Anthropo-geography has to do primarily with the forms and relief of the land.  The relief of the sea floor influences man only indirectly.  It does this by affecting the forms of the coast, by contributing to the action of tides in scouring out river estuaries, as on the flat beaches of Holland and England, by determining conditions for the abundant littoral life of the sea, the fisheries of the continental shelf which are factors in the food quest and the distribution of settlements.  Moreover, the ocean floor enters into the problem of laying telegraph cables, and thereby assumes a certain commercial and political importance.  The name of the Telegraph Plateau of the North Atlantic, crossed by three cables, points to the relation between these and submarine relief.  So also does the erratic path of the cable from southwestern Australia to South Africa via Keeling Island and Mauritius.

Submarine reliefs have yet greater significance in their relation to the distribution of the human race over the whole earth; for what is now a shallow sea may in geologically recent times have been dry land, on which primitive man crossed from continent to continent.  It is vital to the theory of the Asiatic origin of the American Indian that in Miocene times a land bridge spanned the present shallows of Bering Sea.  Hence the slight depth of this basin has the same bio-geographical significance as that of the British seas, the waters of the Malay Archipelago, and the Melanesian submarine platform.  The impressive fact about “Wallace’s Line” is the depth of the narrow channel which it follows through Lombok and Macassar Straits and which, in recent geological times, defined the southeastern shore of Asia.  In all these questions of former land connection, anthropo-geography follows the lead of bio-geography, whose deductions, based upon the dispersal of countless plant and animal forms, point to the paths of human distribution.

[Sidenote:  Mean elevations of the continents.]

The mean elevation of the continents above sea level indicates the average life conditions of their populations as dependent upon relief.  The 1010 meters (3313 feet) of Asia indicate its predominant highland character.  The 330 meters (1080 feet) representing the average height of Europe, and the 310 meters (1016 feet) of Australia indicate the preponderance of lowlands.  Nevertheless, anthropo-geography rarely lends itself to a mathematical statement of physical conditions.  Such a statement only obscures the facts.  The 660 meters (2164 feet) mean elevation of Africa indicates a relief higher than Europe, but gives no hint of the plateau character of the Dark Continent, in which lowlands and mountains are practically negligible features; while the almost identical figure (650 meters or 2133 feet) for both North and South America is the average derived from extensive lowlands in close juxtaposition to high plateaus capped by lofty mountain ranges.  Such mathematical generalizations indicate the general mass of the continental upheaval, but not the way this mass is divided into low and high reliefs.[1026]