CHAPTER XV 



THE BACKGROUND OF DARWINISM: 

 ADAPTATIONS 



THE NATURE OF ADAPTATIONS 



"The adaptation of every species of animal and plant to its 

 environment," says Jordan and Kellogg,' "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 aUke 

 spoken of in a half-figurative way as concessions to environment. And 

 all structures and powers 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. " 



The authors quoted above appreciate what is perhaps the most 

 significant fact about adaptations: that the adaptations are to a large 

 extent molded by the environment and therefore fit the environment. 

 So long as the environment remains uniform, a given species will 

 remain unchanged, except for minor fluctuations and occasional 

 mutations; but if the environment changes, sometimes even slightly, 

 the development of the individual responds in such a way as to give a 

 radically diflferent end product. So we may conclude that a large part 

 of the fitness of the organism to the environment is due to the fact that 

 the development of each individual is molded by the environment so as 

 to fit it. Thus some at least of the apparent mystery of adaptations is 

 dispelled. 



When we think of the fitness of the organism to the environment 

 we take an entirely one-sided view of the matter, for if the organism 

 fits the environment, no less certainly must the environment fit the 

 organism. This idea of the "fitness of the environment" has been 



' From D. S. Jordan and V. L. Kellogg, Evolution and Animal Life. 



194 



