36 Heredity and Social Progress 



The constant repetition of useful acts creates 

 structure and organs that respond instinctively 

 to the situations for which they are functionally 

 fitted. The sum of constantly favorable ele- 

 ments in the environment fixes the amount of 

 structure and the effectiveness of the organs 

 that can develop in a given situation. There 

 is a tendency for organs to reach this efficiency, 

 and for structure to create instinctive responses 

 to all constant relations between organisms and 

 the environment. Upon the introduction of 

 adverse elements, a less complete adjustment 

 results, or if the more complete adjustment is 

 acquired before the adverse element enters, a 

 retrogression occurs. Organs lose efficiency, 

 and structure disappears, or is dwarfed until 

 a new equilibrium is attained in which the 

 adverse element either becomes a part of the 

 environment or some means is acquired of 

 guarding against it. 



To meet this situation, a feeling is generated 

 that in some form is present when struggle 

 with adverse elements is necessary. Instinct 

 is the agent which best utilizes favorable ele- 

 ments, and it grows as these elements become 



