THE GENERAL ASPECTS OF ANIMAL BREEDING 449 
great body of experience which has grown up from the constant applica- 
tion of the method of trial and error in animal breeding. The art of the 
breeders’ craft is not a thing to ridicule, for measured by the rigid test 
of results it abundantly justifies itself. The geneticist with all his 
knowledge of natural law and principle could not successfully compete 
with the practical breeder in the attainment of a definite standard of 
excellence, unless he added to his technical training a fund of practical 
detail. It is moreover too early in the science of genetics rigidly to 
lay down rules of procedure, particularly if those rules at any point are 
at variance with the established mode of practical procedure. It is too 
often the case, as any geneticist will be forced to admit when he reads 
accounts written not more than half a decade ago on the application of 
the principles of genetics to livestock breeding, that proper allowance 
is not often made for the future expansion of our knowledge of genetics 
itself neither with respect to the extent to which it will go nor the direc- 
tion which it may take. From time to time in the chapters that follow, 
we shall have occasion to point out how later developments of the science 
have given room for beliefs formerly scoffed at. 
What then is the service of genetics to practical breeding? Clearly 
the answer to this question lies in a consideration of the fundamental 
contrast between the science and the art of breeding. The object of both 
when applied to practical breeding is to attain and maintain a definite 
standard of excellence. The standard of excellence is the same, at least 
there is no good reason why it should not be identical in both cases. 
With respect to this goal, the art of the breeder merely outlines how it 
may be reached by the utilization of a system of rules of procedure based 
on the results of experience. The science of genetics seeks for the natural 
laws operative in the attainment of standards in general, and in discover- 
ing them of necessity includes in its findings the methods by which they 
may be attained. Obviously the methods of attaining standards are by 
no means dependent upon a knowledge of the underlying principles; 
but they may and in this case evidently have run far ahead of scientific 
knowledge. The service of genetics lies, therefore, in the clarity of 
thought which it promotes, just as knowledge of principle always rein- 
forces art. This then is the service to the skilled breeder, it tells him 
why his methods give the success they do, why some things are true 
and others false, and in case anything is rejected, which is occasionally 
done because of the stubborn tenacity of some erroneous ideas which by 
their very construction are difficult at one time both of verification and 
refutation, it endeavors to describe in terms of the operation of natural 
laws and principles the actual conditions which obtain, and which are 
responsible for the erroneous beliefs, 
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