Transfer of information between senders and receivers, of one kind or another, is essential to all life. David Lewis introduced a game theoretic model of the simplest case, where one sender and one receiver have pure common interest. How hard or easy is it for evolution to achieve information transfer in Lewis signaling?. The answers involve surprising subtleties. We discuss some if these in terms of evolutionary dynamics in both finite and infinite populations, with and without mutation.

The presence of apparently irrational fair play in the ultimatum game remains a focal point for studies in the evolution of social behaviour. We investigate the role of negative assortment in the evolution of fair play in the ultimatum game. Spite—social behaviour that inflicts harm with no direct benefit to the actor—can evolve when it is disproportionally directed at individuals playing different strategies. The introduction of negative assortment alters the dynamics in a way that increases the chance fairness evolves, but at a cost: spite also evolves. Fairness is usually linked to cooperation and prosocial behaviour, but this study shows that it may have evolutionary links to harmful antisocial behaviour.

* Correspondence and requests for materials should be addressed to r.smead@neu.edu. We would like to thank the editors at Nature Climate Change as well as two anonymous reviewers for helpful comments on a previous draft of this manuscript. RLS and RS oversaw the project. RS and PF developed the models and ran simulations. RLS and JB analyzed the status of current climate negotiations and policy. RLS, RS, PF, and JB jointly developed how to apply the model to climate negotiations, derived general recommendations, and wrote the paper.

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Spite, the shady relative of altruism, involves paying a fitness cost to inflict a cost on some recipient. Here, we investigate a density dependent dynamic model for the evolution of spite in populations of changing size. We extend the model by introducing a dynamic carrying capacity. Our analysis shows that it is possible for unconditionally spiteful behavior to evolve without population structure in any finite population. In some circumstances spiteful behavior can contribute to its own stability by limiting population growth.We use the model to show that there are differences between spite and altruism, and to refine Hamilton's original argument about the insignificance of spite in the wild. We also discuss the importance of fixing the measure of fitness to classify behaviors as selfish or spiteful. Biological altruism is social behavior that incurs a fitness cost to confer a fitness benefit on other individuals. If altruism involves paying a cost to benefit another, spite involves paying a cost to inflict a cost on another. After Hamilton (1964a,b) showed that correlated interactions among kin can produce the evolution of altruistic behavior, he and Price (1970) came to realize that spiteful behavior could evolve by a similar process (Hamilton 1970(Hamilton , 1971. Often, spiteful behavior is unstable, but we show that it can evolve and be maintained under specific conditions. We present and analyze a variation on Hamilton's model that includes evolutionary dynamics in populations of changing size.We will use correlation and anticorrelation to describe nonrandom social interactions. Correlation increases the chance of interacting with an individual of the same type, whereas anticorrelation increases the chance of interacting with an individual of a different type. Many have shown that this kind of assortment plays an important role in the evolution of cooperation (Eshel and Cavelli-Sforza 1982, Queller 1985, Skyrms 1996, Fletcher and Doebeli 2009. In contrast, a standard approach for modeling the evolution of spite emphasizes the role of negative relatedness (Grafen 1985, Taylor 1996, Frank 1998, Lehmann et al. 2006, West and Gardner 2010. Our rationale for adopting the first approach is twofold. First, although much of our analysis can be reinterpreted in terms of negative relatedness, we wish to make clear that the formal conditions for the evolution of spite do not directly involve any assumptions about genetic relatedness and can be expressed without these notions. This is important because there are mechanisms that can generate anticorrelation (or negative assortment) that do not depend on genetic composition or recognition. Second, evolutionary dynamics in game theoretic settings often have multiple interpretations, some of which are cultural rather than biological (Hofbauer and Sigmund 1998). Although our model is clearly motivated by the biological interpretation, we suspect that it may be possible to extend some of our analysis to settings of cultural evolution. A more generic approach in terms ...