Why did the stegosaurus have plates, or is biology second-rate because it thinks in therms of ends?

There is something distinctively different about explanation in the biological sciences, as opposed to explanation in the physical sciences. In the former one has functional arguments, arguments making reference to what Aristotle called “final causes.” As in: “The function of the plates on the back of the Stegosaurus was to keep the body at a constant temperature.” Since the Scientific Revolution, such explanations have been forbidden in the physical sciences. Does this then mean that biology is second rate, as is suggested by many including Immanuel Kant? It is argued that the Darwinian mechanism of natural selection explains why there is need of functional explanation in biology and that once this point is grasped, there is no reason to judge biology second rate.