Why was it necessary that fifty years should elapse before men could see what was evident? What had happened in these fifty years? The work of Wolff, dead and forgotten, can have had no influence whatever. The fact was merely that men saw _subsequently_ what it had been previously _impossible for them to see_. A kind of internal maturity must have come about in them, by virtue of which their spiritual eyes were opened, and they saw. When _those eyes were closed_, evidence was useless. Fifty years earlier, a direct attack would have spent itself on insuperable obstacles; but with the lapse of time the subject presented itself, and was simply and universally accepted, not only without a struggle, but without any excitement. This fact might be arguable in relation to the internal maturation of the masses; but it is beyond question in its relation to the individual. When an obvious truth cannot be seen, we must retire, and leave the individual to mature. A struggle "to bring about perception of evidence" would be bitter and exhausting. But when maturity comes, we shall find the seer filled with enthusiasm, and bearing fruit like the vines of the Land of Promise. When in 1859 Charles Darwin expounded the theory of evolution in his book, "The Origin of Species," he recognized the great influence it had had upon the thought of his day, for he wrote in his note-book: "My theory will lead to a philosophy." His conception of the struggle for life and of the natural selection of characteristics, so widely adopted by the thinkers of his day, popularized the principles of Lamarck as to the casual formation of new characteristics in a species by adaptation to environment; Darwin's conception carried these principles along with it--and almost fused them in its own content. These principles, excluding both creation and its finalities, implicitly denied the immortality of the soul. The effect of such a revolution may be imagined; for many centuries the soul had been the _object of life_, and when the fundamental faith of existence was shaken, the life of the conscience itself was convulsed. It may be supposed that there was an anxious search for contradictions in the destructive theory, if on no other grounds than that of the instinct to preserve ancient beliefs, which lies deeply rooted in the human race. But let us take into consideration the two revolutionary principles which so greatly impressed and fired the consciousness of the university students of several generations. One principle was: "There can be no function without an organ." The other principle which created much enthusiasm among studious youths was: "The function creates the organ." What! There is no function without an organ, nor can the function even _exist without_ the organ; and yet, on the other hand, the function without the organ can exist so vigorously as to _create_? No such glaring and tangible contradiction had ever existed in any theory.