Sleep, partner attractiveness and fertility
Research has revealed that women, near ovulation, demonstrate measureable changes in behavior; for example, consuming less calories, paying more attention to their appearance and selectively flirting with men who possess cues for genetic quality (e.g. facial symmetry and features of masculinity), relative to low fertility periods. These changes have been interpreted, within an evolutionary framework, as evidence of strategic responding to current reproductive context, with a view to maximizing probability of conception. In a new study published in PLoS, Brooke Gentle and colleagues investigate whether perceptions of sleep change across the ovulatory cycle and how this relates to perceived ratings of partner attractiveness.
The team of researchers recruited 39 females who reported not taking hormonal contraceptives in the previous three months and asked them to record a sleep diary each day for 32 days, probing morning reflections on sleep quality and total sleep time. The researchers calculated a conception probability score using a standard 29-day length cycle and dates of menstrual onset. Participants engaged in relationships (n=19) were also asked to rate their partner on physical and sexual attractiveness.
Results found no evidence of a relationship between sleep time and conception probability. However, when partner attractiveness was taken into account, a significant relationship was observed, such that women who rated their partner as high on attractiveness also tended to report a reduction in sleep time during a phase of high conception probability relative to low conception probability. A converse relationship was observed for women who rated their partner as low on attractiveness: reporting an increase in total sleep time during a phase of high conception probability relative to low conception probability.
The research team suggest that different reproductive strategies may be at play, explaining differences in patterning of sleep time: “it is possible that in our ancestral past women with more attractive partners strategically reduced their sleep time when the probability of conception was highest, that is, when the energy that would otherwise have been conserved could have net potentially greater returns for ancestral women by being invested in mating activities, such as sexual intercourse.” When considering the group who increased total sleep time during the high-conception period, reporting low partner attractiveness, the authors note: “it is plausible that the fertility-related increase in sleep time we documented among women with less attractive partners reflects a conception-avoidance strategy if, among ancestral women, extending one’s sleeping time might have reduced the possibility of sexual interaction with one’s partner during the night.”
Clearly, these results require replication and further explanations should not be dismissed. However, this study may (re)ignite interest in linking sleep to reproductive behaviors.
Gentle, B.N., Pillsworth, E.G., Goetz, A.T. (2014). Changes in sleep time and sleep quality across the ovulatory cycle as a function of fertility and partner attractiveness. PLOS One, published online 7 April, doi: 10.1371/journal.pone.0092796