AllPsych has an article on this topic of whether nature or nurture causes someone to be gay. Not clear if the article is by Ryan Johnson or Dr.Christopher Heffner. It is rather lengthy and at times a bit confusing . We will attempt to summarize here.
Originally the Amererican Psychological Association (APA) listed homosexuality as a mental disorder. The article makes the valid point that a lot is still not known and is poorly understood. In other words, there is no definitive answer yet.
Alfred Kinsey was one of the first to do some research. He found, not surprisingly, that how you worded questionnaires or surveys influenced the answer. After some tweaking, he found that 30% of males had taken part in a homosexual act leading to an orgasm at a minimum.
Karen Hooker selected gays and heterosexuals, matched by age, IQ and education. Then she did 3 different psychological tests on them and found no difference. Because of this the APA removed homosexuality as a disorder.
In 1975 a statement that homosexuality was not a mental disease was released. Finally, in 1994 it said homosexuality was not a mental illness or moral depravity. Instead, it was how some people express love and sexuality.
DF Swaab, in 1990, found differences in the hypothalamus between gays and straights. About the same time, Laura Allen found other differences in the hypothalamus between the two groups. In 1991, Simon LeVay also looked at the hypothalamus and found yet another difference and that gay men and women were similar and different from heterosexual men.
Another biological experiment was also interesting. The theory was that levels of neuroendocrines affected sexuality, particularly androgens. Female rats given high levels of androgens behaved like males and were attracted to females and tried to mount them. Male rats with restricted androgens were passive and would submit to other male rats.
J. Michael Bailey and Richard Pillard studied twins and homosexuality. 52% of monozygotic twins were both gay, 22% of dizygotic twins were both gay and 5 % of adopted brothers. (We wonder whether being twins would decrease the androgen available to each and therefore increase the likelihood of being gay.) Later studies found the same in women.
Dean Hamer researched whether gayness might be an X linked gene. He studied 40 gay men and found an amazing concordance in 5 areas of the Xq28 region of the X chromosome. The odds were 1/100,000. He postulated and found that there were many more gay men in the mother’s part of the family tree.
Sociobehaviorists don’t believe the biological argument. They say it depends on how the person is raised. In Crete and New Guinea all boys went through homosexual experiences as part of the culture. But in this case, you could say it was forced on them.
Psychoanalytic theories say it is due to parental and family dynamics. But you would think with the negativity around homosexuality, it would lead people to be heterosexual 100% of the time.
David Halperin and Jean Foucault are two main social theorists on the topic of homosexuality. He believes the reason is unresolved Oedipal issues. Discounted by the main psychological community he has believers in groups such as conservative Christians. Foucault says homosexuality was a rarity 100 years ago when it morphed from sodomy to a sort of interior androgyny.
Although these arguments don’t make much sense to us, there is still a lot to learn and it is possible there are impacts of both nature and nurture or environment.