Trust is essential for a secure and flourishing social life, but many economic and philosophical approaches argue that rational people should never extend it, in particular to strangers they will never encounter again. Emerging data on the trust game, a laboratory economic exchange, suggests that people trust strangers excessively (i.e., far more than their tolerance for risk and cynical views of their peers should allow). What produces this puzzling "excess" of trust? We argue that people trust due to a norm mandating that they show respect for the other person's character, presuming the other person has sufficient integrity and goodwill even if they do not believe it privately. Six studies provided converging evidence that decisions to trust follow the logic of norms. Trusting others is what people think they should do, and the emotions associated with fulfilling a social duty or responsibility (e.g., guilt, anxiety) account for at least a significant proportion of the excessive trust observed. Regarding the specific norm in play, trust rates collapse when respect for the other person's character is eliminated as an issue.

Based on the existing literature on worldview beliefs, cynical hostility, and Machiavellian cynicism, we suggest that holding cynical beliefs about human nature can be detrimental for individuals' income. Cynical individuals are more likely to avoid cooperation and trust or to overinvest in monitoring, control, and other means of protection from potential exploitation. As a result, they are more likely to forgo valuable opportunities for cooperation and consequently less likely to reap the benefits of joint efforts and mutual help compared with their less cynical counterparts. Studies 1 and 2, using nationally representative longitudinal surveys of the American population, show that individuals who endorsed cynical beliefs about human nature at baseline earned comparatively lower incomes 9 (Study 1) and 2 (Study 2) years later. In Study 3, applying a multilevel model of change to a nationally representative panel study of the German population, we show that cynical beliefs at baseline undermined an income increase in the course of the following 9 years. In Study 4, the negative effect of cynical beliefs on income proved to be independent of individual differences in the Big Five personality dimensions. Study 5 provided the first tentative evidence of the hypothesized mechanism underlying this effect. Using survey data from 41 countries, it revealed that the negative effect of cynical beliefs on income is alleviated in sociocultural contexts with low levels of prosocial behavior, high homicide rates and high overall societal cynicism levels. Holding cynical beliefs about others has negative economic outcomes unless such beliefs hold true.

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Mate selection requires a prioritization and joint evaluation of different traits present or absent in potential mates. Herein, we focus on two such traits - physical attractiveness and prosociality - and examine how they jointly shape impressions of overall desirability. We report on two related experiments which make use of an innovative methodology combining large samples of raters and target persons (i.e., stimuli) and information on targets' behaviour in economic games representing altruistic behaviour (Experiment 1) and trustworthiness (Experiment 2), two important facets of prosociality. In accordance with predictions derived from a cognitive perspective on mate choice and sexual strategies theory, the results show that the impact of being prosocial on an individual's overall desirability was increased further by them also being physically attractive, but only in long-term mating contexts. Furthermore, we show that men's mate preferences for certain prosocial traits (i.e., trustworthiness) were more context-dependent than women's due to differential evolutionary pressures for ancestral men and women.

In line with the sexual selection for altruism hypothesis, research has shown that men and women typically prefer hypothetical partners who are described as prosocial to otherwise similar individuals. In this study, we consider this hypothesis in the real world by examining whether prosocial behavior conveys actual benefits in terms of real-life mating success. Using a nationally representative annual panel data set, we examine the impact of single individuals’ prosocial behavior on their probabilities of finding a steady partner in the course of the following year. Our results show that single individuals who frequently engaged in prosocial behavior had substantially higher chances of being in a stable relationship the following year. The effect persisted even after accounting for individual differences in the Big Five personality traits and the degree of social involvement.