Whereas, in its beginning, _mind_, or the psychical in all its aspects, was merely a useful property of _body_, all organic progress may be conceived in terms of a change in this original relation between them. In man, the mental or psychical has become the essential thing, and the body its servant. We are well prepared, then, to accept the proposition that in our own day and for our own species, the plane upon which natural selection works has largely been transferred, and, indeed, if any further progress is to be effected, _must_ be transferred, from the bodily or physical to the mental or psychical. A certain most remarkable fact in the anatomy of man may be cited, as we shall see, in support of this proposition. We need not venture upon the controversial ground of the relation or ultimate unity of mind and body; nor need we set up any suggestion of antagonism between them. All, however, are absolutely agreed that the psychical in all its forms, whatever it really be, has a consistent relation of the most intimate kind with that part of the body which we call the nervous system. For our present purposes the nature of this relation matters nothing at all, and in place of the phrase, the “selection of mind,” I should be quite content, if the reader so prefers, to speak of the selection of nerve or nervous selection. And if I may for a moment anticipate the conclusion, we may say that, in and for the future, the process of selection for life and parenthood, as it occurs in mankind, must be based, if the highest results are to be obtained, upon the principle that the selection of bodily qualities other than those of the nervous system is of value only in so far as these serve the nervous or psychical qualities. For practical and for theoretical purposes we must accept the dictum of Professor Forel that “the brain is the man”--or, to be more accurate and less epigrammatic, the nervous system is the man. If, then, we counsel or approve of any selection of bone or muscle or digestion, or any other bodily organ or function; if we select for physical health, physical energy, longevity, or immunity from disease--our estimate of these things, one and all, must be wholly determined by the services which they can perform for the nervous system, whether as its instruments, its guarantors of health and persistence, or otherwise. But we are not to regard any of these things as ends in themselves--notwithstanding the fact that this temptation will constantly beset us. So to do is implicitly to deny and renounce the supreme character of man--which is that, in him, mind or nervous system is the master, and the rest of the body, with all its attributes, the servant.