To apply this, now, to the slow production of man's intellectual faculties, we must, if we would do justice to Darwin's hypothesis of the method in which he was developed as an animal, bear in mind that his mental powers, like his animal structure, have been the necessary acquirement of new powers and capacities by gradation, through the perpetual process of modification, and retention and transmission of the new acquisitions. Darwin, indeed, does not professedly undertake the genealogy of the human mind; but he appears to hold the opinion that in future psychology will be based on the gradual acquisition of each mental power and capacity, as distinguished from their complete production in any one pair, or in any one being; and he refers to Herbert Spencer as having already securely laid the foundation for this new psychology.[115] I take, therefore, the great English naturalist as the person who has most satisfactorily explained the origin of man as an animal, and the great English philosopher as the person who has propounded the most satisfactory theory of the origin of the human mind. The two hypotheses run parallel to and support each other. Man, as respects his mere animal structure, is an organism developed by a slow process of modification out of preceding organisms. His mental faculties have one by one grown out of the operation of the same physical agencies that have formed his animal structure, and they have not been bestowed at once upon any one pair, or upon any one individual of the race. After they have all been acquired, as we now know and recognize them, they have descended to the successive generations of the race. SOPHEREUS. I have studied Mr. Spencer's "System of Psychology," but I do not know whether we understand it alike. You say that he has propounded the most satisfactory theory of the origin of mind. Assuming that mind was evolved as an aggregate of powers and capacities, slowly acquired, _pari passu_ with the evolution of the animal organism, be good enough to tell me whether Mr. Spencer does or does not conclude that mind is anything more than an aggregate of powers and capacities of the nervous organization. I am quite aware of the mode in which he meets the charge of materialism; but waiving for the present the question of materialism, I should be glad to know, according to your understanding of his philosophy, what he considers mind to be.