Testosterone and partnering are linked via relationship status for women and 'relationship orientation' for men.

Cross-cultural evidence links pair bonding and testosterone (T). We investigated what factors account for this link, how casual relationships are implicated, and whether gender/sex moderates these patterns in a North American sample. We gathered saliva samples for radioimmunoassay of T and self-report data on background, health, and social/relational variables from 115 women and 120 men to test our predictions, most of which were supported. Our results show that singles have higher T than long-term (LT) partnered individuals, and that casual relationships without serious romantic commitment are more like singlehood for men and LT relationships for women-in terms of T. We were also able to demonstrate what factors mediate the association between partnering and T: in women, frequency of partnered sexual activity mediated the effect in men, interest in more/new partners mediated the effect. This supported our prediction of relationship status interpretations in women, but relationship orientation in men. Results replicated past findings that neither sexual desire nor extrapair sexuality underlie the T-partnering link. We were able to rule out a large number of viable alternative explanations ranging from the lifestyle (e.g., sleep) to the social (e.g., social support). Our data thus demonstrate pattern and mediators for the development of T-pair bonding associations, and emphasize the importance of neither under- nor overstating the importance of gender/sex in research about the evolution of intimacy.