Physiological differences in gay men and lesbians
Recent studies have found notable differences between the physiology of gay people and non-gay people. There is evidence that:
- 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.[3]
- The suprachiasmatic nucleus was found by Swaab and Hopffman to be larger in gay men than in non-gay men,[70] the suprachiasmatic nucleus is also known to be larger in men than in women.[71]
- The anterior commissure is larger in women than men and was reported to be larger in gay men than in non-gay men,[72] but a subsequent study found no such difference.[73]
- Gay men report, on an average, slightly longer and thicker penises than non-gay men.[74]:biggrin1:
- Gay men's brains respond differently to fluoxetine, a selective serotonin reuptake inhibitor.[75]
- 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).[76]
- The startle response (eyeblink following a loud sound) is similarly masculinized in lesbians and bisexual women.[77]
- Three regions of the brain (medial prefrontal cortex, left hippocampus, and right amygdala) are more active in gay men than non-gay men when exposed to sexually arousing material.[78]
- Gay and non-gay people emit different armpit odors.[79]
- Gay men are more likely to have a counter-clockwise hair whorl pattern.[80]
- 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).[81][82][83]
- Finger length ratios between the index and ring fingers may be different between non-gay and lesbian women.[84][85][76][86][87][88]
[edit] Cognitive differences in gay men and lesbians
Recent studies suggest the presence of subtle differences in the way gay people and non-gay people process certain kinds of information. Researchers have found that:
- Gay men and lesbians are significantly more likely to be left-handed or ambidextrous than are non-gay men and women;[89][90][91] Simon LeVay argues that because "[h]and preference is observable before birth[92]... [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.[3]
- Gay men[93] and lesbians are more verbally fluent than heterosexuals of the same sex[94][95][96] (but two studies did not find this result).[97][98]
- Gay men may receive higher scores than non-gay men on tests of object location memory (no difference was found between lesbians and non-gay women).[99]
[edit] Fraternal birth order
Main article: Fraternal birth order and sexual orientation
There is evidence from numerous studies that homosexual men tend to have more older brothers than do heterosexual men, known as the "fraternal birth order effect."
[100][101] One reported that each older brother increases the odds of being gay by 33%.
[102] The fraternal birth order effect is the strongest known predictor of sexual orientation.
[103] Interestingly, this relation seems to hold only for right-handed males.
[104][105] There has been no observed equivalent for women.
[106] Peter Bearman repeated the experiments, but found no correlation between older brothers and male homosexuality and questions the sampling methods used.
[107]
The effect has been found even in males not raised with their biological brothers, suggesting an in-utero environmental causation.
[103] To explain this finding, a maternal immune response has been hypothesized.
[101] Male fetuses produce H-Y antigens which may be involved in the sexual differentiation of vertebrates.
[101] Other studies have suggested the influence of birth order was not due to a biological, but a social process.
[108]
