Evolutionary Psychology www.epjournal.net – 2014. 12(3): 621-631 ¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯ Original Article The Self-Regulation Effect of Fertility Status on Inbreeding Aversion: When Fertile, Disgust Increases more in Response to Descriptions of One’s Own than of Others’ Inbreeding Jan Antfolk, Department of Psychology and Logopedics, Åbo Akademi University, Turku, Finland. Email: jantfolk@abo.fi (Corresponding author). Debra Lieberman, Department of Psychology, University of Miami, Coral Gables, FL, USA. Anna Albrecht, Department of Psychology and Logopedics, Åbo Akademi University, Turku, Finland. Pekka Santtila, Department of Psychology and Logopedics, Åbo Akademi University, Turku, Finland. Abstract: The ovulatory shift modulates emotions related to female sexuality. Because fertility status only affects the individual’s own opportunity cost, the adaptive value of this shift is expected to stem from self-regulation. To test this assumption we asked women to contemplate various inbreeding descriptions: 1) they themselves having sex with male relatives; 2) their sister having sex with their common male relatives; and 3) an unrelated woman having sex with her male relatives (in 1, but not 2 and 3, negative fitness consequences are affected by the participant’s fertility). We dichotomized the dependent variable disgust (ceiling vs. non-ceiling) and analyzed the interaction between fertility status and description type. The ovulatory shift was stronger in descriptions where they themselves were described as engaging in inbreeding. A smaller increase was also found in reactions to others engaging in inbreeding. We explain the latter effect as due to self- reflection. Keywords: fertility, inbreeding, mate choice, incest, disgust, ovulatory-shift ¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯ Introduction During the menstrual cycle, with an average length of 29 days (Fehring, Schneider, and Raviele, 2006), women’s most fertile phase—the time period during which likelihood of conception is highest—takes place mid-cycle around the day of ovulation (Mihm, Gangooly, and Muttukrishna, 2011; Wilcox, Weinberg, and Baird, 1995). Given the narrow window of fertility, researchers have hypothesized that evolution crafted female sexual psychology to take advantage of sexual opportunities when fertile. For example, it has been suggested that women are more willing to engage in sexual activity during peak fertility.