There are two widely distinct views concerning the relation of man to Nature: the one as old as the history of human thought, the other only now urged upon us by modern science. According to the one, man is the counterpart and equivalent of Nature. He alone has—in fact is—an immortal spirit, and therefore he belongs to a world of his own. According to the other, man is but a part, a very insignificant part of Nature, and connected in the closest way with all other parts, especially with the animal kingdom. He has no world of his own, nor even kingdom of his own: he belongs to the animal kingdom. In that kingdom he has no department of his own: he is a vertebrate. In the department of vertebrates he has no privileged class of his own: he is a mammal. In the class of mammals he has no titled order of his own: he is a primate, and shares his primacy with apes. It is doubtful if he may enjoy the privacy of a family of his own—the Hominidæ—for the structural differences between man and the anthropoid apes are probably not so great as between the sheep family and the deer family.

Now it is evident that these two are only views from different points, psychical and structural.