In recent years, homosexuality has become more openly prevalent and accepted. From my own personal experiences I have come to realize that homosexuals are not just people a person reads about in the newspaper, but they are bosses, professors, friends, and family members. I have grown to respect them as individuals and not to see their homosexuality as the main characteristic of their identity but just another piece of who they are. However, given the increased number of homosexuals in my everyday life, I cannot help but wonder what makes these respected, successful individuals different from everyone else? How did they come to be attracted to the same sex? Were they born this way?
First off, research has shown that genetic factors largely influence sexuality and that sexuality is not a product of the environment. A scientist named John Money studied a child who lost his penis due to an improper circumcision at age 2, and recommended this child be raised as a girl. The child underwent surgery to obtain female sexual organs and then received hormonal treatments. However when this child was growing up, male typical behavior was exhibited even though the child did not know she was genetically a boy. At the age of 14 this child was told that what had happened to her and consequently rejected the female assignment. This person demanded surgery to transform back into a male and then eventually married (2). This is evidence that our gender is primarily influenced by genetics and is fixed at birth. We cannot manipulate gender by surgically, hormonally and socially manipulating people and it is important to establish that gender is not subject to environmental differences when studying sexual orientation. Now I can ask, what differentiates homosexuals from heterosexuals of the same gender?
Continuing on the investigative path of genetics and sexuality, studies have examined the concordance rate for twins and homosexuality and have found that the concordance rate for sexuality in both male in female twins who were monozygotic twins (who share the same genetic make up) was about three times greater than the concordance rate for dizygotic twins: 52% MZ, 22%DZ (1). This suggests a strong genetic influence in homosexuality. But sexual orientation cannot be completely influenced by genetics. Why is there not a 100% concordance rate for monozygotic twins? There has to be other factors, possibly the environment the fetus is in?
One approach taken to examine what other non genetic factors influence sexual orientation is to study the levels of extra cellular hormones circulating in the womb. Researchers have studied humans and other animals to evaluate if levels of testosterone circulating prenatally, affect sexual orientation of the fetus in adulthood.
An experiment that studied intrauterine position during fetal life in mice found that there were distinct differences in sexual behavior between females who were positioned between two males in the uterus (thus being exposed to more testosterone) and females who were in between other females. In adulthood, the female mice which were exposed to more testosterone prenatally were more prone to exhibit masculine sexual behavior such as mounting other females. Their sisters who were not exposed to extra testosterone, exhibited traditional female sexual behaviors such as lordosis and were more likely to be courted by male mice (7). Can we generalize this to humans?
There is a condition known as congenital adrenal hyperplasia (CAH) which exposes the human fetus to increased levels of testosterone in the womb. Research has shown that women with CAH were more prone to produce male typical behaviors as children, were significantly less satisfied with the female sex of assignment and were more likely to be bisexual or homosexual (3).
Also, Instead of exposing a fetus to more testosterone, studies exposing the fetus to less testosterone were conducted by inducing high levels of stress in pregnant female mice. It was found that when the fetus was a male, these males were unwilling to mount other females, and exhibited lordosis, a typical female sexual behavior (8).
This is evidence that shows gender is genetically fixed at birth and that prenatal hormones greatly influence sexuality in adulthood. It also seems that the affected fetus exhibits behaviors consistent with heterosexuals of the opposite gender as with the female mice in between two males in the uterus, human females with CAH and male mice exposed to less testosterone. That leads me to further question do homosexuals act more like the opposite heterosexual gender: are gay men similar to straight women or are they their own completely different gender?
There is scientific research which has implicated that homosexual males are neurologically similar to heterosexual females. One of the most prominent studies conducted by Simon LeVay compared the INAH-3 nucleus in the hypothalamus of presumed male homosexuals to presumed male and female heterosexuals. He found that on average, the male heterosexual INAH-3 nucleus was double the size of homosexual males and heterosexual females (4). Although the study had many potential limitations including that there was an assumption of people being homosexual because they had AIDS, the scientist was personally bias, and that AIDS could have caused this difference, similar implications were found in similar research conducted on rams and ewes. It was found that the sexual dimorphic nucleus (oSDN) in female oriented (heterosexual) rams was larger compared to the oSDN in male-oriented rams and also that the oSDN was similar in size in male-oriented rams and ewes (5).
Researchers have also found that the areas of the hypothalamus of homosexual men respond similar to brains of heterosexual women to the smell of testosterone derivatives. Maximal activation in homosexual men occurred in the anterior hypothalamus, an area highly involved in sexual behavior, which was similar to activation in heterosexual women. These same derivates when smelled by heterosexual men did not cause the same response, but what did cause the same activation in heterosexual men was the scent of estrogen like compounds. The developments of these olfactory areas are related to the hormones circulating prenatally (6).
This research has provided evidence that neural structures and neural activation can be correlated and might influence sexual orientation by illuminating differences in the brain between heterosexuals and homosexuals.
Like Pulitzer prize-winning science author Matt Ridley said, “Nobody in science now believes that sexual orientation is caused by events in adolescence.” From the research presented, there seems to be a clear summary of observations which include, hormones have major effects in sexual behavior and orientation, there are biological differences in the brain in people with different sexual preferences and that these biological differences suggest that homosexual males are similar to heterosexual females. I have found that a majority of the research has focused on homosexual males and think it would be interesting to compare and contrast these results by studying homosexual females in the future. This summary of observations allow me to hypothesize that sexuality is largely influenced by genetics and prenatal hormones and the sexuality of the fetus is most likely already determined at or around birth. However, my greatest ambitions are for me to be proven wrong in that someone else has developed insights on how to be less wrong in the future.
1. Bailey, J.M. & Pillard, R.C. (1991) A genetic study of male sexual orientation. Archives of General Psychiatry, 48, 1089-1096.
2. Hendricks, M. Into the Hands of Babes. (2000, September). John Hopkins Magazine. http://www.jhu.edu/~jhumag/0900web/
3. Hines, M., Brook, C., & Conway, G.S. (2004) Androgen and psychosexual development: core gender identity, sexual orientation and recalled childhood gender role behavior in women and men with congenital adrenal hyperplasia (CAH). Journal of Sex Research. 41, 75-81.
4. LeVay, S. (1991) A difference in hypothalamic structure between heterosexual and homosexual men. Science, 253, 1034-1037.
5. Roselli, C.E., Larkin, K., Schurnk, J.M., & Stormshak, F. (2004) Sexual partner preference, hypothalamic morphology and aromatase in rams. Physiology & Behavior, 83, 233-245.
6. Savic, I., Berglund, H., & Lindstrom, P. (2005) Brain response to putative pheromones in homosexual men. Proc Natl Acad USA., 102, 7356-7361.
7. vom Saal, F.S. (1989) Sexual differentiation in litter-bearing mammals: influence of sex of adjacent fetuses in utero. Journal of Animal Science, 67, 1824-40.
8. Ward, I.L. (1972) Prenatal stress feminizes and demasculinizes the behavior of males. Science, 175, 82-84.