"There's no simple answer in human biology.."
Yes, there fuckin IS.
I make it a rule never to argue with someone who is crazy. The problem is, a crazy person invents his own logic or constructs his own system of deduction. consequently, a normal person using normal logic and facts can never convince a crazy person to agree with him.
This obvious male, convinced he is a female, cannot be convinced the world he lives in is his construct and not reality. Everyone else around already knows this. One day he might have an epiphany and change his mind but where he is right now is his reality is also his fantasy.