[13] H. S. Jennings, "Publications of Carnegie Institute," Washington, No. 16 (1904), pp. 1-256.
Just as inorganic evolution must have made many advances before organisms became possible, so organic evolution must have made many advances before the mental side of life could find distinct expression. But as we cannot retranslate the daily activities of even a very simple animal into chemico-physical language, we are forced at present to conclude that what is called inanimate matter has somehow wrapped up with it the potentiality of life; and as we cannot retranslate behaviour into the metabolism of nerve-cells, we are forced at present to conclude that life has somehow wrapped up with it the potentiality of mind. In other words, what is called the evolution of mind is a genetic description of the stages in its emergence from its state of universal potentiality.
(2) Body and Mind.—A second service Spencer rendered to Psychology was that of linking it to Biology. He gave clear expression to the doctrine, which many workers had been reaching towards, of the correlation of mind and body. Although sagacious thinkers at many different dates had pointed out that the flesh not only wars against the spirit, but in a humiliating way conditions its activity, the recognition of the intimate correlation of body and mind was still requiring its advocate when Spencer wrote his Psychology. Ignoring what had been clearly shown even by Descartes and the truth in Hartley's Observations on Man (1749), there was still a school who practically dealt with the mind and its faculties on the one side, the body and its functions on the other side, as entirely independent existences. The old idea that character inheres in the ghost, and that the body is merely the ghost's house, having no causal relation to it, still lingered in more or less refined form when Spencer set himself to show "that, in both amounts and kinds, mental manifestations are in part dependent on bodily structures. Mind is not as deep as the brain only, but is, in a sense, as deep as the viscera." In a detailed way, he sought to show that "the amounts and kinds of the mental actions constituting consciousness vary, other things equal, according to the rapidity, the quantity, and the quality, of the blood-supply; and all these vary according to the sizes and proportions of the sundry organs which unite in preparing blood from food, the organs which circulate it, and the organs which purify it from waste products." To put it concretely, he contended that when we consider Handel, for instance, "so wonderfully productive, so marvellous for the number and vigour of his musical compositions," we must also remember that he had an unusually active digestion. "And not the quantity of mind only, but the quality of mind also, is in part determined by these psycho-physical connections. Amount and structure of brain being the same, not only may the totality of feelings and thoughts be greater or less according as this or that viscus is well or ill-developed, but the feelings and thoughts may also be favourably or unfavourably modified in their kinds." So morality, as well as mind, is as deep as the viscera.
Here again the general truth which Spencer forcibly expounded, though it was not of course peculiarly his, is one that has met with almost universal recognition. As Prof. G. F. Stout says:—
"The life of the brain is part of the life of the organism as a whole, and inasmuch as consciousness is the correlate of brain-process, it is conditioned by organic process in general. It is clear that the unity and connection of psychical states cannot be clearly conceived without taking into account the unity and connection of the processes of the organism as a whole."[14]
As Prof. James Ward says[15]:—
[14] Op. cit., p. 27.
[15] Naturalism and Agnosticism, 1899, vol. i. p. 10.
"Modern science is content to ascertain co-existences and successions between facts of mind and facts of body. The relations so determined constitute the newest of the sciences, psychophysiology or psychophysics. From this science we learn that there exist manifold correspondences of the most intimate and exact kind between states and changes of consciousness on the one hand, and states and changes of brain on the other. As respects complexity, intensity, and time-order, the concomitance is apparently complete. Mind and brain advance and decline pari passu; the stimulants and narcotics that enliven or depress the action of the one tell in like manner upon the other. Local lesions that suspend or destroy, more or less completely, the functions of the centres of sight and speech, for instance, involve an equivalent loss, temporary or permanent, of words and ideas."
Experience and Intuitions.—The history of psychology discloses a long drawn-out dispute between schools of "empiricists," who said "all our knowledge is derived from experience," and schools of "intuitionalists," who said, "Nay, but we have innate ideas or intuitions which transcend experience." A parallel dispute was long continued in regard to moral ideas. Between the disputants Spencer appeared as a peace-maker, and the reconciliation he proposed was in terms of evolution. We can best express it by a sentence from a letter to John Stuart Mill:—