The New Genetic Evidence on Same-Gender Sexuality: Implications for Sexual Fluidity and Multiple Forms of Sexual Diversity

The New Genetic Evidence on Same-Gender Sexuality: Implications for Sexual Fluidity and Multiple Forms of Sexual Diversity. Lisa M. Diamond. The Journal of Sex Research, Volume 58, 2021 - Issue 7, Feb 23 2021. https://doi.org/10.1080/00224499.2021.1879721

Abstract: In September of 2019, the largest-ever (N = 477,522) genome-wide-association study of same-gender sexuality was published in Science. The primary finding was that multiple genes are significantly associated with ever engaging in same-gender sexual behavior, accounting for between 8–25% of variance in this outcome. Yet an additional finding of this study, which received less attention, has more potential to transform our current understanding of same-gender sexuality: Specifically, the genes associated with ever engaging in same-gender sexual behavior differed from the genes associated with one’s relative proportion of same-gender to other-gender behavior. I review recent research on sexual orientation and sexual fluidity to illustrate how these findings speak to longstanding questions regarding distinctions among subtypes of same-gender sexuality (such as mostly-heterosexuality, bisexuality, and exclusive same-gender experience). I conclude by outlining directions for future research on the multiple causes and correlates of same-gender expression.

Do We Have the Right Categories?

Another avenue for future research involves investigating the degree to which observations of subtypes of same-gender expression and their differing genetic/environmental influences depends on our conceptual framings of gender and sexual orientation. Historically, laypeople and scientists have conceptualized individuals as oriented toward the same gender or the other gender (or both genders), as opposed to being oriented toward women or men (or both). This framing directly affects the type of gender differences we observe. Consider, for example, one of the most robust gender differences in same-gender sexuality: the fact that women show more genital arousal than do men when presented with sexual stimuli depicting their “less-preferred” gender (Chivers & Bailey, 2005; Chivers et al., 2004, 2007). Early work suggested that this “nonspecific” pattern of genital arousal (i.e., arousal that is not specific to one’s preferred gender) characterized all women, but later work showed that nonspecific genital arousal was most pronounced among self-described heterosexual women (reviewed in Chivers, 2017), and scholars have considered a range of social and evolutionary reasons for heterosexual women’s uniqueness in this regard (Chivers, 2017; Diamond, 2017; Kuhle & Radke, 2013).

Yet the definition of heterosexual women as “unique” depends on the classification of sexual stimuli as preferred or non-preferred, according to participants’ self-described patterns of attraction. Within this framework, heterosexual women are unique because they show stronger genital arousal to their non-preferred gender (i.e., women) than do all other groups. But what if we re-classified the sexual stimuli as simply “men” versus “women?” Using this re-classification, exclusively gay men are suddenly the outlier group (Diamond, 2017). Whereas heterosexual women, lesbian women, bisexual women, heterosexual men, and bisexual men all show some degree of genital arousal to sexual stimuli depicting women, gay men do not.

Hence, should we describe heterosexual women’s genital arousal patterns as uniquely “fluid” or gay men’s genital arousal patterns as uniquely “rigid?” How much do these patterns depend on the mechanisms underlying genital versus subjective arousal, given that these mechanisms are distinct (Chivers, 2017), and that concordance between genital and subjective arousal differs for men versus women (Suschinsky et al., 2009)? Furthermore, what is the role of aversion to same-gender versus other-gender stimuli and/or partners (or male versus female stimuli/partners) in shaping subtypes of sexual diversity (see Dehlin et al., 2019; Freund, Langevin, Chamberlayne et al., 1974; Freund, Langevin, Zajac et al., 1974; Jabbour et al., 2020; Safron et al., 2007; Semon et al., 2017)? As reviewed earlier, the Kinsey-type “single continuum” model of sexual orientation (challenged by Ganna et al. 2019) posits exclusive same-gender attractions and exclusive other-gender attractions as polar opposites, but perhaps the true opposite of exclusive same-gender attraction is same-gender aversion or indifference. Models which account for aversion and/or indifference are better suited to including the experiences of asexual individuals (Bogaert et al., 2018; Brotto & Yule, 2017) and those who experience their own attractions as “gender neutral” (Diamond, 2008). Further integration of these nuances into genetically-informed research would make a strong contribution to understanding the nature and development of different forms of sexual diversity.

On this point, it bears noting that a growing body of sexuality researchers now refer to sexual orientations as gynephilic (preferring women), androphilic (preferring men) and biphilic (preferring both genders) rather than “same-gender” and “other-gender” (for example, Antfolk et al., 2017; Chivers, 2017; Huberman & Chivers, 2015; Huberman et al., 2015; Petterson et al., 2018; Semenyna et al., 2017; Skorska & Bogaert, 2020; Snowden et al., 2020; Timmers et al., 2018; Vásquez-Amézquita et al., 2019). There is an intuitive appeal to this approach, given that most individuals describe themselves as desiring aspects of “women” and “men” rather than “sameness” and “otherness.” This approach is also better suited to describing the experiences of transgender and nonbinary individuals, since it focuses on the gender expression of sexual partners without making presumptions about one’s own or one’s partners’ birth-assigned sex/gender. Yet the “same-gender/other-gender” framework represented by the Kinsey scale continues to dominate social scientific research on this topic, perhaps reflecting the cultural dominance of this model of sexual orientation in Western culture (which necessarily feeds back to influence how sexually-diverse individuals come to perceive, understand, and experience their own patterns of eroticism). Certainly, the same-gender/other-gender framing is useful for capturing the fact that heterosexuality is culturally valued and expected, whereas same-gender sexuality is stigmatized and marginalized. The experience of stigma and marginalization is so relevant to the life experiences of individuals with same-gender attractions (and to the likelihood that they will express these attractions) that it seems naive to categorize attractions as “woman-oriented” or “man-oriented” without taking account of which type of attractions are socially permitted versus punished. Yet as we move forward in trying to understand genetic influences on sexuality, we should remain mindful of the extent to which our framing of core constructs (such as same/other versus woman/man) shapes our observations and interpretations.

Questions of Mechanism

Future research on sexual orientation, sexual fluidity, and their genetic/environmental underpinnings may also benefit from closer attention to the full range of conscious and nonconscious processes through which different types of sexual stimuli are attended to, neurologically processed, and responded to (Dickenson et al., 2020; Safron et al., 2007; Safron & Hoffmann, 2017). Such process-oriented work is exemplified by Chivers’s (2017) nuanced and sweeping analysis of the potential contribution of visual attention, implicit and explicit processing, and incentive motivation to heterosexual women’s “nonspecific” patterns of genital arousal. Given that environments fluctuate over the lifespan, whereas genes remain fixed (setting aside for now the complications of epigenetics, Charney, 2012; Ngun & Vilain, 2014; Rice et al., 2012; Richardson & Stevens, 2015), the mechanisms underlying change in sexual experience and expression warrant particularly close study. As reviewed above, sexual fluidity has been defined as a heightened sensitivity to situational change in sexual responsiveness (Diamond, 2008), but this definition leaves unspecified the process through which sexual responsiveness changes at all. There is a growing body of rigorous research on the role of learning and conditioning in human sexual response (Hoffmann, 2012, 2017; Hoffmann, Janssen, & Turner; Klucken et al., 2009), and this work should be more comprehensively integrated into investigations of genetic and environmental influences on same-gender expression.

Of course, the notion of learned or conditioned sexual responses may bring to mind the unfortunate history of behavior-modification approaches to “extinguishing” undesirable sexual impulses (Hoffmann, 2017), which has had particularly harmful effects on sexually-diverse individuals who have been subjected to “conversion” and “reparative” therapies (APA Task Force on Appropriate Therapeutic Responses to Sexual Orientation, 2009). Perhaps because of this history, sexual orientation is commonly (if inaccurately) described as fundamentally immutable (Diamond & Rosky, 2016). Yet from a basic developmental perspective, the role of learning and exposure in human and nonhuman sexual development is well established (reviewed in Hoffmann, 2012, 2017). As Hoffman summarized, conditioning is quite simply “a process by which organisms, including humans, learn about the relationship between events. Through conditioning, we can learn to predict events, we can learn signals for biologically significant stimuli, we can learn the value of stimuli, and we can learn the consequences of our actions. Hence, sexual conditioning can prepare us to respond sexually and can contribute to our erotic preferences and to how we behave sexually” (Hoffmann, 2017, p. 2213).

Positing a role for learning and experience in the expression of same-gender sexuality does not invalidate the notion of genetically influenced sexual predispositions. Rather, drawing from Freund and Blanchard (1993), we might think of genetic influences as differential sensitivities to certain classes of reproductively-relevant stimuli (in this case, “man/woman” may prove a more relevant classification scheme than “other-gender/same-gender”), and our experiences interact with and elaborate these sensitivities to produce consistent – albeit not rigidly static – patterns of desire. Notably, learning and conditioning played an important role in Kinsey’s understanding of same-gender sexuality. As reviewed by Cass (1990), he viewed all forms of sexual preferences as learned. Cass suggested instead (similar to Freund and Blanchard) that individuals possess intrinsic sexual interests, but that these interests could be strengthened by repeated, satisfying same-gender experiences, as well as the process of attaching psychological significance to these experiences (in the form of gay/lesbian/bisexual identification and social validation). Cass posited that such strengthening effects should be more influential for those whose preferences were less “regular, stable, and fixed” to begin with (1990, p. 252), and she speculated that both women and bisexuals were more likely to belong to the latter group.

These thirty-year-old speculations demonstrate that scientific debates about subtypes of same-gender sexuality (bisexual versus exclusive, man-oriented versus woman-oriented, fixed versus fluid) have been longstanding interests within sexuality research (for an even broader historical and cultural view, see Murray, 2000). Ganna et al’s (2019) data do not definitively resolve these questions, but they point toward productive avenues for future study, in addition to suggesting new questions that we had not yet thought to consider.