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The rejection of unfair offers in the ultimatum game (UG) indicates negative reciprocity. The model of strong reciprocity claims that negative reciprocity reflects prosociality because the rejecting individual is sacrificing resources in order to punish unfair behavior. However, a recent study found that the rejection rate of unfair offers is linked to assertiveness (status defense model). To pursue the question what drives negative reciprocity, the present study investigated individual differences in the rejection of unfair offers along with their behavioral and neuronal determinants. We measured fairness preferences and event-related potentials (ERP) in 200 healthy participants playing a computerized version of the UG with pictures of unfair and fair proposers. Structural equation modeling (SEM) on the behavioral data corroborated both the strong reciprocity and the status defense models of human cooperation: Not only more prosocial but also more assertive individuals were more likely to show negative reciprocity by rejecting unfair offers. Experimental ERP results confirmed the feedback negativity (FN) as a neural signature of fairness processing. Multilevel SEM of brain-behavior relationships revealed that negative reciprocity was significantly associated with individual differences in FN amplitudes in response to proposers. Our results confirm stable individual differences in fairness processing at the behavioral and neuronal level.

We use time, rather than money, as the salient component of subjects’ incentives in three workhorse experimental paradigms. The use of waiting time can be interpreted as a special type of real effort condition, in which it is particularly straightforward to achieve experimental control over incentives. The three experiments, commonly employed to study social preferences, are the dictator game, the ultimatum game and the trust game. All subjects in a session earn the same participation fee, but their choices affect the time at which they are permitted to leave the laboratory. Decisions that are associated with greater own payoff translate into the right to depart earlier. The modal proposal in both the dictator and ultimatum games is an equal split of the waiting time. In the trust game, there is substantial trust and reciprocity. Overall, social preferences are evident in time allocation decisions. We compare subjects’ decisions over time and money and find no significant differences in average decisions. The pattern of results suggests that results obtained in the laboratory with money as the medium of reward generalize to other reward media.

Using the evolutionary game theory, this essay researches the game between the service level of public library and the investment of government, establishes the dissymmetrical evolutionary game model and replicator dynamics equation, analyses and discusses the replicator dynamics equation, gets the evolutionary rule and path of the game subject behavior choice.

We focus our attention on the effectiveness of punishing defectors in the evolution of cooperation in rational populations within the threshold public goods game models. We establish two scenarios: defectors will suffer possible punishment whether the game succeeds or not, and defectors will incur punishment only when game fails. A key observation of this paper is that given this assumption, punishing free riders can significantly influence the evolution outcomes, and the results are driven by the specific components of the punishing rule. Particularly, probably punishing defectors always, not only when game fails, can be more effective for maintaining public cooperation and leads to higher total contributions. Intriguingly when defectors face punishment only when game fails, the spread and domination of cooperators can not be ensured even by sufficiently large punishment, which already brings payoff advantages of defectors over cooperators. Further, cooperators are best supported by the large punishment on defectors, and then dominate and stabilize in the population, under the premise that defectors always incur punishment regardless of whether the game ends successfully or not. We hope this work provides some intriguing hints or insights on investigating the collective behaviors by the aid of punishment mechanism.

This study exploits the opening of the experimental lab in Oxford to compare the behavior of students and non-students in a number of classic experimental games, some of which involve other-regarding preferences (Trust Game, Dictator Game, and Public Goods Game) and others which have game forms that are strategically challenging (Beauty-contest and Second-price Auction). We find that students are more likely to behave as selfish and rational agents than non-students. Our findings suggest that students are different than non-students with respect to their social preferences and their ability to reason strategically. Experiments using students are likely to overestimate the extent of selfish and rational behavior in the general population.

Against a backdrop of increased global environmental and economic uncertainty, the resilience and sustainability of urban communities is a paramount concern for decision makers. The work presented here aims to explore how teaching and learning around transition initiatives, based upon social enterprise and reciprocity, might be supported by game theory and strategy simulation environments. Key elements for this are the coevolutionary nature of internal and external organisational contexts. The gaming prototype developed here (Exploring Community Resilience, ExCoRe) is based upon an extension of the Prisoner’s Dilemma as a medium for active learning, but is enacted through a multi-player and dynamic environment. The key learning objectives for the game are to introduce a broad concept of reciprocity and collaboration on a systems level, and the importance of an emergent and responsive ‘learning strategy’ for new start-ups and enterprises. The static nature of the traditional strengths, weaknesses, opportunities, and threats (SWOT) approach is challenged and students are encouraged to appreciate, through establishing game strategy, a much more fluid and dynamic relationship between internal and external environments.

We introduce chaotic variations, modelled by a spatially extended Lorenz system, to the payoffs of the spatial prisoner's dilemma game and study their effects on the evolution of cooperation. We show that chaotic variations of appropriate amplitude promote cooperation over a wide range of payoff parameters at which defection is the only strategy in a sterile environment. An appropriately pronounced chaotic environment can assure permanent domination of cooperation by full anonymity of players and without the aid of secondary strategies, thus designating chaotic payoff variations as a general and stand-alone mechanism for cooperation in the spatial prisoner's dilemma game.

One of the enduring puzzles in biology and the social sciences is the origin and persistence of intraspecific cooperation and altruism in humans and other species. Hundreds of theoretical models have been proposed and there is much confusion about the relationship between these models. To clarify the situation, we developed a synthetic conceptual framework that delineates the conditions necessary for the evolution of altruism and cooperation. We show that at least one of the four following conditions needs to be fulfilled: direct benefits to the focal individual performing a cooperative act; direct or indirect information allowing a better than random guess about whether a given individual will behave cooperatively in repeated reciprocal interactions; preferential interactions between related individuals; and genetic correlation between genes coding for altruism and phenotypic traits that can be identified. When one or more of these conditions are met, altruism or cooperation can evolve if the cost-to-benefit ratio of altruistic and cooperative acts is greater than a threshold value. The cost-to-benefit ratio can be altered by coercion, punishment and policing which therefore act as mechanisms facilitating the evolution of altruism and cooperation. All the models proposed so far are explicitly or implicitly built on these general principles, allowing us to classify them into four general categories.

There is a remarkable resonance between recent findings about medical malpractice litigation and theories about the evolution of co-operation and reciprocity among humans. This should not be altogether surprising: theories of reciprocity seek to explain the behaviours we exhibit when we interact to punish or confer benefits on each other; while civil liability litigation may be just one of modern society’s ways of compelling otherwise unrequited reciprocity. The link between the two fields of study is worth exploring nonetheless. Just as behavioural economics and evolutionary theory offer useful insights for those of us who study legal phenomena, data about the behaviour of people accessing legal institutions may be useful to those who build behavioral theories. This essay is therefore, in a way, a lawyer’s effort to return the favour.

Experiments show that humans cooperate with non-kin, including people they will never meet again, and punish non-cooperators at personal cost. This is called strong reciprocity. It has recently been sug gested, based on evolutionary simulations of an agent-based model inspired by the ultimatum game, that strong reciprocity may arise from individual selection. Ontogenic adaptations were introduced to the model to see how phenotypic plasticity affects the evolution of strong reciprocity. The influence of plasticity is explored by varying the way in which agents adapt. Simulations show that plasticity during an agent's lifetime changes the path of evolution toward interesting behaviors that better approach those observed in humans. As plasticity is increased, the average offers and acceptance threshold also increase.

We used simple economic games to examine pro-social behavior and the lengths that people will take to avoid engaging in it. Over two studies, we found that about one-third of participants were willing to ‘‘exit’’ a $10 dictator game and take $9 instead. The exit option left the receiver nothing, but also ensured that the receiver never knew that a dictator game was to be played. Because most social utility models are defined over monetary outcomes, they cannot explain choosing the ($9, $0) exit outcome over the dominating $10 dictator game, since the game includes outcomes of ($10, $0) and ($9, $1). We also studied exiting using a ‘‘private’’ dictator game. In the private game, the receiver never knew about the game or from where any money was received. Gifts in this game were added innocuously to a payment for a separate task. Almost no dictators exited from the private game, indicating that receivers beliefs are the key factor in the decision to exit. When, as in the private game, the receivers beliefs and expectations cannot be manipulated by exit, exit is seldom taken. We conclude that giving often reflects a desire not to violate others expectations rather than a concern for others welfare per se. We discuss the implications of our results for understanding ethical decisions and for testing and modeling social preferences. An adequate specification of social preferences should include ‘‘psychological’’ payoffs that directly incorporate beliefs about actions into the utility function. 2005 Elsevier Inc. All rights reserved.

Social dilemmas and the evolutionary conundrum of cooperation are traditionally studied through various kinds of game theoretical models such as the prisoner's dilemma, public goods games, snowdrift games or by-product mutualism. All of them exemplify situations which are characterized by different degrees of conflicting interests between the individuals and the community. In groups of interacting individuals, cooperators produce a common good benefitting the entire group at some cost to themselves, whereas defectors attempt to exploit the resource by avoiding the costly contributions. Based on synergistic or discounted accumulation of cooperative benefits a unifying theoretical framework was recently introduced that encompasses all games that have traditionally been studied separately (Hauert, Michor, Nowak, Doebeli, 2005. Synergy and discounting of cooperation in social dilemmas. J. Theor. Biol., in press.). Within this framework we investigate the effects of spatial structure with limited local interactions on the evolutionary fate of cooperators and defectors. The quantitative effects of space turn out to be quite sensitive to the underlying microscopic update mechanisms but, more general, we demonstrate that in prisoner's dilemma type interactions spatial structure benefits cooperation-although the parameter range is quite limited-whereas in snowdrift type interactions spatial structure may be beneficial too, but often turns out to be detrimental to cooperation.

Binmore's Natural Justiceoffers an evolutionary approach to morality, in which moral rules form a cultural system that is robust and evolutionarily stable. The folk theorem is the analytical basis for his theory of justice. I argue that this is a mistake, as the equilibria described by the folk theorem lack dynamic stability in games with several players. While the dependence of Binmore's argument on the folk theorem is more tactical than strategic, this choice does have policy implications. I do not believe that moral rules are solutions to the Nash bargaining problem. Rather, I believe that human beings are emotionally constituted, by virtue of their evolutionary history, to embrace prosocial and altruistic notions of in-group–out-group identification and reciprocity. These aspects of human nature are incompatible with Binmore's notion that humans are self-regarding creatures. I present empirical evidence supporting a specific form of human, other-regarding preferences known as strong reciprocity.

In the economic literature, reciprocity is typically studied in situations of repeated interaction between two individuals. It refers to one individual rewarding kind acts of the other or punishing hostile acts. In contrast, this paper studies indirect reciprocity, where a cooperative action is rewarded by a third actor, not involved in the original exchange. We provide experimental evidence on indirect reciprocity. The experiment is based on the 'repeated helping game' developed by Nowak and Sigmund (J. Theoret. Biol. 194 (1998) 561; Nature 393 (1998) 573), involving random pairing in large groups. Pairs consist of a donor and a recipient. Donors decide whether or not to provide costly 'help' to the recipients they are matched with, based on information about the recipient's behavior in encounters with third parties. We observe clear evidence of indirect reciprocity. Many decision-makers respond to the information about previous decisions (whether or not to help others) of the recipients. In our experiments, this indirect reciprocity is largely based on norms about how often the recipient should have helped others in the past. We show that these norms develop similarly within groups of interacting subjects, but distinctly across groups. This leads to the emergence of group norms.

Generally, with a standard linear public goods game, one observes at the aggregate level that contributions lay between the Nash equilibrium and the social optimum and decrease over time with and end-effect. The purpose of this paper is to see whether these general aggregate results remain available at the group and at the individual levels. At this purpose, six groups of four persons were formed and made to play a public goods game. At the aggregate level, it was found that obtained results corresponded almost to the standard experimental findings in the literature. Using the classification by Isaac, Walker and Thomas ({dy1984}), it was found that at the group level only two groups adopted the standard behaviour and only two groups presented a behaviour similar to what it was obtained at the aggregate level. At the individual level, contributions over time of each subject to the group were compared to the aggregate results and classified into types. Only in one of the six groups individuals adopted an homogeneous behaviour, meantime in the other five groups individuals conducted different behaviours.

Understanding the mechanisms that can lead to the evolution of cooperation through natural selection is a core problem in biology. Among the various attempts at constructing a theory of cooperation, game theory has played a central role. Here, we review models of cooperation that are based on two simple games: the Prisoner's Dilemma, and the Snowdrift game. Both games are two-person games with two strategies, to cooperate and to defect, and both games are social dilemmas. In social dilemmas, cooperation is prone to exploitation by defectors, and the average payoff in populations at evolutionary equilibrium is lower than it would be in populations consisting of only cooperators. The difference between the games is that cooperation is not maintained in the Prisoner's Dilemma, but persists in the Snowdrift game at an intermediate frequency. As a consequence, insights gained from studying extensions of the two games differ substantially. We review the most salient results obtained from extensions such as iteration, spatial structure, continuously variable cooperative investments, and multi-person interactions. Bridging the gap between theoretical and empirical research is one of the main challenges for future studies of cooperation, and we conclude by pointing out a number of promising natural systems in which the theory can be tested experimentally.

Human cooperation is held to be an evolutionary puzzle because people voluntarily engage in costly cooperation, and costly punishment of non-cooperators, even among anonymous strangers they will never meet again. The costs of such cooperation cannot be recovered through kin-selection, reciprocal altruism, indirect reciprocity, or costly signaling. A number of recent authors label this behavior ‘strong reciprocity’, and argue that it is: (a) a newly documented aspect of human nature, (b) adaptive, and (c) evolved by group selection. We argue exactly the opposite; that the phenomenon is: (a) not new, (b) maladaptive, and (c) evolved by individual selection. In our perspective, the apparent puzzle disappears to reveal a biological and evolutionary logic to human cooperation. Group selection may play a role in theory, but it is neither necessary nor sufficient to explain human cooperation. Our alternative solution is simpler, makes fewer assumptions, and is more parsimonious with the empirical data.

Strong reciprocators possess two behavioural dispositions: they are willing to bestow benets on those who have bestowed benets, and they are willing to punish those who fail to bestow benets according to some social norm. There is no doubt that peoples' behaviour, in many cases, agrees with what we would expect if people are strong reciprocators, and Fehr and Henrich argue that many people are, in fact, strong reciprocators. They also suggest that strongly reciprocal behaviour may be brought about by specialised cognitive architecture produced by evolution. I argue that specialised cognitive architecture can play a role in the production of strongly reciprocal behaviour only in a very attenuated sense, and that the evolutionary foundations of strong reciprocity are more likely cultural than biological. To say that people cooperate, trust, oer more than is logically or strategically necessary, and punish those who attempt to short-change them, even when in- curing a cost to themselves, is not to say anything new. What is new are current approaches to explaining such behaviour, where \explain" here means identify- ing the ultimate causal factors responsible for it. The task is to identify the ultimate, not proximate, causal factors, because it is entirely straightforward to identify some proximate causes: the beliefs and desires of the agent at the time of acting. Why did so-and-so choose to oer more than is logically or strategically necessary? Because (one might say) that person believes that that is what they ought to do, and there is no overriding reason to not do what they ought to do. 1 Dissatisfaction with this type of explanation arises because it leaves unanswered the question of where those beliefs ultimately came from. Why those beliefs and not others? To say they were learned seems inadequate because it simply pushes back the inquiry a stage: if the beliefs were learned, from whom were they learned, and why did that person hold those beliefs and choose to propagate them by teaching? A search for the ultimate causal factors is thus a search for the real reasons that people cooperate, trust, and so on. An evolutionary psychological account is a natural one to propose, since it locates the source of certain key motivating beliefs, desires, and dispositions in the tness advantages conferred. Along this

Ernst Fehr and his collaborators have argued that traditional explanations of human cooperation cannot account for strong reciprocity. They provide substantial empirical evidence that strong reciprocity is an important phenomenon that cannot be explained by the traditional models of kin selection or reciprocal altruism. In this note, however, I argue that it will be difficult to test specific adaptive explanations of strong reciprocity because it is apparently unique to humans. Consequently, it is difficult to employ the comparative method, which is one of biology’s best tools for testing adaptationist claims.

Previous experimental and empirical evidence has identified social preferences in the voluntary provision of public goods. A number of competing models of such preferences have been proposed. We provide evidence for one model of behavior in these games, reciprocity (or matching, or conditional cooperation). Consistent with previous research, we find that participants in the voluntary contribution mechanism attempt to match the contributions of others in their group. We also examine participants in a related game with different equilibria, the weakest-link mechanism. Here, in contrast, participants contribute so as to match the minimum contribution of others in their group.

We replicate previous results showing that stakes do not affect offers in the ultimatum game (UG) and show that stakes also have no effect on allocations in the dictator game (DG). Both results are robust to the inclusion of demographic factors.

Experimental evidence suggests that human decisions involve a mixture of self-interest and internalized social norms which cannot be accounted for by the Nash equilibrium behavior of Homo Economicus. This led to the notion of strong reciprocity (or altruistic punishment) to capture the human trait leading an individual to punish norm violators at a cost to himself. For a population with small autonomous groups with collective monitoring, the interplay of intra- and intergroup dynamics shows this to be an adaptive trait, although not fully invasive of a selfish population. However, the absence of collective monitoring in a larger society changes the evolution dynamics. Clustering seems to be the network parameter that controls maintenance and evolution of the reciprocator trait.

In two experiments, the existence and extent of altruistic reciprocity is exploredin the context of a simple experimental game, “the sequential dictator.” Findings show that altruistic reciprocity is frequent and robust, and the reciprocity norm does not erode if stakes are raised. Implications of the findings for social theory and further empirical research are discussed.

Understanding the emergence of cooperation is a fundamental problem in evolutionary biology. Evolutionary game theory has become a powerful framework with which to investigate this problem. Two simple games have attracted most attention in theoretical and experimental studies: the Prisoner's Dilemma and the snowdrift game (also known as the hawk-dove or chicken game). In the Prisoner's Dilemma, the non-cooperative state is evolutionarily stable, which has inspired numerous investigations of suitable extensions that enable cooperative behaviour to persist. In particular, on the basis of spatial extensions of the Prisoner's Dilemma, it is widely accepted that spatial structure promotes the evolution of cooperation. Here we show that no such general predictions can be made for the effects of spatial structure in the snowdrift game. In unstructured snowdrift games, intermediate levels of cooperation persist. Unexpectedly, spatial structure reduces the proportion of cooperators for a wide range of parameters. In particular, spatial structure eliminates cooperation if the cost-to-benefit ratio of cooperation is high. Our results caution against the common belief that spatial structure is necessarily beneficial for cooperative behaviour.

This paper uses a three-games (or triadic) design to identify trusting and reciprocating behavior. A large literature on single-game trust and reciprocity experiments is based on the implicit assumption that subjects do not have altruistic or inequality-averse other-regarding preferences. Such experimental designs test compound hypotheses that include the hypothesis that other-regarding preferences do not affect behavior. In contrast, experiments with the triadic design do discriminate between transfers resulting from trust or reciprocity and transfers resulting from other-regarding preferences that are not conditional on the behavior of others. Decomposing trust from altruism and reciprocity from altruism or inequality aversion is critical to obtaining empirical information that can guide the process of constructing models that can increase the empirical validity of game theory.

How do human groups maintain a high level of cooperation despite a low level of genetic relatedness among group members? We suggest that many humans have a predisposition to punish those who violate group-beneficial norms, even when this imposes a fitness cost on the punisher. Such altruistic punishment is widely observed to sustain high levels of cooperation in behavioral experiments and in natural settings. We offer a model of cooperation and punishment that we call strong reciprocity : where members of a group benefit from mutual adherence to a social norm, strong reciprocators obey the norm and punish its violators, even though as a result they receive lower payoffs than other group members, such as selfish agents who violate the norm and do not punish, and pure cooperators who adhere to the norm but free-ride by never punishing. Our agent-based simulations show that, under assumptions approximating likely human environments over the 100,000 years prior to the domestication of animals and plants, the proliferation of strong reciprocators when initially rare is highly likely, and that substantial frequencies of all three behavioral types can be sustained in a population. As a result, high levels of cooperation are sustained. Our results do not require that group members be related or that group extinctions occur.

This article is extracted from a forthcoming book, ‘Natural Justice’. It is a nontechnical introduction to the part of game theory immediately relevant to social contract theory. The latter part of the article reviews how concepts such as trust, responsibility, and authority can be seen as emergent phenomena in models that take formal account only of equilibria in indefinitely repeated games.

We analyze the replicator equation for two games closely related with the social dilemma occurring in public goods situations. In one case, players can punish defectors in their group. In the other case, they can choose not to take part in the game. In both cases, interactions are not pairwise and payoffs non-linear. Nevertheless, the qualitative dynamics can be fully analyzed. The games offer potential solutions for the problem of the emergence of cooperation in sizeable groups of non-related individuals -- a basic question in evolutionary biology and economics.

Many experimental studies indicate that people are motivated by reciprocity. Rabin (1993) develops techniques for incorporating such concerns into game theory and economics. His model, however, does not fare well when applied to situations with an interesting dynamic structure (like many experimental games), because it is developed for normal form games in which information about the sequential structure of a strategic situation is suppressed. In this paper we develop a theory of reciprocity for extensive games in which the sequential structure of a strategic situation is made explicit. We propose a new solution concept— sequential reciprocity equilibrium—which is applicable to extensive games, and we prove a general equilibrium existence result. The model is applied in several examples, including some well known experimental games like the Ultimatum game and the Sequential Prisoners’ Dilemma.

This paper reports the results of the Ultimatum Game (UG), Dictator Game (DG) and Public Goods Game (PGG) played among the Tsimane, a group of forager-horticulturalists living in the Bolivian Amazon. Game results differ significantly from those commonly reported among modern, westernized populations. Without a long history of anonymous interactions, it is highly suspect whether the Tsimane or other traditional populations play economic games under assumptions of anonymity and one-shot exposure. Employing a behavioral ecology framework, I test predictions that differential market exposure, costs of giving, and experience with cooperation can help explain much of the variance in game outcomes. While these factors sometimes act as important predictors of game behavior, the most significant predictor is village membership. Implications for understanding the role of markets, frequent interaction with strangers, and payoffs to cooperation in daily life can help us better understand cross-cultural variation in pro-social behavior.

Some of the most fundamental questions concerning our evolutionary origins, our social relations, and the organization of society are centred around issues of altruism and selfishness. Experimental evidence indicates that human altruism is a powerful force and is unique in the animal world. However, there is much individual heterogeneity and the interaction between altruists and selfish individuals is vital to human cooperation. Depending on the environment, a minority of altruists can force a majority of selfish individuals to cooperate or, conversely, a few egoists can induce a large number of altruists to defect. Current gene-based evolutionary theories cannot explain important patterns of human altruism, pointing towards the importance of both theories of cultural evolution as well as gene–culture co-evolution.

Several recent theories in behavioral game theory seek to explain the behavior of subjects in experimental bargaining games. These models can be partitioned into two classes: outcome-based and intention-based. Outcome-based models treat the intentions that players attribute to one another as unnecessary for predicting behavior. Intention-based approaches, and in particular the trust and reciprocity (TR) hypothesis, rely on this attribution of intentions in an essential way. We report laboratory data from simple two-person trust games which is inconsistent with outcome-based models, but predicted by the trust and reciprocity hypothesis.

Recent experimental research has revealed forms of human behavior involving interaction among unrelated individuals that have proven difficult to explain in terms of kin or reciprocal altruism. One such trait, strong reciprocity is a predisposition to cooperate with others and to punish those who violate the norms of cooperation, at personal cost, even when it is implausible to expect that these costs will be repaid. We present evidence supporting strong reciprocity as a schema for predicting and understanding altruism in humans. We show that under conditions plausibly characteristic of the early stages of human evolution, a small number of strong reciprocators could invade a population of selfregarding types, and strong reciprocity is an evolutionary stable strategy. Although most of the evidence we report is based on behavioral experiments, the same behaviors are regularly described in everyday life, for example, in wage setting by firms, tax compliance, and cooperation in the protection of local environmental public goods. D 2003 Elsevier Science Inc. All rights reserved.

Homo sapiens is the only species in which we observe extensive cooperation among large numbers of genetically unrelated individuals. Incompatible approaches to explaining cooperation among humans have been offered by sociologists, biologists, and economists. None is wholly successful. Each discipline, moreover, has ignored basic insights of the others. This article explains cooperation by combining central contributions of these disciplines, developing a model of cultural evolution in which we use (a) the sociological concept of the internalization of norms to explain cultural transmission; (b) the biological concepts of vertical and oblique transmission to model the interaction of cultural and biological adaptation; and (c) the economic concepts of rational action and the replicator dynamic to model the interaction between self-interested and altruistic behavior. The article closes with a bioeconomic explanation of the human capacity to internalize norms.

The evolution of cooperation among unrelated individuals in human and animal societies remains a challenging issue across disciplines. In this context, two models have attracted most attention: the prisoner’s dilemma for pairwise interactions and the public goods game for group interactions. The two games share many features as demonstrated by the close linkage of their cores. In spatially structured systems with individuals arranged on a lattice we investigate effects of group size and lattice geometry on the success of cooperators and defectors in compulsory and voluntary interactions. The geometry (square versus honeycomb), i.e., the connectivity turns out to have surprisingly pronounced and robust effects on the fate of cooperators. Apparently they thrive more easily on honeycomb lattices. As expected, it becomes increasingly difficult to promote cooperation in sizable groups but voluntary participation significantly lowers the threshold for persistent cooperative behavior. In fact, this effect is even more pronounced for larger groups. The risk avoiding option to not participate provides additional protection to clusters of cooperators against exploitation and introduces rock-scissors-paper-type cyclic dominance, which gives rise to intriguing spatio-temporal patterns. © 2003 Wiley Periodicals, Inc.

Trust is of great interest in organizational research and the social sciences. It is argued here that any theory of trust ought to treat a set of observed empirical regularities as constraints. A constraint on a theory is either an assumption made in constructing the theory (e.g., we assume people have a tendency to be fair in their dealings with others) or an explanandum (e.g., we must explain the tendency people have to be fair in their dealings with others) for which the theory must account. These constraints are best thought of in an evolutionary framework, with intellectual links to game theory, evolutionary biology and evolutionary psychology. In particular, (1) people are disposed towards fairness and reciprocity, they have (2) cognitive modules and (3) emotional dispositions which safeguard them against cheating and trust violation. Given these three constraints, any theory should consider the (4) evidence for cultural constraints on trust, trusting behavior and decisions. These constraints together point us towards an integrated ecology of trust where culture, individual dispositions and cognition jointly influence observed trusting behavior. Some work, particularly Gintis et al. (2002) on altruism, strong reciprocity and cooperation, suggests such an approach to studying trust. The purpose of this essay is to identify this work, organize it, and argue for its bearing on the study of trust and organizations. Copyright © 2003 John Wiley & Sons, Ltd.

Game theory describes social behaviors in humans and other biological organisms. By far, the most powerful tool available to game theorists is the concept of a Nash Equilibrium (NE), which is motivated by perfect rationality. NE specifies a strategy for everyone, such that no one would benefit by deviating unilaterally from his/her strategy. Another powerful tool available to game theorists are evolutionary dynamics (ED). Motivated by evolutionary and learning processes, ED specify changes in strategies over time in a population, such that more successful strategies typically become more frequent. A simple game that illustrates interesting ED is the generalized Rock-Paper-Scissors (RPS) game. The RPS game extends the children's game to situations where winning or losing can matter more or less relative to tying. Here we investigate experimentally three RPS games, where the NE is always to randomize with equal probability, but the evolutionary stability of this strategy changes. Consistent with the prediction of ED we find that aggregate behavior is far away from NE when it is evolutionarily unstable. Our findings add to the growing literature that demonstrates the predictive validity of ED in large-scale incentivized laboratory experiments with human subjects.

Networks with dependency links are more vulnerable when facing the attacks. Recent research also has demonstrated that the interdependent groups support the spreading of cooperation. We study the prisoner's dilemma games on spatial networks with dependency links, in which a fraction of individual pairs is selected to depend on each other. The dependency individuals can gain an extra payoff whose value is between the payoff of mutual cooperation and the value of temptation to defect. Thus, this mechanism reflects that the dependency relation is stronger than the relation of ordinary mutual cooperation, but it is not large enough to cause the defection of the dependency pair. We show that the dependence of individuals hinders, promotes and never affects the cooperation on regular ring networks, square lattice, random and scale-free networks, respectively. The results for the square lattice and regular ring networks are demonstrated by the pair approximation.

Reciprocity is characterized by individuals actively making it beneficial for others to cooperate by responding to them. This makes it a particularly powerful generator of mutual interest, because the benefits accrued by an individual can be redistributed to another. However, reciprocity is a composite biological function, entailing at least two subfunctions: (i) a behavioral ability to provide fitness benefits to others and (ii) a cognitive ability to evaluate the benefits received from others. For reciprocity to evolve, these two subfunctions must appear together, which raises an evolutionary problem of bootstrapping. In this article, I develop mathematical models to study the necessary conditions for the gradual emergence of reciprocity in spite of this bootstrapping problem. I show that the evolution of reciprocity is based on three conditions. First, there must be some variability in behavior. Second, cooperation must pre-evolve for reasons independent of reciprocity. Third, and most significantly, selection favors conditional cooperation only if the cooperation expressed by others is already conditional, that is, if some reciprocity is already present in the first place. In the discussion, I show that these three conditions help explain the specific features of the instances in which reciprocity does occur in the wild. For instance, it accounts for the role of spatial symmetry (as in ungulate allogrooming), the importance of synergistic benefits (as in nuptial gifts), the facilitating role of collective actions (as in many instances of human cooperation), and the potential role of kinship (as in primate grooming).

Humans regularly help strangers, even when interactions are apparently unobserved and unlikely to be repeated. Such situations have been simulated in the laboratory using anonymous one-shot games (e.g., prisoner’s dilemma) where the payoff matrices used make helping biologically altruistic. As in real-life, participants often cooperate in the lab in these one-shot games with non-relatives, despite that fact that helping is under negative selection under these circumstances. Two broad explanations for such behavior prevail. The “big mistake” or “mismatch” theorists argue that behavior is constrained by psychological mechanisms that evolved predominantly in the context of repeated interactions with known individuals. In contrast, the cultural group selection theorists posit that humans have been selected to cooperate in anonymous one-shot interactions due to strong between-group competition, which creates interdependence among in-group members. We present these two hypotheses before discussing alternative routes by which humans could increase their direct fitness by cooperating with strangers under natural conditions. In doing so, we explain why the standard lab games do not capture real-life in various important aspects. First, asymmetries in the cost of perceptual errors regarding the context of the interaction (one-shot vs. repeated; anonymous vs. public) might have selected for strategies that minimize the chance of making costly behavioral errors. Second, helping strangers might be a successful strategy for identifying other cooperative individuals in the population, where partner choice can turn strangers into interaction partners. Third, in contrast to the assumptions of the prisoner’s dilemma model, it is possible that benefits of cooperation follow a non-linear function of investment. Non-linear benefits result in negative frequency dependence even in one-shot games. Finally, in many real-world situations individuals are able to parcel investments such that a one-shot interaction is turned into a repeated game of many decisions.

Why would natural selection favor the prevalence of cooperation within the groups of selfish individuals? A fruitful framework to address this question is evolutionary game theory, the essence of which is captured in the so-called social dilemmas. Such dilemmas have sparked the development of a variety of mathematical approaches to assess the conditions under which cooperation evolves. Furthermore, borrowing from statistical physics and network science, the research of the evolutionary game dynamics has been enriched with phenomena such as pattern formation, equilibrium selection, and self-organization. Numerous advances in understanding the evolution of cooperative behavior over the last few decades have recently been distilled into five reciprocity mechanisms: direct reciprocity, indirect reciprocity, kin selection, group selection, and network reciprocity. However, when social viscosity is introduced into a population via any of the reciprocity mechanisms, the existing scaling parameters for the dilemma strength do not yield a unique answer as to how the evolutionary dynamics should unfold. Motivated by this problem, we review the developments that led to the present state of affairs, highlight the accompanying pitfalls, and propose new universal scaling parameters for the dilemma strength. We prove universality by showing that the conditions for an ESS and the expressions for the internal equilibriums in an infinite, well-mixed population subjected to any of the five reciprocity mechanisms depend only on the new scaling parameters. A similar result is shown to hold for the fixation probability of the different strategies in a finite, well-mixed population. Furthermore, by means of numerical simulations, the same scaling parameters are shown to be effective even if the evolution of cooperation is considered on the spatial networks (with the exception of highly heterogeneous setups). We close the discussion by suggesting promising directions for future research including (i) how to handle the dilemma strength in the context of co-evolution and (ii) where to seek opportunities for applying the game theoretical approach with meaningful impact.

Strong negative reciprocity, that is, sanctions imposed on norm violators at the punisher's own expense, has powerful cooperation-enhancing effects in both real-life and experimental game situations. However, it is plausible that punishment may obtain alternative roles depending on social context and the personality characteristics of participants. We examined the occurrence of punishing behavior among 80 subjects in a strongly competitive Public Goods game setting. Despite the punishment condition, the amount of the contributions decreased steadily during the game. The amount of contributions had no significant effect on received and imposed punishments. The results indicate that certain social contexts (in this case, intensive competition) exert modifying effects on the role that punishment takes on. Subjects punished each other in order to achieve a higher rank and a financially better outcome. Punishment primarily functioned as a means of rivalry, instead of as a way of second-order cooperation, as strong reciprocity suggests. These results indicate the need for the possible modification of the social conditions of punishment mechanisms described by the strong reciprocity theory as an evolutionary explanation of human cooperation.