Sexual Orientation and Fluctuating Asymmetry in Men and Women

Abstract

Previous research suggests that individuals' sexual orientation may be affected by developmental instability (DI) induced by exposure to prenatal stresses. We tested this relationship using fluctuating asymmetry (FA), the small random deviations from symmetry that arise in otherwise bilaterally symmetrical traits as a consequence of developmental noise and developmental instability. Differences among individuals reflect variation in their exposure to and ability to accommodate for stresses experienced during development as well as to developmental noise that arises due to cellular stocasticity. FA measurements for 156 heterosexual and 132 homosexual men and women participants provided strong support for the developmental instability hypothesis: FA was significantly higher in both male and female homosexuals (men: four of seven bilateral traits and composite FA values (cFA); women: five of seven bilateral traits and composite FA values). Although finger-length ratios (FLRs), an indirect marker for prenatal hormones, were sex-atypical (e.g., feminized) for homosexual men, we failed to detect any relationship between FA levels and 2D:4D finger-length ratios (FLRs). Hence, although elevated levels of developmental stress appear to be linked to shifts in sexual orientation, the underlying mechanism does not seem to be connected to sex-atypical prenatal hormones. Additional analyses with sex atypical individuals are needed to confirm this.

The Relationship Between Digit Ratio (2D:4D) and Sexual Orientation in Men from China

“…Our results suggested that 2D:4D of homosexual men was significantly higher compared to that of heterosexual men. This result supports the findings of some previous work on the relationship between 2D:4D and male sexual orientation (e.g., Hall & Schaeff, 2008;Lippa, 2003;Manning et al, 2007) suggesting that low prenatal androgen exposure in particular may be associated with homosexuality in men (Collaer & Hines, 1995;Ellis & Ames, 1987;Rahman & Wilson, 2003a).…”

“…This result supports the findings of some previous studies (Hall & Schaeff, 2008;Hiraishi et al, 2012;McFadden & Shubel, 2002), but conflicts with other work (Lippa, 2003;Manning et al, 2007). Manning et al (1998) suggested that the right hand 2D:4D is likely to reflect prenatal androgen exposure more strongly than the left hand.…”

“…For instance, some studies only assessed sexual identity (e.g., Lippa, 2003;Williams et al, 2000), whereas others examined both sexual identity and sexual fantasy (e.g., Manning, 2005), sexual fantasy and sexual behavior (e.g., Robinson & Manning, 2000), or assessed a combination of sexual identity, sexual fantasy, and sexual behavior (e.g., Hall & Schaeff, 2008;McFadden & Shubel, 2002). Such studies also differed in the criteria (the cut-off values for homosexuals) used to classify individuals as homosexual.…”

“…For instance, some studies using the 5-point Kinsey-like scale (which ranges from 1 to 5) to assess sexual orientation classified individuals with a score of 4 and 5 as homosexuals (e.g., Manning, 2005;Putz, Gaulin, Sporter, & McBurney, 2004). Among studies using a 7-point Kinsey-like scale (which ranges from 0 to 6) to assess sexual orientation, homosexuals have been categorized as those with a score of 6 (e.g., Hall & Schaeff, 2008), with a score of 5 and 6 (e.g., Rahman, 2005), or with a score equal to or higher than 2 (e.g., Kangassalo et al, 2011;Rahman & Wilson, 2003a, b). Studies using the 9-point Kinsey-like scale (which ranges from 1 to 9) to assess sexual orientation have classified individuals with a total score of 11 or less on three items as homosexuals (Kraemer et al, 2006(Kraemer et al, , 2009.…”

Fluctuating Asymmetry and Sexual Orientation in Men and Women

“…However, Rahman (2005) analyzed a composite index consisting of nine traits, which may have obscured more subtle effects. Further, Hall and Schaeff (2008), who also assessed some of the same traits we did, reported that mean FAs were higher among gay men on four of seven traits plus the composite index and among lesbians on five of seven traits and the composite index when compared with heterosexuals. Considering the inconsistency in the data examining the relationship between handedness and sexual orientation, the lack of agreement among the studies examining other indices of DI is not surprising.…”