Originally posted by dsmtuner1
Now the last sentence: Don't tell me people who are gay don't choose to be. My dad and mom were married 25 years, before my dad walked out and went into a life of homosexuality. I still talk to my DAD sometimes and know his views on it.

Simon LeVay explains the basics of this theory:

In experimental animals it’s been well established that the sexual differentiation of the body and brain results primarily from the influence of sex hormones secreted by the testes or ovaries (Arnold 2002). Males have high levels of testosterone in fetal life (after functional development of the testes) and around the time of birth, as well as at and after puberty. Females have low levels of all sex hormones in fetal life, and high levels of estrogens and progestagens starting at puberty. High prenatal testosterone levels organize the brain in a male-specific fashion; low levels testosterone permits it to organize in a female-specific fashion. Hormones at puberty activate the circuits laid down in prenatal life but do not fundamentally change them. Thus, the range of sexual behaviors that adult animals can show is determined in large part by their prenatal/perinatal hormone exposure—manipulating these hormone levels can lead to atypical sex behavior or preference for same-sex sex partners as well as a range of other gender-atypical characteristics.<79>

Originally posted by American Psychological Association
Is Sexual Orientation a Choice?

No, human beings can not choose to be either gay or straight. Sexual orientation emerges for most people in early adolescence without any prior sexual experience. Although we can choose whether to act on our feelings, psychologists do not consider sexual orientation to be a conscious choice that can be voluntarily changed.