Masanori Takezawa

The Logic of Social Sharing: An Evolutionary Game Analysis of Adaptive Norm Development

Although norms can potentially serve useful constructs to understand human minds, being fundamentally social in evolutionary as well as cultural senses, there are as yet no useful psychological theories of adaptive norm development. This article provides an illustrative model about how a norm emerges in a society. We focus on the “communal-sharing norm” in primordial societies, a norm designating uncertain resources as common properties to be shared with other members. Based on anthropologicalfindings, we develop a theory about how the communal-sharing norm emerges and is maintained. Then, using evolutionary computer simulations, we test several hypotheses about the conditions under which the norm will dominate social resource sharing. We further test behavioral implications of the norm, demonstrating that uncertainty involved in resource acquisition is a key factor that triggers the psychology of sharing even in highly industrialized societies. Finally, we discuss the importance of norm construct for analyzing the dynamic relation between minds and society.

Social sharing and risk reduction : Exploring a computational algorithm for the psychology of windfall gains

Sharing important resources widely beyond direct kin group members is one of the core features characterizing human societies. Moreover, generalized exchange involving many community members (e.g., meat sharing in bands) seems to be a uniquely human practice. This paper explores a computational algorithm for the psychology of social sharing that may underlie such practices, based on the risk-reduction hypothesis in food sharing of Kaplan and Hill [Curr. Anthropol. 26 (1985) 223]. We predicted that, independent of the amount of effort actually invested, uncertainty involved in resource acquisition is a key factor that triggers the psychology of social sharing for both acquirers and nonacquirers of a resource. It was also predicted that the ‘‘windfall effect’’ is independent of individual preferences as to modern distributive ideologies. Four multisample/multimethod studies, using Japanese and American participants, and laboratory as well as vignette experiments, supported these predictions: although the identical fungible resource (money) was under consideration, different psychological processes were triggered, depending on the degree of uncertainty involved in the money acquisition. Implications of the windfall effect for egalitarianism in resource sharing, observed not only in

Two distinct neural mechanisms underlying indirect reciprocity

Significance Humans help strangers even if the strangers will not directly help them in the future. The so-called indirect reciprocity seems to support large-scale cooperation in human society. We revealed functional and anatomical neural bases of two types of indirect reciprocity by combining group and neuroimaging experiments. Reputation-based indirect reciprocity activated the precuneus, a brain region associated with self-centered cognition. Indirect reciprocity occurring as a succession of pay-it-forward behaviors specifically recruited the anterior insula, a region related to affective empathy. Furthermore, task-irrelevant neural fingerprints of these brain regions are predictive of the individual’s tendency of cooperation. These results in particular explain why we often conduct seemingly irrational cooperation such as pay-it-forward reciprocity. Cooperation is a hallmark of human society. Humans often cooperate with strangers even if they will not meet each other again. This so-called indirect reciprocity enables large-scale cooperation among nonkin and can occur based on a reputation mechanism or as a succession of pay-it-forward behavior. Here, we provide the functional and anatomical neural evidence for two distinct mechanisms governing the two types of indirect reciprocity. Cooperation occurring as reputation-based reciprocity specifically recruited the precuneus, a region associated with self-centered cognition. During such cooperative behavior, the precuneus was functionally connected with the caudate, a region linking rewards to behavior. Furthermore, the precuneus of a cooperative subject had a strong resting-state functional connectivity (rsFC) with the caudate and a large gray matter volume. In contrast, pay-it-forward reciprocity recruited the anterior insula (AI), a brain region associated with affective empathy. The AI was functionally connected with the caudate during cooperation occurring as pay-it-forward reciprocity, and its gray matter volume and rsFC with the caudate predicted the tendency of such cooperation. The revealed difference is consistent with the existing results of evolutionary game theory: although reputation-based indirect reciprocity robustly evolves as a self-interested behavior in theory, pay-it-forward indirect reciprocity does not on its own. The present study provides neural mechanisms underlying indirect reciprocity and suggests that pay-it-forward reciprocity may not occur as myopic profit maximization but elicit emotional rewards.

Does imitation benefit cue order learning

Inferences are often based on uncertain cues, and the accuracy of such inferences depends on the order in which the cues are searched. Previous research has shown that people and computers progress only slowly in individual learning of cue orderings through feedback. A clue to how people (as opposed to computers) solve this problem is social learning: By exchanging information with others, people can learn which cues are relevant and the order in which they should be considered. By means of simulation, we demonstrate that imitate-the-best and imitate-the-majority speed up individual learning, whereas a third social rule, the Borda rule, does not. Imitate-the-best also leads to a steep increase in learning after a single social exchange, to cue orders that are more accurate than ecological validity, and to faster learning than when individuals gain the learning experience of all other group members but learn without social exchange. In two experiments, we find that people speed up cue learning in a similar way when provided with social information, both when they obtain the information from the experimenter or in free discussions with others.

Revisiting ''The Evolution of Reciprocity in Sizable Groups'': Continuous reciprocity in the repeated n-person prisoner's dilemma

For many years in evolutionary science, the consensus view has been that while reciprocal altruism can evolve in dyadic interactions, it is unlikely to evolve in sizable groups. This view had been based on studies which have assumed cooperation to be discrete rather than continuous (i.e., individuals can either fully cooperate or else fully defect, but they cannot continuously vary their level of cooperation). In real world cooperation, however, cooperation is often continuous. In this paper, we re-examine the evolution of reciprocity in sizable groups by presenting a model of the n-person prisoners dilemma that assumes continuous rather than discrete cooperation. This model shows that continuous reciprocity has a dramatically wider basin of attraction than discrete reciprocity, and that this basins size increases with efficiency of cooperation (marginal per capita return). Further, we find that assortative interaction interacts synergistically with continuous reciprocity to a much greater extent than it does with discrete reciprocity. These results suggest that previous models may have underestimated reciprocitys adaptiveness in groups. However, we also find that the invasion of continuous reciprocators into a population of unconditional defectors becomes realistic only within a narrow parameter space in which the efficiency of cooperation is close to its maximum bound. Therefore our model suggests that continuous reciprocity can evolve in large groups more easily than discrete reciprocity only under unusual circumstances.

New Methods in Quantitative Ethnography : Economic Experiments and Variation in the Price of Equality

A new method for quantitatively documenting concerns for economic fairness has the potential for identifying variation in prosociality within and across societies. Multiple dictator games conducted in two small‐scale societies presented decision makers with a choice between an equitable and an inequitable payoff distribution. The games varied in terms of the type of inequality the decision maker faced and the cost to the decision maker of eliminating inequality. A novel set of statistical models directly links experimental results and player heterogeneity with the formal theory of inequality aversion. The experimental method can be generalized to allow maximum flexibility in data analysis.

Reinforcement Learning Explains Conditional Cooperation and Its Moody Cousin.

Direct reciprocity, or repeated interaction, is a main mechanism to sustain cooperation under social dilemmas involving two individuals. For larger groups and networks, which are probably more relevant to understanding and engineering our society, experiments employing repeated multiplayer social dilemma games have suggested that humans often show conditional cooperation behavior and its moody variant. Mechanisms underlying these behaviors largely remain unclear. Here we provide a proximate account for this behavior by showing that individuals adopting a type of reinforcement learning, called aspiration learning, phenomenologically behave as conditional cooperator. By definition, individuals are satisfied if and only if the obtained payoff is larger than a fixed aspiration level. They reinforce actions that have resulted in satisfactory outcomes and anti-reinforce those yielding unsatisfactory outcomes. The results obtained in the present study are general in that they explain extant experimental results obtained for both so-called moody and non-moody conditional cooperation, prisoner’s dilemma and public goods games, and well-mixed groups and networks. Different from the previous theory, individuals are assumed to have no access to information about what other individuals are doing such that they cannot explicitly use conditional cooperation rules. In this sense, myopic aspiration learning in which the unconditional propensity of cooperation is modulated in every discrete time step explains conditional behavior of humans. Aspiration learners showing (moody) conditional cooperation obeyed a noisy GRIM-like strategy. This is different from the Pavlov, a reinforcement learning strategy promoting mutual cooperation in two-player situations.

Reinforcement learning accounts for moody conditional cooperation behavior: experimental results.

In social dilemma games, human participants often show conditional cooperation (CC) behavior or its variant called moody conditional cooperation (MCC), with which they basically tend to cooperate when many other peers have previously cooperated. Recent computational studies showed that CC and MCC behavioral patterns could be explained by reinforcement learning. In the present study, we use a repeated multiplayer prisoner’s dilemma game and the repeated public goods game played by human participants to examine whether MCC is observed across different types of game and the possibility that reinforcement learning explains observed behavior. We observed MCC behavior in both games, but the MCC that we observed was different from that observed in the past experiments. In the present study, whether or not a focal participant cooperated previously affected the overall level of cooperation, instead of changing the tendency of cooperation in response to cooperation of other participants in the previous time step. We found that, across different conditions, reinforcement learning models were approximately as accurate as a MCC model in describing the experimental results. Consistent with the previous computational studies, the present results suggest that reinforcement learning may be a major proximate mechanism governing MCC behavior.

Cooperation and Trust in Japanese and British Samples: Evidence from Incomplete Information Games

Most human relationships are characterized by reciprocal patterns of give-and-take that can be studied using a decision-making task called the Centipede game. The game involves 2 players alternating in choosing between cooperation and defection, with their choices affecting payoffs to themselves and the co-player. We compared trust and cooperation of Japanese and U.K. samples in the Centipede game. To increase the game’s applicability to real-life decision situations, we added 3 treatment conditions to manipulate payoff information. Our between-subjects design comprised the following 4 conditions: (a) full payoff information, (b) full payoff information framed as percentages, (c) partial payoff information with absolute (own payoff) information only, and (d) partial payoff information with relative information only. Comparing Japanese and U.K. students’ decisions, the Japanese cooperated significantly more frequently than the British. The manipulation of payoff information also affected decision making. In Japan, both treatment conditions with incomplete information yielded significantly higher cooperation levels than the control. In the U.K., only the condition with absolute payoff information produced significantly higher cooperativeness. Overall, these findings suggest that Japanese samples cooperate more frequently in repeated interactions than British samples and that this may be due to the assurance-based trust elicited by reciprocal relationships that has been identified as a typical feature of Japanese culture. In situations with incomplete information, expectations about the stake size may guide decision making, with lower expectations resulting in higher cooperation levels.

Transient nature of cooperation by pay-it-forward reciprocity.

Humans often forward kindness received from others to strangers, a phenomenon called the upstream or pay-it-forward indirect reciprocity. Some field observations and laboratory experiments found evidence of pay-it-forward reciprocity in which chains of cooperative acts persist in social dilemma situations. Theoretically, however, cooperation based on pay-it-forward reciprocity is not sustainable. We carried out laboratory experiments of a pay-it-forward indirect reciprocity game (i.e., chained gift-giving game) on a large scale in terms of group size and time. We found that cooperation consistent with pay-it-forward reciprocity occurred only in a first few decisions per participant and that cooperation originated from inherent pro-sociality of individuals. In contrast, the same groups of participants showed persisting chains of cooperation in a different indirect reciprocity game in which participants earned reputation by cooperating. Our experimental results suggest that pay-it-forward reciprocity is transient and disappears when a person makes decisions repeatedly, whereas the reputation-based reciprocity is stable in the same situation.