FITNESS AND ADAPTATION 67 



forces and agents remotely connected with that partic- 

 ular river, or its terrain. 



If it is difficult here to trace the chain of cause and 

 effect to the sources of fitness and adaptation, how much 

 more difficult is it to trace them in the rivers and 

 streams of life? 



It is evident that in forming our judgments of vital 

 processes, we cannot limit the scope of our vision to any 

 one aspect of life, or to purely vital phenomena only. 

 The windows of our mind must look in all directions 

 upon the world about us. The reader may be assured 

 that the biologist, with such an outlook, studies even 

 the simplest problems of life in no other attitude than 

 one of profound humility. But he jealously guards his 

 provinces, and is chiefly moved to dogmatism by the 

 petty dogmatism of others. 



IV. Temporary and Permanent Fitness 



In the larger sum of more elaborate adaptations, it 

 is easy to confuse secondary, incidental, or perhaps even 

 for the moment useless, fitness with that which is more 

 fundamental and universal. In the case of man and 

 his machines, for example, it is evident that while iron 

 is fit for many cooperative mechanical uses, it is also 

 fitted to form the chief constituent of the earth nucleus. 

 It is also fitted to form a vital constituent of all living 

 tissues. It cannot readily become unfitted for these 

 basic purposes, owing to the stability of its qualities. 

 But by the very same tokens, in a rapidly advancing 

 life, iron may quickly become unfit for many mechan- 

 ical uses when a better material to these ends becomes 

 available, or when man himself becomes capable of 



