THEORETICAL ARTICLE Are Women Sexually Fluid? The Nature of Female Same-Sex Attraction and Its Evolutionary Origins Menelaos Apostolou 1 # Springer International Publishing AG, part of Springer Nature 2017 Abstract The notion that female sexuality is fluid, meaning that women can experience attractions for either men or wom- en depending on the circumstances, has been widely accepted by the academic community. Accordingly, scholars have attempted to develop evolutionary models that could explain why selection forces have favored sexual fluidity in women. The present paper reviews longitudinal studies on sexual at- traction which indicate that the great majority of women do not have a fluid sexuality, but have instead stable attractions over time. Moreover, the current paper reviews studies on arousal, in order to demonstrate that they indicate a weak correlation between sexual arousal and sexual attraction in women, and not that women are attracted to both sexes. The evolutionary implications of the findings on female sexuality are further explored. Keywords Sexual fluidity . Same-sex attraction . Homosexuality . Sexual arousal Introduction Same-sex attraction is evolutionary puzzling: People who are attracted to members of the same sex are expected to suffer costs in their reproductive success, since they divert their lim- ited resources toward outlets that cannot lead to child-bearing. On this basis, we would expect that strong negative selection pressures would remove from the gene pool any dispositions for same-sex attraction. Yet, this did not happen, with a con- siderable proportion of the population experiencing varying degrees of same-sex attraction (Dickson et al. 2013; LeVay 2010; Ott et al. 2011). In turn, the relative high prevalence of these dispositions in the population gave rise to much theoriz- ing on their evolutionary origins (Bailey et al. 2016). This theorizing focused predominantly on male same-sex attraction (LeVay 2010); yet, same-sex attraction is more com- mon in women than in men (Calzo et al. 2017; Savin-Williams et al. 2012). Discovering the reasons for the high prevalence of same-sex attraction in women constitutes a major challenge for evolutionary scholars. For any such attempts to be fruitful, we first need to make clear what these attempts have to ex- plain. Romantic and sexual attractions to opposite or same-sex individuals were seen as stable over time (LeVay 2010), a position which has been challenged (Baumeister 2000; Diamond 2008b). The purpose of the current paper is to re- view several lines of evidence in order to examine the nature of female same-sex attraction. Sexual Fluidity Sexual orientation is usually seen as an enduring pattern or disposition to experience sexual or romantic attractions to- ward people of the same sex, the other sex, or both sexes (Institute of Medicine 2011). This definition reflects the, until recently, prevailing position that sexual orientation is an early determined, stable trait that is highly resistant to change (Bell et al. 1981; Ellis and Ames 1987; Haldeman 1991; Money 1987). This position is supported by evidence from different lines of research, including conversion therapy outcome stud- ies which, document very low success rates in treatment at- tempts to alter sexual orientation (Haldeman 1991, 1994), and studies suggesting a developmental continuity between * Menelaos Apostolou m.apostolou@gmail.com 1 Department of Social Sciences, University of Nicosia, 46 Makedonitissas Ave, 1700 Nicosia, Cyprus Evolutionary Psychological Science https://doi.org/10.1007/s40806-017-0128-2