Variation of Instinct, i8l 



ercise of only a part of this original gift ; while a 

 change of circumstances will instantly call the rest 

 of the knowledge and skill into play. Those who 

 see the change for the first time, wonder at what 

 seems to them manifestations of wisdom on the 

 part of the actor. Mistakes have been made in 

 the study of animals, from want of careful observa- 

 tion in regard to the nature and conditions of such 

 changes in instinctive action. 



It is probable that instincts may be strength- 

 ened in certain directions, and weakened in others, 

 and changed in quality. If this cannot be done di- 

 rectly, it certainly can be done indirectly, by affect- 

 ing the functions of the body, which are the chief 

 agencies in bringing the instincts into play, and af- 

 fecting their strength and quality. 



There is great plasticity in the organic and su- 

 per-sensuous part of the lower tribes even ; sufficient 

 to give them a fair chance in the world ; and when 

 we come to the higher animals, we have a still 

 greater plasticity of nature ; so that qualities and 

 habits can be secured and transmitted, as tenden- 

 cies at least, from one generation to another. 



This is so well understood by breeders that they 

 will, in time, secure almost any form or color which 

 they desire, — not because they have any power to 

 change these directly, but because they take advan- 

 tage of the tendency in all animals to vary and to 

 inherit the peculiarities of parents. In like man- 

 ner, any peculiar manifestation of an instinct can be 

 fixed by selection in breeding. The breeder is at- 

 tracted by some habit of an animal, which would 



