394 AGRICULTURE. 



II. Improvement. 



As time went on people became more civi- 

 lized. Their habits, customs, ambitions and 

 demands changed. With this change in the 

 people themselves many changes in domestic 

 animals followed, as a natural consequence. It 

 was a general change in the direction of im- 

 provement, although this was not always the 

 case. 



There are three natural laws which are orreat 

 factors in affectincr animal form and character 

 in its reproduction, and make change possible. 

 They are 



1. Heredity. 



2. Variation. 



3. Selection. 



III. Heredity. 



Ribot defines heredity as " that biological law 

 by which all living beings tend to repeat them- 

 selves in their descendants." This is the law 

 which makes possible the resemblance between 

 a parent and offspring, and is well expressed in 

 the common saying that " like produces like." 

 It is this principle upon which we depend 

 for the transmission of milk-producing quali- 

 ties in dairy cattle, speed in race-horses, etc., 

 and by which we are able to maintain a 

 standard of breed, characteristics or type in 

 animals. 



