It’s worth thinking about, though, that many (possibly most) trans people, before HRT, are observed to have hormone levels like testosterone and estrogen consistent with normal levels for most members of their birth sex. Trans people largely agree that whatever it is that causes their innate sense of gender, it is very likely not down to either socialization or hormones — or at least not down to postnatal or pubertal hormone levels. Exposure to intrauterine hormones that affect fetal brain development are being looked at, but experts don’t have anything like enough knowledge to make conclusions about causation.