Q-Continuum-kin

Gender was introduced about the 1970s to represent the social construct of the sex based caste system. In the 80s "gender bending" fashion became popular where men and women rebelled against strict gender roles but there was no confusion the men in belly shirts were still men and women wearing angular shoulder pads were still women. In the 90s grunge became a thing and people dumped the elaborate clothing. Men and women were basically wearing the same outfits. No one really used the word "gender" except in academia. In the 00s people were starting to incorrectly use the word "gender" as a more polite way to say "sex" but were often corrected by others from academia and transgender people at the time would say "no gender is a social construct" because they actually understood the academic writings behind it. 3rd wave feminism is brewing where people are putting into writing about how every type of oppression links to every other type. By the 10s gays had become normalized and gay marriage legalized. All those giant gay rights organizations were desperate to stay in business so they shifted over to "trans rights" and needed to come up with some new catch phrases. Tumblr exists where teenagers make really bad takes on academic writings.

This is about the time the public is fully confusing the word "gender" and now transgender people have flipped 180 on that definition. Now instead of correcting people they are now saying the terms "man and woman" are the social constructs and therefore detached from "sex" which was still generally accepted as biological. I think that puts the pin in your timeline. I think the "TWAW" thing is some sloganeering from the newly refocused gay trans rights groups.

More recently in the now 20s they have been saying some more crazy shit that sex itself is the social construct and the only "real" thing is their "gender identity".

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I don't think it's so much a memo went out as much as the slogans reinforce the clusterB delusions so they feed off each other.