I dislike the term "gender" in linguistics. Many languages have grammatical gender that has nothing to do with masculine/feminine. "Noun class" gives the idea better. Noun classes in Indo-European and a couple other major language families happen to somewhat align with grammatical markers indicating animal/human sex. But it doesn't have to. Many languages make an animate/inanimate distinction. It is one of those myst…
I just looked up Danish - it used to have masculine, feminine and neuter, but masculine disappeared into feminine. The theory given here is that it was a consequence of bilinguals simplifying things:
https://dialekt.ku.dk/dialekter/dialekttraek/navneordenes_ko...
It wouldn't surprise me if modern English is a result of the same kind of multilingual simplification.