During the last forty years a great number of works on comparative animal psychology have appeared, principally occasioned by the great impulse which Darwin gave in 1859 by his work on The Origin of Species, and by the application of the idea of evolution to the province of psychology. The more important of these works we owe to Romanes and Sir J. Lubbock, in England; to W. Wundt, L. Büchner, G. Schneider, Fritz Schultze, and Karl Groos, in Germany; to Alfred Espinas and E. Jourdan, in France; and to Tito Vignoli, in Italy.
In Germany, Wilhelm Wundt, of Leipzig, is considered to be the ablest living psychologist; he has the inestimable advantage over most other philosophers of a thorough zoological, anatomical, and physiological education. Formerly assistant and pupil of Helmholtz, Wundt had early accustomed himself to follow the application of the laws of physics and chemistry through the whole field of physiology, and, consequently, in the sense of Johannes Müller, in psychology, as a subsection of the latter. Starting from this point of view, Wundt published his valuable “Lectures on human and animal psychology” in 1863. He proved, as he himself tells us in the preface, that the theatre of the most important psychic processes is in the “unconscious soul,” and he affords us “a view of the mechanism which, in the unconscious background of the soul, manipulates the impressions which arise from the external stimuli.” What seems to me, however, of special importance and value in Wundt’s work is that he “extends the law of the persistence of force for the first time to the psychic world, and makes use of a series of facts of electro-physiology by way of demonstration.”
Thirty years afterwards (1892) Wundt published a second, much abridged and entirely modified, edition of his work. The important principles of the first edition are entirely abandoned in the second, and the monistic is exchanged for a purely dualistic stand-point. Wundt himself says in the preface to the second edition that he has emancipated himself from the fundamental errors of the first, and that he “learned many years ago to consider the work a sin of his youth”; it “weighed on him as a kind of crime, from which he longed to free himself as soon as possible.” In fact, the most important systems of psychology are completely opposed to each other in the two editions of Wundt’s famous Observations. In the first edition he is purely monistic and materialistic, in the second edition purely dualistic and spiritualistic. In the one psychology is treated as a physical science, on the same laws as the whole of physiology, of which it is only a part; thirty years afterwards he finds psychology to be a spiritual science, with principles and objects entirely different from those of physical science. This conversion is most clearly expressed in his principle of psycho-physical parallelism, according to which “every psychic event has a corresponding physical change”; but the two are completely independent, and are not in any natural causal connection. This complete dualism of body and soul, of nature and mind, naturally gave the liveliest satisfaction to the prevailing school-philosophy, and was acclaimed by it as an important advance, especially seeing that it came from a distinguished scientist who had previously adhered to the opposite system of monism. As I myself continue, after more than forty years’ study, in this “narrow” position, and have not been able to free myself from it in spite of all my efforts, I must naturally consider the “youthful sin” of the young physiologist Wundt to be a correct knowledge of nature, and energetically defend it against the antagonistic view of the old philosopher Wundt.
This entire change of philosophical principles, which we find in Wundt, as we found it in Kant, Virchow, Du Bois-Reymond, Karl Ernst Baer, and others, is very interesting. In their youth these able and talented scientists embrace the whole field of biological research in a broad survey, and make strenuous efforts to find a unifying, natural basis for their knowledge; in their later years they have found that this is not completely attainable, and so they entirely abandon the idea. In extenuation of these psychological metamorphoses they can, naturally, plead that in their youth they overlooked the difficulties of the great task, and misconceived the true goal; with the maturer judgment of age and the accumulation of experience they were convinced of their errors, and discovered the true path to the source of truth. On the other hand, it is possible to think that great scientists approach their task with less prejudice and more energy in their earlier years—that their vision is clearer and their judgment purer; the experiences of later years sometimes have the effect, not of enriching, but of disturbing, the mind, and with old age there comes a gradual decay of the brain, just as happens in all other organs. In any case, this change of views is in itself an instructive psychological fact; because, like many other forms of change of opinion, it shows that the highest psychic functions are subject to profound individual changes in the course of life, like all the other vital processes.
For the profitable construction of comparative psychology it is extremely important not to confine the critical comparison to man and the brute in general, but to put side by side the innumerable gradations of their mental activity. Only thus can we attain a clear knowledge of the long scale of psychic development which runs unbroken from the lowest, unicellular forms of life up to the mammals, and to man at their head. But even within the limits of our own race such gradations are very noticeable, and the ramifications of the “psychic ancestral tree” are very numerous. The psychic difference between the crudest savage of the lowest grade and the most perfect specimen of the highest civilization is colossal—much greater than is commonly supposed. By the due appreciation of this fact, especially in the latter half of the century, the “Anthropology of the uncivilized races” (Waitz) has received a strong support, and comparative ethnography has come to be considered extremely important for psychological purposes. Unfortunately, the enormous quantity of raw material of this science has not yet been treated in a satisfactory critical manner. What confused and mystic ideas still prevail in this department may be seen, for instance, in the Völkergedanke of the famous traveller, Adolf Bastian, who, though a prolific writer, merely turns out a hopeless mass of uncritical compilation and confused speculation.
The most neglected of all psychological methods, even up to the present day, is the evolution of the soul; yet this little-frequented path is precisely the one that leads us most quickly and securely through the gloomy primeval forest of psychological prejudices, dogmas, and errors, to a clear insight into many of the chief psychic problems. As I did in the other branch of organic evolution, I again put before the reader the two great branches of the science which I differentiated in 1866—ontogeny and phylogeny. The ontogeny, or embryonic development, of the soul, individual or biontic psychogeny, investigates the gradual and hierarchic development of the soul in the individual, and seeks to learn the laws by which it is controlled. For a great part of the life of the mind a good deal has been done in this direction for centuries; rational pedagogy must have set itself the task at an early date of the theoretical study of the gradual development and formative capacity of the young mind that was committed to it for education and formation. Most pedagogues, however, were idealistic or dualistic philosophers, and so they went to work with all the prejudices of the spiritualistic psychology. It is only in the last few decades that this dogmatic tendency has been largely superseded even in the school by scientific methods; we now find a greater concern to apply the chief laws of evolution even in the discussion of the soul of the child. The raw material of the child’s soul is already qualitatively determined by heredity from parents and ancestors; education has the noble task of bringing it to a perfect maturity by intellectual instruction and moral training—that is, by adaptation. Wilhelm Preyer was the first to lay the foundation of our knowledge of the early psychic development in his interesting work on The Mind of the Child. Much is still to be done in the study of the later stages and metamorphoses of the individual soul, and once more the correct, critical application of the biogenetic law is proving a guiding star to the scientific mind.
A new and fertile epoch of higher development dawned for psychology and all other biological sciences when Charles Darwin applied the principles of evolution to them forty years ago. The seventh chapter of his epoch-making work on The Origin of Species is devoted to instinct. It contains the valuable proof that the instincts of animals are subject, like all other vital processes, to the general laws of historic development. The special instincts of particular species were formed by adaptation, and the modifications thus acquired were handed on to posterity by heredity; in their formation and preservation natural selection plays the same part as in the transformation of every other physiological function. Darwin afterwards developed this fundamental thought in a number of works, showing that the same laws of “mental evolution” hold good throughout the entire organic world, not less in man than in the brute, and even in the plant. Hence the unity of the organic world, which is revealed by the common origin of its members, applies also to the entire province of psychic life, from the simplest unicellular organism up to man.
To George Romanes we owe the further development of Darwin’s psychology and its special application to the different sections of psychic activity. Unfortunately, his premature decease prevented the completion of the great work which was to reconstruct every section of comparative psychology on the lines of monistic evolution. The two volumes of this work which were completed are among the most valuable productions of psychological literature. For, conformably to the principles of our modern monistic research, his first care was to collect and arrange all the important facts which have been empirically established in the field of comparative psychology in the course of centuries; in the second place, these facts are tested with an objective criticism, and systematically distributed; finally, such rational conclusions are drawn from them on the chief general questions of psychology as are in harmony with the fundamental principles of modern monism. The first volume of Romanes’s work bears the title of Mental Evolution in the Animal World; it presents, in natural connection, the entire length of the chain of psychic evolution in the animal world, from the simplest sensations and instincts of the lowest animals to the elaborate phenomena of consciousness and reason in the highest. It contains also a number of extracts from a manuscript which Darwin left “on instinct,” and a complete collection of all that he wrote in the province of psychology.
The second and more important volume of Romanes’s work treats of “Mental evolution in man and the origin of human faculties.” The distinguished psychologist gives a convincing proof in it “that the psychological barrier between man and the brute has been overcome.” Man’s power of conceptual thought and of abstraction has been gradually evolved from the non-conceptual stages of thought and ideation in the nearest related mammals. Man’s highest mental powers—reason, speech, and conscience—have arisen from the lower stages of the same faculties in our primate ancestors (the simiæ and prosimiæ). Man has no single mental faculty which is his exclusive prerogative. His whole psychic life differs from that of the nearest related mammals only in degree, and not in kind; quantitatively, not qualitatively.
I recommend those of my readers who are interested in these momentous questions of psychology to study the profound work of Romanes. I am completely at one with him and Darwin in almost all their views and convictions. Wherever an apparent discrepancy is found between these authors and my earlier productions, it is either a case of imperfect expression on my part or an unimportant difference in application of principle. For the rest, it is characteristic of this “science of ideas” that the most eminent philosophers hold entirely antagonistic views on its fundamental notions.