Partner selection biases induced by resource inequality

We conducted two experiments using one-shot prisoner's dilemma games to examine how inequality shapes partner selection and cooperation. Results show that participants tended to choose partners with similar economic status, reinforcing segregation. When partners were self-selected, cooperation rates did not differ between groups. However, when partners were randomly assigned, richer participants cooperated more than poorer ones. These findings suggest that inequality promotes similarity-based partner selection. Even when rich and poor players face identical payoff structures and contribute under equal cost–benefit conditions, the mere presence of unequal endowment levels can induce social division. • Inequality does bias the interaction-partner selection even with equal payoffs. • Inequality does not affect cooperation rate in a one-shot prisoner's dilemma game. • Cooperation rate is higher for the rich group when partners are matched randomly.