Identical Twins – A Window into the Development of Sexual Orientation

I investigate how identical twins with discordant sexual orientations differ in traits related to their sexual orientation in order to understand how non-genetic factors affect their distinct development. Importantly, across my studies I use methods that do not rely on self-report in order to examine their differences on an objective level. I previously presented findings that indicated that although genetically identical twins with discordant sexual orientations differ in their observable masculinity and femininity, they are more similar to each other than what they perceive. In my current talk, I will present further work conducted with the twins, which assessed the degree to which self-assessments of sexual orientation reflected observable differences in sexual arousal within pairs. In addition, I will present work, which looked at the extent to which differences in the twins’ sexual orientation related to differences in their finger length ratios, a putative biomarker of exposure to hormones during early development.