grasslands of Africa, present the picture of a great
thoroughfare swept by pressing throngs. Other regions, more secluded,
appear as quiet nooks, made for a temporary halt or a permanent rest.
Here some part of the passing human flow is caught as in a vessel and
held till it crystallizes into a nation. These are the conspicuous areas
of race characterization. The development of the various ethnic and
political offspring of the Roman Empire in the naturally defined areas
of Italy, the Iberian Peninsula, and France illustrates the process of
national differentiation which goes on in such secluded-locations.

III. INVESTIGATIONS AND PROBLEMS

1. Isolation in Anthropogeography and Biology

A systematic treatise upon isolation as a sociological concept remains
to be written. The idea of isolation as a tool of investigation has been
fashioned with more precision in geography and in biology than in
sociology.

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