Darwin himself early perceived that his doctrine, if true, must apply to man--in so far, at least, as his bodily frame is concerned. Man is in this an animal, and closely related to other animals. To have claimed for him a distinct origin would have altogether discredited the theory, though it might be admitted that, man having appeared, his free volition and his moral and social instincts would at once profoundly modify the course of the evolution. On the other hand, the gulf which separates the reason and the conscience of man from instinct and the animal intelligence of lower creatures opposed an almost impassable barrier to the union of man with lower animals; and the attempt to bridge this gulf threatened to bring the theory into a deadly struggle with the moral, social, and religious instincts of mankind. In face of this difficulty, Darwin and most of his followers adopted the more daring course of maintaining the evolution of the whole man from lower forms, and thereby entered into a warfare, which still rages, with psychology, ethics, philology, and theology.
It is easy for shallow evolutionists unaware of the tendencies of their doctrine, or for latitudinarian churchmen careless as to the maintenance of truth if only outward forms are preserved and comprehension secured, to overlook or make light of these antagonisms, but science and common sense alike demand a severe adherence to truth. It becomes, therefore, very important to ascertain to what extent we are justified in adopting the agnostic evolution in its relation to life and man on scientific grounds. Perhaps this may best be done by reviewing the argument of Haeckel in his work on the evolution of man--one of the ablest, and at the same time most thorough, expositions of monistic evolution as applied to lower animals and to men.
Ernst Haeckel is an eminent comparative anatomist and physiologist, who has earned a wide and deserved reputation by his able and laborious studies of the calcareous sponges, the radiolarians, and other low forms of life. In his work on _The Evolution of Man_ he applies this knowledge to the solution of the problem of the origin of humanity, and sets himself not only to illustrate, but to "prove," the descent of our species from the simplest animal types, and even to overwhelm with scorn every other explanation of the appearance of man except that of spontaneous evolution. He is not merely an evolutionist, but what he terms a "monist," and the monistic philosophy, as defined by him, includes certain negations and certain positive principles of a most comprehensive and important character. It implies the denial of all spiritual or immaterial existence. Man is to the monist merely a physiological machine, and nature is only a greater self-existing and spontaneously-moving aggregate of forces. Monism can thus altogether dispense with a Creative Will as originating nature, and adopts the other alternative of self-existence or causelessness for the universe and all its phenomena. Again, the monistic doctrine necessarily implies that man, the animal, the plant, and the mineral are only successive stages of the evolution of the same primordial matter, constituting thus a connected chain of being, all the parts of which sprang spontaneously from each other. Lastly, as the admixture of primitive matter and force would itself be a sort of dualism, Haeckel regards these as ultimately one, and apparently resolves the origin of the universe into the operation of a self-existing energy having in itself the potency of all things. After all, this may be said to be an approximation to the idea of a Creator, but not a living and willing Creator. Monism is thus not identical with pantheism, but is rather a sort of atheistic monotheism, if such a thing is imaginable; and vindicates the assertion attributed to a late lamented physical philosopher--that he had found no atheistic philosophy which had not a God somewhere.