so, what causes all of these things like asexuality and transexuality?

it's randomness. chance. error.

accepting that what our dna does is turn us into smart machines that can be more efficiently programmed by the environment essentially puts us at the whim of the universe, itself. as individuals, we're just the sum of our experiences.

so, there isn't a normal sexuality or a normal gender expression, relative to our dna. this arises solely and exclusively through the "machine learning" we go through as we actually exist. if heterosexuality is more common than homosexuality, it is only as a reflection of the dominant society. if we decided that homosexuality was normal, then we'd all be programmed that way by society, and we'd all grow up gay.

so, i'm essentially taking a tabula rasa position on this. 

and, what it means is that things like historical statistics are kind of meaningless, because the assumption should be variation rather than stasis.