Research in human geography has as its object the study of man in his relations to the earth. Students of civilization, like Montesquieu and Buckle, sought to explain the culture and behavior of peoples as the direct result of the physical environment. Friedrich Ratzel with his "thorough training as a naturalist, broad reading, and travel" and above all, his comprehensive knowledge of ethnology, recognized the importance of direct effects, such as cultural isolation. Jean Brunhes, by the selection of small natural units, his so-called "islands," has made intensive studies of isolated groups in the oases of the deserts of the Sub and of the Mzab, and in the high mountains of the central Andes. Biology indicates isolation as one of the factors in the origin of the species. Anthropology derives the great races of mankind--the Caucasian, the Ethiopian, the Malay, the Mongolian, and the Indian--from geographical separation following an assumed prehistoric dispersion. A German scholar, Dr. Georg Gerland, has prepared an atlas which plots differences in physical traits, such as skin color and hair texture, as indicating the geographical distribution of races. 2. Isolation and Social Groups Anthropogeographical and biological investigations have proceeded upon the assumption, implicit or explicit, that the geographic environment, and the physical and mental traits of races and individuals, _determine_ individual and collective behavior. What investigations in human geography and heredity actually demonstrate is that the geographic environment and the original nature of man _condition_ the culture and conduct of groups and of persons. The explanations of isolation, so far as it affects social life, which have gained currency in the writings of anthropologists and geographers, are therefore too simple. Sociologists are able to take into account forms of isolation not considered by the students of the physical environment and of racial inheritance. Studies of folkways, mores, culture, nationality, the products of a historical or cultural process, disclose types of social contact which transcend the barriers of geographical or racial separation, and reveal social forms of isolation which prevent communication where there is close geographical contact or common racial bonds. The literature upon isolated peoples ranges from investigations of arrest of cultural development as, for example, the natives of Australia, the Mountain Whites of the southern states, or the inhabitants of Pitcairn Island to studies of hermit nations, of caste systems as in India, or of outcast groups such as feeble-minded "tribes" or hamlets, fraternities of criminals, and the underworld of commercialized prostitution. Special research in dialects, in folklore, and in provincialism shows how spatial isolation fixes differences in speech, attitudes, folkways, and mores which, in turn, enforce isolation even when geographic separation has disappeared.