Some years ago I read about a male pastor who was kicked out of his denomination because it came out that he sometimes wanted to identify as a woman. Most of the time he was fine with presenting himself as a man, but some of the time he wanted to present as a woman and even chose a female name for that part of himself.
His church freaked out, of course, and gave him the ax. Yet there was a reasonable explanation for this pastor's behavior. Before he was born, when he was still in his mother's womb, he had a fraternal twin sister. Instead of separating and becoming another person, she somehow ended up fusing back with him so that the two of them formed a single person. As a result he was, in his biological make up, 70% male and 30% female. There is even a term for someone who is has two different sets of DNA as a result of absorbing a fraternal twin back into their body in utero: human chimera.
In the current debate over transgender people, many Christians are saying that it is just plain common sense that if someone is biologically male then he should view himself as male, and if someone is biologically female then she should see herself as female. Period. With no room for debate. If this were an ideal, unfallen world prior to Genesis chapter 3, I would heartily agree. But here and now, living in this messy, fallen state of humankind, it is not so. Instead we have this case of a pastor who was biologically both male and female. If biology directly determines one's personal sense of gender self-identity, then this pastor was being true to that principle. Even the proportion of time he wanted to spend as male versus female was true to the proportion that he was biologically male versus female.
Yet the reason this pastor was run out of his denomination was that he looked physically male and therefore he was expected to act and identify as such exclusively. The basis for his wanting to identify partly as female was hidden from the human eye, and yet it was very real. It could even have been scientifically proven through genetic testing.
In the case of transgender individuals, just because the basis for their desire to identify with a gender opposite of their (apparent) biological sex is hidden from our eyes, that doesn't mean it isn't real. Are we really so arrogant that we can dismiss this crisis of identity that they feel, as if we know everything there is to know about human beings, our mysterious formation in the womb, the human brain, genetics, and the origins of gender identity? The discovery that human chimeras exist is a relatively recent one. Who knows what else there is to discover about ourselves as human beings?
Here's something else to consider. Why do Christians need to know if there is a scientific explanation for the transgender experience before we stop our mistreatment of them: this merciless sneering and mocking and condemning of people whom we have made zero effort to understand? I thought the Bible was the basis of everything we do. We already know that Jesus commanded us to love people and refrain from judging them, because after all we do not see the heart and have no idea what sort of challenges they may be facing.
Of course, we can always wait around for science to uncover the reasons for the transgender experience--someday--before we feel like taking seriously Jesus' command to love these people. It's just that, given the way we normally scorn modern science almost as much as we do transgender people, I think that would be extremely ironic.