@afewbugs one of my favourite mind-blowing things about sexual diversity in biology is that not only are "male" and "female" not a simple binary, sex itself exists on a continuum: there are intermediaries between "this species [or even individual] has sexes" and "this species/individual doesn't". See e. g. bacterial fertility-inhibiting factors that control conjugation; which is all sex really is when you get down to it, a factor that limits which individuals can exchange genes with each other.