Except that there is no such scientific proof. The few studies that have been done have been of adults, many of whom had already “transitioned” and/or taken hormones (so causality cannot be inferred). And those few studies have been refuted.
In order to prove being transgender is innate, researchers would have to do brain scans of a huge number of newborn babies who had had zero life experience outside the womb. Then those babies would have to be left alone, allowed to grow up with no one telling them they are the opposite sex (since experience molds kids’ brains). The people would have to be followed into adulthood, and then the scans from infancy compared. There would have to be some indication that the babies’ brains differed as indicated by their declared identity as adults. You’d also have to have a large control group of babies who grew up not thinking they were the opposite sex, and find a brain region that strongly correlated “felt” gender with actual sex in the two groups.
No such research has been done. No one is recruiting babies for such studies. In fact, the research that has been done shows that the vast majority (75% or more) of gender dysphoric kids outgrow the feeling of being the opposite sex and grow up to be gay or lesbian.
The study they’re referring to is Zhou et al., which used the brains of a handful of post-mortem long term transitioners–none of whom had been on hormones for LESS than five years, and many who had been on them for over a quarter century.
Since hormones affect the brain, it’s probable that these post-mortem findings were simply the result of these pre-mortem hormones, and not an innate aspect of the brain.
In fact, as recently as two or three weeks ago, scientists in Nature and a couple other academic journals were talking about the fact that, after making a neurological map of male and female brains in situ via MRIs, they determined that the ONLY difference in male and female brains at the outset is a difference in size, and THAT can be directly attributed to the volume of the cranial cavity and nothing else.
ALL subsequent brain sex theories use Zhou, so they’re all bunk too
Science requires that the theory be thrown out when data disprove it. Belief systems, OTOH, retain the theory and ignore the disproving data.