Abstract
Recent advances in moral decision-making research show people are hyperaltruistic by being more willing to sacrifice monetary gains to spare others from suffering than to spare themselves. Yet other studies indicate an opposite egoistic bias: subjects are less willing to harm themselves for others' benefits than for their own. These results underscore the complexities of moral decisions and demand a mechanistic explanation for hyperaltruistic preferences. We investigated hyperaltruism using trade-off choices combining monetary gains and painful electric shocks and choices combining monetary losses and shocks. Study 1 revealed that switching the decision context from gains to losses effectively eliminated the hyperaltruistic preference, accompanied by the altered relationship between subjects' instrumental harm (IH) trait attitudes and relative pain sensitivities. In the pre-registered study 2, we found that oxytocin, a neuropeptide linked to parochial altruism, restored the context-dependent hyperaltruistic preference. Furthermore, oxytocin increased the degree to which subjects framed the task as harming others, which mediated the correlation between IH and relative pain sensitivities. Thus, the loss decision context and oxytocin diminished and restored the mediation effect of subjective harm framing, respectively. Our results help elucidate the psychological processes underpinning the contextual specificity of hyperaltruism and carry implications in promoting prosocial interactions.