The strong reciprocity model of the evolution of human cooperation has gained some acceptance, partly on the basis of support from experimental findings. The observation that unfair offers in the ultimatum game are frequently rejected constitutes an important piece of the experimental evidence for strong reciprocity. In the present study, we have challenged the idea that the rejection response in the ultimatum game provides evidence of the assumption held by strong reciprocity theorists that negative reciprocity observed in the ultimatum game is inseparably related to positive reciprocity as the two sides of a preference for fairness. The prediction of an inseparable relationship between positive and negative reciprocity was rejected on the basis of the results of a series of experiments that we conducted using the ultimatum game, the dictator game, the trust game, and the prisoner’s dilemma game. We did not find any correlation between the participants’ tendencies to reject unfair offers in the ultimatum game and their tendencies to exhibit various prosocial behaviors in the other games, including their inclinations to positively reciprocate in the trust game. The participants’ responses to postexperimental questions add support to the view that the rejection of unfair offers in the ultimatum game is a tacit strategy for avoiding the imposition of an inferior status.

In a series of experiments, we demonstrate that certain players of an economic game reject unfair offers even when this behavior increases rather than decreases inequity. A substantial proportion (30 -40%, compared with 60 -70% in the standard ultimatum game) of those who responded rejected unfair offers even when rejection reduced only their own earnings to 0, while not affecting the earnings of the person who proposed the unfair split (in an impunity game). Furthermore, even when the responders were not able to communicate their anger to the proposers by rejecting unfair offers in a private impunity game, a similar rate of rejection was observed. The rejection of unfair offers that increases inequity cannot be explained by the social preference for inequity aversion or reciprocity; however, it does provide support for the model of emotion as a commitment device. In this view, emotions such as anger or moral disgust lead people to disregard the immediate consequences of their behavior, committing them to behave consistently to preserve integrity and maintain a reputation over time as someone who is reliably committed to this behavior. emotion ͉ fairness ͉ reciprocity E motions, rather expressed publicly or experienced only privately in the absence of observers, may serve us well in the long run. Experimental research on economic games provides intriguing insights into this phenomenon in the context of understanding constraints on self-regarding behavior. The ultimatum game (1-5) is the game most often used in the social sciences to demonstrate the existence of preferences that are not strictly self-regarding such as inequity aversion and reciprocity. The ultimatum game is played by 2 players-a proposer and a responder. The proposer, is provided $X by the experimenter and then given the opportunity to make a proposal concerning how to divide the money with the responder. The responder is given 2 alternatives-to either accept or reject the proposal. If the proposal is accepted, each player receives the amount specified in the proposal. If the proposal is rejected, neither party receives any money. In a typical experiment, the responder does not know who the proposer is and the two never meet. Furthermore, the game is played only once. As a result, it is not possible for a responder to reject an unfair offer to communicate directly to the proposer that she should behave more fairly in the future.According to the self-regarding actor model typically used in economic game theory a rational, cognitively competent selfregarding responder should accept any proposal that provides some money, no matter how small the amount. A rational proposer who expects this response should therefore propose to give the minimal non-0 amount to the responder. However, the results of ultimatum game experiments generally do not support this prediction. The modal division proposed is a 50-50 split, and extremely unfair proposals are rare (2, 3). Furthermore, the majority of responders typically reject unfair offers that give them Ͻ20-30% o...

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Behavioral and neuroscientific studies explore two pathways through which internalized social norms promote prosocial behavior. One pathway involves internal control of impulsive selfishness, and the other involves emotion-based prosocial preferences that are translated into behavior when they evade cognitive control for pursuing self-interest. We measured 443 participants' overall prosocial behavior in four economic games. Participants' predispositions [social value orientation (SVO)] were more strongly reflected in their overall game behavior when they made decisions quickly than when they spent a longer time. Prosocially (or selfishly) predisposed participants behaved less prosocially (or less selfishly) when they spent more time in decision making, such that their SVO prosociality yielded limited effects in actual behavior in their slow decisions. The increase (or decrease) in slower decision makers was prominent among consistent prosocials (or proselfs) whose strong preference for prosocial (or proself) goals would make it less likely to experience conflict between prosocial and proself goals. The strong effect of RT on behavior in consistent prosocials (or proselfs) suggests that conflict between prosocial and selfish goals alone is not responsible for slow decisions. Specifically, we found that contemplation of the risk of being exploited by others (social risk aversion) was partly responsible for making consistent prosocials (but not consistent proselfs) spend longer time in decision making and behave less prosocially. Conflict between means rather than between goals (immediate versus strategic pursuit of self-interest) was suggested to be responsible for the time-related increase in consistent proselfs' prosocial behavior. The findings of this study are generally in favor of the intuitive cooperation model of prosocial behavior.prosocial behavior | economic game | social value orientation | decision time | heuristic cooperation T he question of how humans succeeded in creating and maintaining large-scale cooperation has occupied social and biological scientists for the past few centuries (1-8). Social scientists traditionally sought answers to this question by focusing on the critical role of internalized social norms that constitute the internal norm enforcement system (1-3). Recent neuroscientific and behavioral studies extended this traditional normenforcement view of human prosociality in two directions. The first direction is to identify the neural mechanisms exerting cognitive control of the selfish drive. Neuroscientists have found structural and neural correlates of prosocial and norm-enforcing choices in economic games. Experimental evidence shows that prosocial choices in economic games are positively related to cortical gray matter volume, cortical thickness, and activation of the brain areas that exert control over selfish impulsive drives, such as the anterior cingulate cortex (9, 10), dorsolateral prefrontal cortex (DLPFC) (11-13), and temporoparietal junction (14). Impairment of the DLPFC...

Human prosociality has been traditionally explained in the social sciences in terms of internalized social norms. Recent neuroscientific studies extended this traditional view of human prosociality by providing evidence that prosocial choices in economic games require cognitive control of the impulsive pursuit of self-interest. However, this view is challenged by an intuitive prosociality view emphasizing the spontaneous and heuristic basis of prosocial choices in economic games. We assessed the brain structure of 411 players of an ultimatum game (UG) and a dictator game (DG) and measured the strategic reasoning ability of 386. According to the reflective norm-enforcement view of prosociality, only those capable of strategically controlling their selfish impulses give a fair share in the UG, but cognitive control capability should not affect behavior in the DG. Conversely, we support the intuitive prosociality view by showing for the first time, to our knowledge, that strategic reasoning and cortical thickness of the dorsolateral prefrontal cortex were not related to giving in the UG but were negatively related to giving in the DG. This implies that the uncontrolled choice in the DG is prosocial rather than selfish, and those who have a thicker dorsolateral prefrontal cortex and are capable of strategic reasoning (goal-directed use of the theory of mind) control this intuitive drive for prosociality as a means to maximize reward when there are no future implications of choices.ultimatum game | dictator game | strategic reasoning | DLPFC | prosocial behavior

Japanese participants in Study 1 exhibited a self-effacing tendency when no reason for their self-evaluation was provided. However, they exhibited a self-enhancing tendency when they were offered a monetary reward for the correct evaluation. In Study 2, Americans, especially American men, exhibited a self-enhancing tendency whereas Japanese exhibited a self-effacing tendency when no reason for making the evaluation was presented. This cultural difference disappeared when participants were provided with a monetary reward for correctly evaluating their performance level. These results support the view that the modesty observed in self-evaluation among Japanese participants is a 'default strategy' to avoid offending others.

Homo economicus, a model for humans in neoclassical economics, is a rational maximizer of self-interest. However, many social scientists regard such a person as a mere imaginary creature. We found that 31 of 446 residents of relatively wealthy Tokyo suburbs met the behavioral definition of Homo economicus. In several rounds of economic games, participants whose behavior was consistent with this model always apportioned the money endowed by the experimenter to themselves, leaving no share for their partners. These participants had high IQs and a deliberative decision style. An additional 39 participants showed a similar disregard for other people's welfare, although they were slightly more altruistic than those in the Homo economicus group. The psychological composition of these quasi-Homo economicus participants was distinct from that of participants in the Homo economicus group. Although participants in the latter group behaved selfishly on the basis of rational calculations, those in the former group made selfish choices impulsively. The implications of these findings concerning the two types of extreme noncooperators are discussed.