Some studies have found correlations between physiology of people and their sexuality. These studies provide evidence which they claim suggests that:Gay men report, on an average, slightly longer and thicker penises than non-gay men.
Gay men and straight women have, on average, equally proportioned brain hemispheres. Lesbian women and straight men have, on average, slightly larger right brain hemispheres.
The VIP SCN nucleus of the hypothalamus is larger in men than in women, and larger in gay men than in heterosexual men.
The average size of the INAH-3 in the brains of gay men is approximately the same size as INAH 3 in women, which is significantly smaller, and the cells more densely packed, than in heterosexual men's brains.
The anterior commissure is larger in women than men and was reported to be larger in gay men than in non-gay men, but a subsequent study found no such difference.
Gay men's brains respond differently to fluoxetine, a selective serotonin reuptake inhibitor.
The functioning of the inner ear and the central auditory system in lesbians and bisexual women are more like the functional properties found in men than in non-gay women (the researchers argued this finding was consistent with the prenatal hormonal theory of sexual orientation).
The suprachiasmatic nucleus was found by Swaab and Hopffman to be larger in gay men than in non-gay men, the suprachiasmatic nucleus is also known to be larger in men than in women.
The startle response (eyeblink following a loud sound) is similarly masculinized in lesbians and bisexual women.
Gay and non-gay people emit different underarm odors.
Gay and non-gay people's brains respond differently to two human sex pheromones (AND, found in male armpit secretions, and EST, found in female urine).
One region of the brain (amygdala) is more active in gay men than non-gay men when exposed to sexually arousing material
Finger length ratios between the index and ring fingers may be different between non-gay and lesbian women.
Gay men and lesbians are significantly more likely to be left-handed or ambidextrous than non-gay men and women;Simon LeVay argues that because "[h]and preference is observable before birth... [t]he observation of increased non-right-handness in gay people is therefore consistent with the idea that sexual orientation is influenced by prenatal processes," perhaps heredity
Gay men have increased ridge density in the fingerprints on their left thumbs and pinkies