“ One common response is to say something like, “I was born with a female brain despite having a male body.” Many times, this is a purposeful oversimplification on the trans person’s part — an attempt to distill down the complexities of the transgender experience into a sound-bite that the average cisgender person can comprehend.”
And many times, this is not an oversimplification, but exactly what has happened. There’s plenty of research in animals showing that male brain development is driven by the action of testosterone, and that if that hormone isn’t produced in sufficient amounts during the critical period in prenatal development when sex differences in the brain arise, the result is a male with a female brain and female behaviour (and conversely, administering external testosterone during this critical period can produce females with male brains).
I suspect one reason this fact of nature tends to be left out of the transgender debate, is because the pharmaceutical industry and doctors have, over the years, administered treatments containing high doses of artificial female hormones to literally millions of pregnant women, in an attempt to prevent miscarriages and premature births. In adult men, the same hormones used in these treatments act as chemical castration agents — they shut down testicular testosterone production. If they have the same effect on unborn babies (and why wouldn’t they?), then, in theory at least, use of these drugs could be producing male babies with female brains. An unknown but potentially quite large quantity of synthetic hormones derived from testosterone were also used, but have since been withdrawn because they turned out to cause male development in female fetuses.