156 PRINCIPLES OF STOCK-BREEDING. 



make their appearance in a single family, or in a few 

 individuals that are closely related, in-and-in breeding 

 must necessarily be resorted to to secure their perpe- 

 tuity. From these considerations it must be obvious 

 that, in the improvement of a breed, in-and-in breed- 

 ing tends to produce uniformity in the characteristics 

 of a family by fixing desirable variations and making 

 them dominant. 



From the uniformity thus obtained in the heredi- 

 tary tendencies of the organization the dominant 

 characters of all the immediate ancestors being the 

 same the power of hereditary transmission is like- 

 wise increased, as observed in what is now called pre- 

 potency. If the hereditary transmission of desirable 

 variations were not intensified by the process of in- 

 breeding, or otherwise, they would unavoidably be- 

 come latent by the preponderance of the more stable 

 characters of the original type. 1 



1 The difficulty of fixing a particular variation that presents a 

 marked divergence from the normal condition of an animal, may be 

 illustrated as follows : If we suppose the hereditary tendencies of the 

 animal to be represented by one hundred and the desired variation by 

 one, the chances of its being perpetuated by the animal when bred 

 with another, that had not an equal susceptibility to variation in the 

 same direction, would be only one in one hundred under the most 

 favorable conditions ; but when there is a tendency to the dominance 

 of other characters, the chances of its repetition will be less. Or, if 

 among one thousand animals of a given breed there are but two that 

 present a slight variation of a particular character, the chances of its 

 being preserved, if the animals in which it occurs are not bred to- 

 gether, would evidently be but two in one thousand, even in case the 

 variation was not more difficult to preserve than the ordinary char- 

 acters, while in the case of a variation of a highly-artificial character 

 that would be likely to be obscured by more stable characters, the 

 chances of its preservation would be materially diminished. 



