When Darwin saw animal breeders selecting certain desired characteristics in animals to be bred, he assumed this is what nature did. Nature selected characteristics that would result in a fitter animal. Here Darwin is re-ifying nature. That is, he is attributing being to nature which is just an expression. Third, you could just as well say that y evolved from x, i.e., chimps evolved from humans.
Many evolutionists commit the fallacy of ignoratio elenchi.
Evolution is true because Special Creation is refuted. I have heard evolutionists admit that they believe in evolution because the only alternative, creationism, is preposterous. Explanation must not be confused with refutation. You never establish one position by refuting another. E. Evolutionists often commit the fallacy of scientism or reductionism, i.e., what the net does not catch ain't fish.