It has been scientifically documented, through both biology and psychology. Nature and nurture both have a role in determining whether one becomes homosexual. The exact debate is how much each one plays a role.
http://www.sciencedaily.com/releases/2008/06/080617151845.htm
http://allpsych.com/journal/homosexuality.html
There's no clear-cut theory to this or anything explaining whether babies can literally be BORN gay, but it is certain that it is a mix of biological and environmental factors.
I read both of those, and it was quite interesting. However, there were many more examples of biological relationships (physical similarities and differences in brains etc.) with homosexuality than psychological/sociocultural reasons. Also, I would say that the latter were not examples of "scientific documentations", rather they were theories without scientific evidence. I'm not dismissing anything, but scientifically speaking, judging from what you have provided, there are more reasons to believe that sexuality is a matter of nature.
Anyway, I don't see how this is proof that sexuality is a result of both nurture and nature.
xxpbdudexx said:Why would a man raised in a homosexual home NOT be more likely to be homosexual, and why would someone raised in a Christian home who view homosexuality as a sin NOT be heterosexual. Of course, it still does sometimes happen, and that discrepancy can be related to the biological factors of some people being born with more of a predisposition to become homosexual later in life than other.
Both of those could be accounted for the openness to (in the case of a child raised by same-sex parents (I'm assuming that's what you meant by "a homosexual home")) or rejection of (in the case of the other) homosexuality. A person raised in the latter may in fact be homosexual but would not express it, because s/he was taught it was a sin; likewise in the former, the person would be comfortable with expressing his/her homosexuality because s/he was (assumedly) taught that it is acceptable to do so. A person does not become homosexual when they express it.