During the years when Darwin was patiently elaborating the theory of “descent with modification” which was destined within his own lifetime to bring about a revolutionary transformation in the philosophy of nature, Huxley did much to organize the science of Biology as a definite branch of natural history. His great energy and industry, his passion for exact knowledge and his genius for clear and comprehensive statement made him one of the outstanding scientists of England. As professor of Natural History at the Royal School of Mines, and later in the Royal College of Surgeons, and as publicist and member of numerous commissions on science and education, he was in a position to throw a tremendous weight of influence to the support of his convictions, should he be drawn into a scientific controversy. When in 1859 Darwin published the “Origin of Species,” Huxley was one of the small group of eminent scientists whose favorable judgment Darwin felt would be necessary if the theory of natural selection were to command the attention of the scientific world. Darwin did not invent the doctrine of evolution. This idea had from time to time suggested itself to men’s minds whenever a naturalistic account of creation was attempted. The increase of knowledge of comparative anatomy, of geology and of zoölogy, and the discovery of certain structural likenesses and differences among both living organisms and the fossil remains which were found in the several layers of the earth’s surface, could not fail to suggest to many minds the thought that perhaps all forms of life might be related in one comprehensive evolutionary process. Although the evidence against the dogma of special creation was rapidly accumulating, no valid explanation had been found. Lamarcks’ theory that the structural modifications which characterize the various species of organisms were the result of effort and use and of special energizing and development of various organs, was under discussion. The theory did not, however, interest Huxley, because it implied that modifications which occurred as a result of effort and use could be inherited, a belief for which there was not sufficient evidence. Darwin’s book put the whole problem in a new light, and stated the hypotheses of organic evolution as an alternative to “special creation” in terms which were comprehensible to a mind trained in natural science. Heretofore a mysterious principle of development had been substituted for a miracle of creation. Darwin did not invoke any such principle but with good scientific logic sought his explanation of the origin of species in the casual connections among observable facts.