cally by several
generations of residence in a temperate land. Their changes have been
chiefly cultural. The Englishman has altered only superficially in the
various British colonial lands. Constant intercourse and the progress of
inventions have enabled him to maintain in diverse regions approximate
uniformity of physical well-being, similar social and political ideals.
The changed environment modifies him in details of thought, manner, and
speech, but not in fundamentals.

Moreover, civilized man spreading everywhere and turning all parts of
the earth's surface to his uses, has succeeded to some extent in
reducing its physical differences. The earth as modified by human action
is a conspicuous fact of historical development.[234] Irrigation,
drainage, fertilization of soils, terrace agriculture, denudation of
forests and forestration of prairies have all combined to diminish the
contrasts between diverse environments, while the acclimatization of
plants, animals and men works even more plainly to the same end of
uniformity. The unity of the human race, varied only by superficial
differences, reflects the unity of the spherical earth, whose
diversities of geographical feature nowhere depart greatly from the mean
except in point of climate. Differentiation due to geography, therefore,
early reached its limits. For assimilation no limit can be forseen.

[Sidenote: Geographical origins.]

In view of this constant differentiation on the one hand, and
assimilation on the other, the historical movement has made it difficult
to trace race types to their origin; and yet this is a task in which
geography must have a hand. Borrowed civilizations and purloined
languages are often so many disguises which conceal the truth of ethnic
relationships. A long migration to a radically different habitat, into
an outskirt or detached location protected from the swamping effects of
cross-breeding, results eventually in a divergence great enough to
obliterate almost every cue to the ancient kinship. The long-headed
Teutonic race of northern Europe is regarded now by ethnologists as an
offshoot of the long-headed brunette Mediterranean race of African
origin, which became bleached out under the pale suns of Scandinavian
skies. The present distribution of the various Teutonic stocks is a
geographical fact; their supposed cradle in the Mediterranean basin is a
geographical hypothesis. The connecting links must also be geographical.
They must