Cross-Cultural Evidence for the Genetics of Homosexuality

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Mexico’s third gender sheds light on the biological correlates of sexual orientation

By Debra W. Soh

The reasons behind why people are gay, straight, or bisexual have long been a source of public fascination. Indeed, research on the topic of sexual orientation offers a powerful window into understanding human sexuality. The Archives of Sexual Behavior recently published a special edition devoted to research in this area, titled “The Puzzle of Sexual Orientation.” One study, conducted by scientists at the University of Lethbridge in Alberta, Canada, offers compelling, cross-cultural evidence that common genetic factors underlie same-sex, sexual preference in men.

In southern Mexico, individuals who are biologically male and sexually attracted to men are known as muxes. They are recognized as a third gender: Muxe nguiiu tend to be masculine in their appearance and behavior, while muxe gunaa are feminine. In Western cultures, they would be considered gay men and transgender women, respectively.

Several correlates of male androphilia — biological males who are sexually attracted to men — have been shown across different cultures, which is suggestive of a common biological foundation among them. For example, the fraternal birth order effect—the phenomenon whereby male androphilia is predicted by having a higher number of biological older brothers—is evident in both Western and Samoan cultures.

Interestingly, in Western society, homosexual men, compared with heterosexual men, tend to recall higher levels of separation anxiety — the distress resulting from being separated from major attachment figures, like one’s primary caregiver or close family members. Research in Samoa has similarly demonstrated that third-gender fa’afafine—individuals who are feminine in appearance, biologically male, and attracted to men—also recall greater childhood separation anxiety when compared with heterosexual Samoan men. Thus, if a similar pattern regarding separation anxiety were to be found in a third, disparate culture—in the case, the Istmo region of Oaxaca, Mexico—it would add to the evidence that male androphilia has biological underpinnings.

The current study included 141 heterosexual women, 135 heterosexual men, and 178 muxes (61 muxe nguiiu and 117 muxe gunaa). Study participants were interviewed using a questionnaire that asked about separation anxiety; more specifically, distress and worry they experienced as a child in relation to being separated from a parental figure. Participants rated how true each question was for them when they were between the ages of 6 to 12 years old.

Muxes showed elevated rates of childhood separation anxiety when compared with heterosexual men, similar to what has been seen in gay men in Canada and fa’afafine in Samoa. There were also no differences in anxiety scores between women and muxe nguiiu or muxe gunaa, or between the two types of muxes.

When we consider possible explanations for these results, social mechanisms are unlikely, as previous research has shown that anxiety is heritable and parenting tends to be in response to children’s traits and behaviors, as opposed to the other way around. Biological mechanisms, however, offer a more compelling account. For instance, exposure to female-typical levels of sex steroid hormones in the prenatal environment are thought to “feminize” regions of the male brain that are related to sexual orientation, thereby influencing attachment and anxiety.

On top of this, studies in molecular genetics have shown that Xq28, a region located at the tip of the X chromosome, is involved in both the expression of anxiety and male androphilia. This suggests that common genetic factors may underlie the expression of both. Twin studies additionally point to genetic explanations as the underlying force for same-sex partner preference in men and neuroticism, a personality trait that is comparable to anxiety.

These findings suggest childhood separation anxiety may be a culturally universal correlate of androphilia in men. This has important implications for our understanding of children’s mental health conditions, as subclinical levels of separation anxiety, when intertwined with male androphilia, may represent a typical part of the developmental life course.

As it stands, sexual orientation research will continue to evoke widespread interest and controversy for the foreseeable future because it has the potential to be used—for better or worse—to uphold particular socio-political agendas. The moral acceptability of homosexuality has often hinged on the idea that same-sex desires are innate, immutable, and therefore, not a choice. This is clear when we think about how previous beliefs around homosexuality being learned were once used to justify (now discredited) attempts to change these desires.

The cross-cultural similarities evinced by the current study offer further proof that being gay is genetic, which is, in itself, an interesting finding. But we as a society should challenge the notion that sexual preferences must be non-volitional in order to be socially acceptable or safe from scrutiny. The etiology of homosexuality, biological or otherwise, should have no bearing on gay individuals’ right to equality.

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