Impartial altruism is a widely-held moral ideal which argues that social and physical distance should not influence decisions to help others. Its value is enshrined in foundational religious and philosophical texts, from the Bible’s parable of the Good Samaritan to Buddhism’s Metta Sutta, which positions universal love among the highest aspirations, and even in contemporary teachings from the Effective Altruism movement.

However, impartial altruism is rare in practice. Most people would rather show preference to close others over distant others. This is probably because many social relationships, such as between spouses or close friends, entail a certain level of favoritism and preference over others. Indeed, past research has found that when impartiality is pitted against relational obligations, most people view it as more appropriate to prioritize social closeness. This suggests impartial altruism may be admired in theory but rare in practice in part because it carries (or is perceived to carry) costs to close relationships. But this idea has never been tested.

To test whether impartial altruism necessarily comes at a cost of lower-quality relationships, we recruited a group of real-world impartial altruists (people who have anonymously donated one of their kidneys to a stranger in need) and these altruists' closest other (e.g., a spouse, best friend, family member, etc.) to take an online survey. We asked the altruists and their closest others to complete a survey about their relationship satisfaction. We also included a behavioral task in the survey to measure impartial decision-making (where participants made decisions allocating money between close vs. distant others). We then had pairs of control participants (who had not donated a kidney but opted into the study) and their closest other also take the same online survey.

We found that altruists were the most impartial, giving more money to distant others. Interestingly, we found that altruists’ close others were the next most impartial, with controls and controls’ close others being the least impartial. These findings suggest a form of value homophily–a love of similar values–such that close relationship partners possess similar levels of impartial altruism. This value homophily may explain the next set of findings in our research: that the close others of impartial altruists reported similarly high levels of relationship satisfaction compared to those of controls and their close others.

In conclusion, our research found that in the real world, impartial altruism does not come at the cost of close relationships, and that this perhaps is because of value homophily.