Nationality dominates gender in decision-making in the Dictator and Prisoner's Dilemma Games.

Across a variety of contexts, adults tend to cooperate more with ingroup members than outgroup members. However, humans belong to multiple social groups simultaneously and we know little about how this cross-categorization affects cooperative decision-making. Nationality and gender are two social categories that are ripe for exploration in this regard: They regularly intersect in the real world and we know that each affects cooperation in isolation. Here we explore two hypotheses concerning the effects of cross-categorization on cooperative decision-making. First, the additivity hypothesis (H1), which proposes that the effects of social categories are additive, suggesting that people will be most likely to cooperate with partners who are nationality and gender ingroup members. Second, the category dominance hypothesis (H2), which proposes that one category will outcompete the other in driving decision-making, suggesting that either nationality or gender information will be privileged in cooperative contexts. Secondarily, we test whether identification with-and implicit bias toward-nationality and gender categories predict decision-making. Indian and US Americans (N = 479), made decisions in two cooperative contexts-the Dictator and Prisoner's Dilemma Games-when paired with partners of all four social categories: Indian women and men, and US American women and men. Nationality exerted a stronger influence than gender: people shared and cooperated more with own-nationality partners and believed that own-nationality partners would be more cooperative. Both identification with-and implicit preferences for-own-nationality, led to more sharing in the Dictator Game. Our findings are most consistent with H2, suggesting that when presented simultaneously, nationality, but not gender, exerts an important influence on cooperative decision-making. Our study highlights the importance of testing cooperation in more realistic intergroup contexts, ones in which multiple social categories are in play.