My response to the "what causes this?" question is always the same: I don't care.

It doesn't matter to me whether this is a genetic condition, a hormonal imbalance in the womb, a psychological thing, or even an "unconscious decision" that I made.

My identity is still valid.

I don't know if there's proof, and like valenstein, I'm not sure I want proof. I know who I am, and that's good enough for me.