Moral judgment and decision-making based on interpersonal relationships with relatives and non-relatives: A systematic review

Human beings live in a social world; therefore, a big part of our daily judgments is influenced by our interpersonal relationships. In interpersonal situations, one should choose between compromising the principle of equality and harming their relationships with others. Various studies have been conducted on moral judgments based on interpersonal relationships. Given the devastating consequences of relationship-based moral judgments, such as increase discriminatory behaviors and racism, it is crucial to examine this kind of judgments. This study reviews philosophical theories, evolutionary biology, and the psychology of relationship-based moral judgment and finds genetic and emotional relationships influencing moral judgments and factors influencing these types of judgments through empirical studies.

This study is a systematic review investigation in which studies published between 1950 and 2020 were examined. A search for articles was conducted in Comprehensive Portal of Human Sciences, SID, PubMed, ISI (Web of Science), and Google Scholar using related keywords such as Moral, Moral judgment, Moral decision making, Equality, Altruistic, Close-relationship in Persian and English. The research results were 210 theoretical and experimental articles. Accordingly, 56 studies were selected for review by studying the abstracts based on inclusion and exclusion criteria.

Despite the general acceptance of the principles of moral equality and impartiality, or the acceptance of the moral status, empirical research has shown that genetic relatedness and emotional intimacy influence our moral judgments when increasing the level of genetic relationship, emotional closeness, and familiarity utilitarian judgment decrease. Also, multiple factors are involved in moral judgments based on interpersonal relationships such as helping cost, gender, cognitive bias, and moral disengagement. People prefer to save only their close relatives when the cost of help is deadly. Gender is another factor that influences relationship-based judgments. Men help their family members more than women in threatening situations, but this difference is not seen in relationships with partners. Relationship-based moral judgments are prone to cognitive bias and moral disengagement like (or perhaps more than) other types of judgments. People try to reduce the complexity of moral situations using cognitive bias like Self-interest bias and actor-observer bias and reduce the level of self-blame resulting from ignoring the principle of fairness using moral disengagement like moral justification and dehumanization. Although the principle of equality is universally accepted, the results of empirical studies show that people considered relationships in their moral judgments, and evolutionary theories can even explain this effect.  As a result, the definition of moral concepts such as impartiality and equality should be reconsidered by applying these concepts to daily human life.

 In general, despite significant advances in identifying factors influencing relationship-based moral judgments, there are still areas that need to be studied. First, most previous studies examined moral judgments only through short answer questions that these questions were different in each of them. Thus, their results are incomparable. Second, the participants were from high socioeconomic states and western countries, so the results cannot be generalized to other socioeconomic states and cultures. Third, most previous studies used Thorolly dilemmas that focused on decision-making about life and death, far away from the people’s routine decisions. Finally, no study has yet focused on the impact of ethnic and religious similarities on moral judgments.