Here's a long and fascinating article about the biology of sexual orientation that explores many of the potential issues: genetics, in utero factors such as hormones, and post-natal experiences and influences. It's a great overview of the topic, and it's presented without much of an agenda. The author, Neil Swidey, even goes out of his way to point out that most religious conservatives object to homosexual behavior and recognize that sexual orientation is not really a choice. As I've written before, it doesn't matter whether or not homosexuality is a choice; no one can be blamed for the temptations they face, only for giving into them. The same goes for heterosexuals who have sex outside of marriage.