50 SOUTHERN rOKK PRODUCTION 



changes have been brought about by the process of 

 domestication. In the first place, it has brought about a 

 marked increase in their efficiency for converting feed 

 into pork. It is true that through domestication they 

 have lost to a marked degree their capacity to survive 

 adverse conditions, but this is not detrimental to their 

 usefulness and value, for they should not be forced to 

 withstand adverse conditions under present methods of 

 production. Economically, therefore, their value has been 

 increased through the loss of their capacity to withstand 

 the vicissitudes of climate and insufficient food supply. 

 A bit of reflection tells us that this is not only true of 

 swine, but that it is likewise true of other domestic 

 animals and plants, and we find it a general rule that 

 those plants or animals which are the most persistent 

 are the least valuable. 



Origin of breeds and strains of swine. — While we may 

 be continually making new breeds and strains of swine, 

 we do not make the material from which new breeds and 

 strains arise. We are able to make our new strains only 

 by utilizing the inherent variations already present in 

 our animals. We control, develop and magnify these 

 variations as much as we are able by controlling the 

 environment. Any marked variations are referred to as 

 sports or mutations, which mutations cannot be isolated 

 and experimented with, but which have been studied 

 enough that we know that they are inherited as units, 

 hence the term unit characters, which is sometimes 

 applied to them. It is b}' the assembling of the right 

 sorts of these variations that we are able to form new 

 breeds and strains. We simply collect into one animal, 

 or into a few animals, those characters and groups of 



