CHAPTER VI. 



THE ADJUSTMENT OF ORGANISMS TO ENVIRONMENT. 

 "Life is response to the order of nature." — Brooks. 



In this chapter we shall attempt a more careful examina- 

 tion of the phenomena of fitness, selecting arbitrarily for 

 the purpose, out of a world-full of examples, a few that seem 

 fairly illustrative and typical. 



Plants and animals, which were primitively much alike 

 and lived under more or less uniform conditions, have multi- 

 plied, differentiated, specialized, and spread to every habit- 

 able part of the globe, and have become adapted to condi- 

 tions of utmost diversity and complexity. Fitness to meet 

 these conditions is a necessity of existence under them. 

 Unfitness so pronounced as not to adm.it of getting a living 

 or of leaving descendants, would mean for any species speedy 

 elimination. That all living things are adjusted to their 

 places in the world is most obvious; how this has come 

 about is a subject of much speculation at the present day. 

 We may not be able to determine whether the initiative of 

 the variable organism or the impress of environing condi- 

 tions has been the major factor in producing the results, but 

 we can at least see the sort of facts on which all the theories 

 advanced in their explanation are based. As a matter of 

 convenience we will divide our studies of this subject into 

 three groups, according to the more prominent phenomena 

 involved, as follows: 



Adjustment in place and time. 

 Adjustment in manner of life. 

 Adjustment in bodily characteristics. 



