We do not discuss the anatomical, physiological, and mental characteristics of man considered as an individual; but we are interested in the diversity of these traits in groups of men found in different geographical areas and in different social classes. It is our task to inquire into the causes that have brought about the observed differentiation, and to investigate the sequence of events that have led to the establishment of the multifarious forms of human life. In other words, we are interested in anatomical and mental characteristics in so far as they are peculiar to groups of men living under the same biological, geographical, and social environment, and as determined by their past. Thus we are concerned with the effects of the climate and products of a country upon human life, with the influence of heat and of cold upon the bodily frame, with modifications in the life of communities brought about by geographical isolation, and with those due to the sufficiency or insufficiency of food-supply. No less interesting to us are the phenomena of dependence of human life upon those social conditions that find expression in the customary mode of nutrition and occupation; in the effects of contact between neighboring groups of people; in modifications brought about by migrations; and in the forms of life as influenced by the density of population. To understand these modifications, we require a knowledge of individual anatomy, physiology, and psychology, because the establishment of a characteristic social group can be brought about only by a parallel development which occurs in all the individuals exposed to similar influences.
Thus it appears that the genesis of the types of man, considered from an anatomical, physiological, and psychological point of view, is the chief object of anthropological research. When our problem is formulated in this manner, we recognize at once that a separation of anthropological methods from the methods of biology and psychology is impossible, and that certain problems of anthropology can be approached only from the point of view of these sciences. It might perhaps even be said that the investigation of the types of man is a purely biological problem, and that the only questions involved are such as can be treated by the application of those biological methods which are gradually clearing up the genesis of the types of animals and plants. A similar claim may be made in regard to the psychological problems. If there are any laws determining the growth and development of the human mind, they can be only laws that act in the individual, and consequently they must be determined by the application of individual psychology.
Thus an examination of our problems suggests that the whole group of anthropological phenomena may be evanescent, that they may be at bottom biological and psychological problems, and that the whole field of anthropology belongs either to the one or to the other of these sciences.
Nevertheless, anthropological phenomena possess a very genuine interest and unity. This is largely due to the fact that everything that concerns our own species is of special interest to us. The feeling of solidarity of mankind, but more particularly of the individual with his people and with the class of society to which he belongs, which finds in our day its strongest expression in the strife of the nations, has brought it about that the minute differences between the physical organization of different races, types, and social groups, have arrested attention much more vigorously than similar differences in the rest of the animal kingdom have done; and points of view have early become important that until recent times have received little attention on the part of biologists, or that have not yet claimed their attention. The distribution of distinct psychological types in man has proved an even more fascinating study, the investigation of which has led to problems that the inductive psychology of modern times is not yet ready to attack.
This centralization of interest in the manifestations of life in social units has determined the course of development of anthropology.
Anthropological research leads us to two fundamental questions: Why are the tribes and nations of the world different, and how have the present differences developed? The first question, if it can be solved adequately, will always lead us to biological and psychological laws that act on man as an individual, in which we see the single event mirrored in one broad generalization. But even if we should have succeeded in reducing to a series of laws the multiplicity of events which manifest themselves in the development of new types and in the growth of new mental activities, a strong interest will remain in the actual developments which have occurred among the various peoples of the world.
This is true not only of anthropology, but also of biology and genetic psychology, and of other sciences describing the sequence of events in the universe; and the intense modern interest in evolution expresses the recognition of the importance of what might be called the historical view-point.
In this sense, anthropology is the science that endeavors to reconstruct the early history of mankind, and that tries, wherever possible, to express in the form of laws ever-recurring modes of historical happenings. Since written history covers a brief span of time, and relates in fragmentary records the fates of a few only of the multitude of peoples of the earth, the anthropologist must endeavor by methods of his own to clear up the darkness of past ages and of remote parts of the world.
While, from this theoretical point of view, anthropology must devote itself to the investigation of human types and human activities and thought the world over, its actual field of work is much more restricted. Biology and psychology on the one hand, and history, economics, sociology, and philology on the other, have taken up anthropological problems, each from its own point of view, and each in connection with its own subject of investigation. As a matter of fact, the field of work as theoretically outlined would require such a vast variety of training, that no single person could possibly hope to master it. The special task that is actually assigned at the present time to the anthropologist is the investigation of the primitive tribes of the world that have no written history, that of prehistoric remains and of the types of man inhabiting the world at present and in past times. It will be recognized that this limitation of the field of work of the anthropologist is more or less accidental, and originated because other sciences occupied part of the ground before the development of modern anthropology.