Many studies have been done, but there is no conclusive answer as to what turns people gay.  A variety of ideas have been presented, though.

 

1. A link between exposure to higher levels of androgens in utero and female homosexuality has been found[1].

2. The “Older Male Siblings Theory”

   1. This theory proposes that the mother’s body has an immune reaction to a male fetus growing inside her. In each additional male pregnancy that a woman has, the immune response grows stronger. This immune response may cause an increased chance of having a homosexual male child[1].

3. Master gene for homosexuality:

   1. Studies have shown a genetic link for homosexuality in fruit flies, but no such link has been seen in humans. Such a link may exist, but one has not yet been found[1].

4. Heritability

   1. Male homosexuality appears to be more heritable than female homosexuality[1].

5. Enlarged hypothalamuses

   1. Gay males have larger hypothalamuses than their straight counterparts. In fact, gay male hypothalamuses resemble and function similarly to female hypothalamuses. However, it is unknown if the enlarged hypothalamus leads to homosexuality or of homosexuality leads to larger hypothalamuses[1].

 

 

 

[1] Gazzaniga, Michael S., Todd F. Heatherton, and Diane F. Halpern. "People Differ in Sexual Orientations."Psychological Science. 5th ed. New York: W.W. Norton &, 2016. 443-45. Print.