[elhudy]

We do have adjectives to distinguish things that other animals do. When a baby sucks on a teat it is mammalian. When turtle dives underwater then comes out on land to bathe, it is amphibious. When something takes flight it is avian.

Humans are unequivocally more advanced than other animals, so to represent those actions which wouldn't otherwise occur without human presence, we use the term "unnatural". It's a nice adjective - albeit in the context of transgender modification "unnatural" serves no scientific basis, it is just a descriptor, if that's what you're getting at.