THE EFFECT OF CLIMATE AND WEATHER 327 



similarly subject to climatic influences. According to this 

 interpretation a biological process of selection weeds out 

 certain types in certain regions. Occupations are often the 

 basis of selection, but occupations in turn depend largely on 

 climate, especially in primitive communities. Thus where rice- 

 culture prevails the family which cannot force itself to 

 undergo the degree of steady work required to plant the rice, 

 guard it, and keep up the little canals and dikes needed for 

 irrigation is almost sure to be either poorly nourished, so that 

 it does not raise many children, or else to be forced into 

 another group which gets a hving in some other way. 



The most far-reaching of all chmatic factors in producing 

 deep-seated mental differences appears to be the seasons. In 

 warm moist fands some sort of food can be procured at 

 almost any season. Where a long dry season occurs this is 

 not so easy, and where there is a cold winter practically no 

 food can be procured for many months except by hunting. 

 Under these latter circumstances an agricultural population 

 can scarcely survive unless it possesses sufficient foresight 

 to see that in summer suppHes of food, skins and the like 

 are laid by for winter. It must also possess sufficient intelli- 

 gence to plan for such supplies, sufficient energy to gather 

 far more than is needed for immediate use, and sufficient 

 self-control to husband the suppfies through the whole of the 

 period of scarcity. In a tropical climate many people can 

 survive without these qualities; in a region with well- 

 defined winters, such mental weaklings tend to be weeded 

 out, leaving only the more intelligent, energetic and self- 

 controlled. That such selection is the primary cause of the 

 apparent biological difference in the mental powers of 

 tropical and non-tropical races has never been positively 

 proved, and perhaps never will be. Yet as a working hypothe- 

 sis it seems to fit the facts extremely well. 



ACCLIMATIZATION 



Our last topic in connection with climate is acclimatization, 

 especially as it concerns the white man in the tropics. The 

 materials for an intelligent opinion as to this much-debated 

 problem have already been presented. Mankind presumably 

 originated in one or more climatic provinces which were 



