(3) Problems of hereditary response or in stinct. These properly belong to the general science of genetics and only by reason of neces sity does the genetic psychologist attempt their solution. They include all questions concerning instinct as consciousness and as adapted re sponse. In this field a most important question is, "How do instincts originate?* The distant goal of the student of psychic heredity is the ability to create and to control instinctive characteristics.
(4) Problems of individual acquisition, ex perience or habit. These can be solved com pletely only in conjunction with problems of instinct, for acquisition is grafted upon heredity. The evolution of the learning process or proc esses, and the development of modes of learn ing in various species of organism, constitute a most fascinating and practically important field of inquiry. Language habits are at present commanding attention, as they manifest them selves in infrahuman and in human organisms.
(5) Problems of imagination. These in clude all questions concerning the genesis of memory, of reproductive imagination and of creative imagination as well. They are of obvious importance, since the transition from mere awareness of the present moment of life to more or less definite consciousness of yes terday and of to-morrow separates the lower from the higher organisms.
(6) Problems of thought and reasoning. Although these are intimately bound up with problems of imagination, they may be discussed separately because reasoning is a form of think ing peculiar to recent stages in mental evolu tion. It may or may not prove to be distinc tively human, but at any rate it exists in com plex form only among the higher mammals. The student of reasoning is beginning to ask, instead of the old question, °Do animals reason?", "What is the genesis and natural history of reasoning processes?* (7) Problems of the relation of mind to body. Mental evolution exists for the scientist in association with an organism. It is one of his tasks to discover whether there exists some definite mode of energy which should be desig nated as psychic, and if so, how this energy is produced and how it influences behavior. The notion that mind is epiphenomenal, aloof from life, a sort of penumbra, is in disfavor.
It remains to indicate, briefly, the chief achievements of genetic psychology. The most
notable achievements may be summarized under the captions mental development and mental evolution. In both fields of genetic description, progress has been rapid during the last two or three decades.
Mental Darwin's notes on the mental development of one of his children set the fashion. Ever since, parents, teachers and more disinterested psychological observers have followed his lead. The resulting diary records of mental growth in infancy, childhood and adolescence are invaluable.
The work of Preyer in Germany is conspicu ous in the early history of ontogenetic psy chology, for he observed carefully, collected and systematically arranged the data of others, and in his several books offered what long remained the best systematic discussion of child psychology. His studies extend even to the mental life of the foetus or embryo, for in common with many other observers, he recog nized signs of mental life prior to the physical incident of birth.
To Preyer and his European contemporaries, psychology owes chiefly its data on (1) the early stages of sensory development: the first appearance of sensory functions in the indi vidual, their characteristics, relations and their role in individual development; (2) the essen tial features of the growth of perceptual con sciousness; (3) the important stages in the de velopment of will; (4) the nature and order of co-ordination in experience and in response; (5) the history of language habits ,• and (6) the development of imagination, thought, reasoning.
To these several groups of facts, important contributions have been made in recent years, so that psychology possesses to-day a good working outline of the development of the human mind. Such an outline may not be re produced here even briefly, but it may be ob tained from the works of Preyer, Tracy and Stumpfl, Baldwin, Hall and others.
The diary method, by which from day to day new and changing facts of mental life are recorded, has been supplanted by more definitely planned and systematic experimental observation.
Preyer, Kussmaul and others used the ex perimental method nearly 40 years ago in the study of children. Baldwin experimented with his children, and like Darwin set a fashion. But since experimentation with in fants and young children is difficult, progress has been halting.