It's not a belief, it's a conclusion based on evidence.
A basic summary of the available evidence is available: The Biological Basis of Gender Incongruence
It's also rather telling you seem to be hung up on male to female transitions.
Oh look, So's Law (no internet points for you today).
No, that's not what I'm saying at all.
I'm saying the evidence from studies of transgender individuals, along with twins studies, shows there is at least a partial biological basis for the phenomenon of gender identity and sex presentation not being aligned. And, I'm saying that this biological basis is due a complex array of causes (some genetic/epigenetic, some to do with brain structures and likely some to do with hormone receptor activity), which we don't have close to a full understanding of yet.
But, you do you champ. Keep up the pater. That's some might fine nonsense you got goin there.
I'm old enough to remember eerily similar moral panics occurring during the 1980s and 1990s. Old enough to ensure that my school age children aren't being spoon fed religiously inspired bigotry like I was. Old enough that I was arguing online about these same things in the early 2000s. Old enough that I'm angry how little the needle has been moved on this in my lifetime.
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