Gender Nonconformity of Identical Twins with Discordant Sexual Orientations: Evidence from Video Recordings.

Gender nonconformity (femininity in males, masculinity in females) is more common in non-heterosexual (bisexual and homosexual) than heterosexual individuals. In the past research (Watts, Holmes, Raines, Orbell, & Rieger, 2018b), identical twins discordant for sexual orientation were perceived more similar in their gender nonconformity than unrelated heterosexual and non-heterosexual people. Yet, these perceptions were based on photographs, which do not contain all aspects of gender nonconformity, such as movement and sound. This could have led to an underestimation of observable difference within twin pairs. We examined evaluations of video recordings from adult identical twins with discordant sexual orientations (eight male pairs, 11 female pairs). These twins were a small subset of those who participated in Watts et al. (2018b). Non-heterosexual twins were rated as significantly more gender nonconforming than their heterosexual co-twins, but only when males and females were combined. Their difference was smaller than the analogous difference between identical twins who were concordant heterosexual (three male pairs, three female pairs) and, unrelated to them, identical twins who were concordant non-heterosexual (six male pairs, two female pairs). These patterns were partially confirmed with twins' self-reported gender nonconformity. Shared influences possibly made twins from discordant pairs somewhat similar in their gender nonconformity, even if non-shared factors differentiated their sexual orientations.