MHC-correlated odour preferences in humans and the use of oral contraceptives

Previous studies in animals and humans show that genes in the major histocompatibility complex (MHC) influence individual odours and that females often prefer odour of MHC-dissimilar males, perhaps to increase offspring heterozygosity or reduce inbreeding. Women using oral hormonal contraceptives have been reported to have the opposite preference, raising the possibility that oral contraceptives alter female preference towards MHC similarity, with possible fertility costs. Here we test directly whether contraceptive pill use alters odour preferences using a longitudinal design in which women were tested before and after initiating pill use; a control group of non-users were tested with a comparable interval between test sessions. In contrast to some previous studies, there was no significant difference in ratings between odours of MHC-dissimilar and MHC-similar men among women during the follicular cycle phase. However, single women preferred odours of MHC-similar men, while women in relationships preferred odours of MHC-dissimilar men, a result consistent with studies in other species, suggesting that paired females may seek to improve offspring quality through extra-pair partnerships. Across tests, we found a significant preference shift towards MHC similarity associated with pill use, which was not evident in the control group. If odour plays a role in human mate choice, our results suggest that contraceptive pill use could disrupt disassortative mate preferences.     

Non‐verbal mate retention behaviour in women and its relation to couple's relationship adjustment and satisfaction

The function of mate retention strategies is to preserve the bond between romantic partners and to prevent desertion, which is also why such behaviours are often elicited by the presence of a potential rival. Most existing studies on mate retention are based on self‐reports, which are prone to various biases. In this study, we observed non‐verbal behaviour of 47 long‐term romantic heterosexual couples during their interview with a female experimenter, whom the women in the couples may have perceived as a potential rival. We measured non‐verbal displays of mate retention tactics (direct guarding, intimacy inducement, appearance enhancement, and love and care display), as well as relationship maintenance strategies of openness and positivity. We expected that relationship quality as reported by both partners in the couple would be positively associated with ‘benefit‐provisioning’ mate retention behaviours and negatively associated with a ‘cost‐inflicting’ mate retention tactic (direct guarding). Relationship quality was assessed by Spanier's Dyadic Adjustment Scale using both the total score of dyadic adjustment and a Dyadic Satisfaction subscale. We found a significant association between both partners' dyadic adjustment and satisfaction and woman's appearance enhancement behaviours (such as self‐touch, hair flip and primp) in the presence of her partner and a potential rival. We also found a negative association between partner's dyadic adjustment and woman's direct guarding of partner using short looks, and a positive association between woman's intimacy‐inducing behaviour using long gaze and her own dyadic satisfaction and her partner's dyadic adjustment. Our results highlight the specific role of female attractiveness in later stages of romantic relationships within the context of mate retention and draw attention to the significance of the use of observational techniques in addition to self‐reports.