36 PRINCIPLES OF BREEDING. 



been domesticated and widely disseminated, it now 

 oifers varieties of wide departure from the original 

 type, and which have been nurtured into self-sustain- 

 ing breeds, distinguished from each other by the pos- 

 session of peculiar characteristics. 



Among what are usually reckoned the more active 

 causes of variation may be named climate, food and 

 habit. 



Animals in cold climates are provided with a thicker 

 covering of hair than in warmer ones. Indeed, it is 

 said that in some of the tropical provinces of South 

 America, there are cattle which have an extremely 

 rare and fine fur in place of the ordinary pile of hair. 

 Various other instances could be cited, if necessary, 

 going to show that a beneficent Creator has implanted 

 in many animals, to a certain extent, a power of accom- 

 modation to the circumstances and conditions amid 

 which they are reared. 



The supply of food, whether abundant or scanty, is 

 one of the most active cases of variation known to be 

 within the control of man. For illustration of its 

 effect, let us suppose two pairs of twin calves, as nearly 

 alike as possible, and let a male and a female from 

 each pair be suckled by their mothers until they wean 

 themselves, and be fed always after with plentj^ of the 

 most nourishing food ; and the others to be fed with 



