Darwin, although an excellent and self-confident scientist, was modest, retiring, and greatly hampered by ill-health contracted during his “Beagle” voyage. He was forced to leave the work of publicly defending his theories to other men, the most noted of whom was Thomas Henry Huxley, the “Bulldog of Evolution.” Huxley was an accomplished scientist, a powerful speaker, and one of the finest of European writers of science for the every-day man. He wrote, taught, and lectured in defense of the evolution theory; after a long, hard day at the university, he would spend the evening lecturing before crowds of workingmen from London’s factories, telling them how one species came from another, and how a single-celled creature developed into a complex animal with hundreds of millions of cells in its body, at the same time reconstructing during its growth the entire evolutionary history of its kind. It was largely because of the lectures and magazine articles of this tireless scientist, who believed in the truth of evolution, and enjoyed the task of fighting for his beliefs, that Darwin achieved so early an almost complete victory over the scientists who opposed him. Of course, the triumph was not all-embracing; there are still a few people who follow the natural sciences and yet refuse to believe that one species can arise, either by natural selection or by some other means, from another species without the interference of a deity. And the public at large, particularly that portion of it which lives far away from museums, zoological gardens, and centers where illustrated talks on natural science are regularly given, still believes in the theory of special creation. But that belief neither signifies defeat for Darwin and his followers, nor casts doubt upon the essential truth of their ideas; it simply means that the theory of evolution is still relatively young, and that popular education is in its infancy. CHAPTER VI. THE POST-DARWINIANS: DEVRIES AND THE MUTATION THEORY. The period between 1860 and 1900 was occupied largely by elaborations of the Darwinian conception of evolution, and arguments as to whether or not organic descent was a fact. In those four decades there were many famous workers--Alfred Russell Wallace, co-discoverer with Darwin of the theory of selection; Weismann and Haeckel, Germany’s great evolutionists; the philosopher, Spencer; Cope, the American paleontologist, and Huxley, the English champion of scientific rationalism--these, and a host of others spent their lives in demonstrating the workings of evolution. But unfortunately, the opposition which they encountered forced them to write and work largely along lines of argument and thus much of their work was fruitless so far as the discovery of new principles is concerned.