Sexual Arousal Patterns of Women: A Test of Alternative Hypotheses

Unlike men's, women's sexuality is understudied and not taken as seriously by science and society (Chivers, 2016). It was only recently acknowledged that women's sexuality is profoundly different (Bailey, 2009): Most women, including heterosexual women, are sexually aroused to both genders, whereas most men are aroused to one preferred gender. This has been demonstrated with genital vasocongestion and pupil dilation to sexual videos showing males or females (Rieger et al., 2015).

A prominent proposal for women's unique sexual arousal patterns is that forced copulation happened throughout human evolution, and the pressure for women to protect against genital injury was so strong that they have evolved to respond to any sexual stimulus with arousal and lubrication, even if the stimulus is subjectively un-arousing (Suschinsky & Lalumière, 2011). This evolutionary hypothesis has been challenged in one study assessing lubrication - a methodology that is rarely used but could revolutionise our understanding of women's sexual arousal. In that study, women only lubricated to their subjectively preferred sexual videos but to no other kind of sexual videos, which questions the validity of the hypothesis (Sawatsky, Dawson, & Lalumière, 2018).

Furthermore, the evolutionary hypothesis ignores other potential reasons for women's bisexual arousal patterns. Sex differences in sexual arousal could be attributed to sex differences in empathy. As women have a greater affective empathy, on average, compared to men (Stuijfzand et al., 2016), they may be more likely to share the emotional state of females shown in sexual videos and experience the sexual arousal with them. Moreover, women, more than men, depend on their physical appeal when competing for mates, and are therefore more distressed by physically attractive rivals (Buunk & Fisher, 2009). Thus, women may be aroused from stress by viewing attractive rivals in sexual videos, and this stress coincidentally triggers physiological sexual arousal.

In Study 1, I will examine the evolutionary hypothesis in 270 men and women with different sexual orientations by measuring their genital vasocongestion and pupil dilation (with penile gauges, vaginal probes, and eye trackers) to sexual videos showing males or females. I will also assess their subjective arousal and, importantly, women's lubrication (via litmus strips) to each video. Sexual videos will include narratives that describe the actor either as a caring lover or a person seeking non-consensual sex (no such acts will be shown), to test whether women respond sexually, including lubrication, to all sexual videos, even if these are subjectively unpleasant. Study 2 will use the same participants as Study 1. Participants' selfreported empathy and intrasexual competition (both in general, plus specifically towards the actors in the videos) will be assessed alongside measures of sexual arousal, to examine whether women's bisexual arousal pattern is due to sex differences in empathy and intrasexual competition. Such sex differences could be found even if the evolutionary hypothesis is not supported, and therefore offer powerful alternative explanations. Study 3 will also test sex differences in empathy, competition, and sexual arousal, but outside the lab via an online experiment that includes manipulations of participants' empathy and competition in order to examine causality and the generalisability of findings.

Advanced Quantitative Methods will be used in the collection of large data sets, mix-factorial regressions, multiple imputations, and mediation analyses on boot-strapped samples. The proposed research will have an impact on the study of female sexual arousal by scrutinising a prominent but hardly tested evolutionary hypothesis, and by potentially providing evidence for alternative explanations. Thus, this research can increase our understanding of female sexuality.