leads to high death function uη (x, y) is given by Eq. 1. Our approach is related to the one used rates and much destruction of property. The rule of evolved for modeling the evolution of preferences in economics and biological liter- ature (54–57). to limit the costs of such conflicts (49, 50). Thus, there is a para- dox here. In us-vs.-them games, norm-driven cooperation tends Strategy Revision. After each collective action and punishment stages, to evolve more easily than in us-vs.-nature games even though with probability ν each individual updates his strategy using myopic opti- the evolution of cooperation in the former drives down mean fit- mization (58). Specifically, first, the individual computes four values ness and in the latter increases it. As is very often the case when uη (0, 0), uη (0, 1), uη (1, 0), uη (1, 1) under the assumption that all other indi- strategic interactions are important, naive adaptationism would viduals keep their strategies. Then, the individual chooses a combination of lead to the wrong conclusion here. (x, y) values giving the largest utility value uη (x, y) with probability 1 − e, Institutions are the human-devised constraints and rules or, with probability e, chooses a random combination of (x, y). Parameter that structure political, economic, and social interactions (51). e is the error rate of optimization. This approach implies each individual knows/estimates the total contribution of his peers and the total number of Examples include , economy, , , property punishers among them. Nonupdating individuals keep their strategies for rights, and democratic institutions. A growing number of studies the next round. show that social norms can define the success of establishment and the direction of evolution of various social institutions (52, Biological Fitness, Group Survival, and Individual Reproduction. We define 53). As a result, the same institutions may function differently in biological fitness as different cultures. Simultaneously, social institutions affect the w = 1 + π − copt (1 − η) − cint η, [4] development or nature of norms and other cultural traits (53). Building a predictive theory of social institutions is hardly pos- where π is the average material payoff of the individual across all Q rounds. sible without explicitly considering an evolved human ability to In the right-hand side of Eq. 4, the last two terms describe the cost of finding a strategy optimizing material payoff and the genetic/physiological cost of internalize social norms. the ability to internalize norms; copt and cint are the corresponding param- eters. Note that we assume that the cost of optimization decreases as the Methods strength of norm internalization grows. Each generation consists of Q rounds with three stages: a collective action To implement selection, we use a two-level Fisher–Wright framework. stage, a punishment stage, and a strategy revision stage. Group selection is captured by making each group in the new generation independently descend from a group in the previous generation with prob- Collective Actions. The variable x specifies the effort of a focal individual ability proportional to their average success in collective actions P across Q from a particular group in a specific collective action: x = 1 (cooperation) rounds. Individual selection within each group is implemented by first inde- and x = 0 (defection). The material payoff of the individual from a collective pendently choosing n parents from the group members with probabilities action is proportional to biological fitness w and then producing n offspring subject to random mutation. Offspring production is followed by random dispersal π = − CA bP cx, [2] of half of the offspring (interpreted as females, ref. 42).

where b and c are constant benefit and cost parameters. Function P gives the ACKNOWLEDGMENTS. We thank K. Rooker, J. van Cleve, and reviewers. This normalized value of the resource produced or secured by the group. In us- P work was supported by the National Institute for Mathematical and Bio- vs.-nature games, we define P = X/(X+X0). Here X = x is the total group logical Synthesis through NSF Award EF-0830858 (to S.G.), The University effort and X0 is a half-success parameter (24, 34). (If X = X0, the probability of Tennessee, Knoxville, and by US Army Research Office Grant W911NF- of group success P is equal to one-half. The larger X0, the more group effort 14-1-0637 (to S.G.).

1. Wrong D (1961) The oversocialized concept of man in modern . Am Socio 5. Simpson B, Willer R (2015) Beyond altruism: Sociological foundations of cooperation Rev 26:183–193. and prosocial behavior. Annu Rev Sociol 41:43–63. 2. Granovetter M (1985) Economic action and : The problem of embed- 6. Lapinski MK, Rimal RN (2005) An explication of social norms. Comm Theor 15:127– dedness. Am J Sociol 91:481–510. 147. 3. Richerson PJ, Boyd R (2005) Not by Genes Alone: How Culture Transformed Human 7. Bicchieri C (2006) The Grammar of Society: The Nature and Dynamics of Social Norms Evolution (Univ of Chicago Press, Chicago). (Cambridge Univ Press, Cambridge, UK). 4. Weber EU, Ames D, Blais AR (2005) How do I choose thee? Let me count the ways: A 8. Axelrod R (1986) An evolutionary approach to norms. Am Polit Sci Rev 80:1095–1011. textual analysis of similarities and differences in modes of decision making in China 9. Gintis H (2003) The hitchhiker’s guide to altruism: Gene-culture coevolution, and the and the United States. Manag Organ Rev 1:87–118. internalization of norms. J Theor Biol 220:407–418.

6072 | www.pnas.org/cgi/doi/10.1073/pnas.1703857114 Gavrilets and Richerson Downloaded by guest on October 1, 2021 Downloaded by guest on October 1, 2021 3 arlt ,FruaoL(04 ouint h olcieato rbe nbetween- in problem action collective the to solution A conflict (2014) of L Fortunato strategy S, the Gavrilets and dilemma 33. volunteer’s a dynamics. as adaptive Cooperation (2009) on M questions Archetti 20 32. (2005) S Gavrilets D, Waxman 31. 9 aetC rusnA rntH oa A imn 20)Vafedmt coer- to freedom Via (2007) K Sigmund MA, Nowak H, Brandt A, altruism. Traulsen order C, second Hauert a 29. as Selfishness (2008) DS punishment. Wilson altruistic OT, of evolution Eldakar The (2003) 28. P Richerson S, Bowles H, Gintis R, Boyd 27. explaining in role essential an plays selection group Cultural (2016) al. et P, Richerson groups. 25. heterogeneous in problem action Collective (2015) norms. S social Gavrilets of evolution 24. the and action Collective (2000) E Ostrom 23. (1985) PJ Richerson R, Boyd 22. (1981) MW Feldman LL, Cavalli-Sforza 21. kingdom: animal the in imitation of evolution and nature the On (1992) A Whiten 17. (2015) I Morris 16. 0 eizSH id ,Mesz E, Kisdi SAH, Geritz 30. (1965) M Olson 26. incentives. and Values cooperation: of scope The (2008) G Tabellini 20. the and norm-psychology coevolution, Culture-gene (2011) J Henrich M, Chudek 18. and Cognitive : modern (1997) of L Kuczynski roots JE, Grusec The 15. (2012) R Marois internal- JW, of analysis economic Buckholtz An citizens? 14. good make good conflict. Do human (2000) R in Cooter imperatives sacred 13. and Religious (2013) J Ginges S, Atran social 12. of coevolution The foundations: Theoretical (2014) J Ensminger prosociality. J, of puzzle Henrich the Solving 11. (2003) H Gintis 10. 9 olsS itsH(2011) H Gintis S, Bowles 19. arlt n Richerson and Gavrilets ru oflc ihwti-ru inequality. within-group with conflict group games. goods public in 1139–1154. 35–57. USA Sci Approach titative n h dpiegot n rnhn fteeouinr tree. evolutionary the of branching and growth adaptive the and punishment. costly of emergence The cion: USA Sci Acad Natl Proc MA). Cambridge, Press, Univ (Harvard evidence. the of sketch A cooperation: human B Lond Soc 14:137–158. Chicago). Press, 905–950. research. of century a of Reappraisal Princeton). Press, Univ ton Theory Contemporary of Handbook PictnUi rs,Princeton). Press, Univ (Princeton prosociality. human of emergence enforcement. their and norms social of 655–661. foundations neural norms. ized 19–44. pp 336:855–857. York), New Perspective, Foundation, Sage Cross-Cultural (Russel in J Punishment Henrich J, and Ensminger Fairness eds Norms: societies. complex Social of with institutions imenting the and markets, , intrinsic norms, 105:6982–6986. 370:20150016. aLwRev Law Va oaes amr,adFsi ul:HwHmnVle Evolve Values Human How Fuels: Fossil and Farmers, Foragers, oi fCletv cin ulcGosadteTer fGroups of Theory the and Goods Public Action: Collective of Logic PictnUi rs,Princeton). Press, Univ (Princeton 100:3531–3535. vlBiol Evol J 86:1577–1601. oprtv pce:HmnRcpoiyadIsEvolution Its and Reciprocity Human Species: Cooperative A n ,Mt A 19)Eouinr iglrstrategies singular Evolutionary (1998) JAJ Metz G, ena ´ utr n h vltoayProcess Evolutionary the and Culture aetn n hlrnsItraiaino aus A Values: of Internalization Children’s and Parenting 22:2192–2200. rnsCgi Sci Cognit Trends Wly e York). New (Wiley, d tdBehav Stud Adv utrlTasiso n vlto:AQuan- A Evolution: and Transmission Cultural Science a Commun Nat ea ri Sci Brain Behav ainSoc Ration 316:1905–1907. 15:218–226. 21:239–283. 5:3526. 15:155–187. 39:e30. a Neurosci Nat Ui fChicago of (Univ cnPerspect Econ J rcNt Acad Natl Proc vlBiol Evol J Econ J Q hlTasRoy Trans Phil vlEcol Evol (Prince- Science Exper- 123: 18: 12: 15: 1 ot C(1990) DC North 51. (2009) F Fukuyama 50. (2009) BR Weingast JJ, Wallis intra-group DC, and North conflict Intergroup 49. (2010) H Orzen B, Herrmann J, Brandts K, Abbink 48. (2009) K Konrad 47. (2005) RD Guthrie 46. (2016) P Turchin 45. (2014) 33- J A Henrich cultures: J, loose and Ensminger tight 44. between Differences (2011) al. et MJ, Gelfand 43. unique (2008) show B societies Chapais hunter-gatherer in 42. patterns Co-residence (2011) al. et KR, Hill 41. primates. other and chimpanzees in exchange Reciprocal (2006) JC Mitani and well-being 40. affective employee conflict, psychopaths, Corporate model. (2014) evolutionary CR integrated Boddy An 39. sociopathy: of sociobiology The (1995) L Mealey 38. 8 adomW (2010) WH preferences. Sandholm of evolution 58. dynamic the and selection Equilibrium (2012) TWL Norman evolution the 57. for theory A (2009) J Roughgarden MW, Feldman preferences. J, Cleve of Van evolution E, dynamic Akcay The 56. (2007) Y Spiegel C, Shannon stable? A, evolutionarily Heifetz altruism 55. Is (1998) W Guth institutions. H, and Culture Bester (2015) P 54. process. Giuliano historical A, the Alesina and Culture 53. (2012) N Nunn 52. distribution, Emergence, societies: mammalian in Leadership (2016) al. et pheno- “cooperative JE, a Smith display Humans 37. (2014) DG Rand MA, Nowak A, Peysakhovich 36. humans: in types cooperative investigating Experiments (2005) brain. D collaborative Houser R, the Kurzban and 35. action Collective (2015) S Gavrilets 34. History UK). Human bridge, Recorded Interpreting for Framework game. contest experimental an in punishment Earth on Cooperators York). Societies New Complex Foundation, of Sage Institutions the and Markets, Motivation, Intrinsic Norms, study. MA). Cambridge, Press, Univ (Harvard structure. pp social Berlin), human (Springer, CP Schaik van PM, Kappeler eds Humans, 107–119. and Primates in tion behaviour. work counterproductive Sci Brain Behav rde MA). bridge, Behav Econ Game perspectives. ultimate USA and proximate integrating other-regard of Theor 211–221. York). New Press, Univ bridge payoff. and power, stable. temporally and general domain is that type” simulations. and theory evolutionary 102:1803–1807. to complement A 12:20141067. 106:19061–19066. Science 32:251–286. Fra,Sru n iox e York). New Giroux, and Straus (Farrar, 332:1100–1104. 18(3):523–541. taeyadDnmc nContests in Dynamics and Strategy lrscey o 000Yaso a aeHmn h Greatest the Humans Made War of Years 10,000 How Ultrasociety: nttto,IsiuinlCag n cnmcPerformance Economic and Change Institutional , rmvlKnhp o arBnigGv it oHmnSociety Human to Birth Gave Pair-Bonding How : Primeval h aueo aelti Art Paleolithic of Nature The 74:311–320. h rgn fPltclOdr rmPeua ie oteFrench the to Times Prehuman From Order: Political of Origins The rnsEo Evol Ecol Trends ouainGmsadEouinr Dynamics Evolutionary and Games Population BrsaBos hpi,CT). Chaplin, Books, (Beresta Science PNAS hoeia onain:TeCeouino Social of Coevolution The Foundations: Theoretical 331:1286–1289. | u Bus J ue6 2017 6, June 31:54–66. ilneadSca res Conceptual A Orders: Social and Violence mEo Rev Econ Am 121:107–121. Ui fCiaoPes Chicago). Press, Chicago of (Univ cnTerDev Theor Econ | Ofr nvPes Oxford). Press, Univ (Oxford a Commun Nat cnLit Econ J o.114 vol. CmrdeUi rs,Cam- Press, Univ (Cambridge rcNt cdSiUSA Sci Acad Natl Proc cnBhvOrgan Behav Econ J 100:420–447. 53:898–944. | 27:S108–S126. 5:4939. rcNt cdSci Acad Natl Proc o Interface Soc R J o 23 no. MTPes Cam- Press, (MIT Coopera- | (Russel (Cam- 6073 Econ 34:

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