Evolutionarily stable in-group favoritism and out-group spite in intergroup conflict

We study conflict between two groups of individuals. Using Schaffer`s (1988) concept of evolutionary stability we provide an evolutionary underpinning for in-group altruism combined with spiteful behavior towards members of the rival out-group. We characterize the set of evolutionarily stable combinations of in-group favoritism and out-group spite and find that an increase in in-group altruism can be balanced by a decrease in spiteful behavior towards the out-group

Inferring to C or not to C: Evolutionary games with Bayesian inferential strategies

Strategies for sustaining cooperation and preventing exploitation by selfish agents in repeated games have mostly been restricted to Markovian strategies where the response of an agent depends on the actions in the previous round. Such strategies are characterized by lack of learning. However, learning from accumulated evidence over time and using the evidence to dynamically update our response is a key feature of living organisms. Bayesian inference provides a framework for such evidence-based learning mechanisms. It is therefore imperative to understand how strategies based on Bayesian learning fare in repeated games with Markovian strategies. Here, we consider a scenario where the Bayesian player uses the accumulated evidence of the opponent's actions over several rounds to continuously update her belief about the reactive opponent's strategy. The Bayesian player can then act on her inferred belief in different ways. By studying repeated Prisoner's dilemma games with such Bayesian inferential strategies, both in infinite and finite populations, we identify the conditions under which such strategies can be evolutionarily stable. We find that a Bayesian strategy that is less altruistic than the inferred belief about the opponent's strategy can outperform a larger set of reactive strategies, whereas one that is more generous than the inferred belief is more successful when the benefit-to-cost ratio of mutual cooperation is high. Our analysis reveals how learning the opponent's strategy through Bayesian inference, as opposed to utility maximization, can be beneficial in the long run, in preventing exploitation and eventual invasion by reactive strategies.Comment: 13 pages, 9 figure

The evolution of social norms

Evolutionary game theory provides the tools to analyze which strategies, or patterns of behaviour, emerge over time through a process of adaptation. Social norms can be defined as patterns of behaviour with certain characteristics. Evolutionary game theory thus provides one perspective on how social norms are formed and maintained. Prisoner's dilemma games can be used to study the conditions under which cooperative norms emerge. Bargaining games can be used to address the formation of fairness norms. However, being more congenial to analyzing norms that somehow focus on material payoffs, it is not a given that evolutionary game theory can adequately address norms focusing on rights or virtues.Evolutionary game theory Social norms

Good standing and cooperation

Indirect reciprocity is generally considered one of the leading mechanisms to explain how cooperation may emerge by natural selection. The basic intuition is that establishing a reputation of being a helpful individual increases the probability of being in turn helped. Two models have been proposed to describe how indirect reciprocity may work: the standing model (Sugden, 1986/2004) and the image-scoring model (Nowak and Sigmund, 1998a,b). Although there is evidence that the former model would perform better under a wide set of circumstances, it is often maintained that it requires individuals with an implausibly large capacity of processing recursive information. In this paper I argue that this is not actually the case. I then suggest that the information needed by the image-scoring model, under reasonable assumptions, may be sufficient for the standing model to work. Finally I emphasize that even if the hypothesis of indirect reciprocity is unable to give a fair account of the ecological bases of cooperation, it has inspired a deal of research precious to social sciences.Cooperation, Indirect reciprocity, Good standing, Image-Scoring.

Static Stability in Games

Static stability of equilibrium in strategic games differs from dynamic stability in not being linked to any particular dynamical system. In other words, it does not make any assumptions about off-equilibrium behavior. Examples of static notions of stability include evolutionarily stable strategy (ESS) and continuously stable strategy (CSS), both of which are meaningful or justifiable only for particular classes of games, namely, symmetric multilinear games or symmetric games with a unidimensional strategy space, respectively. This paper presents a general notion of local static stability, of which the above two are essentially special cases. It is applicable to virtually all n-person strategic games, both symmetric and asymmetric, with non-discrete strategy spaces.Stability of equilibrium, static stability

In Vino Veritas: The Economics of Drinking

It is argued that drug consumption, most commonly alcohol drinking, can be a technology to give up some control over one’s actions and words. It can be employed by trustworthy players to reveal their type. Similarly alcohol can function as a “social lubricant” and faciliate type revelation in conversations. It is shown that both separating and pooling equilibria can exist; as opposed to the classic results in the literature, a pooling equilibrium is still informative. Drugs which allow a gradual loss of control by appropriate doses and for which moderate consumption is not addictive are particularly suitable because the consumption can be easily observed and reciprocated and is unlikely to occur out of the social context. There is a tradeoff between the effi ciency gains due to the signaling eff ect and the loss of productivity associated with intoxication. Long run evolutionary equilibria of the type distribution are considered. If coordination on an exclusive technology is effi cient, social norms or laws can raise effi ciency by legalizing only one drug.Asymmetric Information, Drinking, Drug Consumption, Signaling, Social Norms

On the Evolution of Preferences

A common feature of the literature on the evolution of preferences is that evolution favors nonmaterialistic preferences only if preference types are observable at least to some degree. We argue that this result is due to the assumption that in each state of the evolutionary dynamics some Bayesian Nash equilibrium is played. We show that under unobservability of preference types, conditional on selecting some self-confirming equilibrium as a rule for mapping preference into behavior, non-selfish preferences may be evolutionarily successful.evolution of preferences, altruism, learning, self-confirming equilibrium