This paper reports independent studies supporting the proposal that human standards of attractiveness reflect the output of psychological adaptations to detect fitness-relevant traits. We tested novel a priori hypotheses based on an adaptive problem uniquely faced by ancestral hominin females: a forward-shifted center of mass during pregnancy. The hominin female spine possesses evolved morphology to deal with this adaptive challenge: wedging in the third-to-last lumbar vertebra. Among ancestral women, vertebral wedging would have minimized the net fitness threats posed by hypolordosis and hyperlordosis, thereby creating selective pressures on men to prefer such women as mates. On this basis, we hypothesized that men possess evolved mate preferences for women with this theoretically optimal angle of lumbar curvature. In Study 1, as hypothesized, men's attraction toward women increased as women's lumbar curvature approached this angle. However, vertebral wedging and buttock mass can both influence lumbar curvature. Study 2 thus employed a forced-choice paradigm in which men selected the most attractive woman among models exhibiting the same lumbar curvature, but for different morphological reasons. Men again tended to prefer women exhibiting cues to a degree of vertebral wedging closer to optimum. This included preferring women whose lumbar curvature specifically reflected vertebral wedging rather than buttock mass. These findings reveal novel, theoretically anchored, and previously undiscovered standards of attractiveness.

Although research has made progress in elucidating the benefits exchanged within same- and opposite-sex friendships formed between heterosexual men and women, it is less clear why straight women and gay men form close relationships with one another. The current experiments begin to address this question by exploring a potential benefit hypothesized to be uniquely available to straight women and gay men in the context of these friendships: trustworthy mating advice. Experiment 1 revealed that straight women perceive mating-relevant advice from a gay man to be more trustworthy than similar advice offered by a straight man or woman. Experiment 2 demonstrated that gay men perceive mating advice offered by a straight woman to be more trustworthy than advice offered by a lesbian woman or another gay man. Overall, the results provide initial experimental evidence that relationships between gay men and straight women may be characterized by a mutual exchange of mating-relevant benefits in the absence of sexual interest or competition.

Previous findings indicate that heterosexual women experience a greater sense of comfort and trust in their friendships with gay men than in their friendships with heterosexual individuals. In the present studies, we tested a hypothesis that not only explains why women exhibit increased trust in gay men but also yields novel predictions about when (i.e., in what contexts) this phenomenon is likely to occur. Specifically, we propose that gay men's lack of motives to mate with women or to compete with them for mates enhances women's trust in gay men and openness to befriend them. Study 1 demonstrated that women placed greater trust in a gay man's mating-but not non-mating (e.g., career) advice-than in the same advice given by heterosexual individuals. Study 2 showed that women perceived a gay man to be more sincere in scenarios relevant to sexual and competitive mating deception. In Study 3, exposing women to a visualization of increased mating competition enhanced their trust in gay men; when mating competition was salient, women's trust in mating information from a gay man was amplified. Study 4 showed that women who perceived higher levels of mating competition were more open to befriending gay men. Together, these converging findings support our central hypothesis, which not only provides a distal explanation for the trust that straight women place in gay men, but also provides novel insights into previously unidentified contexts that facilitate the formation and strengthening of this unique bond.

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