No one has a "choice".
It is all chemistry.
Depends on testosterone or estrogen.
Nothing else.
The only problem is the genitalia and mental gender orientation of puberty are 13 years apart, so can be not aligned.
Wait. Are we talking actual science? If we are, I'd like to make a comment:
It's not nature "versus" nurture, it's nature AND nurture.
You're talking about a developing brain. Which way that goes, is unquestionably influenced by nurture. The science is rock solid on this point.
I mean... how to say this... I'm looking for a way that won't trigger the liberals 'cause that's not my purpose... but I can't think of a way...
Remember BF Skinner and the blank slate? Well, it isn't quite a blank slate, it's a "programmed" blank slate. The etch-a-sketch has boundaries, right?
Even in a person with a hormonal predisposition, you can "force the brain to go the other way". You CAN make a normal person into a gay person, and vice versa - but only if you do it during what's called the "developmental critical period". I've done this with lab rats, myself personally.
There are two other scientific observations of relevance:
The first is, if you put enough rats into the same cage, more of them will turn gay. The "incidence of homosexuality" increases with the population density.
The other is, both homosexuality and gender dysphoria can occur spontaneously "late in life". Like, age 50. I know all kinds of people like that, they're married with three kids and suddenly when they're near retirement they decide they're gay and they want to go off and live with their boyfriend. Um... Bruce Jenner, trans at age 50, right?
So, our brains keep developing, throughout life. Most of us tend to be stable that way, but some of us aren't, we might go this way or that way at any given moment. My point being, this too is biological, it's not a random immoral whim necessarily.
Distinguishing these situations, really does take an expert. Something "more" than an MD probably, but "at least" an MD, a genuine psychiatrist, and one whose first inclination is NOT to prescribe drugs.
The idea that a teacher in an elementary school could identify "which child is a transgender candidate" is, frankly, ludicrous.
I'm very sorry, but none of these ignorant uncredentialed uneducated politicians are going to influence my child. EITHER way. My job is to protect my child from such predatory assholes. I don't care WHAT their reason is, if they had a bad day or got up on the wrong side of the bed, I don't care. They need to keep their grubby little paws OFF my child's developing brain.