An evolutionary game approach to culture: Illustration by an adaptive norm development

1. An evolutionary game approach to culture:Illustration by an adaptive norm development Tatsuya Kameda (Hokkaido University) tkameda@let.hokudai.ac.jp http://lynx.let.hokudai.ac.jp/members/kameda CEFOM/21, 2nd Workshop Culture, Norm, and Evolution Hokkaido University, Aug. 6-8, 2003

2. Overview • Resurgence of collective constructs (e.g., norms, conventions, values) in social sciences • How can we study these collective constructs fruitfully? – Adaptive perspective • Evolutionary game theory as a useful research tool • An illustration with communal-sharing norm in primordial societies

3. Social norm • Cialdini & Trost (1998) “Social norms are rules and standards that are understood by members of a group, and that guide and/or constrain social behavior without the force of laws. These norms emerge out of interaction with others; they may or may not be stated explicitly, and any sanctions for deviating from them come from social networks, not the legal system” (p.152). • Socially-shared rules that emerge and are sustained through people's autonomous interaction, not necessarily with formal regulating authorities or forces such as laws

4. Theory of norm development? • Emergence and sustainability of social norms as core issues for any theory of social norms. • But, do we have a reasonable theory of norm development in this sense? • Classic studies on norm development (e.g., Sherif, 1936; Jacobs & Campbell, 1961): adaptively irrelevant “norms” • Social/cultural learning as a general engine for norm development, but…

5. Theory of norm development? • A more fundamental question: Why some beliefs are acquired socially and are maintained as a shared rule, while other beliefs are not. • Adaptive/evolutionary perspective • Beliefs that help us acquire a fit behavior in a given social/physical environment are more likely to be transmitted culturally and maintained as a social norm.

6. Illustration: Norms about food-sharing in primordial societies • Kaplan & Hill (1985): Fieldwork on the Ache foragers in Paraguay • Collected resources (vegetables, fruits) • Kin-sharing • Hunted game (peccary, monkey, deer) • Communal-sharing including non-family members widely • Existence oftwo different sharing rules/norms in the same society: Why?

7. Why communal-sharing of hunted games? • Risk-reduction hypothesis • Acquisition of a meat is a highly variable, uncertain prospect, compared to the provision of collected resources. • Communal-sharing system functions as a collective-risk reduction device. • By including more individuals in the risk-pooling group, the variance in food supply decreases exponentially.

8. Intuitively appealing, but truly adaptive explanation? • Problem of egoism in social sharing • Hunted meat is often regarded as a common property or public goods in hunter-gather societies. • What if egoists emerge in the group who just share others’ acquisitions but are never willing to share his own acquisition? • Emphasizing adaptive function of the whole system, but silent about how those egoists are precluded in the group. • Need a theory based on individual-level adaptation rather than group-level adaptation.

9. A theory about development of the communal sharing norm • Proposing a theory based on individual-level adaptation • Using an evolutionary game analysis • Maynard Smith (1982): Evolutionary biology • Axelrod (1984): Introduction to social sciences

10. Evolutionary game • Represents various behavioral/cognitive properties of individuals as strategies in a game. • Examines how each strategy performs in the game against other strategies in terms of net profit. • More fit strategies proliferate in the population gradually (via social/cultural learning). • Different from classical game theory, it does not assume players with super-intelligent information processing ability.

11. Applying the evolutionary game analysis to adaptive norm development • EGA: “Does the interaction among given individual behavioral/cognitive strategies lead to a stable collective state (“evolutionary equilibrium”) where the population is dominated by a single strategy (or a set of strategies)?” • Social norm: a stable set of socially-shared behavioral/cognitive properties (Cialdini & Trost, 1998) • EGA is particularly suited for examining adaptive norm developments in societies.

12. Our model: 4 behavioral strategies about sharing under uncertainty

13. Acquirer with a resource of value V (e.g., hunted meat) Basic Model Depending on behavioral strategies, some individuals may demand communal sharing of the resource. Refusal of the acquirer to share the resource leads to fights that may incur cost C to each loser. Key Question: Can communal sharers outperform other types of members inthe population?

14. Evolutionary computer simulations • Implement the four behavioral strategies in a same population and let them interact. • A strategy that achieves higher profit than the other strategies increase its proportion in the population gradually. • Emergence of a stable equilibrium over time?

15. Results of a simulation starting with nearly 100% egoists in the population Stable Evolvable from nearly zero

16. 2nd-(and higher-) order free-riding? How can this issue be solved?

17. “Lukewarm” norm-enforcers (1st -order free riders) Committed Enforcers Tolerant toward the lukewarm members (2nd-order free riders) Intolerant > Communal sharers >

18. However, the infinite regress is blocked. • The lukewarm members (1st-order free rider) quickly acquire behavioral propensity to be less reactive (less likely to engage in fighting when refused access to the resource) against intolerant members (p2), than against non-sharers (p1). p1 > p2 • Lukewarm members’ p1 is already small. Thus, p2 is negligible. That is, lukewarm members back off, when refused to access the resource by the intolerant members. • So, no fitness differences accrue between the tolerant and the intolerant members. Tolerant members can survive, while effectively eliminating the lukewarm members. • See Kameda, Takezawa & Hastie (2003) for details.

19. “Communal-sharing mind” under uncertainty? Conceptually parallel patterns were also obtained with American samples (see Kameda, Takezawa, Tindale, & Smith, 2002)

20. Conclusion • Communal-sharing ideology can develop to a stable equilibrium (-- socially-shared rule) under uncertainty, as a result of individual-level fitness maximization. • Although living in modern societies (US and Japan), “communal-sharing minds” are triggered easily for uncertain resources. • Such an operation of mind is adaptiveunder uncertainty. • Evolutionary game analysis is a powerful research tool to understand various micro-macro dynamics in our societies.

21. Some thought experiment: Two imaginary commentators • Promising conclusion, but any limitations in the current communal-sharing model? • Two imaginary commentators • A behavioral ecologist • A comparative institutional economist

22. Behavioral ecologist • “An interesting talk. Methodologically sound and theoretically coherent with work in behavioral ecology.” • One critical question – “Given your model, why don’t chimps (or other social animals) engage in communal sharing? They may have the same adaptive problem of uncertainty-reduction in food supply, but no primates other than humans have a broad food-sharing system. What elements in your model limit its scope just to humans? Some sophisticated cognitive mechanisms are assumed in your model?”

23. A comparative institutional economist • “I like your talk, but share the concern with the behavioral ecologist.” • “…Technological and ecological factors… may not be the sole determinants in the selection of a (social) equilibrium; historical and social factors may also matter. Otherwise, norms are nothing but a mechanical transformation of technological and ecological characteristics…” (Aoki, 2001, p.50)

24. What do these (imaginary) criticisms imply? • My model: Communal-sharing norm as evoked by the local ecological conditions • High variance (uncertainty) in meat supply • Group-living: no “privacy” • Behavioral ecologist: Chimps and other social animals may have the same local ecological condition. Then, why don’t they have the communal-sharing norm? Do they lack sophisticated cognitive mechanisms? What exactly are these mechanisms? • Comparative institutional economist: Just a mechanical transformation of ecological characteristics into a “norm”? Specific historical and social factors leading to the norm? Any role of beliefs?

25. “Evoked culture” vs. “Epidemiological culture” • Tooby & Cosmides (1992) • Evoked culture: “Culture triggered by local circumstances; Shared local conditions lead to within-group behavioral similarities and between-group behavioral differences.” • Local ecological conditions evoke culture. • Epidemiological culture: “Culture maintained by constructing shared representations.” • Traditional conceptualization of culture (“transmitted culture”) in social sciences (e.g., Sperber, 1996)

26. (cont’d) • Evolutionary psychologists tend to emphasize the role of evoked culture in human societies. • However, in the evoked culture, cultural beliefs, in principle, do not play a unique, independent role from behavior. Beliefs are just psychological counterparts (reflections) of the adaptive behavior in the local environment, and might even be argued as a redundant concept. • However, cultural beliefs matter! • Chimps vs. humans (re. cultural capacities) • Social/historical changes

27. Challenges! • So, real challenge is to go beyond the evoked culture and theoretically incorporate the epidemiological (transmitted) culture into the adaptive perspective. • Cross-fertilization among different disciplines is essential. • Psychology • Evolutionary anthropology • Economics (comparative institutional analysis) • Game-theoretic framework (including evolutionary and repeated game approaches) provides a common platform.

28. References • Aoki, M. (2001). Toward a comparative institutional analysis. MIT Press. • Axelrod, R. (1986). An evolutionary approach to norms. American Political Science Review, 80, 1095- 1111. • Axerlod, R. (1984). The evolution of cooperation. Basic books. • Boyd, R., & Richerson, P.J. (1985). Culture and the evolutionary process. U. Chicago Press. • Boyd, R., & Richerson, P.J. (1996). Why culture is common, but cultural evolution is rare. Proceedings of the British Academy, 88, 77-93. • Cialdini, R. B., & Trost, M. R. (1998). Social influence: Social norms, conformity, and compliance. In D. T. Gilbert, S. T. Fiske, & G. Lindzey (Eds.), The handbook of social psychology (4th ed., Vol. 2, pp. 151-192). McGraw-Hill. • Foley, R. (1987). Another unique species: Patterns in human evolutionary ecology. Academic Press. • Kameda, T., & Nakanishi, D. (2002). Cost-benefit analysis of social/cultural learning in a non-stationary uncertain environment. Evolution and Human Behavior, 23, 373-393. • Kameda, T., & Nakanishi, D. (2003). Does social/cultural learning increase human adaptability? Rogers’s question revisited. Evolution and Human Behavior, 4, 242-260. • Kameda, T., Takezawa, M., & Hastie, R. (2003). The logic of social sharing: An evolutionary game analysis of adaptive norm development. Personality and Social Psychology Review, 7, 2-19. • Kameda, T., Takezawa, M., Tindale, R. S., & Smith, C. (2002). Social sharing and risk reduction: Exploring a computational algorithm for the psychology of windfall gains. Evolution and Human Behavior, 23, 11-33. • Kaplan, H., & Hill, K. (1985). Food sharing among Ache foragers: Tests of explanatory hypotheses. Current Anthropology, 26, 223-246. • Maynard Smith, J. (1982). Evolution and the theory of games. Cambridge U. Press. • Sperbar, D. (1996). Explaining culture: A naturalistic approach. Blackwell. • Tooby, J., & Cosmides, L. (1992). The psychological foundations of culture. In J.H.Barkow, L.Cosmides, & J.Tooby (Eds.), The adapted mind: Evolutionary psychology and the generation of mind (pp.19- 136). Oxford U. Press. • Yamagishi, T. (1986). The provision of a sanctioning system as a public good. Journal of Personality and Social Psychology, 50, 110-116.