The spandrels of Santa Barbara? A new perspective on the peri-ovulation paradigm

Numerous recent studies document peri-ovulatory increases in women's physical attractiveness and in their preferences for certain male traits, which appear to be linked to cyclical fluctuation in levels of ovarian hormones. Changes in physical traits are subtle, leading to the widespread conclusion that cues of ovulation are adaptively concealed. It has been argued that concealment enables women to pursue a mixed-mating strategy characterized by pair-bonding with opportunistic extrapair copulation with high-quality mates when conception is possible. Men's preferences for peri-ovulatory cues and women's cyclical preference shifts are thus also argued to reflect distinct psychological adaptations. Here, we re-interpret the evidence for each of these putative adaptations and argue that cyclic changes need not result from incomplete concealment of ovulatory status. We also emphasize that ovarian hormone levels underpin between-individual differences in both women's attractiveness and their mate preferences, which influence the sexes' mate-choice decisions. We contrast the salience and efficiency of these within- and between-individual effects, and suggest that, although both effects have the potential to influence mating behavior, the between-individual effects are stronger and more robust. This introduces the possibility that both men's increased attraction towards peri-ovulatory women and women's cyclical shifts in preference for certain male traits may not constitute adaptations per se, but are, instead, inevitable by-products, or perceptual spandrels, of putative adaptations related to between-individual differences in reproductive potential. Our framework parsimoniously explains several observable phenomena and potentially could transform the way evolutionary researchers interpret changes in behavior associated with the menstrual cycle.