VARIATION. 67 



named that the chief importance of the laws of 

 variation centers. The causes of general vari- 

 ation are many and often obscure. They are 

 often the long accumulated force of years sud- 

 denly unloosed; they are sometimes the long 

 continued attrition through generations of 

 unfortunately situated individuals. Changed 

 conditions, of climate, soil, food, or environ- 

 ment of any sort is then one of the great causes, 

 hence the great cause of change which we are 

 able to observe in domestication, involving as 

 it does in many cases the most radical changes 

 of environment. It is quite impossible to do 

 more than indicate in outline some of the more 

 notable facts connected with the operation of 

 these causes. They are chiefly important to 

 the cattle-breeder on account of two phases. 

 First, the development of a new and valuable 

 quality by taking advantage of the operation 

 of this law; and second, the encouragement of 

 the tendency to the loss (atrophy) of some ex- 

 isting feature which is deemed undesirable 

 where the law is operating to destroy it; or the 

 checking of this action by the proper change of 

 conditions of life where the feature that is be- 

 ing atrophied is desirable. As examples of 

 these cases we may take the Jersey, Holstein, 

 and Hereford cattle. In the Jersey by choos- 

 ing an artificial method of feeding, the breed- 

 ers of these cattle developed to an abnormal 



