In 3 studies, the authors searched for nonlinearities as possible clues to context-sensitive mechanisms involved in mating decisions. Participants judged targets' sexual desirability, marital desirability, or social status on the basis of information about income or number of past sexual partners. Because one cannot know in advance where nonlinearities occur or measure all values of independent variables, a "zoom and focus" method was used. The authors began by sampling a wide range of values, followed by successively more focused examination of potentially interesting regions. Across studies, income and desirability were linked exponentially, particularly for male targets and marriage partners. Sexual partners and desirability were sometimes linked nonmonotonically, with more partners first increasing, then decreasing, desirability. The authors discuss how nonmonotonic functions may suggest competing underlying processes.

This study assessed whether previously reported sex differences in jealousy could be accounted for by other related emotions. Participants were presented with hypothetical scenarios involving both a sexual and an emotional infidelity, then were asked how jealous, angry, hurt, and disgusted they would be (using continuous scales). The results replicate the sex difference in response to sexual and emotional infidelity, demonstrate that it is robust when continuous measures are used, and confirm that it is unique to jealousy. Sex differences did not emerge for anger, hurt, or disgust. Instead, sexual infidelity elicited greater anger and disgust, and less hurt, than emotional infidelity, for both women and men. The results also suggest that it is the jealous response to an emotional infidelity that best discriminates women from men, and that both women and those participants in a serious, committed relationship reported significantly greater intensity in their emotional reactions, as compared to men and those not in a committed relationship.

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Although heterosexual women and men consistently demonstrate sex differences in jealousy, these differences disappear among lesbians and gay men as well as among heterosexual women and men contemplating same-sex infidelities (infidelities in which the partner and rival are the same sex). Synthesizing these past findings, the present paper offers a reproductive threat-based model of evolved sex differences in jealousy that predicts that the sexes will differ only when the jealous perceivers' reproductive outcomes are differentially at risk. This model is supported by data from a web-based study in which lesbians, gay men, bisexual women and men, and heterosexual women and men responded to a hypothetical infidelity scenario with the sex of the rival randomly determined. After reading the scenario, participants indicated which type of infidelity (sexual versus emotional) would cause greater distress. Consistent with predictions, heterosexual women and men showed a sex difference when contemplating opposite-sex infidelities but not when contemplating same-sex infidelities, whereas lesbians and gay men showed no sex difference regardless of whether the infidelity was opposite-sex or same-sex.

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