vergence 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.]

[Sidenote: Differentiation versus assimilation.]

Historical development advances by means of differentiation and
assimilation. A change of environment stimulat