GENETIC PSYCHOLOGY. The study of the evolution and development of mind is termed genetic psychology. It is the historical aspect, or division, of the general science of mental life, and it is therefore definable, as con trasted with other branches of the science, only in terms of its purpose or aim, which is genetic description. As compared with the genetic psychologist, the student of human psychology is a narrow specialist, for he is intent upon one particular form of mind among the myriads which exist or have existed in the course of the evolution of life.
Divisions.— With respect to its major ma terials, genetic psychology is divisible into two parts— the study of the development or growth of mind in the individual (technically called the ontogenesis of mind), and the study of the evolution of mind on the earth (technically, the phylogenesis of mind). The nearest popular equivalent for the term psycho-ontogenesis is child psychology; and for psychophylogenesis, animal psychology.
The study of the development' of mind in the individual is less difficult and, in many other respects, more satisfactory than that of the evolution of mind, for whereas many of the steps or stages in the latter process have com pletely disappeared by reason of the extinction of the types of organism to which they be longed, the various stages in individual de velopment are continuously presented for observation. The mental life of the dinosaur cannot, now, be scientifically described because the organism no longer exists, and further, be cause records of its structure, habits and habitat are extremely meagre. But by contrast, the growth of mind in the mouse, rat, cat, dog, monkey, man, may be described in detail, since each day and hour new individuals of these types are coming into being. The story of mental evolution can be told only very incom pletely from direct observation, whereas that of mental growth or development can be told wholly and in detail.
These two divisions of genetic psychology are intimately related and necessarily supple ment one another, since the process of phy logenesis is repeated more or less completely in the growth of every individual. According to the theory of recapitulation, mental develop ment in man presents, cinematographically, the major steps or stages in mental evolution. The mental constitution of the gamete, with which, structurally, the existence of the human individual begins, is perhaps comparable with that of certain one-celled plants or animals; that of the foetus may more or less closely resemble that of various invertebrates; that of the new-born infant may be compared with certain types of lower vertebrate. And so,
as the individual develops, racial type after type of mental organization appears, plays its genetic role and disappears. Just as in the development of the body, structures, such for example as the gill slits, appropriate to earlier types of organization, appear, function par tially or completely for a time, and partially or wholly disappear. Apparently, nothing which has existed in the organic realm is totally lost. Even the extinct dinosaur may have bequeathed to us humans certain briefly visible and func tional structures. Who knows but that for some brief period in our existence we are in form, behavior and experience amceba-like, fish-like, monkey-like. G. Stanley Hall, the foremost of genetic psychologists, has pictur esquely expressed this idea. "In this process the individual in a general way repeats the history of its species, passing slowly from the protozoan to the metazoan stage, so that we have all traversed in our own bodies ameboid, helminthoid, piscian, amphibian, anthropoid, ethnoid, and we know not how many intercalary stages of ascent." 'Vol. 1, p. 2).
Studies in individual mental development constantly suggest problems in mental evolution and the reverse. Thus, the investigation of reacting tendencies or methods of adaptation to environment in an organism at different stages suggests the question, "Do these various ten dencies to action and adaptive responses rep resent different levels of mental evolution? Are they the characteristic and appropriate modes of response of various existing or ex tinct types of organism?" Otherwise stated, "Do we human beings at first react ineffectively as does the fish, turtle or guinea pig; later, more highly adaptively as does the dog; still later, more intelligently as does the monkey or anthropoid ape?" Such crude questions as these are being asked to-day not idly or vainly, for it is obviously possible to obtain definite, if not complete, answers. There is developing an interest in the problems of genetic psy chology which promises soon to tear aside the vale of ignorance and reveal the related proc esses of mental development and 'volution.