The traditions of the Delaware Indians and Sioux in the north of the United States territory, and of the Creeks in the south, commence with each stock group as a united body, which, as it migrates, splits into tribes and sends out offshoots developing different dialects. Here was tribal differentiation after entry into the general stock area, the process going on during migration as well as after the tribes had become established in their respective habitats. Culture, however, made little progress till after they became sedentary and took up agriculture to supplement the chase.[219] Tribes sometimes wander far beyond the limits of their stock, like the Iroquoian Cherokees of East Tennessee and North Carolina or the Athapascan Navajos and Apaches of arid New Mexico and Arizona, who had placed twenty or thirty degrees of latitude between themselves and their brethren in the basins of the Yukon and Mackenzie rivers. Such inevitably come into contrasted climatic conditions, which further modify the immigrants. [See map page 54.]
Wide digressions differentiate them still further from the parent stock by landing them amid different ethnic and social groups, by contact with whom they are inevitably modified. The Namaqua Hottentots, living on the southern margin of the Hottentot country near the frontier of the European settlements in Cape Colony, acquired some elements of civilization, together with a strain of Boer and English blood, and in some cases even the Dutch vernacular. They were therefore differentiated from their nomadic and warlike kinsmen in the grasslands north of the Orange River, which formed the center of the Hottentot area.[220] A view of the ancient Germans during the first five or six centuries after Christ reveals differentiation by various contacts in process along all the ragged borders of the Germanic area. The offshoots who pushed westward across the Rhine into Belgian Gaul were rapidly Celticized, abandoning their semi-nomadic life for sedentary agriculture, assimilating the superior civilization which they found there, and steadily merging with the native population. They became Belgae, though still conscious of their Teutonic origin.[221] The Batavians, an offshoot of the ancient Chatti living near the Thuringian Forest, appropriated the river island between the Rhine and the Waal. There in the seclusion of their swamps, they became a distinct national unit, retaining their backward German culture and primitive type of German speech, which the Chatti themselves lost by contact with the High Germans.[222] Far away on the southeastern margin of the Teutonic area the same process of assimilation to a foreign civilization went on a little later when the Visigoths, after a century of residence on the lower Danube in contact with the Eastern Empire, adopted the Arian form of Christianity which had arisen in the Greek peninsula.[223] The border regions of the world show the typical results of the historical movement—differentiation from the core or central group through assimilation to a new group which meets and blends with it along the frontier.
Geographic conditions of heterogeneity and homogeneity.
Entrance into a naturally isolated district, from which subsequent incursions are debarred, gives conditions for divergence and the creation of a new type. On the other hand, where few physical barriers are present to form these natural pockets, the process of assimilation goes on over a wide field. Europe is peculiar among the family of continents for its "much divided" geography, commented upon by Strabo. Hence its islands, peninsulas and mountain-rimmed basins have produced a variegated assemblage of peoples, languages and culture. Only where it runs off into the monotonous immensity of Russia do we find a people who in their physical traits, language, and civilization reflect the uniformity of their environment.[224]
Africa's smooth outline, its plateau surface rimmed with mountains which enclose but fail to divide, and its monotonous configuration have produced a racial and cultural uniformity as striking as Europe's heterogeneity. Constant movements and commixture, migration and conquest, have been the history of the black races, varied by victorious incursions of the Hamitic and Semitic whites from the north, which, however, have resulted in the amalgamation of the two races after conquest.[225] Constant fusion has leveled also the social and political relations of the people to one type; it has eliminated primordial groups, except where the dwarf hunters have taken refuge in the equatorial forests and the Bushmen in the southwestern deserts, just as it has thwarted the development of higher social groups by failure to segregate and protect. It has sown the Bantu speech broadcast over the immense area of Central Africa, and is disseminating the Hausa language through the agency of a highly mixed commercial folk over a wide tract of the western Sudan. The long east-and-west stretch of the Sudan grasslands presents an unobstructed zone between the thousand-mile belt of desert to the north and the dense equatorial forests to the south, between hunger and thirst on one side, heat and fever and impenetrable forests on the other. Hence the Sudan in all history has been the crowded Broadway of Africa. Here pass commercial caravans, hybrid merchant tribes like the Hausa, throngs of pilgrims, streams of peoples, herds of cattle moving to busy markets, rude incursive shoppers or looters from the desert, coming to buy or rob or rule in this highway belt. [See map page 105.]
Differentiation versus assimilation.
Historical development advances by means of differentiation and assimilation. A change of environment stimulates variation. Primitive culture is loath to change; its inertia is deep-seated. Only a sharp prod will start it moving or accelerate its speed; such a prod is found in new geographic conditions or new social contacts. Divergence in a segregated spot may be overdone. Progress crawls among a people too long isolated, though incipient civilization thrives for a time in seclusion. But in general, accessibility, exposure to some measure of ethnic amalgamation and social contact is essential to sustained progress.[226] As the world has become more closely populated and means of communication have improved, geographical segregation is increasingly rare. The earth has lost its "corners." All parts are being drawn into the circle of intercourse. Therefore differentiation, the first effect of the historical movement, abates; the second effect, assimilation, takes the lead.