The term social discounting refers to the decrease of a subjective value of a reward to be shared with one or more people compared to a reward exclusive to an individual. Similarly to temporal and probabilistic discounting, this process can have an adaptive function. Based on Trivers' reciprocal altruism and Hamilton's inclusive fitness theories, the following hypotheses were formulated: (1) there should be discounting relative to the degree of a partner's loyalty, i.e. the subjective value of a resource to be shared with another person should decrease as that person's loyalty decreases; (2) the rate of social discounting relative to the partner's loyalty should be lower for relatives than for unrelated recipients; (3) the rate of social discounting should be negatively correlated with agreeableness; (4) the rate of social discounting when sharing with an unrelated person should be negatively correlated with neuroticism; (5) there should be a positive correlation between the rate of social and probabilistic discounting. In order to verify these hypotheses, we measured the rate of social discounting in 200 subjects aged 18-53 years. The results confirmed hypotheses one, two, and three.
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