THE EFFECT OF CLIMATE AND WEATHER 3OI 



the extreme climate leave the people enough energy for the 

 advancement of civiHzation? Both history and geography 

 seem to answer in the negative, for the intrusions of civihzed 

 people in such regions are sporadic and temporary and the 

 permanent inhabitants invariably stand very low in 

 civihzation. 



The Onas of Tierra del Fuego, the Indians of the moistest 

 Amazon forests, the primitive pre-Arabic people of central 

 Arabia, the most northerly Ostiaks and Samoyedes of Siberia, 

 and the shepherds of the highest, coldest parts of Tibet illus- 

 trate the two-fold effect of hfe near the chmatic Hmits. Such 

 people are kept in a low stage of civihzation partly by their 

 inabihty to wrest from their poor environment a sufficient sur- 

 plus of food and other commodities to give them the leisure 

 to make new inventions and devise new modes of hfe, and 

 partly by their tremendous physiological handicap. They must 

 indeed be constitutionally vigorous in order to survive, but a 

 large part of their vigor is consumed in resisting extremes of 

 chmate. Bitter cold, intense heat, over-powering sunshine, 

 or hot, enervating humidity may not kill a man or even 

 make him sick, but they diminish his surplus energy. He 

 uses up so much of his strength in keeping his blood at the 

 right temperature and so often fails to do this that in his 

 leisure moments he is tired and sleepy, and rarely possesses 

 the extra energy which enables men in better climates to 

 advance civilization. Thus the climatic limits of civilization 

 or progress seem to be much narrower than those of the 

 human race as a whole, and those of the race are narrower 

 than those of the individual. 



CLIMATIC OPTIMA 



I. Temperature. Interesting and important as are climatic 

 limits, they do not concern us so closely as do chmatic 

 optima. The optimum or most favorable condition for each 

 climatic factor varies in accordance with the other factors, 

 but if those other factors remain constant, the optimum 

 for any one factor can be fairly accurately determined. 

 The optimum temperature for various living organisms 

 is shown in Figure i. Low temperature is represented on the 

 left and high on the right; the vertical height of each curve 



