140 SOCIAL EVOLUTION 



of peasants and shepherds, wringing from upland pas- 

 ture and scant field a miserable subsistence. " 24 



Thus far we have discussed climatic differences as 

 though they occurred in certain fixed bands circling tin- 

 earth. But climate in any given locality is, as we all 

 know from our own experience, a relatively variable 

 quantity. Aside from seasonal change there is much 

 latitude of variation. This climatic cycle when con- 

 sidered in its wider aspect, that is, leaving out the tem- 

 porary fluctuations of the year, and concentrating our 

 attention upon changes that occur or recur over tin- 

 IM riod of many years or even centuries, is an important 

 cause of movements of population. Recognition of the 

 part played in history by climatic changes has led to tli 

 formulation of the theory of pulsatory climatic changes 

 by Ellsworth Huntington. 25 "It seems to be true, as a 

 principle, that, in regions occupied by the ancient em- 

 pires of Eurasia and northern Africa, unfavorable 

 changes of climate have been the cause of depopulation, 

 war, migration, the overthrow of dynasties, and the de- 

 cay of civilization; while favorable changes have made 

 it possible for nations to expand, grow strong, and de- 

 velop the arts and sciences. " 26 However, this by no 

 means implies that all invasions and all prosperity are 

 supposed to be due to climatic causes, but merely that 

 climate has been one of the important factors in pro- 

 ducing such results. 27 



"In relatively dry regions increasing aridity is a dire 

 calamity, giving rise to famine and distress. These, in 

 turn, are fruitful causes of wars and migrations, which 



j<f., p. 558. 



M The Pulse of Asia, 1907. 



w Huntington I //< ,/,/ /M Transformation, 1910, p. 251. 

 ** Huntington, "Changes of Climate and History," p. 215. 



