If any one doubts the importance of the tetrahedral form, let him consider how evolution would have been hampered if the land of the globe were arranged as isolated masses in low latitudes, while oceans took the place of the present northern continents. The backwardness of the indigenous life of Africa shows how an equatorial position retards evolution. The still more marked backwardness of Australia with its kangaroos and duck-billed platypuses shows how much greater is the retardation when a continent is also small and isolated. Today, no less than in the past, the tetrahedral form of the earth and the relation of the tetrahedron to the poles and to the equator preserve the conditions that favor rapid evolution. They are the dominant factors in determining that America shall be one of the two great centers of civilization. If North and South America be counted as one major land mass, and Europe, Asia, and Africa as another, the two present the same general features. Yet their mountains, plains, and coastal indentations are so arranged that what is on the east in one is on the west in the other. Their similarity is somewhat like that of a man's two hands placed palms down on a table. On a map of the world place a finger of one hand on the western end of Alaska and a finger of the other on the northeastern tip of Asia and follow the main bones of the two continents. See how the chief mountain systems, the Pacific "cordilleras," trend away from one another, southeastward and southwestward. In the centers of the continents they expand into vast plateaus. That of America in the Rocky Mountain region of the United States reaches a width of over a thousand miles, while that of Asia in Tibet and western China expands to far greater proportions.