The present work investigated potential hormonal influences on sex differences in sexual arousal, with most men being aroused to one sex, and most women being aroused to both sexes. Within women, I also investigated whether prenatal hormonal influences explain why homosexual women have more male-typical arousal, and are more masculine, than heterosexual women. Chapter 1 summarises the literature. In Chapter 2, I investigated whether sex differences in sexual arousal, reflected in genital response and pupil dilation to sexual stimuli, are related to the sex difference in prenatal androgen exposure, reflected in a putative biomarker, the second to fourth finger digit ratio (2D:4D). In Chapter 3, I examined whether homosexual women's male-typical sexual arousal is explained by their male-typical 2D:4D, as compared to heterosexual women. Chapter 4 investigated whether homosexual women's behavioural masculinity is explained by their male-typical 2D:4D. Finally, Chapter 5 explored an alternative explanation for the sex difference in arousal: That unlike men, women may empathise with actors depicted in explicit sexual stimuli, and thus mirror female actors' sexual arousal by becoming aroused themselves. Overall, we confirmed hypothesised sex differences in sexual arousal, empathy, and 2D:4D. However, there was no evidence that these sex differences were interlinked. In women, we confirmed sexual orientation differences in sexual arousal and masculinity-femininity, but failed to replicate the previously reported sexual orientation difference in 2D:4D. Moreover, there was no evidence that women's sexual arousal patterns or masculinity were related to their 2D:4D. In sum, studied sex and sexual orientation differences might be driven by other factors than prenatal androgen exposure. However, the limitations of 2D:4D need to be considered. Furthermore, sex differences in empathy does not serve as an alternative explanation (alternative to androgen exposure) for sex differences in sexual arousal patterns
