196 THE BREEDING OF ANIMALS 



186. Importance of variability. The inherent tend- 

 ency to vary which exists in all organic beings makes the 

 improvement of domestic races possible. Inorganic 

 compounds are fixed in composition and physical char- 

 acter. Pure gold cannot be improved. The individual 

 animal has within its own organic constitution not only 

 the capacity for, but a noticeable tendency toward, varia- 

 tion from the characters of its ancestors. This fact lies 

 at the very foundation of the successful improvement 

 of domestic animals. If it were true that the offspring 

 was identical in character with the parent, then improve- 

 ment would be impossible. 



In developing new varieties, the breeders' efforts 

 are sometimes first directed toward encouraging the 

 tendency to variation. If the particular form which 

 the breeder is endeavoring to improve possesses an unusual 

 tendency to vary, then a large number of new characters 

 or new combinations of characters will occur. Some of 

 these will be desirable, but many will be less desirable 

 than in the parent forms. The individuals which possess 

 the most useful and valuable characteristics will be pre- 

 served by selection. After desirable variations have 

 occurred, the next step is to fix these by heredity so that 

 they may become racial characteristics and be trans- 

 mitted with some degree of regularity from parent to 

 offspring. 



187. Morphological variations. The variations which 

 are of interest to the animal-breeder exhibit many differ- 

 ent forms. 



Morphological variations are those affecting the form. 

 These may be merely differences in size, as in the case 

 of two pigs possessing the same characters and the same 

 relative development of characters but differing in size. 



