In defining the appearance of the individual mind by the awakening of self-consciousness, we make it possible to distinguish, from the monistic physiological point of view, between "soul" (psyche) and "spirit" (pneuma). There is a soul even in the maternal ovum and the paternal spermatozoon (cf. chapter xi.); there is an individual soul in the stem-cell (cytula) which arises at conception by the blending of the parent cells. But the mind proper, the thinking reason, develops out of the animal intelligence (or earlier instincts) of the child only with the consciousness of its personality as opposed to the outer world. At the same time the child reaches the higher stage of personality, which law has for a long time taken under its protection and made morally responsible to society by education. This shows how erroneous and untenable, from the physiological point of view, are the ideas still embodied in our code as to the psychic life and the mind of the embryo and the new-born infant. They came mostly from the canon law of the Catholic Church.
The dualistic ideas of the soul of the human embryo which were taught by the Church in the Middle Ages are particularly interesting from the psychological point of view; and at the same time they are of great practical importance even in our own day, since many of their moral consequences form an important element in canon law, and have passed from this into civil law. This influential canon law was formed under ecclesiastical authority from the decisions of Church councils and the decretals of the popes. It is, like most of the dogmas and decrees which civilization owes to this powerful hierarchy, a curious tissue of old traditions and new fictions, political dogmas, and crass superstition. It is directed to the despotic ruling of the uneducated masses and the exclusive dominion of the Church—a Church that calls itself Christian while thus acting as the very reverse of pure Christianity. The canon law takes its name from the dogmatic rules (or canons) of the Church. They involuntarily suggest the metal tubes which are so often the ultima ratio regis in the wars of Christian nations. The canonical regulations of the Church, as implements of a crude spiritual despotism, have no more to do with the ethical laws of pure reason than the cannons of secular authorities have as naked organs of physical force. We might write the motto, Ultima ratio ecclesiæ (the last argument of the Church), over the sacred Corpus Juris Canonici. A collection of later papal decretals which forms an appendix to the books of canon law was very happily given the official title of Extravagantes. Among the "extravagant" nonsense which the papacy included in canon law as a moral code for believers is its view of the psychic life of the embryo. The "immortal soul" is supposed to enter the soulless embryo only several weeks after conception. As theologians and metaphysicians are very much divided as to the period of this entrance of the soul, and know nothing about the structure of the embryo and its development, we will only recall the fact that the human fœtus cannot be distinguished from that of the anthropoid ape and other mammals even in the sixth week of its development. The outline of the five cerebral vesicles and the three higher sense-organs (nose, eye, and ear vesicle) is discernible in the head; the two pairs of limbs can be traced in the shape of four simple roundish unjointed plates; and the pointed tail sticks out at the lower part, the rudimentary legacy from our long-tailed ape-ancestors. Although the cortex is not yet developed at this stage, the embryo may be considered to have a "soul" (cf. chapters xiv. and xv. of my Anthropogeny, and plates 8-14).
It is said to be a great merit of canon law that it was the first to extend legal protection to the human embryo, and punished abortion with death as a mortal sin. But as this mystical theory of the entrance of the soul is now scientifically untenable, we should expect them consistently to extend this protection to the fœtus in its earlier stages, if not to the ovum itself. The ovary of a mature maid contains about 70,000 ova; each of these might be developed into a human being under favorable circumstances if it united with a male spermium after its release from the ovary. If the state is so eager for the multiplication of its citizens in the general interest, and regards prolific reproduction as a "duty" of its members, this is certainly a "sin of omission." It punishes abortion with several years' imprisonment. But while civil law thus takes its inspiration from canon law, it overlooks the physiological fact that the ovum is a part of the mother's body over which she has full right of control; and that the embryo that develops from it, as well as the new-born child, is quite unconscious, or is a purely "reflex machine," like any other vertebrate. There is no mind in it as yet; it only appears after the first year, when its organ, the phronema in the cortex, is differentiated. This interesting fact is explained by the biogenetic law, which shows that the ontogeny of the brain is a condensed recapitulation of its phylogeny in virtue of the laws of heredity.
The biogenetic law applies just as much to the brain, the organ of mind, as to any other organ of the human body. On the strength of the ontogenetic facts, which fall under direct observation, we infer that there was a corresponding development in the phylogenetic series of our animal ancestors. A significant confirmation of this inference is found in comparative anatomy. It shows that in all the skull-animals (craniota)—from the fishes and amphibia up to the apes and man—the brain is developed in the same way, as a vesicular distension of the ectodermal medullary tube. This simple oval cerebral vesicle first divides into three and afterwards five successive vesicles by transverse constriction (Anthropogeny, chapter xxiv., plate 24). It is the first of these vesicles, the cerebrum, that afterwards becomes the chemical laboratory of the mind. In the lower craniota (fishes and amphibia) the cerebrum remains very small and simple. It only reaches a notably higher stage in the three chief classes of the vertebrates, the amniotes. As these land-dwelling and air-breathing craniota have more difficult work to do in the struggle for life than their lower aquatic ancestors, we find much more varied and complex habits among them. These hereditary habits are gradually converted into instincts by functional adaptation and progressive heredity; and with the further development of consciousness in the higher mammals we have at last the appearance of reason. The gradual unfolding of the mental life is accompanied step by step with the advance of its anatomic organ, the phronema in the cortex. Recent careful investigations of the ontogeny and histology of the origin of mind (by Flechsig, Hitzig, Edinger, Ziehen, Oscar Vogt, etc.) have given us an interesting insight into the mysterious processes of its phylogeny.
While the comparative anatomy of the cortex gives us a good idea of the gradual historical development of the mind in the higher classes of vertebrates, we get at the same time from their fossilized remains positive indications as to the period of time in which this phylogenesis has slowly taken place. The historical series in which the classes of vertebrates have succeeded each other in the great periods of the organic history of the earth is directly demonstrated by their fossil remains—the real commemorative medals of natural creation—and gives us a most valuable record of the ancestral history of our race and of the mind. The oldest strata that contain vertebrate remains form the huge Silurian System, which were, on the latest calculations, formed more than a hundred million years ago. They contain a few fossil fishes. In the succeeding Devonian System these are followed by the dipneusta, transitional forms between the fishes and the amphibia. The latter, the oldest four-footed and five-toed vertebrates, appear in the Carboniferous Period. They are succeeded in the Permian, the next system, by the oldest amniotes, the primitive reptiles (tocosauria). It is not until the next period (the Triassic) that the oldest mammals are found, small primitive monotremes (pantotheria), then marsupials in the Jurassic, and the first placentals in the Cretaceans. The great wealth of varied and highly organized forms which are contained in this third and last sub-class of the mammals appear only in the succeeding Tertiary Period. The numbers of well-preserved skulls which these placentals have left behind in fossil form are particularly important, because they give us an idea of the quantitative and qualitative formation of the brain within the various orders; thus, for instance, in the modern carnivora the brain is from two to four times, and in the modern ungulates from six to eight times, as large (in proportion to the size of the body) as in their earliest Tertiary ancestors. It is also found that the cortex (the real organ of mind) has developed in the Tertiary Period at the expense of the other parts of the brain. The duration of this Cænozoic Period has lately been calculated at three million years (according to other geologists twelve to fourteen or more million years). It was, at all events, sufficient to make possible the gradual development of the human mind from the lower intelligence of our ape-ancestors and the instincts of the older placentalia.
We have given the physiological name of the "phronema," as the real organ of mind or the instrument of reason, to that part of the cortex on the normal anatomic condition of which the action of the human mind depends. The remarkable investigations during the last few decades of the finer texture of the grey cortex (or cortical substance of the cerebrum) have shown that its structure—a real anatomic "wonder of life"—represents the most perfect morphological product of plasm; and its physiological function—mind—is the most perfect action of a "dynamo-machine," the highest achievement that we know anywhere in nature. Millions of psychic cells or neurona—each of them of an extremely elaborate fibril molecular structure—are associated as special thought-organs (phroneta) at certain parts of the cortex, and these again are built up into a large harmonious system of wonderful regularity and capacity. Each phronetal cell is a small chemical laboratory, contributing its share to the unified central function of the mind, the conscious action of reason. Scientists are still very far from agreement as to the extent of the phronema in the cortex and its delimitation from the neighboring sense-centres (sensoria). But they are all agreed that there is such a central organ of mind, and that its normal anatomic and chemical condition is the first requisite for the life of the human mind. This belief—one of the foundations of monistic psychology—is confirmed by the study of psychiatry.
The study of the diseased organism has greatly furthered our knowledge of the normal frame. Diseases are so many physiological experiments made by nature herself under special conditions, which experimental physiology would often be unable to arrange artificially. The thoughtful physician or pathologist can often obtain most important knowledge of the function of organs by carefully observing them during disease. This is especially true of diseases of the mind, which always have their immediate foundation in an anatomical or chemical modification of certain parts of the brain. Our advancing knowledge of the localization of mental functions, or of their connection with special phroneta or organs of thought, is for the most part based on the experience that the destruction of the one is followed by the extinction of the other. Modern psychiatry, the empirical science of mental disease, has thus become an important element of our monistic psychology. If Immanuel Kant had studied it and had visited the asylum wards for a few months, he would certainly have escaped the dualist errors of his philosophy. We may say the same of the modern metaphysical psychologists who built up a mystic theory of an immortal soul without knowing the anatomy, physiology, and pathology of the brain.
The comparative anatomy, physiology, and pathology of the brain, in concurrence with the results of ontogeny and phylogeny, have led us to form the sound monistic principle that the human mind is a function of the phronema, and that the neurona of the latter, or the phronetal cells, are the real elementary organs of mental life. Hence modern energism is perfectly justified in regarding mental energy (in all its forms) from the same point of view as all other forms of nervous energy, and in fact all manifestations of energy in organic or inorganic nature. Fechner's psychophysics had already shown that a part of this nervous energy is measurable and mathematically reducible to the mechanical laws of physics (Riddle, chapter vi.) Ostwald has, in his Natural Philosophy, lately emphasized the fact that all the manifestations of mental life, not only sensation and will, but even thought and consciousness, can be reduced to nervous energy. Hence we may distinguish what are called mental forces from the other expressions of nervous energy as phronetic energy. The monistic research of Ostwald on the energy-processes in mental life (chapter xviii.), consciousness (chapter xix.), and will (chapter xx.) is very notable, and confirms the views I advanced in the second part of the Riddle (chapters vi., x., and xi.). Ostwald has, however, caused some misunderstanding by insisting on substituting his idea of energy for the pure notion of substance (as Spinoza had formulated it), and by rejecting the other attribute of substance, matter. His supposed "Refutation of Materialism" is a mere attack on windmills; his energism (the consistent dynamism of Leibnitz, etc.) is just as one-sided as its apparent opposite, the consistent materialism of Democritus, Holbach, etc. The latter makes matter precede force; the former regards matter as the product of force. Monism escapes the one-sidedness of both systems, and, as hylozoism, refuses to separate the two attributes of substance, space-filling matter and active energy. This applies to mental life just as to any other natural process; our mental forces or phronetic energies are just as much bound up with the neuroplasm, the living plasm of the neurona in the cortex, as the mechanical energy of our muscles is with the contractile myoplasm, the living muscular substance.
In the exhaustive study of consciousness which I gave in the tenth chapter of the Riddle I sought to show that this enigmatic function—the central mystery of psychology—is not a transcendental problem, but a natural phenomenon, subject to the law of substance, as much as any other psychic power. The child's consciousness only develops long after its first year, and grows as gradually as any other psychic function; like these, it is bound up with the normal anatomic and chemical condition of its organs, the phroneta in the cortex. Consciousness develops originally out of unconscious functions (as an "inner view," or mirroring, of the action of the phronema); and at any time an unconscious process in the cortex may come within the sphere of consciousness by having the attention directed to it. On the other hand, conscious actions, which need a good deal of attention when they are first learned (such as playing the piano), may become unconscious through frequent repetition and practice. The fact that chemical energy is converted in the phronetal cells during any of these actions is proved by the fatigue and exhaustion which prolonged mental work causes in the brain, just as mechanical work does in the muscles. Fresh matter has to be supplied by the food before the mental work can be continued. Moreover, it is well known that various drinks have a considerable influence on consciousness (coffee and tea, beer and wine); and the temporary extinction of it under chloroform or ether is an analogous fact. Again, the familiar phenomena of the dream, the deviations from normal consciousness, hallucinations, delusions, etc., must convince every impartial thinker that these mental functions are not of a metaphysical character, but physical processes in the neuroplasm of the brain, and thoroughly dependent on the law of substance.
In complete contrast to this natural monistic conception of the human mind, which is, in my opinion, definitely established by nineteenth-century science, we have the older dualistic estimate of it which is still widely accepted both by unlearned and learned, especially metaphysicians and theologians. I have already dealt in the Riddle (chapter xi.) with the grounds for this belief in an immaterial soul, and expressed my conviction that "the belief in the immortality of the human soul is in flagrant contradiction to the soundest empirical principles of modern science." I must refer the reader to what I said there about thanatism and athanatism, only reminding him once more of the immense influence of the Kantist philosophy in maintaining this belief in the spirituality of the soul. Kant derived from the introspective study of his own gifted mind an extremely high estimate of human reason, and he fallaciously transferred this estimate to the human mind generally. He did not perceive that it is either wholly wanting in the savage, or does not rise much above the stage which has been reached by the intelligence of the dog, horse, elephant, and other advanced animals.