[280] Eleventh Census of the United States, _Report on Population_, Part I, map p. 23. Washington, 1894. [281] W.Z. Ripley, Races of Europe, Chapters 7, 8, 11. New York, 1899. [282] H.R. Mill, International Geography, p. 910. New York, 1902. [283] _Ibid._, pp. 832, 836. [284] Ratzel, History of Mankind, Vol. III, pp. 175, 257. London, 1896-1898. [285] E.C. Semple, American History and its Geographic Conditions, pp. 280-287. Boston, 1903. [286] C.E. Akers, History of South America, 1854-1894, pp. 501-502, 556-562. New York, 1904. [287] E.A. Freeman, Historical Geography of Europe, p. 14. London, 1882. [288] Helmolt, History of the World, Vol. VI, pp. 125-132, map. New York, 1902-1906. Ripley, Races of Europe, pp. 274, 297, 308, 472-473. New York, 1899. [289] H.J. Mackinder, Britain and the British Seas, pp. 183-191. London, 1904. [290] W.Z. Ripley, Races of Europe, pp. 26, 353, 361-365. Map. New York, 1899. [291] Ratzel, History of Mankind, Vol. I, 214-218. London, 1896-1898. CHAPTER VI GEOGRAPHICAL AREA [Sidenote: The size of the earth.] Every consideration of geographical area must take as its starting point the 199,000,000 square miles (510,000,000 square kilometers) of the earth's surface. Though some 8,000,000 square miles (21,000,000 square kilometers) about the poles remain unexplored, and only the twenty-eight per cent. of the total constituting the land area is the actual habitat of man, still the earth as a whole is his planet. Its surface fixes the limits of his possible dwelling place, the range of his voyages and migrations, the distribution of animals and plants on which he must depend. These conditions he has shared with all forms of life from the amoeba to the civilized nation. The earth's superficial area is the primal and immutable condition of earth-born, earth-bound man; it is the common soil whence is sprung our common humanity. Nations belong to countries and races to continents, but humanity belongs to the whole world. Naught but the united forces of the whole earth could have produced this single species of a single genus which we call Man. [Sidenote: Relation of area to life.]