@pie @druid they're essential because it's a very basic dichotomy in order to reproduce and protect offspring, and perform other extremely basic roles such as making sure your mate doesn't get killed
These are the basic building blocks of all life, gender binary and sexual dimorphism evolved so that species can have separate roles and abilities while still continuing the same species
The evolution of sex and the different roles they form is why you are even around to have a discussion where you equate self expression to gender theory (for whatever insane reason)