Close relationship partners of impartial altruists do not report diminished relationship quality and are similarly altruistic

Impartial altruism is often considered a moral ideal but is rare in practice. Instead, generosity typically decreases as social distance increases, a phenomenon termed social discounting. Most people prefer this partiality in their close relationships and view impartial altruists as poorer relationship partners. This suggests real-world impartial altruism may be rare because it reduces—or is perceived to reduce—the quality of close relationships. To investigate this, we compared patterns of generosity and social relationship quality in a rare sample of individuals who had engaged in extraordinary real-world impartial altruism (altruistic kidney donors; n = 59) and their closest friend or family member (n = 59) to controls (n = 71) and their closest others (n = 71). We designed a direct test of third-party social discounting, which experimentally confirmed real-world altruists’ impartiality, finding that they are more likely than controls to split resources evenly between close and distant others rather than favoring close others. However, we found no statistically significant association between impartial altruism and social relationship quality. Instead, we found that altruists’ close others also show more impartiality than controls. This suggests value homophily (shared moral values) among altruists, which may represent a protective factor for close relationships in the context of impartial altruism. Altruistic kidney donors and their closest relationship partners reported similar higher levels of impartial altruism as compared to control participants and their closest relationship partners. Partners of donors reported similar levels of partner affection as did partners of controls.