DescriptionAn emerging explanation of poverty focuses on the attentional demands induced by a scarcity mindset and the effect of such demands on subsequent decision making. We build on this work by investigating the impact of resource scarcity on prosocial behavior. Specifically, we experimentally induce scarcity and then have agents play an indefinitely repeated prisoner's dilemma game in which individual and collective gains stand in conflict. Our findings suggest that relative to control participants, those experiencing scarcity are more likely to cooperate with each other and are more sensitive to reciprocity motivations. These results stand in direct conflict with the low levels of cooperation predicted by the existing bandwidth account of scarcity. We therefore propose an alternative account in which scarcity induces reciprocal altruism by altering an agent's expectations and beliefs about the behavior of others with whom they are interacting.