The word "gender" comes from the Proto Indo European root "gene", which is believed to have meant "concerned with reproduction". This has filtered down into the English words "progenation" (the act of having children), "genus" (biological "family"), "generation", and of course "gene" and "genome".
The word "sex" comes from the Latin (sexus), and was probably introduced into Old English around the time of the conversion to Christianity. By contrast the word "gender" was brought by the Normans. As is common with the merger of Old English and Norman French, the word with the Norman root ("gender") became more highbrow and connected purely to the scientific distinction between men and women, and the Old English "sex" continued to mean the more "common" act of intercourse as well as being a synonym for "gender".
The same thing happened with other pairings of synonyms: most "utility" (in day to day usage) words continued to be Old English, whereas the more "highbrow" (intellectual) words used by the educated or well-spoken were French. An example of this is the synonym pair "weird" and "perverse". The Old English adjective "weird" originally meant "having the power to shape destiny" in a Norse Shamanic sense, but became pejorative with the advent of Christianity when such practices were outlawed. The French adjective "perverse" came directly with the Normans, and originally meant "wicked". The "utility word" weird can be used in many contexts, and the word "perverse" only in a context where something is considered unnatural, not merely odd. Yet where the words overlap they are synonyms, much in the same way as "gender" and "sex".
Having now established the linguistic precedent for such Anglo-French synonym pairs, with one having a wider range of meaning to the other, we move on to the point that gender is different from sex. There is no linguistic evidence to suggest that the meaning of this word has evolved organically, as it would have over several hundred years, because the perceived difference between the two nouns was not apparent until the 1970s in certain extreme left circles, and the 2010s when it was brought into popular discourse by transgender activists.
Therefore we can conclude that the alleged shift in meaning in the word "gender" was introduced to the population by design and from a biased political source with the aim of achieving a political goal (that of the acceptance of multiple genders, in direct contrast Post too long. Click here to view the full text.