The Destiny of Man. 57 



surface of the adult civilized brain. The 

 plastic period of adolescence, lengthened 

 in civilized man until it has come to cover 

 more than one third of his lifetime, is thus 

 the guaranty of his boundless progressive- 

 ness. Inherited tendencies and aptitudes 

 still form the foundations of character ; but 

 individual experience has come to count as 

 an enormous factor in modifying the ca- 

 reer of mankind from generation to gener- 

 ation. It is not too much to say that the 

 difference between man and all other liv- 

 ing creatures, in respect of teachableness, 

 progressiveness, and individuality of char- 

 acter, surpasses all other differences of 

 kind that are known to exist in the uni- 

 verse. 



