We have reached the point where it can be seen that evolution, when elevated from a biological hypothesis into a theory of the universe, is in need of the theistic postulate in order to make it workable. Theism, in fact, offers a twofold advantage to the evolution theory. It satisfies the causal demand, and it furnishes the means of combining the two ideas of continuity and progress which have impressed themselves so deeply upon the mind of our generation. In the first place it satisfies the causal demand. If evolution is but the unfolding of the implicit, as the preformation view would have it, an explanation is naturally sought for the marvellous properties of the original star-dust, or mind-stuff, or the primordial living germ. The more mechanical the interpretation of the course of things becomes, the more insistent, again, will be the questions, Who made the mechanism? Who drives the mechanism? Even from the standpoint of epigenesis, the appearance of an entirely new element, which by hypothesis is not merely implicit in the previous state of things, must be referred to some adequate cause or ground. Evolution, in any of its forms, is the name of a method rather than of a cause; and "logic compels the evolutionist to assume a force that was not evolved, but which existed before evolution began."[86] 86: F. H. Headley, "Problems of Evolution," p. 155. If we interpret the power behind evolution in a theistic sense, and believe that God is immanent in nature and in the life of man, we are not absolved from the task of tracing as far as possible the natural history of life and mind, but we may view that history from a standpoint from which both origin and progressive development become intelligible. No scientific hypothesis is able in itself to carry us all the way from "concentrating nebulæ to the thoughts of poets." A theory of the universe which shall do justice to the conceptions both of continuity and progress can best be framed with the aid of the category of purpose. The continuity is preserved in the unity of the developing plan, no stage of which is sudden or abrupt, but is related "filially" to the stage and the stages which preceded. The relation between two stages is not like that between the two members of an equation, a relation of exact equivalence between the evolved and the involved. There is a really new element in the later stage if there is a real progress. But the new factor comes not in dramatic or spectacular fashion; it comes without observation, and comes not to destroy but to fulfill.