Why are some people straight and others are not?

Why are some people attracted to the same sex and others are not? Do you think sexual orientation is determined by our innate biology, social conditioning, cultural influences, or a combination of these things?

From my understanding of human sexuality and the Nature vs Nurture debate, as with all of personal traits and characteristics of human beings, I think we all have biological predispositions that may be more likely to be experienced based on certain environmental factors.

I always used to think my sexuality was 100% set in stone from the day I was conceived, but as I have grown older I realize my attraction and preference for women goes much deeper than a basic biological attraction. They’re are also cultural and sociological reasons as to why being with men is unappealing to me and for why I find masculine women attractive.

What are your thoughts, opinions, and experiences with this?