344 THE HISTORY OF CREATION. 



which, according to the laws of cumulative adaptation 

 (vol. i. p. 233) and established inheritance (vol. i. p. 216), lead 

 to the origin of new functions, and thus also to new forms of 

 the organs. Here, as everywhere, the interaction between 

 function and organ goes hand in hand. Just as the mental 

 faculties of man have been acquired by the progressive 

 adaptation of the brain, and been fixed by continual trans- 

 mission by inheritance, so the instincts of animals, which 

 differ from them only in quantity, not in quality, have arisen 

 by the gradual perfecting of their mental organ, that is, 

 their central nervous system, by the interaction of Adapta- 

 tion and Inheritance. Instincts, as is well known, are in- 

 herited, but experiences and, consequently, new adaptations 

 of the animal mind, are also transmitted by inheritance ; 

 and the training of domestic animals to difierent mental 

 activities, which wild animals are incapable of accomplish- 

 ing, rests upon the possibility of mental adaptation. We 

 already know a series of examples, in which such adapta- 

 tions, after they had been transmitted through a succession 

 of generations, finally appeared as innate instincts, and yet 

 they have only been acquired from the ancestors of the 

 animals. Inheritance has here caused the result of training 

 to become instinct. The characteristic instincts of sporting 

 dogs, shepherd's dogs, and other domestic animals, and the 

 natural instincts of wild animals, which they possess at 

 birth, were in the first place acquired by their ancestors by 

 adaptation. They may in this respect be compared to 

 man's " knowledge a priori," which, like all other know- 

 ledge, was originally acquired by our remote ancestors, " a 

 posteriori," by sensuous experience. As I have already 

 remarked, it is evident that "knowledge a priori" arose 



