The Victorian age then added humanity to nature and art as the subject-matter of literature. But it went further than that. For the first time since the Renaissance, came an era which was conscious of itself as an epoch in the history of mankind, and confident of its mission. The fifteenth and sixteenth centuries revolutionized cosmography, and altered the face of the physical world. The nineteenth century, by the discoveries of its men of science, and by the remarkable and rapid succession of inventions which revolutionized the outward face of life, made hardly less alteration in accepted ways of thinking. The evolutionary theory, which had been in the air since Goethe, and to which Darwin was able to give an incontrovertible basis of scientific fact, profoundly influenced man's attitude to nature and to religion. Physical as apart from natural science made scarcely less advance, and instead of a world created in some fixed moment of time, on which had been placed by some outward agency all the forms and shapes of nature that we know, came the conception of a planet congealing out of a nebula, and of some lower, simpler and primeval form of life multiplying and diversifying itself through succeeding stages of development to form both the animal and the vegetable world. This conception not only enormously excited and stimulated thought, but it gave thinkers a strange sense of confidence and certainty not possessed by the age before. Everything seemed plain to them; they were heirs of all the ages. Their doubts were as certain as their faith. "There lives more faith in honest doubt Believe me than in half the creeds." said Tennyson; "honest doubt," hugged with all the certainty of a revelation, is the creed of most of his philosophical poetry, and what is more to the point was the creed of the masses that were beginning to think for themselves, to whose awakening interest his work so strongly appealed. There were no doubt, literary side-currents. Disraeli survived to show that there were still young men who thought Byronically. Rossetti and his school held themselves proudly aloof from the rationalistic and scientific tendencies of the time, and found in the Middle ages, better understood than they had been either by Coleridge or Scott, a refuge from a time of factories and fact. The Oxford movement ministered to the same tendencies in religion and philosophy; but it is the scientific spirit, and all that the scientific spirit implied, its certain doubt, its care for minuteness, and truth of observation, its growing interest in social processes, and the conditions under which life is lived, that is the central fact in Victorian literature.