EXCURSIONS OF AN EVOLUTIONIST 



plasticity. The creature's career is no longer ex- 

 clusively determined by heredity. There is a 

 period after birth when its character can be 

 slightly modified by what happens to it after 

 birth, that is, by its experience as an individual. 

 It becomes educable. It is no longer necessary 

 for each generation to be exactly like that which 

 has preceded. A door is opened through which 

 the capacity for progress can enter. Horses and 

 dogs, bears and elephants, parrots and monkeys, 

 are all teachable to some extent, and we have 

 even heard of a learned pig. Of learned asses 

 there has been no lack in the world. 



But this educability of the higher mammals 

 and birds is after all quite limited. By the be- 

 ginnings of infancy the door for progressiveness 

 was set ajar, but it was not all at once thrown 

 wide open. Conservatism still continued in fash- 

 ion. One generation of cattle is much like an- 

 other. It would be easy for foxes to learn to 

 climb trees, and many a fox might have saved 

 his life by doing so ; yet quick-witted as he is, 

 this obvious device never seems to have occurred 

 to Reynard. Among slightly teachable mam- 

 mals, however, there is one group more teach- 

 able than the rest. Monkeys, with their greater 

 power of handling things, have also more in- 

 quisitiveness and more capacity for sustained at- 

 tention than any other mammals ; and the higher 

 apes are fertile in varied resources. The orang- 

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