Close on the heels of the study of human anatomy was the study of the rest of the living world.  Needed to improve both domesticated animals and plants, farmers and hunters found it useful to learn as much as possible about their subjects.  Later, the study of animals was used as an alternative to studying humans directly; a practice not ended until the early 22nd century.  With the eventual discoveries of Darwin and Mendel, it was found that as a part of the natural scheme of things, humankind was ever more reliant on a careful study of Biology.