Alexandria's Notes

The Science of Transgender People and Gender Identity

2 min read

Biology of Gender Identity

  • The Endocrine Society states there are biological underpinnings of gender identity. 1
    1. attempts to change gender identity in intersex patients to match external genitalia or chromosomes are typically unsuccessful;
    2. identical twins (who share the exact same genetic background) are more likely to both experience transgender identity as compared to fraternal (non-identical) twins;
    3. among individuals with female chromosomes (XX), rates of male gender identity are higher for those exposed to higher levels of androgens in utero relative to those without such exposure, and male (XY)-chromosome individuals with complete androgen insensitivity syndrome typically have female gender identity;
    4. there are associations of certain brain scan or staining patterns with gender identity rather than external genitalia or chromosomes.

Genetics / Heritability of Trans Identities

  • “The fact that trans identities are at least partially genetic is not really disputable at this point.” 2
    • “Twin studies for trans identities have confirmed strong genetic roots in over a dozen studies now. While results vary from study to study, due largely to methodological differences, most studies find that between 30-50% of gender incongruence is heritable.” 2

Brain Science

  • What physiologically changes make us trans is a much more fraught question. The candidate most often cited—sexually dimorphic brain shape—was decisively struck down in 2021 by a massive metastudy that shredded the very idea that brains are shaped differently based on sex. 2

Intersex

  • The rate of sexually ambiguous traits may be as high as 2% of live births. 3

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Footnotes

  1. Endocrine Society. 2020. “Transgender Health: An Endocrine Society Position Statement.” Endocrine.org. Endocrine Society. December 16, 2020. https://www.endocrine.org/advocacy/position-statements/transgender-health. ↩

  2. Doc Impossible. 2023. “There Are 385.5 Million Trans People Alive Today.” Substack.com. Stained Glass Woman. March 13, 2023. https://stainedglasswoman.substack.com/p/there-are-3855-million-trans-people. ↩ ↩2 ↩3

  3. Blackless, Melanie, Anthony Charuvastra, Amanda Derryck, Anne Fausto-Sterling, Karl Lauzanne, and Ellen Lee. “How Sexually Dimorphic Are We? Review and Synthesis.” American Journal of Human Biology 12, no. 2 (2000): 151–66. https://doi.org/10.1002/(SICI)1520-6300(200003/04)12:2<151::AID-AJHB1>3.0.CO;2-F. ↩

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