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Why are some people gay? And why are there trans people?

I’ve studied in an all-boys school and since a very young age, I noticed that not all boys in our class were similar in terms of masculinity and masculine behaviors.

On one end of the spectrum, there were those highly aggressive, dominant, super-masculine boys who often had a passion for sports and bullying other kids. 

Then there was this large group, the middle of the bell curve, of slightly less masculine boys who acted in a more civilized way, though occasionally showing the same behaviors as the first group.

What intrigued me the most was the third, much smaller of category boys- the boys who behaved like girls. There were three such boys in our class and they walked, talked and moved very differently than other boys.

Specifically, they had a feminine gait, a feminine voice, and feminine mannerisms. They showed little or no interest in sports, athleticism or physical conflict. They were among the most sociable boys in our class.

Of course, it wasn’t just me who noticed that they were different. Other boys recognized this difference too and often teased them by calling them “gay” or “girl”. One of the highly aggressive guys in our class even admitted to finding one such girly boy attractive and made sexual advances towards him.

Genetic and hormonal basis of homosexuality

Homosexuality cuts across human cultures1 and has been observed throughout human history. Moreover, it’s found in numerous animal species ranging from birds to monkeys. This suggests that it has a biological basis.

A study conducted in 1991 found that monozygotic twins (identical twins) are more likely to be both homosexuals. Since such twins share the same genetic make-up, it was a strong indication that the trait of homosexuality had a genetic component.2

It was later found that the gene or group of genes responsible for homosexual behavior are likely to be present on the X chromosome which a person can only inherit from their mother. A 1993 study compared DNA of 40 pairs of homosexual brothers and found that 33 had the same genetic markers in the Xq28 region of the X chromosome.3

Since homosexuality is likely inherited from the mother's side, the same study also showed an increased rate of same-sex orientation in the subjects' maternal uncles and cousins but not in their fathers and paternal cousins.

This finding was supported by a recent genome-wide scan which demonstrated significant linkage of DNA markers on X chromosome and male homosexual orientation.4

Role of hormones in sexual orientation

There's strong evidence that sexual orientation in our brains is set when we’re still in the womb. We all start as females having a female brain. Then, depending on the exposure to male hormones (mainly testosterone), our bodies and brains are masculinized.5

It’s this masculinization of the brain, which is largely responsible for typical male psychological traits such as dominance, aggression, spatial ability, etc.

If neither the body nor the brain is masculinized, the fetus grows to be a female. If the male hormone exposure is significantly low, the fetus may grow to be a super-feminine female.

If the brain is masculinized with large doses of testosterone, the fetus is likely to grow up to be a super-masculine male. Comparatively lesser doses mean a lower degree of masculinization.

Conceive of the brain having two regions- one responsible for sexual orientation and the other for gender-typical behavior. If both the regions are masculinized, the fetus becomes a heterosexual male.

If only the ‘sexual orientation’ region is masculinized, the fetus becomes a heterosexual male with feminine behavior because his brain region for gender-typical behavior remains female.

Similarly, if the body is masculinized but both the brain regions described above aren’t, the fetus may become a homosexual male (with a sexual orientation similar to heterosexual females) with feminine behavior.

The last possibility is that the body and brain region responsible for gender-typical behavior are both masculinized but not the sexual orientation region, producing a gay person with masculine body and behavior. This is why gay bodybuilders who’re also engineers exist.

Same is true for women. They can be lesbians and feminine at the same time, even though it seems counter-intuitive.

The brains of gay and heterosexual people appear to be organized differently. Patterns of brain organization appear similar between lesbian and heterosexual men. Gay men appear, on average, more 'female-typical' in brain pattern responses and lesbian women more 'male-typical'.6

Gays are likely to show behaviors opposite to their sex in childhood.7 Other studies show that gay men navigate in a similar way to women and prefer masculine-faced men.

Adult women with Congenital Adrenal Hyperplasia (CAH), a condition where the female fetus is exposed to abnormally large amounts of testosterone, are more likely to be lesbians compared to the general population.These women also show male-typical childhood play behavior.

If, during the early stages of pregnancy, testosterone is suppressed by stress, sickness or medications, the chance of giving birth to a gay boy dramatically increases. According to a German study, pregnant mothers who suffered severe stress during the second world war were six times more likely to give birth to a gay son. 

One key marker showing how much testosterone a person was exposed to during development is the ratio of the size of the index finger to the ring finger of the right hand (known as the 2D:4D ratio).

In men, the ring finger tends to be longer while in women both the fingers tend to be more or less equal in size. But homosexual women, on average, have considerably shorter index finger compared to their ring finger.9

2D:4D ratio gay vs straight
The finger lengths shouldn't be compared by looking at the level of their tops but by measuring each finger length from top to bottom. There's a good chance this hand belongs to a male heterosexual.

What this hormonal theory doesn’t seem to explain is bisexuality. However, it’s likely an intermediate masculinization stage between a strictly homosexual (extremely rare) and a strictly heterosexual (extremely common) sexual orientation states.

Origins of transsexualism

If the body of a person is male but his brain isn’t masculinized to the extent that he’s not only attracted to males (the way females are) but also thinks he’s a female, this results in a male-to-female transsexual. The person is biologically male but has a female brain. The same principle holds for female-to-male transsexuals i.e. a female body with a male brain.  

The area in the brain essential for sexual behavior, known as BSTc, is larger in men than in women. A study showed that male-to-female transsexuals had female-sized BSTc.

A 2016 literature review10 on the topic concluded that "Untreated transsexuals who have an early onset of gender dysphoria (disconnect between gender identity and biological sex) show a distinct brain morphology which is different from that shown by heterosexual males and females."

It’s important to note that environment has little or no role to play in all this. Genetic males who, through accidents, or being born without penises, were subjected to sex change and raised as adults, were typically attracted to women.11 Being gay or trans is as much a 'choice' as being straight.

My classmates were probably right

It’s highly likely that at least one of my three effeminate classmates was gay. When my other classmates called them “gay” teasingly, it’s possible they were right because studies show that homosexuals (especially males) can be identified with a good deal of accuracy by their body type and motion.12 Also, voice tends to be a powerful 'gay detection' cue having an accuracy of around 80%. 


1. Bailey, J. M., Vasey, P. L., Diamond, L. M., Breedlove, S. M., Vilain, E., & Epprecht, M. (2016). Sexual orientation, controversy, and science. Psychological Science in the Public Interest17(2), 45-101.

2. Bailey, J. M., & Pillard, R. C. (1991). A genetic study of male sexual orientation. Archives of general psychiatry48(12), 1089-1096.

3. Hamer, D. H., Hu, S., Magnuson, V. L., Hu, N., & Pattatucci, A. M. (1993). A linkage between DNA markers on the X chromosome and male sexual orientation. SCIENCE-NEW YORK THEN WASHINGTON-261, 321-321.

4. Sanders, A. R., Martin, E. R., Beecham, G. W., Guo, S., Dawood, K., Rieger, G., ... & Duan, J. (2015). Genome-wide scan demonstrates significant linkage for male sexual orientation. Psychological medicine45(7), 1379-1388.

5. Collaer, M. L., & Hines, M. (1995). Human behavioral sex differences: a role for gonadal hormones during early development?. Psychological bulletin118(1), 55.

6. Savic, I., & Lindström, P. (2008). PET and MRI show differences in cerebral asymmetry and functional connectivity between homo-and heterosexual subjects. Proceedings of the National Academy of Sciences105(27), 9403-9408.

7. Bailey, J. M., & Zucker, K. J. (1995). Childhood sex-typed behavior and sexual orientation: A conceptual analysis and quantitative review. Developmental Psychology31(1), 43.

8. Meyer-Bahlburg, H. F., Dolezal, C., Baker, S. W., & New, M. I. (2008). Sexual orientation in women with classical or non-classical congenital adrenal hyperplasia as a function of degree of prenatal androgen excess. Archives of sexual behavior37(1), 85-99.

9. University Of California, Berkeley. (2000, March 30). UC Berkeley Psychologist Finds Evidence That Male Hormones In The Womb Affect Sexual Orientation. ScienceDaily. Retrieved December 15, 2017 from

10. Guillamon, A., Junque, C., & Gómez-Gil, E. (2016). A review of the status of brain structure research in transsexualism. Archives of sexual behavior45(7), 1615-1648.

11. Reiner, W. G. (2004). Psychosexual development in genetic males assigned female: the cloacal exstrophy experience. Child and Adolescent Psychiatric Clinics of North America13(3), 657-674.

12. Johnson, K. L., Gill, S., Reichman, V., & Tassinary, L. G. (2007). Swagger, sway, and sexuality: Judging sexual orientation from body motion and morphology. Journal of personality and social psychology93(3), 321.