Recall what Thomas wrote in passing regarding the emergence of new things: Species, also, that are new, if any such appear, existed beforehand in various active powers; so that animals, and perhaps even new species of animals, are produced by putrefaction by the power which the stars and elements received at the beginning.(Summa theologica, Part I Q73 A1 reply3) His point was, following Augustine, that God had endowed matter with natures capable of acting directly, and so new things could arise from the natural powers created in the beginning. He was wrong about the "putrefaction," but "mutation" is surely another form of corruption, and "the stars and elements" will do for "material bodies."
-Mike Flynn