196 THE PROBLEMS OF EVOLUTION 



part to do its work at a fairly even rate in spite of 

 the uncertainty of its surroundings. The total 

 activity of the organism may therefore be much 

 more constant than the conditions of environment, 

 and many processes of the individual body may 

 seem wholly independent of external conditions 

 because of their remarkable constancy in a variable 

 environment. But the fluctuations must be met. 

 There are always changes to which the individual 

 must adjust itself in order that its vital processes 

 may go on within normal limits, and there are 

 often conditions of less importance to which it 

 must respond by the production of non-adaptive 

 characters, merely because the potentialities of 

 its heritage and the existing stimuli lead to such 

 an end. And if the changed environment be per- 

 manent, then all individuals of the species must 

 be adjusted to it. Whether the adjustment be 

 directly adaptive, potentially adaptive, or purely 

 incidental, it provides a new factor in the vital 

 complex and a potential basis for other changes in 

 the course of evolution. 



From the lowest type of organic response to the 

 highest there is little fundamental difference with 

 respect to adjustment to environment save in com- 

 plexity. The simple tropisms of primitive organ- 

 isms result in effective adjustment of the individual 

 within its limits of possibility. The highest type 

 of intelligence likewise operates for the mainte- 



