It is particularly interesting to glance at the central nervous system of the vertebrates, the great stem of which we regard ourselves as the crowning point. Here again the anatomical and embryological facts speak a clear and unambiguous language. In all vertebrates, from the lowest fishes up to man, the psychic organ makes its appearance in the embryo in the same form—a simple cylindrical tube on the dorsal side of the embryonic body, in the middle line. The anterior section of this "medullary tube" expands into a club-shaped vesicle, which is the beginning of the brain; the posterior and thinner section becomes the spinal cord. The cerebral vesicle divides, by transverse constrictions, into three, then four, and eventually five vesicles. The most important of these is the first, the cerebrum, the organ of the highest psychic functions. The more the intelligence develops in the higher vertebrates, the larger, more voluminous, and more specialised does the cerebrum become. In particular, the grey mantle or cortex of the cerebrum, its most important part, only attains in the higher mammals the degree of quantitative and qualitative development that qualifies it to be the "organ of mind" in the narrower sense. Through the famous discoveries of Paul Flechsig eleven years ago we were enabled to distinguish eight fields in the cortex, four of which serve as the internal centres of sense-perception, and the four that lie between these are the thought-centres (or association-centres) of the higher psychic faculties—the association of impressions, the formation of ideas and concepts, induction and deduction. This real organ of mind, the phronema, is not yet developed in the lower mammals. It is only gradually built up in the more advanced, exactly in proportion as their intelligence increases. It is only in the most intelligent forms of the placentals, the higher ungulates (horse, elephant), the carnivores (fox, dog), and especially the primates, that the phronema attains the high grade of development that leads us from the anthropoid apes direct to the savage, and from him to civilised man.
We have learned a good deal about the special significance of the various parts of the brain, as organs of specific functions, by the progress of the modern science of experimental physiology. Careful experiments by Goltz, Munk, Bernard, and many other physiologists, have shown that the normal consciousness, speech, and the internal sense-perceptions, are connected with definite areas of the cortex, and that these various parts of the soul are destroyed when the organic areas connected with them are injured. But in this respect Nature has unconsciously given us the most instructive experiments. Diseases in these various areas show how their functions are partially or totally extinguished when the cerebral cells that compose them (the neurona or ganglionic cells) are partially or entirely destroyed. Here again Virchow, who was the first to make a careful microscopic study of the finest changes in the diseased cells, and so explain the nature of the disease, did pioneer work. I still remember very well a spectacle of this kind (in the summer of 1855, at Würzburg), which made a deep impression on me. Virchow's sharp eye had detected a small suspicious spot in the cerebrum of a lunatic, though there seemed to be nothing remarkable about it on superficial examination. He handed it to me for microscopic examination, and I found that a large number of the ganglionic cells were affected, partly by fatty degeneration and partly by calcification. The luminous remarks that my great teacher made on these and similar finds in other cases of mental disorder, confirmed my conviction of the unity of the human organism and the inseparable connection of mind and body, which he himself at that time expressly shared. When he abandoned this Monistic conception of the psychic life for Dualism and Mysticism twenty years afterwards (especially after his Munich speech in 1877), we must attribute this partly to his psychological metamorphosis, and partly to the political motives of which I spoke in the last chapter.
We find another series of strong arguments in favour of our Monistic psychology in the individual development of the soul in the child and the young animal. We know that the new-born child has as yet no consciousness, no intelligence, no independent judgment and thought. We follow the gradual development of these higher faculties step by step in the first years of life, in strict proportion to the anatomical development of the cortex with which they are bound up. The inquiries into the child-soul which Wilhelm Preyer began in Jena twenty-five years ago, his careful "observations of the mental development of man in his early years," and the supplementary research of several more recent physiologists, have shown, from the ontogenetic side, that the soul is not a special immaterial entity, but the sum-total of a number of connected functions of the brain. When the brain dies, the soul comes to an end.
We have further proof in the stem-history of the soul, which we gather from the comparative psychology of the lower and higher mammals, and of savage and civilised races. Modern ethnography shows us in actual existence the various stages through which the mind rose to its present height. The most primitive races, such as the Veddahs of Ceylon, or the Australian natives, are very little above the mental life of the anthropoid apes. From the higher savages we pass by a complete gradation of stages to the most civilised races. But what a gulf there is, even here, between the genius of a Goethe, a Darwin, or a Lamarck, and an ordinary philisthine or third-rate official. All these facts point to one conclusion: the human soul has only reached its present height by a long period of gradual evolution; it differs in degree, not in kind, from the soul of the higher mammals; and thus it cannot in any case be immortal.
That a large number of educated people still cling to the dogma of personal immortality in spite of these luminous proofs, is owing to the great power of conservative tradition and the evil methods of instruction that stamp these untenable dogmas deep on the growing mind in early years. It is for that very reason that the Churches strive to keep the schools under their power at any cost; they can control and exploit the adults at will, if independent thought and judgment have been stifled in the earlier years.
This brings us to the interesting question: What is the position of the "ecclesiastical evolution" of the Jesuits (the "latest course of Darwinism"), as regards this great question of the soul? Man is, according to Wasmann, the image of God and a unique, immaterial being, differing from all other animals in the possession of an immortal soul, and therefore having a totally different origin from them. Man's immortal soul is, according to this Jesuit sophistry, "spiritual and sensitive," while the animal soul is sensitive only. God has implanted his own spirit in man, and associated it with an animal soul for the period of life. It is true that Wasmann believes even man's body to have been created directly by God; but, in view of the overwhelming proofs of our animal descent, he leaves open the possibility of a development from a series of other animals, in which case the Divine spirit would be breathed into him in the end. The Christian Fathers, who were much occupied with the introduction of the soul into the human embryo, tell us that the immortal soul enters the soulless embryo on the fortieth day after conception in the case of the boy, and on the eightieth day in the case of the girl. If Wasmann supposes that there was a similar introduction of the soul in the development of the race, he must postulate a moment in the history of the anthropoid apes when God sent his spirit into the hitherto unspiritual soul of the ape.
When we look at the matter impartially in the light of pure reason, the belief in immortality is wholly inconsistent with the facts of evolution and of physiology. The ontogenetic dogma of the older Church, that the soul is introduced into the soulless body at a particular moment of its embryonic development, is just as absurd as the phylogenetic dogma of the most modern Jesuits, that the Divine spirit was breathed into the frame of an anthropoid ape at a certain period (in the Tertiary period), and so converted it into an immortal soul. We may examine and test this belief as we will, we can find in it nothing but a piece of mystic superstition. It is maintained solely by the great power of tradition and the support of Conservative governments, the leaders of which have no personal belief in these "revelations," but cling to the practical conviction that throne and altar must support each other. They unfortunately overlook the circumstance that the throne is apt to become merely the footstool to the altar, and that the Church exploits the State for its own, not the State's, good.
We learn further, from the history of this dogma, that the belief in immortality did not find its way into science until a comparatively late date. It is not found in the great Monistic natural philosophers who, six centuries before the time of Christ, evinced a profound insight into the real nature of the world. It is not found in Democritus and Empedocles, in Seneca and Lucretius Carus. It is not found in the older Oriental religions, Buddhism, the ancient religion of the Chinese, or Confucianism; in fact, there is no question of individual persistence after death in the Pentateuch or the earlier books of the Old Testament (which were written before the Babylonian Exile). It was Plato and his pupil, Aristotle, that found a place for it in their dualistic metaphysics; and its agreement with the Christian and Mohammedan teaching secured for it a very widespread acceptance.
Another psychological dogma, the belief in man's free-will, is equally inconsistent with the truth of evolution. Modern physiology shows clearly that the will is never really free in man or in the animal, but determined by the organisation of the brain; this in turn is determined in its individual character by the laws of heredity and the influence of the environment. It is only because the apparent freedom of the will has such a great practical significance in the province of religion, morality, sociology, and law, that it still forms the subject of the most contradictory claims. Theoretically, determinism, or the doctrine of the necessary character of our volitions, was established long ago.
With the belief in the absolute freedom of the will and the personal immortality of the soul is associated, in the minds of many highly educated people, a third article of faith, the belief in a personal God. It is well known that this belief, often wrongly represented as an indispensable foundation of religion, assumes the most widely varied shapes. As a rule, however, it is an open or covert anthropomorphism. God is conceived as the "Supreme Being," but turns out, on closer examination, to be an idealised man. According to the Mosaic narrative, "God made man to his own image and likeness," but it is usually the reverse; "Man made God according to his own image and likeness." This idealised man becomes creator and architect and produces the world, forming the various species of plants and animals like a modeller, governing the world like a wise and all-powerful monarch, and, at the "Last Judgment," rewarding the good and punishing the wicked like a rigorous judge. The childish conceptions of this extramundane God, who is set over against the world as an independent being, the personal creator, maintainer, and ruler of all things, are quite incompatible with the advanced science of the nineteenth century, especially with its two greatest triumphs, the law of substance and the law of Monistic evolution.