Evidence of partner choice heuristics in a one-shot bargaining game

Economists and psychologists have developed a variety of models to explain human behavior in the ultimatum game, but none can adequately account for all of the available data. Across two studies using a face perception paradigm, we provide evidence that people use evolved, specialized heuristics for long-term cooperative partner choice to calibrate their generosity toward ultimatum game partners. Men and women played one-shot ultimatum games for real incentives with partners represented by face photographs. Men were more generous toward partners who were stronger, and who appeared more attractive, more prosocial, more productive, healthier and higher in social status; the effect of strength was mediated by productivity, but not dangerousness, suggesting that men implemented heuristics designed for partner choice rather than the asymmetric war of attrition. Moreover, men reduced their earnings by cooperating selectively with valuable long-term partners. Women also gave better treatment to valuable-appearing partners, but appeared to prioritize partner choice less than men did, relative to game earnings and intrasexual competition. The results suggest that people treat the ultimatum game as though it were an opportunity to establish a cooperative relationship with a new partner, and implications are discussed for an evolved psychology of cooperative partner choice.