CONDITIONS OF DEVELOPMENT. 241 



formances of the action assume almost an exact 

 similarity. This principle of nervous action ex- 

 plains why the instinctive actions of all individuals 

 of a species resemble each other so closely. 



There is, however, generally a slight difference 

 between the instinctive actions of different individ- 

 uals. This is due to a difference in surroundings. 

 The delicate organisation with which the instinct 

 is connected responds to very slight differences. 

 This peculiar response to new conditions is what 

 is called "intelligence." It is, however, only the 

 necessary response of a complex organisation to 

 new and unusual conditions. Instinct is the neces- 

 sary response to usual conditions ; intelligence is 

 the necessary response to unusual conditions. Thus 

 by instinct a bird's nest is planned ; by intelligence 

 it is adapted to the peculiar requirements of the 

 location and materials at hand. The difference 

 between instinct and intelligence is therefore 

 neither fundamental nor very wide. The great im- 

 pelling motives of mankind may be classed as 

 instincts. Such are the instincts of self-preserva- 

 tion, procreation, loving and caring for one's chil- 

 dren and friends, with the consequent desire for 

 power, knowledge, and wealth. The responsive 

 adaptation of each individual to those conditions 

 of environment which are new and unique in his 



