In previous chapters we have gained some idea of the topography of the New World and of the climate in its relation to plants and animals. We have also seen that climate has much to do with human energy. We have not, however, gained a sufficiently clear idea of the distribution of climatic energy. A map of the world showing how energy would be distributed if it depended entirely upon climate clarifies the subject. The dark shading of the map indicates those regions where energy is highest. It is based upon measurements of the strength of scores of individuals, upon the scholastic records of hundreds of college students, upon the piecework of thousands of factory operatives, and upon millions of deaths and births in a score of different countries. It takes account of three chief climatic conditions--temperature, humidity, and variability. It also takes account of mental as well as physical ability. Underneath it is a map of the distribution of civilization on the basis of the opinion of fifty authorities in fifteen different countries. The similarity of the two maps is so striking that there can be little question that today the distribution of civilization agrees closely with the distribution of climatic energy. When Egypt, Babylonia, Greece, and Rome were at the height of their power this agreement was presumably the same, for the storm belt which now gives variability and hence energy to the thickly shaded regions in our two maps then apparently lay farther south. It is generally considered that no race has been more closely dependent upon physical environment than were the Indians. Why, then, did the energizing effect of climate apparently have less effect upon them than upon the other great races? Why were not the most advanced Indian tribes found in the same places where white civilization is today most advanced? Climatic changes might in part account for the difference, but, although such changes apparently took place on a large scale in earlier times, there is no evidence of anything except minor fluctuations since the days of the first white settlements. Racial inheritance likewise may account for some of the differences among the various tribes, but it was probably not the chief factor. That factor was apparently the condition of agriculture among people who had neither iron tools nor beasts of burden. Civilization has never made much progress except when there has been a permanent cultivation of the ground. It has been said that "the history of agriculture is the history of man in his most primitive and most permanent aspect." If we examine the achievements and manner of life of the Indians in relation to the effect of climate upon agriculture and human energy, as well as in relation to the more obvious features of topography and vegetation, we shall understand why the people of aboriginal America in one part of the continent differed so greatly from those in another part. In the far north the state of the inhabitants