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.