THE HUMAN OR PRESENT PERIOD. 537 



in the early evolution and distribution of the human race. Relation- 

 ship to the open, semi-arid, or mildly humid plains and fertile valleys 

 that bordered on the desert barriers, was probably influential in lead- 

 ing to that control of the plant and animal kingdom that has made 

 man the most influential of all biological agencies. Powell and others 

 hold that agriculture owed its chief early evolution to arid conditions 

 which induced man to irrigate and cultivate the plants necessary for 

 his sustenance, and tended to fix his abode in the watered tracts. It 

 is urged that the watering and slight culture of chosen plants in an 

 arid tract was a less formidable task to ill-equipped primitive peoples, 

 than the subjugation of competitive plants in a humid region. How- 

 ever this may be, there are various reasons why the open lands of 

 semi-aricl or mildly humid regions, with their varied floras and faunas 

 and their active expansive life, with its sharp competitions in fleetness, 

 alertness, and sagacity, and its occasional crises of drought and storm, 

 should have fostered a favorable evolution in primitive man. The 

 cereals he learned to cultivate were chiefly members of the grass family 

 that grew natively on the plains, and the animals he domesticated 

 were largely also those of the plains. To us it seems also significant 

 that the centers of early civilization were all regions of relatively high 

 barometer, of descending air-currents, and of semi-arid or mildly humid 

 atmospheric conditions, all of which seem to be more favorable to 

 activity of mind and body than prevailing low barometer, ascending 

 air-currents, and humidity. 



The physiographic associations of the progressive stages of civiliza- 

 tion of the white races are suggestive. The most ancient recorded 

 civilizations lay in the valleys of the Nile and Euphrates on fertile 

 plains, but bounded by inhospitable deserts or mountain tracts, and 

 in latitudes near 30° N. The somewhat later civilizations of Assyria, 

 Palestine, and Phoenicia lay a few degrees farther north under simi- 

 lar conditions, but with sea-contact, another of the expansive influ- 

 ences, added in the case of Phoenicia. The succeeding civilization of 

 Greece lay about 5° farther north, under clear skies, pure dry air, high 

 barometer, and abundant sea-contact. The center of the more wile 

 and militant Roman civilization lay still another 5° farther north. The 

 later medieval and early modern civilization centered about France, 

 another subequal step northward, while present gravitation of power 

 and intellectual development is toward still more northerly latitudes. 



