CHAPTER XXXI 
THE SELECTION PROBLEM IN ANIMAL BREEDING 
There are two general views respecting the effectiveness of selection, 
namely, that it depends upon the isolation of hereditary material of the 
most excellent kind, or in metaphor that selection separates the gold 
from the dross, and secondly that it is due to modification of germinal 
elements, that by selecting in a specific direction the hereditary material 
itself is actually molded in a corresponding fashion. The two inter- 
pretations are fundamentally at variance each with the other; one 
interpretation would have it that the hereditary elements are relatively 
constant, at least that they are not subject to gradual continuous change; 
the other interpretation favors a belief in factor inconstancy, insignificant 
fluctuating variability as it were in factors themselves, which provides 
opportunity by appropriate selection for actual modification of germinal 
elements. These opposed views have already been discussed at some 
length in other chapters, it remains to apply the conclusions therein 
reached to practical animal breeding operations; and to discuss certain 
other phases of the selection problem which are of particular interest 
in practical work. 
In spite of vigorous statements to the contrary, there seems to be 
little reason to doubt that the isolation view of selection can account for 
all results which have been communicated thus far with respect to this 
question, whether of practical experience or of experimental research. 
In the preceding chapter we had occasion to consider, in passing, the 
reduction which had occurred in trotting records during the past one 
hundred years. Data of this kind are not lacking in the annals of agri- 
culture, and are often offered as evidence in support of the belief in the 
gradual accumulation of favorable increments in the development of 
breeds. But although this old Darwinian idea of inprovement in animals 
is very generally subscribed to, at least verbally, by practical men, it 
is nevertheless true. that whenever a critical examination is made of 
specific instances the support for it largely disappears. 
The American Standard Bred Horse.—In Table LXIII are given the 
data which indicate how the trotting record has been lowered during 
the history of racing in America. A parallel table might be given to 
show how the pacing record has been reduced. Now although these 
records have been used on the one hand in support of belief in the inheri- 
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