198 DIFFICULTIES ON THEORY. Chap. VI. 



ately made conscious of this by reflecting on the differ- 

 ences in the breeds of our domesticated animals in 

 different countries, — more especially in the less civilized 

 countries where there has been but little artificial selec- 

 tion. Careful observers are convinced that a damp cli- 

 mate affects the growth of the hair, and that with the 

 hair the horns are correlated. Mountain breeds always 

 differ from lowland breeds ; and a mountainous country 

 would probably affect the hind limbs from exercising 

 them more, and possibly even the form of the pelvis' ; 

 and then by the law of homologous variation, the front 

 limbs and even the head would probably be affected. 

 The shape, also, of the pelvis might affect by pressure 

 the shape of the head of the young in the womb. The 

 laborious breathing necessary in high regions would, we 

 have some reason to believe, increase the size of the 

 chest ; and again correlation would come into play. 

 Animals kept by savages in different countries 

 often have to struggle for their own subsistence, 

 and would be exposed to a certain extent to natural 

 selection, and individuals with slightly different consti- 

 tutions would succeed best under different climates ; 

 and there is reason to believe that constitution and 

 colour are correlated. A good observer, also, states that 

 in cattle susceptibility to the attacks of flies is correlated 

 with colour, as is the liability to be poisoned by certain 

 plants ; so that colour would be thus subjected to the 

 action of natural selection. But we are far too 

 ignorant to speculate on the relative importance of 

 the several known and unknown laws of variation; 

 and I have here alluded to them only to show that, 

 if we are unable to account for the characteristic 

 differences of our domestic breeds, which nevertheless 

 we generally admit to have arisen through ordinary 

 generation, we ought not to lay too much stress on our 



