@ghost_bird yes, so it’s a bit complicated! in the 18th and 19th century, a major goal of science was essentially, like you say, positioning white people (and particularly white men) as “most/highest evolved”, in order to justify their continued colonialism of other peoples and lands; consequently, it was necessary to figure other bodies as lacking or less‐developed in various ways.

HOWEVER, with respect to gender and sexuality in particular, this required a denial of sorts, since scientists of this time included the gender binary as a marker of being “well‐evolved”. this resulted in a fundamental assumption that any gender variance within white people was a result of degeneracy “from the outside” and not endemic to white people themselves. so you would have queerness frequently being racialized as other, and consequently outside of the scope of white medicine.

this didn’t REALLY start to change until around the turn of the 20th century, when scientists started refiguring queerness in terms of mental illness, and importantly, a mental illness which it might be possible to “cure”—the white queer no longer was someone outside the scope of white medicine, but rather someone who it might be possible to “recondition” for participation in productive white society. AT THIS TIME, gender and sexuality were still largely conflated, and one theory was that homosexuality was the result of a sexual “inversion”, which we might think of as transness.

gender and sexuality wouldn’t really be split in a medical sense for another half‐century, when white gay men… basically threw trans people under the bus by saying “sexuality is a personal choice unrelated to gender; we are perfectly capable of upholding normative masculine gender norms and being a part of productive (white) male society”. by splitting up gender and sexuality, white gay men were able to align themselves with the white cis male norm and code themselves as productive and healthy (unlike transsexuals, who were still pathologized/Other). this culminated in homosexuality being removed from, for example, the DSM, in the 70s.

so this is why “mid twentieth century” is the date cited here. prior to that point, gender and sexuality were not distinct concepts, and they were only recently considered within the scope of white medicine AT ALL. but that all derives from the same notions of medicine you discuss as happening in centuries prior.

as for my initial critique, many of these changes (the splitting of gender and sexuality; the splitting of gender and sex—these are two VERY DIFFERENT models of gender btw) were the direct result of agitations BY AND WITHIN gay male (in the former case) or feminist (in the latter case) theorists/activists/people. so treating them as independent inventions of science feels, to me, to be disguising their real roots.

(for more on this subject, I would recommend the book “Imagining Transgender” by David Valentine.)