Well I think we should caveat this as “in humans there is a tendency for sex to fall under two large umbrellas of typical characteristics” as there’s millions of small caveats for many mammals (its speculated parthenogenesis could naturally occur in humans under certain conditions).
Because of how early some features tend to develop in mammals there’s less variation than in other types of animals.
Outside mammals: Amphibians, Reptiles and Birds have many species that can change sex.
Outside animals: Plants and fungi are an absolute mess.
Well I think we should caveat this as “in humans there is a tendency for sex to fall under two large umbrellas of typical characteristics” as there’s millions of small caveats for many mammals (its speculated parthenogenesis could naturally occur in humans under certain conditions).
Because of how early some features tend to develop in mammals there’s less variation than in other types of animals.
Outside mammals: Amphibians, Reptiles and Birds have many species that can change sex.
Outside animals: Plants and fungi are an absolute mess.