CHAPTER XVI 

 ADAPTATIONS 



It is a wise provision of nature that trees shall not grow up into 

 the sky. GOETHE. 



THE adaptation of every species of animal and plant to its 

 environment is a matter of everyday observation. So perfect 

 is this adaptation in its details that its main facts tend to 

 escape our notice. The animal is fitted to the air it breathes, 

 the water it drinks, the food it finds, the climate it endures, 

 the region which it inhabits. All its organs are fitted to its 

 functions: all its functions to its environment. Organs and 

 functions are alike spoken of in a half-figurative way as con- 

 cessions to environment. And all structures and pow r ers are 

 in this sense concessions, in another sense, adaptations. As 

 the loaf is fitted to the pan, or the river to its bed, so is each 

 species fitted to its surroundings. If it were not so fitted, it 

 would not live. But such fitness on the vital side leaves large 

 room for variety in characters not essential to the life of the 

 animal. Thus we ascribe nonessential characters to variation, 

 preserved by heredity and guarded by isolation. Vital or 

 adaptive characters originate in the same way, but these are 

 preserved in heredity and guarded and intensified by selection. 



The strife for place in the crowd of animals makes it neces- 

 sary for each one to adjust itself to the place it holds. As the 

 individual becomes fitted to its condition, so must the species 

 as a whole. The species is therefore made up of individuals 

 that are fitted or may become fitted for the conditions of life. 

 As the stress of existence becomes more severe, the individuals 

 fit to continue the species are chosen more closely. This choice 

 is the automatic work of the conditions of life, but it is none 

 the less effective in its operations, and in the course of centuries 



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