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Key points
- There is much confusion on social media among the terms sex, gender, and sexual preference.
- Sexual preference/orientation refers to the expressions of one’s predilections or sexual desires.
- Sexual preference/orientation may be based upon traditional chromosomal influences and epigenetic phenomenon.
By Frederick L. Coolidge, Professor, University of Colorado, Colorado Springs, USA; and Apeksha Srivastava, Doctoral Candidate, Indian Institute of Technology Gandhinagar, India.
This post is Part 3 of a three-part series. Read Part 1 and Part 2.
Overview: Many recent editorialists, particularly in regard to trans women (MTW) and trans men (WTM), have noted that a trans woman still possesses XY chromosomes, and a trans man still possesses XX chromosomes. These same editorialists subsequently castigate trans people for presenting or identifying themselves as women or men.
One major problem with their arguments is that they are conflating or misconstruing the scientific terms of sex, gender, and sexual preference and their individual heritable bases. The purpose of this series of posts is to delineate the three terms and provide a clearer basis for their use.
Definition: The term sexual preference (synonymous with sexual orientation) refers to the expressions of one’s predilections or sexual desires. The term sex refers to one’s biological genitalia (e.g., penis or vagina) at birth and the reproductive organs associated with them (e.g., testicles, ovaries, etc.). The term gender refers to one's presentation or identification with the cultural stereotypic behaviors of a man, woman, both, or neither.
Sexual Preference (Part 3): The term sexual preference refers to one’s choice of a sexual partner, and it is also commonly labeled as sexual orientation or sexuality. The term heterosexual is used when one’s biological sex is the opposite of the biological sex of one’s preferred sexual partner, and the term homosexual is used when one’s biological sex is the same as the biological sex of one’s preferred sexual partner.
The term bisexual typically denotes a person who is attracted, either romantically or sexually, to both men and women. Although less frequently used, the term pansexual (where pan means "all" or "every" in Greek) refers to one’s attraction towards others, regardless of their sex or gender preference.
Just as sex and gender are heritable, so is sexual preference. There has been consistent evidence for male and female homosexuality (varying from 0.5 percent to 10 percent), both historically and worldwide. There is also evidence for its heritability.
However, it is also clear that there is no single gene or gene sequence has been yet identified for one’s sexual preference. Further, sexual preference is not based, as biological sex is, upon simple chromosome arrangements, e.g., XX, XY, but there may exist some complex relationships between them.
Generally, higher concordance (similarity or agreement on behavior) rates between identical twins than between fraternal twins are indicative of a genetic or heritable influence because identical twins theoretically share 100 percent of their DNA while fraternal twins share only about 50 percent of their DNA.
Thus, one line of scientific evidence for the heritability of sexual preference comes from the higher concordance rates of homosexuality in identical twins than in fraternal twins. The second line of evidence comes from pedigree analysis studies where homosexuality is more prevalent in some family trees across generations than in others.
It is also important to note that the twin concordance rates for homosexuality are not as high as with other genetically complex human behaviors, such as intelligence or schizophrenia. The latter phenomenon suggests factors other than XX and XY chromosomal arrangements may be operating upon sexual preference.
One of these factors may reside in epigenetics—that is, modifications to DNA that do not alter its chromosomal sequence but regulate the way genes express themselves, either physically or behaviorally. Specifically, the human fetal hormonal environment typically feminizes XX fetuses and masculinizes XY fetuses. In the case of homosexuality, the opposite sometimes occurs as a result of epigenetic phenomena in the fetal environment.
These phenomena are not yet well understood but are known to be complex interactions between basic DNA influences, hormones, and internal (fetal conditions) and external environmental factors (e.g., the mother’s nutrition, exposure to toxins, stress, etc.). As an example of this epigenetic complexity, the heritability of traits may or may not be transmissible over generations. The latter phenomenon may explain why homosexuality appears to be more prominent in some families, but it may skip generations.
In summary, sexual preferences like heterosexuality, homosexuality, and pansexuality are heritable traits, although they can be possibly altered, as noted earlier, by the internal fetal environment and external environmental influences such as cultural mores, interpersonal interactions, social media, and other external factors. The latter phenomena may partially explain the recent increase in people who do not identify as exclusively heterosexual, although a greater cultural acceptance may also partially explain the increase.
References
Englert, P., Dinkins, E. G., Fradella, H. F., & Sumner, J. M. (2016). An overview of sex, gender, and sexuality. Sex, Sexuality, Law, and (In)justice, 1–30.
Rice, W. R., Friberg, U., & Gavrilets, S. (2012). Homosexuality as a consequence of epigenetically canalized sexual development. The Quarterly Review of Biology, 87(4), 343–368.
