[xdennis]

> Some even believe that there are only two genders!

i.e. almost everyone a few years ago. Worldwide, most people still don't think there can be more than two sexes.

[Natsu]

Sex and gender are different, though. Sexologist John Money came up with the idea of using the then purely grammatical term 'gender' to describe how people presented themselves.

So originally people's gender expression was more or less just advertising their sex roles for mating. Now it's more of a lifestyle/aesthetic thing with huge amounts of variation that aren't really anchored to biological sex in any meaningful way except insofar as they adopt the aesthetics of one of the biological sexes.