68 Actual Races in History. 



of the brain, rapidity of development, duration of 

 life. 



77. The answer is simple and positive. The 



various conditions of life in which men 

 Conditions of have been placed are amply sufficient to 



account for all the modifications that 

 characterize human races. By conditions of life 

 we mean the soil, cold, heat, dryness, humidity, 

 light, drink, food, resources and the like. Such 

 various conditions in the environment have made 

 acclimatization necessary, and naturalization possi- 

 ble. That is to say, new conditions of life have 

 appealed to a certain self-adjusting power in the 

 human constitution, and have brought about in it 

 a degree of harmony between the constitution and 

 its environment. This approximating harmony is 

 called acclimatization. If it is rendered perfect, it 

 is naturalization, and implies that our common 

 human nature has put on in the given circum- 

 stances some special characters and aptitudes; 

 which make up an acquired or second nature, ex- 

 actly adapted to the new conditions of life. 



78. Let me illustrate these adaptations by recur- 

 ring for a moment to our old argument of analogy 

 (No. 59). Sheep have a woolly fleece, as we know to 

 our great comfort in winter clothing. But in the heat 

 of Africa the sheep change their fashion, and put 

 on a short and smooth hair. Just the reverse takes 

 place with the wild boars, when they pass from a 

 warmer to a colder climate. They are accustomed 



