CHAPTER IV
I. INTRODUCTION
1. Geological and Biological Conceptions of Isolation
Relations of persons with persons, and of groups with groups, may be either those of isolation or those of contact. The emphasis in this chapter is placed upon isolation, in the next chapter upon contact in a comparison of their effects upon personal conduct and group behavior.
Absolute isolation of the person from the members of his group is unthinkable. Even biologically, two individuals of the higher animal species are the precondition to a new individual existence. In man, postnatal care by the parent for five or six years is necessary even for the physiological survival of the offspring. Not only biologically but sociologically complete isolation is a contradiction in terms. Sociologists following Aristotle have agreed with him that human nature develops within and decays outside of social relations. Isolation, then, in the social as well as the biological sense is relative, not absolute.
The term "isolation" was first employed in anthropogeography, the study of the relation of man to his physical environment. To natural barriers, as mountains, oceans, and deserts, was attributed an influence upon the location of races and the movements of peoples and the kind and the degree of cultural contact. The nature and the extent of separation of persons and groups was considered by geographers as a reflex of the physical environment.
In biology, isolation as a factor in the evolution and the life of the species, is studied from the standpoint of the animal group more than from that of the environment. Consequently, the separation of species from each other is regarded as the outcome not only of a sheer physical impossibility of contact, but even more of other factors as differences in physical structure, in habits of life, and in the instincts of the animal groups. J. Arthur Thomson in his work on "Heredity" presents the following compact and illuminating statement of isolation as a factor in inheritance.
The only other directive evolution-factor that biologists are at all agreed about, besides selection, is isolation—a general term for all the varied ways in which the radius of possible intercrossing is narrowed. As expounded by Wagner, Weismann, Romanes, Gulick, and others, isolation takes many forms—spatial, structural, habitudinal, and psychical—and it has various results.
It tends to the segregation of species into subspecies, it makes it easier for new variations to establish themselves, it promotes prepotency, or what the breeders call "transmitting power," it fixes characters. One of the most successful breeds of cattle (Polled Angus) seems to have had its source in one farmsteading; its early history is one of close inbreeding, its prepotency is remarkable, its success from our point of view has been great. It is difficult to get secure data as to the results of isolation in nature, but Gulick's recent volume on the subject abounds in concrete illustrations, and we seem warranted in believing that conditions of isolation have been and are of frequent occurrence.
Reibmayr has collected from human history a wealth of illustrations of various forms of isolation, and there seems much to be said for his thesis that the establishment of a successful race or stock requires the alternation of periods of inbreeding (endogamy) in which characters are fixed, and periods of outbreeding (exogamy) in which, by the introduction of fresh blood, new variations are promoted. Perhaps the Jews may serve to illustrate the influence of isolation in promoting stability of type and prepotency; perhaps the Americans may serve to illustrate the variability which a mixture of different stocks tends to bring about. In historical inquiry into the difficult problem of the origin of distinct races, it seems legitimate to think of periods of "mutation"—of discontinuous sporting—which led to numerous offshoots from the main stock, of the migration of these variants into new environments where in relative isolation they became prepotent and stable.[94]