Individuals are consistently observed to be risk-averse over gains and risk-seeking over losses. This study examined whether increased social distance would change these behavioral patterns. To test our hypothesis, social distance was manipulated by asking the participants to make decisions either for themselves or for another person (Experiment 1), either for a known person or for an unknown person (Experiment 2), and either for a close friend or for a distant friend (Experiment 3). The results of Experiments 1 and 3 showed that increased social distance made people more risk-neutral, and such an effect was stronger in the gain domain than in the loss domain. However, the effect of social distance was not observed in Experiment 2. These findings suggest that risk preferences are influenced by the social distance between decision makers and beneficiaries.

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We study the emergence of conditional cooperation in the presence of both intra-group and inter-group selection. Individuals play public goods games within their groups using conditional strategies, which are represented as piecewise linear response functions. Accordingly, groups engage in conflicts with a certain probability. In contrast to previous studies, we consider continuous contribution levels and a rich set of conditional strategies, allowing for a wide range of possible interactions between strategies. We find that the existence of conditional strategies enables the stabilization of cooperation even under strong intra-group selection. The strategy that eventually dominates in the population has two key properties: (i) It is unexploitable with strong intra-group selection; (ii) It can achieve full contribution to outperform other strategies in the inter-group selection. The success of this strategy is robust to initial conditions as well as changes to important parameters. We also investigate the influence of different factors on cooperation levels, including group conflicts, group size, and migration rate. Their effect on cooperation can be attributed to and explained by their influence on the relative strength of intra-group and inter-group selection.

In order to study whether common fate induced by shared risk can promote cooperation, I introduce two types of risks into a public goods game: risk that is common among all group members (the COM treatment), and risk that is independent across individuals (the IND treatment). In both treatments, zero contributions is the only equilibrium. In contrast to the equilibrium analysis, contributions to the public goods in the experiment approach zero under the independent risk but remain at high levels when the common risk is present. Analysis of the data reveals that different reactions to beliefs are fundamental to this treatment effect. While beliefs and contributions in the first periods, as well as the belief formation processes, are similar across treatments, subjects in the IND treatment are significantly less cooperative than those in the COM treatment with the same beliefs. A large variation in group contributions is observed in the COM treatment. Further analysis shows that initial beliefs can explain most of the variation in the long-run contribution level, implying the importance of beliefs in shaping the players' experience and establishing group norms.

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