of light and colour tells on the colouring of animals, and impartially protects them when they are preyed upon, or helps them to secure their prey; and this influence is frequently explainable by chemical or electric agencies originating in the environment of the animal, acting on the blood, and thus influencing pigmentation of the skin,[85] but chemistry is helpless to account for the manner in which nature shapes the contour of the wing of a tropical butterfly and paints upon it the veinings of a leaf, or protects a harmless fly by giving it a resemblance to a stinging one, or protects a caterpillar by making it look like a vicious and dangerous reptile. Yet all these protective arrangements are evidently, at bottom, facts of the same order. Protoplasm lives and responds not only discretely in the lowest unit perceptible by the microscope, but collectively in the connected groups of these units called multicellular organisms, and in the disconnected groups of these organisms called species. It really responds not to the exercise of function or to the play of physical forces, but to vital tendencies of the organism. There seems an expansive force in nature which, though working strictly under the dominion of physical laws, is capable of using the combinations brought about by those laws for the preservation and development of life. It is in love with life, it is ever pressing toward action and self-realization, and all roads are one to it if they lead to that end. In it are included the very chemical and physical agencies which it obeys, and also that something beyond which eludes the analysis of the laboratory. How it acts, under what conditions, what limitations, why here in one way, there in another, are questions of profound interest, the fringe of which philosophy has hardly begun to touch. Nor is philosophy yet in a position to do more, for the scientific conception of nature is but a recent birth of thought; much remains to do in the collection and organization of the facts with which the framework must be filled in, and a philosophy which does not keep closely in touch with scientific fact can have no message for the modern world. But it does seem possible to discern, and it shall now be our endeavour to set forth, in broad outline, certain principles of deep significance from which we may obtain an answer to the question: What can we learn from the physical universe that has a bearing on the spiritual life of man? CHAPTER VI THE DIRECTIVE THEORY OF EVOLUTION “Who is there that cannot distinguish between the actual cause of a thing and that without which the cause could never be a cause?”—Plato, Phædo.