The Neuroscience of Homosexuality (Why Attraction Isn't a Choice)

Emanuela Brun
Jun 7
2 min read

Updated: Jun 13

Why are some people attracted to the same sex? Science says: it’s not a choice, it’s not a phase, and it’s definitely not something that can or should be changed. 🏳️‍🌈

Sexual orientation is the result of a complex interaction between the brain, genetics, prenatal biology, and environment.

Here's what neuroscience reveals:

1. Brain Structure

In 1991, neuroscientist Simon LeVay found that a small cluster of neurons in the hypothalamus (INAH-3) differed in size between heterosexual and homosexual men (not better, not worse, just different).
A 2008 study by Ivanka Savic showed that gay men and lesbian women had unique patterns of brain symmetry and connectivity, distinct from heterosexual counterparts. This suggests that the brain is organized for orientation early on, possibly before birth.

🧠 These differences are not about being more "masculine" or "feminine"—they reflect neurodiversity, not stereotypes.

2. Genetics & Epigenetics

There’s no single “gay gene”, but genetic research (like the 2019 Ganna et al. study) shows that multiple genes contribute small effects to sexual orientation.
Twin studies consistently show that identical twins are more likely to share the same sexual orientation than fraternal twins, pointing to a heritable component.

3. Prenatal Factors

Hormones in the womb (especially androgens like testosterone) affect brain sexual differentiation.
The fraternal birth order effect shows that men with more older biological brothers have a higher likelihood of being gay, possibly due to maternal immune responses over successive male pregnancies.
This effect does not apply to lesbians, suggesting different biological pathways for male and female same-sex attraction.

4. The Fertile Mother Hypothesis

Studies show that the maternal female relatives of gay men tend to have higher fertility. This may indicate an evolutionary mechanism: genes that increase attraction to the same sex in men might increase reproductive success in women, balancing out across generations.

5. Environment, Identity & Experience Matter Too

Of course biology isn’t everything.

While the foundation of sexual orientation is largely biological, human sexuality is also shaped by: