450 GENETICS IN RELATION TO AGRICULTURE 
The Service of Genetics in Education.— Up to this point, the discussion 
of the general aspects of animal breeding has been based upon the prac- 
tical methods of procedure followed by the most successful animal 
breeders. The rules of procedure which they follow have been handed 
down from herdsmen to herdsmen, they are the traditions of the art of 
animal breeding. They have of course always been modified in directions 
which the genius of each herdsman may dictate, for indeed much of the 
success of particular breeders has depended upon the aptitude which they 
as individuals have shown in dealing with problems of the moment. But 
these rules of breeding and the methods of employing them to best ad- 
vantage are not known to any great proportion of the animal breeders of 
any rural districts. In the United States it is estimated that the number 
of pure-bred livestock in any state does not greatly exceed 2 per cent. 
of the total number. Now not even all breeders of pure-bred livestock 
have attained to the high standard of perfection which we have employed 
as the basis of discussion in this chapter. To the great body of breeders 
even the empirical rules of practical breeding, therefore, are either un- 
known or imperfectly understood. 
In considering the service of genetics to this class of animal breeders 
to whom the best practical methods are merely a mass of confused detail, 
and to the prospective animal breeder who is just approaching the subject, 
we must take into account certain pedagogical principles. It is a sound 
major premise that any established mode of procedure in animal breeding 
must of necessity owe whatever measure of success it achieves to its 
conformance with the operation of underlying natural laws. It is also 
true that a knowledge of these underlying laws, by providing a common 
explanation for rules of procedure which at first sight appear unrelated 
and sometimes positively contradictory, tends to simplify the task of 
learning and applying the proper methods in actual breeding operations. 
To the novice, therefore, a thorough grounding in the principles of varia- 
tion and heredity provides the firm foundation to which he may later 
add the superstructure of a complete practical knowledge. Since it is 
much easier to remember related things than to hold in mind a confusing 
mass of technical detail, the novice who has a thorough grounding in 
principle may, by constantly searching for the reason in every new detail 
of procedure dictated by experience, so bind every fact to his interrelated 
body of principle that law and empirical procedure form together an effec- 
tive, codrdinated working equipment. 
The Personal Equipment of the Animal Breeder.—Now that we have 
considered some of the outstanding features of animal breeding as related 
to genetics, we may well go on to a consideration of the method of attack 
in seeking to apply the principles of genetics, whether with a view to 
harmonizing existing procedure with them or in an effort to use them as a 
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