THE BREEDING OF ANIMALS, IN GENERAL 75 



classes of variation are kept clearly in mind. Not all kinds 

 of variation are desired. The qualitative variations are most 

 sought. 



PROXIMATE CAUSES OF VARIATION 



The conditions that bring about variation are worthy much 

 consideration since one, by modifying these conditions, can aid 

 in producing variation in a desired direction. For example, if 

 we want to increase the milk flow of cattle, the conditions 

 that will cause them to vary in that direction are of much im- 

 portance and should be well understood. In general, variation 

 results from enviromnent, from crossing dissimilar animals, and 

 from use or disuse, all of which are under the control of man. 



Environment. — Of all the external conditions bringing about 

 variation in farm animals, those influences that we sum up 

 under the term "environment " are by far the most important. 

 As a matter of fact, it is through the ability to change the 

 environment of animals that man is able to induce variation and 

 improvement. Among animals in a state of nature, we define 

 environment as those conditions of cUmate and food that con- 

 cern the life of the animal. Among farm animals the conditions 

 of environment are somewhat changed or enlarged, and we are 

 accustomed to think of it as the sum of all of those conditions 

 that are influenced through association with man. The chief 

 factors of environment through which man seeks to control or 

 improve farm animals are those of climate, food, and care. The 

 environment means the " surroundings." 



The climate and the kind of animals that exist in it are closely 

 related. The characters that are most often affected are those 

 that tave to do with size and the external covering of the animal. 

 The natural relation of chmate to size is that animals inhabiting 

 cold climates are usually small as compared with those of the 

 same species inhabiting warm climates. Man modifies the 

 natural effect of climate through the housing that he affords farm 



