132 THE BREEDING OF ANIMALS 



vidual may profoundly influence its development through 

 seeking a favorable environment and through habitual 

 use or disuse of its inherited tendencies. 



123. Development. The full realization of the in- 

 herited capacities of an animal is accomplished through 

 its environment and training. The most important 

 factors concerned in the environment of an animal are 

 food and climate, and these acting upon the inherited 

 qualities of the animal may profoundly influence the 

 actual characteristics of the individual. In order that 

 the inherent characteristics of any organic being may 

 attain to full development, a sufficient supply of food 

 must be available. When food is scarce, the individual 

 may be unable to develop, and what it may ultimately 

 become, may be greatly influenced by this lack of 

 food. A full and sufficient food supply may cause the 

 individual to develop beyond the average condition of 

 the species, particularly if the average environment does 

 not furnish a generous supply of food. 



The training of the individual, likewise, is an important 

 factor in determining its ultimate development. Any 

 function of an animal which is not exercised may retro- 

 grade or in some .cases practically disappear. The 

 milking function in domestic cattle is a good example of 

 the influence of both development and exercise or train- 

 ing. The highly developed dairy breeds of cattle, when 

 generously fed and carefully milked, produce very much 

 more milk than their wild ancestors. Individual cows 

 of modern dairy breeds, if starved and carelessly milked 

 or neglected, will fail to develop the highly specialized 

 milking function. 



124. Heredity defined. In much of the literature 

 of biology pertaining to heredity, there is a lack of definite- 



