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Abstract

The Ultimatum Game (UG) measures cooperative tendencies in humans. A proposer offers to split a given sum of money between self and a responder, who may accept or reject the offer. If accepted, each receives the proposed split; if rejected, nobody receives anything. We studied the effect of the putative responder’s degree of facial symmetry (fluctuating asymmetry, FA) on the offer he/she received in opposite-sexed UGs. Symmetry is an important measure of biological quality so subjects were expected to receive higher offers when symmetrical than asymmetrical. In a sample of Jamaicans, individuals played two UGs with opposite-sexed responders, a symmetrical photo of a Lebanese and an asymmetrical one. Individuals do indeed give more to symmetrical responders (p = 0.032). When subjects are asked their motivation, a striking dichotomy emerges: those who cite ‘attractiveness’ as a motive, give strongly to symmetrical responders while those citing ‘need’ invariably give more to asymmetrical ones (p < 0.0001). Females also show a nearly significant tendency to cite need as a motive more often than do males.