The worst of it is that the idea of development, of evolution, is a perfectly sound and useful one in certain spheres of activity. In science, for instance, the idea works and is helpful. The successive modifications and improvements by which the latest type of steam-engine has been evolved from Stevenson’s “Puffing Billy,” or the latest type of air-ship from the Montgolfier balloon, form a series of steps which are related and connected with each other, and they are so intimately connected that the latest step sums up and supersedes all the others. No one would travel with Stevenson’s engine who could employ a British or American engine of the latest type. There we have a definite system of development--of growth, improvement, and increased proficiency. And we find the same thing if we look at science as a whole, as a body of knowledge of a special kind. Its problems are tied together, subordinated and co-ordinated, unified in one vast system, so that we can represent its history as a single line of progress or retreat. But art is not like science. Donatello’s sculpture is not a growth from the sculpture of Pheidias or Praxiteles in the same way that the London and North-Western engine is a growth from Stevenson’s model; nor was Raphael’s work developed from Giotto’s in the same way. Works of art are separate and independent things. That is why Donatello has not superseded Pheidias, nor Raphael Giotto; and that is why the world cherishes the earliest works of art quite as much as the later ones.