shall have disappeared, there will be one
variety the less in humanity. So the process of assimilation advances,
here by the simple elimination of weaker divergent types of men, there
by amalgamation and absorption into the stock of the stronger.

This unity of the human species has been achieved in spite of the fact
that, owing to the three-fold predominance of the water surface of the
globe, the land surface appears as detached fragments which rise as
islands from the surrounding ocean. Among these fragments we have every
gradation in size, from the continuous continental mass of
Eurasia-Africa with its 31,000,000 square miles, the Americas with
15,000,000, Australia with nearly 3,000,000, Madagascar with 230,000,
and New Zealand with 104,000, down to Guam with its 199 square miles,
Ascension with 58, Tristan da Cunha with 45, and the rocky Islet of
Helgoland with its scant 150 acres. All these down to the smallest
constitute separate vital districts.

[Sidenote: Isolation and differentiation.]

Small, naturally defined areas, whether their boundaries are drawn by
mountains, sea, or by both, always harbor small but markedly individual
peoples, as also peculiar or endemic animal forms, whose differentiation
varies with the degree of isolation. Such peoples can be found over and
over again in islands, peninsulas, confined mountain valleys, or
desert-rimmed oases. The cause lies in the barriers to expansion and to
accessions of population from without which confront such peoples on
every side. Broad, uniform continental areas, on the other hand, where
nature has erected no such obstacles are the habitats of wide-spread
peoples, monotonous in type. The long stretch of coastal lowlands
encircling the Arctic Ocean and running back into the wide plains of
North America and Eurasia show a remarkable uniformity of animal and
plant forms[298] and a striking similarity of race through the Lapps, the
Samoyedes of northern Russia, the various Mongolian tribes of Arctic
Siberia to Bering Strait, and the Eskimo, that curiously transitional
race, formerly classified as Mongolian and more recently as a divergent
Indian stock; for the Eskimos are similar to the Siberians in stature,
features, coloring, mode of life, in everything but head-form, though
even the cephalic indices approach on the opposite shores of Bering
Sea.[299] Where geography draws no dividing line, ethnology finds it
difficult to do so. Where the continental land-