acilities of dispersal often give animal forms a wide or cosmopolitan
distribution. Man, by appropriating the mobile forces in the air and
water to increase his own powers of locomotion, has become a
cosmopolitan being, and made the human race reflect the unity of
atmosphere and hydrosphere.

Always the eternal unrest of the moving waters has knocked at the door
of human inertia to arouse the sleeper within; always the flow of stream
and the ebb of tide have sooner or later stirred the curiosity of the
land-born barbarian about the unseen destination of these marching
waters. Rivers by the mere force of gravity have carried him to the
shores of their common ocean, and placed him on this highway of the
world. Then from his sea-girt home, whether island or continent, he has
timidly or involuntarily followed the track which headland-dotted coast,
or ocean current, or monsoon, or trade wind marked out for him across
the pathless waters, so that at the gray dawn of history he appears as
a cosmopolite, occupying every part of the habitable earth.

These sporadic oversea wanderings, with intervals of centuries or
milleniums between, opened to his occupancy strange and remote lands, in
whose isolation and new environment he developed fresh variations of
mind, body and cultural achievements, to arm him with new weapons in the
struggle for existence. The sea which brought him bars him for a few
ages from his old home, till the tradition of his coming even is lost.
Then with higher nautical development, the sea loses its barrier nature;
movements of people, and trade recross its surface to unite those who
have been long severed and much differentiated in their mutual
remoteness. The ensuing friction and mingling weed out the less fit
variations of each, and combine in the new race the qualities able to
fortify a higher type of man. Not only seas and oceans, but also
mountains and deserts serve to isolate the migrant people who once has
crossed them; but wastes of water raise up the most effective barriers.

[Sidenote: Oceans and seas in universal history.]

The transformation of the ocean into a highway by the development of
navigation is a late occurrence in the history of man and is perhaps the
highest phase of his adaptation to environment, because an adaptation
which has placed at his disposal that vast water area constituting
three-fourths of the earth's surface from which he had previously been
excluded. Moreover, it was