When making ethical decisions, university students appear to prioritize fairness and the fate of the worst-off over either reducing total harm or obeying unconditional moral precepts, according to a study. Woo-Young Ahn and colleagues designed an experimental dilemma that pits a utilitarian approach—which seeks to minimize total harm—against an approach promoted by philosopher John Rawls, which emphasizes improving the situation of the worst-off person. Fifty-two paid volunteers from a university in South Korea were asked to allocate harm—here, the discomfort of plunging a hand into ice water—while inside fMRI scanners. In each trial, participants pressed buttons to choose between a single person experiencing a hand in ice water or a group of 3 or 4 people each experiencing the same harm for shorter times. Crucially, however, the summed time of the group was larger than the total time for the single person, representing more harm overall. In some trials, the screen shown to participants included a default option already selected. In these cases, participants could not press any buttons at all, avoiding personally causing harm. The authors expected this to be a popular approach for those who wanted to avoid causing harm directly. Most people chose to allocate the harm to the group, causing more harm overall but less unfairness. Participants chose to give 68 seconds of additional icy-cold discomfort to the group, on average, to save the lone individual from being disproportionately targeted. There was little evidence of a bias toward the default option, suggesting that participants did not feel that personally causing harm was prohibited. According to the authors, brain imaging suggests that mentalizing—modeling the mental experiences of others—is involved in this moral decision-making, along with valuation networks.
PNAS Nexus
Decomposing the neurocomputational mechanisms of deontological moral preferences
7-Apr-2026