Abstract. Intrasexual competition implies viewing the confrontation with same-sex individuals, especially in the context of contact with the opposite-sex, in competitive terms. After constructing the items for the preliminary scale and after conducting a pilot study, in two studies with a total of 706 participants from The Netherlands and Canada, a 12-item scale for individual differences in intrasexual competition was developed that was sex neutral, and that had a high degree of crossnational equivalence. In The Netherlands, sociosexuality, sex drive and social comparison orientation were independently related to intrasexual competition. In Canada, intrasexual competition was strongly, and independently of the Big Five, related to social comparison orientation, but only among women. There was no effect of birth order, but sibling rivalry did correlate with intrasexual competition. Among men, intrasexual competition was more strongly, and differently, related to the Big Five than among women. Among women, intrasexual competition was predicted by a lack of agreeableness, and among men by a high level of neuroticism and extraversion.
Keywords: intrasexual competition, individual differences, Big Five
INDIVIDUAL DIFFERENCES IN INTRASEXUAL COMPETITIONIntrasexual competition refers to rivalry with same-sex others over access to mates. Darwin (1871) already recognized the importance of intrasexual competition for sexual selection, and suggested that it evolved as an important behavioral adaptation for attracting mates and for gathering resources necessary for reproduction and offspring care. In most species males invest little in their offspring and engage in often fierce competition with other males over the access to females, whereas females show few signs of intrasexual competition. However, because in humans both