THE HUMAN OR PRESENT PERIOD. 535 



tively dry descending air-currents prevailed, rather than with the 

 dense forests of the equatorial belt where ascending air-currents and 

 excessive humidity prevailed. Subsequent history, as well as the 

 nature of the case, teach us that extreme desert conditions and excess- 

 ive heights are prohibitive, that semi-arid conditions of varying and 

 precarious intensities lead to nomadic habits, sparse distribution, and 

 limited social and civic evolution; while well-watered plains and fer- 

 tile valleys, under congenial skies, invite fixed habitation and the 

 development of stable civil and social institutions. Excessive humidity 

 and dense forests, on the other hand, tend to limitation and repression, 

 in a primitive people, as does also extreme ruggeclness of surface. 

 Ascending atmospheric currents, with low barometer, high tempera- 

 ture, air-saturation, excessive precipitation, and lowering skies tend 

 to physical and intellectual lassitude and inactivity. Descending 

 atmospheric currents, high barometer, dry air, cool temperature, and 

 clear skies tend to physical and intellectual activity. In a primitive 

 state, before the control of accessory agencies was adequately acquired, 

 it is presumed that a warm climate was more helpful than a severe 

 one. From these considerations and from historical evidence arises 

 the presumption that the primitive centers of virile evolution and radia- 

 tion of the race lay somewhere in the open or diversified country of 

 the warm tract of the largest of the continents, between the excesses 

 of aridity and humidity, expressed in the deserts on the one side, and 

 the dense forests on the other. From this, or from some analogous 

 tract in that quarter of the globe, there seem to have been four great 

 divergent movements. These were complicated by reverse move- 

 ments, cross-migrations, and various anomalies, but only the dominant 

 features can be mentioned here, and these but briefly. 



(1) The most voluminous movement seems to have been north- 

 eastward between the great desert and mountain tract of Central Asia 

 on the one hand, and the Pacific on the other, attended by diver- 

 gences eastward to many of the islands of the Pacific. When the 

 higher latitudes were reached, there followed a lateral spreading both 

 east and west, encircling the arctic regions, and sending a branch down 

 the full length of the American continent. This movement embraced 

 the great complex of Mongoloid races, including the Malayan and the 

 original American races. Previous to the disturbing events of recent 

 centuries, this branch had developed three notable centers of civiliza- 



