Innate Homosexualtiy: Fact or Fiction?

It is no secret that Alison Bechdel is a lesbian and her father is gay.  However, what I find the most intriguing is whether or not homosexuality was an innate aspect in their lives, or was it something that they learned about themselves along the way.  The text hints to both reasons.  Bechdel states, "In Cannes, I argued compellingly for the right to exchange my tank suit for a pair of shorts" (73).  It seems as though that Bechdel was aware of her masculine tendencies from a young age.  In fact, she even says that she noticed these homosexual feelings at the age of four or five when her and her father went into the diner and she saw a rather "butchy" looking female.  She had decided that this masculine image was what she felt defined her.  But can we say that she was born with this homosexual trait?  It is not scientifically proven that homosexuals possess a specific gene that straight people do not, or vise versa.  I would argue that the influences on Bechdel's life played an important role in her sexuality.  The more her father pushes her to be a "girl," the more she veers away towards a more masculine personality.  This persuasion of her father's could be a benefactor in her decision of homosexuality.  She may be unconsciously rebelling her father's wishes, or compensating for his lack of masculinity (i.e., because he was gay as well and possessed more feminine tendencies).  She states, "while I was trying to compensate for something unmanly in him . . . he was attempting to express something feminine through me" (98).  My Ultimate question, and potential paper topic, would be is homosexuality something people are born with, or born into?