What is your definition of nature? I believe you're calling nature "the wild" when in reality nature is the entire universe. If chimps starting cooking "in nature" as you would call it, would that be "unnatural?" Anything that happens in the universe is natural. Wild is the term that denotes the undomesticated, non-human part of nature that you're referring to. Nature is all that is, humans came from nature, they had to, everything did. You cannot remove yourself from nature anymore than you can remove yourself from it's laws such as gravity, chemical interaction laws, etc. Nature being used to refer to the wild is one of my pet peeves and the reason why we have isles of junk food labeled "all natural" in supermarkets.
I mean, you say chemical x is not natural, but where did it come from? Mined from the earth maybe, which is nature, mined by a vehicle that itself was mined from the earth and built with tools from the earth or sea or grown like trees for wood. And the lab it's synthesized in is all built from things taken from the wild, nature as you call it, and transformed by other things taken from the wild.
And I would say those who practice beastiality, it IS their nature. How can you NOT follow your nature? That's like not being yourself, no matter what you are, you are yourself. Anything you do IS by reflexive definition your nature, just like whatever you write is your literature and whatever you say is your speech.