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 different 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 4 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 
