It was during these two centuries of progress that the basis of our modern methods of evolutionary investigation was laid. Oddly enough, this was done, not by the naturalists of the time, but by the natural philosophers, such as Bacon and Leibnitz. They found their source of inspiration in the Greek literature, especially the writings of Aristotle, incorporating material offered by the leading naturalists of their times. Probably their biggest contribution was in giving a proper direction to evolutionary research; they saw clearly that the important thing was not what had taken place among animals, but what changes and variations were going on under the very eyes of the investigators. By establishing the fact that evolution was nothing more than individual variations on a stupendously large scale, they brought variation into prominence and laid the foundation for Darwin’s final triumph. The second great achievement of the philosophers was their proof of the principle of natural causation. From Bacon, the earliest, to Kant, one of the last of these workers, this principle was the object of continued study and enthusiasm. Each of them believed that the world, and in fact, the universe was governed by natural causes instead of by the constant interference of a man-like Creator. Of course, this attitude was hailed as the rankest heterodoxy, and was under the ban of the church. Nevertheless, it prevailed, and has stood as a pillar of all natural philosophy of the present day. Francis Bacon (1561-1626) was the first of the natural philosophers of later-day Europe. He was familiar with the Greek science, but revolted strongly against the authority given it. So radical was his attitude that he went to wholly unjustifiable lengths in attacking the Greeks, calling them “children ... prone to talking and incapable of generation.” This enmity may partly explain Bacon’s failure to put into practice the excellent ideas which he voiced in his epigrams, maxims, and aphorisms. He did, it is true, suggest the means whereby the natural causes of which he wrote might be discovered, but he did little investigation himself. Bacon was too near the reactionarism of the middle ages to consistently practice the inductive method of study, and as a result his work was not of lasting value.