Modern Science has investigated a phenomena that has existed since before Jesus was born, in which people would not identify with the gender and body with which they were born.
In some societies they were called two spirited, and were shamans and holy people, in others they were a recognised third gender and appeared in the original creation myth. In Rome there were the Cybelle where transgendered women would have primative surgery and serve as priestesses to their Goddess….
What modern science first learned was that people who suffered from Body/Brain gender disconnect, known as Gender Identity Disorder could be helped by hormones, and then by gender conforming surgery.
Then when we started examining the brains of deceased transgendered individuals we found brain structures identical to those found in their identified gender (i.e. female for mtf).
Finally when our brain imaging technology finally caught up, we were able to example the living brains of pre-hormonal therapy transgender people and find absolute and irrefutable proof that their brains are structured like the brains of their identified gender even with no hormone therapy.
That is what modern science has taught us.