In the five branches of science I have enumerated, pure monism has been universally and exclusively admitted (as far as they relate to inorganic nature) in the second half of the nineteenth century. There is no question in them to-day of the wisdom and power of the Creator. This is equally true of geology, astronomy, mathematics, chemistry, and physics. It is otherwise with the remaining sciences which deal with organic nature; in these we have not yet succeeded in giving a physical explanation and mathematical formulation of all phenomena. Hence vitalism enters with its dualistic notions, and splits the science into two different branches—natural science (physics in the wider sense) and mental science (metaphysics); fixed natural laws are supposed to rule only in the former, while in the latter we still have the "freedom" of the spirit and the supernatural. This applies, first of all, to biology in the broadest sense (including anthropology and all the sciences that relate to man). In the preceding chapters of biological philosophy we have sought to refute vitalism in every form, and to secure the exclusive acceptance of monism and mechanicism in every branch of the science of life.
Anthropology is still, as it has been for centuries, taken in many different senses. In the widest sense, it embraces the whole vast science of man, just as zoology (in my opinion) deals with all parts of the animal world. Since I regard anthropology as a part of zoology, I naturally extend the principles of monism to both. However, this general monistic conception of the science of man has met with only a restricted acceptance up to the present. As a rule, the term "anthropology" is restricted to the natural history of man, which includes the anatomy and physiology of the human organism, embryology, prehistoric research, and a small part of psychology. But this "official anthropology," as most of our anthropological societies (especially in Germany) conceive it, generally excludes phylogeny, the greater part of psychology, and all the mental sciences, which are regarded as metaphysical in the narrower sense. I endeavored to show in my Anthropogeny thirty years ago that man (as a placental mammal of the order of primates) is no less unified an organism (with body and soul) than any other vertebrate, and that, therefore, every aspect of his being should be dealt with monistically.
As is well known, the views of experts and laymen alike are very much divided as to the place of psychology in the scheme of the sciences. The great majority of the professional psychologists, and of educated people generally, adhere still to the antiquated dogma, with its religious foundation, that man's soul is immortal and an independent immaterial entity. This dualistic view has been supported in the schools especially by the authority of Plato, Descartes, and Kant; in religion by the authority of Christ, Paul, and Mohammed; in education and the state by the authority of most governments; and in physiology by most of the older, and even some recent, physiologists. On this view, psychology is a special mental science, having only an external and limited connection with natural science. But modern comparative and genetic psychology, the anatomy and physiology of the brain, have, in the course of the last forty years, established the monistic view that psychology is a special branch of cerebral physiology, and that therefore all its parts and their application belong to this section of biology. The soul of man is a physiological function of the phronema. As I have fully explained the monistic conception of psychology in chapters vi.-xi. of the Riddle, and supported it with all the arguments of anatomy, physiology, ontogeny, and phylogeny in my Anthropogeny, I need not go further into the subject.
The science of language shares the fate of its sister, psychology; by one section of its representatives it is taken monistically as a natural science, and by another section it is dualistically conceived as a branch of mental science. On the old metaphysical view, speech was regarded as an exclusive property of man, either a gift of the gods or an invention of social man. But in the course of the nineteenth century the monistic and physiological position that speech is a function of the organism, and has been gradually developed like all other functions, has been established. The comparative psychology of the higher animals showed that in various classes the thoughts, feelings, and desires of the gregarious animals are communicated partly by signs or touch, partly by sounds (the chirrup of the cricket, the cry of the frog, the whistle of many reptiles, song of birds and singing-apes, roaring of carnivora and ungulates, etc.). The ontogeny of speech showed that its gradual development in the child is (in accordance with the biogenetic law) a recapitulation of its phylogenetic process. Comparative philology taught that the languages of the different races have been formed polyphyletically, or independently of each other. The experimental physiology and pathology of the brain showed that a definite small region of the cortex (the Broca fissure) is the centre of speech, and that this central organ, in conjunction with other parts of the phronema and the larynx (the peripheral organ), produces articulate speech.
Historical science is, like philology or psychology, still conceived in different senses by experts. Very often history is wrongly taken to mean the record of events that have occurred in the course of the development of civilized life—the history of peoples and states (humorously described as "the history of the world"), of civilization, of morals, etc. This is merely an anthropocentric feeling that in the strictly scientific sense "history" can only be used for the record of man's doings. In this sense history is opposed to nature, the one dealing with the province of morally free phenomena (with preconceived aim), and the other comprising the province of natural law (without preconceived aim). As if there were no "natural history," or as if cosmogony, geology, ontogeny, and phytogeny were not historical sciences! Although this dualistic and anthropistic view still prevails in our universities, and state and Church protect the venerable tradition, there can be no doubt that sooner or later it will be replaced by a purely monistic philosophy of history. Modern anthropogeny shows us the intimate connection between the evolution of the human individual and that of the race; and by means of prehistoric and phylogenetic research it joins what is called the history of the world to the stem-history of the vertebrates.
Medicine belongs to the front rank of practical or applied sciences. In its long and interesting history it teaches how it is only a monistic knowledge of nature, not a dualistic notion of revelation, that affords the foundations of true science and the profitable application of this to the most important aspects of practical life. Medicine was originally the business of the priests, and for thousands of years it was under the influence of mystic and superstitious ideas which were connected with religious dogmas. However, two thousand years ago the great physicians of classic antiquity made a serious effort to provide a solid base for medical practice by a thorough anatomic and physiological study of the human frame. But in the general reaction of the Middle Ages superstitious and miraculous ideas once more defeated independent scientific investigation. Disease was supposed to be the work of evil spirits (as Christ thought) which had to be exorcised. Miracles are still thought to take place, even in cultured circles. I need only mention the wonders of patent medicines, magnetic cures, Christian Science, and other charlatanry. However, the great development of science in the nineteenth century, especially the astonishing advance of biology about the middle of the century, gradually shaped medicine into the monistic science which assuages so much pain and suffering in humanity to-day. Pathology, the science of disease, and therapeutics, the rational science of healing, are grounded now on the safe methods of physics and chemistry and a thorough knowledge of the human organism. Disease is no longer regarded as a special entity that comes on the body like an evil spirit or mysterious organism, but is conceived as a baneful disturbance of its normal activity. Pathology is only a branch of physiology; it studies the changes that take place in the tissues and cells under abnormal and dangerous conditions. When the causes of these changes are poisons or foreign organisms (such as bacteria or amœbæ), the art of healing has to remove them and restore the normal equilibrium of the functions.
The science of mental disease is a special branch of medicine; it has the same relation to it as psychology has to physiology. However, as pathological psychology it deserves special consideration, not only on account of its extreme practical importance, but also because of its theoretical interest. The misleading dualist idea of body and soul that has perverted our notions of mental life from the oldest times has led people to regard mental disorders as special phenomena, at one time directly as evil spirits that enter from without into the human body, at another time as mysterious dynamic occurrences affecting the mystic being of the soul (independently of the body). These dualistic and still wide-spread and mischievous errors have caused the most fatal mistakes in the treatment of mental disease; they have had the most unfortunate effect on juristic and social and other aspects of practical life. But the ground has been cut from under these irrational and superstitious ideas by modern psychiatry, which regards all mental disease as a disorder of the brain, and traces it to changes in the cortex that lie at the root of all psychoses (delusions, lunacy, etc.). As we call this central organ of mind the phronema, we may say: Psychiatry is the pathology and therapeutics of the phronema. In many disorders we have already succeeded in anatomically and chemically tracing the changes in the psychic or phronetal cells (the neurona in the phronema). These acquisitions of the pathological anatomy and physiology of the phronema have a great philosophic interest, because they throw a good deal of light on the monistic conception of psychic life. As the greater part (sixty to ninety per cent.) of these diseases are hereditary, and they have mostly been acquired gradually by the ancestors of the patient, they also afford clear proof of progressive heredity, or the inheritance of acquired characters.
Thousands of years ago, when barbaric races began to adapt themselves to civilized life, they had a concern for their bodily health and strength. In classic antiquity the care of the body by baths, gymnastic exercises, etc., was greatly developed, and connected with religious ceremonies. The splendid aqueducts and baths of Greece and Rome show how much importance they attached to the external and internal use of water. The Middle Ages brought reaction in this province like so many others. As Christianity depreciated this life and said it was merely a preparation for the life to come, it led to a disdain of culture and of nature; and as it regarded man's body only as the temporary prison of his immortal soul, it attached no importance to the care of it. The frightful plagues that swept away millions of men in the Middle Ages were only fought with prayer, processions, and other superstitious devices, instead of with rational hygienic and sanitary measures. We have only gradually learned to discard this superstition. It was not until the second half of the nineteenth century that a sound knowledge of the physiological functions and environment of the organism induced people once more to have a concern for bodily culture. All that modern hygiene now does for the public health, especially the improvement of the dwellings and food of the poorer classes, the prevention of disease by healthier habits, baths, athletics, etc., can be traced to the monistic teaching or reason, and is altogether opposed to the Christian belief in Providence and the dualism connected therewith. The maxim of modern hygiene is: God helps those who help themselves.
The remarkable progress of technical science in the nineteenth century, which has stamped our age as "an age of machinery," is a direct consequence of the immense advance of theoretical science. All the privileges and comforts which modern life gives us are due to scientific discoveries, especially in physics and chemistry. We need only recall the enormous importance of steam and electric machinery, modern mining, agriculture, and so on. If by these means modern industry and international commerce have prospered beyond all expectations, we owe this to the practical application of empirical truths. "Mental science" and metaphysical speculation have had nothing to do with it. There is no need of further proof that all the technical sciences have a purely monistic character, like their exact sources, physics and chemistry.