This study investigated the hypothesis that universal psychological adaptations produce personality variation when individuals differentially face adaptive problems that shifted the cost-benefit tradeoffs of alternative personality strategies in ancestral environments. The current research tested the hypothesis that psychological adaptations calibrate individual differences in neuroticism as a functional response to social exclusion. If psychological adaptations produce neuroticism in response to social exclusion, and heritable components of individuals' social partner value influence their likelihood of being excluded, then individual differences in social partner value should yield heritable differences in neuroticism. Three conceptually distinct sub-studies tested hypotheses derived from this conceptual framework. Sub-study 1 tested the relationship between individuals' mate value, social exclusion, and neuroticism. Individuals' mate value exhibited both a direct effect on neuroticism and an indirect effect through the experience of social exclusion. Sub-study 2 investigated sexual jealousy as a specialized class of neuroticism in response to infidelity. As predicted, individuals' mate value predicted the likelihood of their partners' infidelity and their own mate guarding behavior. Sub-study 3 manipulated the threat of infidelity to test for functional shifts in neuroticism in response to relationship exclusion. Participants read vignettes describing their mates' certain fidelity, uncertain fidelity, and certain infidelity, and wrote what they would think, feel, say, and do in response to each scenario. An independent sample assessed participants' personalities based on these cognitive, affective, and behavioral responses. As predicted, participants' neuroticism tracked relationship exclusion; participants' neuroticism levels increased with infidelity threat. These findings are consistent with the hypothesis that a universal psychological mechanism adaptively calibrates neuroticism levels in response to relationship exclusion; the certain absence or presence of the adaptive problem of relationship exclusion should deactivate or activate anti-exclusion mechanisms in all individuals. Above this situational effect, under conditions of uncertain infidelity -- in which the threat of infidelity would have ancestrally varied with men's (but not women's) mate value -- men's mate value predicted their neuroticism. Together, these findings support the hypothesis that humans possess psychological adaptations that functionally calibrate neuroticism levels. More broadly, they highlight the heuristic value of an evolutionary adaptationist framework for the study of personality and individual differences. / text