of the modern civilized state.  Hence we may lay down the rule that change in areal relations, both of the individual to his decreasing quota of land, and of the state to its increasing quota of the earth’s surface is an important index of social and political evolution.  Therefore the rise and decline not only of peoples but of whole civilizations have depended upon their relations to area.  Therefore problems of area, such as the expansion of a small territory, the economic and political mastery of a large one, dominate all history.

[Sidenote:  The Oikoumene.]

Humanity’s area of distribution and historical movement call the Oikoumene.  It forms a girdle around the earth between the two polar regions, and embraces the Tropics, the Temperate Zones, and a part of the North Frigid, in all, five-sixths of the earth’s surface.  This area of distribution is unusually large.  Few other living species so nearly permeate the whole vital area, and many of these have reached their wide expansion only in the company of man.  Only about 49,000,000 square miles (125,000,000 square kilometers) of the Oikoumene is land and therefore constitutes properly the habitat of man.  But just as we cannot understand a nation from the study of its own country alone, but must take into consideration the wider area of its spreading activities, so we cannot understand mankind without including in his world not only his habitat but also the vastly larger sphere of his activities, which is almost identical with the earth itself.  The most progressive peoples to-day find their scientific, economic, religious and political interests embracing the earth.

[Sidenote:  Unity of the human species in the relation to the earth.]

Mankind has in common with all other forms of life the tendency toward expansion.  The more adaptable and mobile an organism is, the wider the distribution which it attains and the greater the rapidity with which it displaces its weaker kin.  In the most favored cases it embraces the whole vital area of the earth, leaving no space free for the development of diversity of forms, and itself showing everywhere only superficial distinctions.  Mankind has achieved such wide distribution.  Before his persistent intrusions and his mobility, the earth has no longer any really segregated districts where a strongly divergent type of the man animal might develop.  Hence mankind shows only superficial distinctions of hair, color, head-form and stature between its different groups.  It has got beyond the point of forming species, and is restricted to the slighter variations of races.  Even these are few in comparison with the area of the earth’s surface, and their list tends to decrease.  The Guanches and Tasmanians have vanished, the Australians are on the road to extinction; and when they 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.