Yes this. We could lose the ability to speak words or understand the concept of a newspaper and everyone would still recognise everyone else's sex.
It's a pretty fundamental requirement for survival of the species. All mammals have two sexes, and for a lot of them ability to recognise sex is inbuilt - even across species. Many dogs, for example, recognise the sex of humans (some dogs don't like and recognise men, whatever their gender identity).
We'll lose the ability to speak before we lose the ability to recognise sex.