Harm to others outweighs harm to self in moral decision making

Abstract

Concern for the suffering of others is central to moral decision making. How humans evaluate others' suffering, relative to their own suffering, is unknown. We investigated this question by inviting subjects to trade off profits for themselves against pain experienced either by themselves or an anonymous other person. Subjects made choices between different amounts of money and different numbers of painful electric shocks. We independently varied the recipient of the shocks (self vs. other) and whether the choice involved paying to decrease pain or profiting by increasing pain. We built computational models to quantify the relative values subjects ascribed to pain for themselves and others in this setting. In two studies we show that most people valued others' pain more than their own pain. This was evident in a willingness to pay more to reduce others' pain than their own and a requirement for more compensation to increase others' pain relative to their own. This "hyperaltruistic" valuation of others' pain was linked to slower responding when making decisions that affected others, consistent with an engagement of deliberative processes in moral decision making. Subclinical psychopathic traits correlated negatively with aversion to pain for both self and others, in line with reports of aversive processing deficits in psychopathy. Our results provide evidence for a circumstance in which people care more for others than themselves. Determining the precise boundaries of this surprisingly prosocial disposition has implications for understanding human moral decision making and its disturbance in antisocial behavior.

Keywords: altruism; decision making; morality; social preferences; valuation.

Fig. 1.

Experimental design. (A) Subjects remained in separate testing rooms at all times and were randomly assigned to roles of decider and receiver (Fig. S1). (B–E) In each trial the decider chose between less money and fewer shocks, vs. more money and more shocks. The money was always for the decider, but in half the trials the shocks were for the decider (B and D) and in the other half the shocks were for the receiver (C and E). In all trials, if the decider failed to press a key within 6 s the highlighted default (top) option was registered; if the decider pressed the key, the alternative (bottom) option was highlighted and registered instead. In half the trials, the alternative option contained more money and shocks than the default (B and C), and in the other half the alternative option contained less money and fewer shocks than the default (D and E).

Fig. 2.

Harm aversion for self and other in study 1 (A–C) and study 2 (D–F). (A and D) Estimates of harm aversion for self and other. Error bars represent SEM difference between κ_self and κ_other. (B and E) Distribution of hyperaltruism (κ_other − κ_self) across subjects. (C and F) Correlations between harm aversion for self and other. *P < 0.05, **P < 0.01.

Fig. 3.

Slowing when deciding for others predicts hyperaltruistic valuation of pain. (A) Deciders were slower to decide when choices affected others, relative to when choices affected themselves. Error bars represent the SEM. *P < 0.05. (B) The degree of slowing when deciding the fate of others (relative to oneself) predicted the degree of hyperaltruism, (r = 0.419, P = 0.006).