No evidence that inbreeding avoidance is up-regulated during the ovulatory phase of the menstrual cycle

Mate preferences and mating-related behaviors are hypothesized to change over the menstrual cycle in ways that function to increase reproductive fitness. Results of recent large-scale studies suggest that many of these hormone-linked behavioral changes are less robust than was previously thought. One specific hypothesis that has not yet been subject to a large-scale test is the proposal that women’s preference for associating with male kin is down-regulated during the ovulatory (high-fertility) phase of the menstrual cycle. Consequently, we used a longitudinal design to investigate the relationship between changes in women’s steroid hormone levels and their perceptions of faces experimentally manipulated to possess kinship cues (Study 1). Analyses suggested that women viewed men’s faces displaying kinship cues more positively (i.e., more attractive and trustworthy) when estradiol-to-progesterone ratio was high. Since estradiol-to-progesterone ratio is positively associated with conception risk during the menstrual cycle, these results directly contradict the hypothesis that women’s preference for associating with male kin is down-regulated during the ovulatory (high-fertility) phase of the menstrual cycle. Study 2 employed a daily diary approach and found no evidence that women reported spending less time in the company of male kin or thought about male kin less often during the fertile phase of the menstrual cycle. Thus, neither study found evidence that inbreeding avoidance is up-regulated during the ovulatory phase of the menstrual cycle.