30 Heredity and Social Progress 



the unspecialized. 1 \ The parts most used and 

 hence of the greatest importance to animals 

 become highly specialized in their mechan- 

 ism and restrict activity within fixed limits. 

 As a consequence highly specialized animals 

 are less versatile and have less power of adopt- 

 ing new habits. Within a limited sphere they 

 are more efficient in a struggle for existence, 

 but are incapable of the large modifications 

 that a radical change in environment necessi- 

 tates. The highly specialized die out when 

 great changes in the environment occur, leaving 

 the less specialized types which alone^ are ca- 

 pable of enough modification to meet the new 

 situation. There is no connection between the 

 highest representative of one type and the low- 

 est of another. It is the lower and less spe- 

 cialized forms of each that are closely related, 

 and the line of progress to other types is from 

 the less specialized of each type. \ Use has cre- 

 ated many automatic habits, but these have little 

 power of adaptation to new conditions. Per- 

 fection in one direction is not the parent of 

 future progress in another. The new develop- 



1 " The Origin of the Fittest, 1 ' p. 398. 



