III. In the same way we must regard the third stage, the unconscious memory of those animals which have a nervous system, as a reproduction of the corresponding “unconscious presentations” which are stored up in certain ganglionic cells. In most of the lower animals all memory is unconscious. Moreover, even in man and the higher animals, to whom we must ascribe consciousness, the daily acts of unconscious memory are much more numerous and varied than those of the conscious faculty; we shall easily convince ourselves of that if we make an impartial study of a thousand unconscious acts we perform daily out of habit, and without thinking of them, in walking, speaking, writing, eating, and so forth.
IV. Conscious memory, which is the work of certain brain-cells in man and the higher animals, is an “internal mirroring” of very late development, the highest outcome of the same psychic reproduction of presentations which were mere unconscious processes in the ganglionic cells of our lower animal ancestors.
The concatenation of presentations—usually called the association of ideas—also runs through a long scale, from the lowest to the highest stages. This, too, is originally and predominantly unconscious (“instinct”); only in the higher classes of animals does it gradually become conscious (“reason”). The psychic results of this “association of ideas” are extremely varied; still, a very long, unbroken line of gradual development connects the simplest unconscious association of the lowest protist with the elaborate conscious chain of ideas of the civilized man. The unity of consciousness in man is given as its highest consequence (Hume, Condillac). All higher mental activity becomes more perfect in proportion as the normal association extends to more numerous presentations, and in proportion to the order which is imposed on them by the “criticism of pure reason.” In dreams, where this criticism is absent, the association of the reproduced impressions often takes the wildest forms. Even in the work of the poetic imagination, which constructs new groups of images by varying the association of the impressions received, and in hallucinations, etc., they are often most unnaturally arranged, and seem to the prosaic observer to be perfectly irrational. This is especially true of supernatural “forms of belief,” the apparitions of spiritism, and the fantastic notions of the transcendental dualist philosophy; though it is precisely these abnormal associations of “faith” and of “revelation” that have often been deemed the greatest treasures of the human mind (cf. [chap. xvi].).
The antiquated psychology of the Middle Ages (which, however, still numbers many adherents) considered the mental life of man and that of the brute to be two entirely different phenomena; the one it attributed to “reason,” the other to “instinct.” In harmony with the traditional story of creation, it was assumed that each animal species had received a definite, unconscious psychic force from the Creator at its formation, and that this instinct of each species was just as unchangeable as its bodily structure. Lamarck proved the untenableness of this error in 1809 by establishing the theory of Descent, and Darwin completely demolished it in 1859. He proved the following important theses with the aid of his theory of selection:
1. The instincts of species show individual differences, and are just as subject to modification under the law of adaptation as the morphological features of their bodily structure.
2. These modifications (generally arising from a change of habits) are partly transmitted to offspring by heredity, and thus accumulate and are accentuated in the course of generations.
3. Selection, both artificial and natural, singles out certain of these inherited modifications of the psychic activity; it preserves the most useful and rejects the least adaptive.
4. The divergence of psychic character which thus arises leads, in the course of generations, to the formation of new instincts, just as the divergence of morphological character gives rise to new species.
Darwin’s theory of instinct is now accepted by most biologists; Romanes has treated it so ably, and so greatly expanded it in his distinguished work on Mental Evolution in the Animal World, that I need merely refer to it here. I will only venture the brief statement that, in my opinion, there are instincts in all organisms—in all the protists and plants as well as in all the animals and in man; though in the latter they tend to disappear in proportion as reason makes progress at their expense.
The two chief classes of instincts to be differentiated are the primary and secondary. Primary instincts are the common lower impulses which are unconscious and inherent in the psychoplasm from the commencement of organic life; especially the impulses to self-preservation (by defence and maintenance) and to the preservation of the species (by generation and the care of the young). Both these fundamental instincts of organic life, hunger and love, sprang up originally in perfect unconsciousness, without any co-operation of the intellect or reason. It is otherwise with the secondary instincts. These were due originally to an intelligent adaptation, to rational thought and resolution, and to purposive conscious action. Gradually, however, they became so automatic that this “other nature” acted unconsciously, and, even through the action of heredity, seemed to be “innate” in subsequent generations. The consciousness and deliberation which originally accompanied these particular instincts of the higher animals and man have died away in the course of the life of the plastidules (as in “abridged heredity”). The unconscious purposive actions of the higher animals (for instance, their mechanical instincts) thus come to appear in the light of innate impulses. We have to explain in the same way the origin of the “à priori ideas” of man; they were originally formed empirically by his predecessors.[16]