METHODS OF BREEDING 583 
breeding and a greatly lessened tendency toward the production of de- 
fectives. There is a measure of truth in this belief for line-breeding, 
by the mating of animals of slightly wider relationship than those used in 
inbreeding, permits the introduction and intermingling of hereditary ele- 
ments from slightly different lines of descent. It is in this that we must 
seek the explanation for the greater success which line-breeding has had 
among most practical breeders. That explanation is not far to seek, for if 
the production of defectives depends upon factors which are distributed 
in Mendelian fashion, and there is no reason to believe that it does not, 
then any introduction of diverse hereditary elements is likely to result 
in the neutralization of the defective elements in both hereditary systems, 
for only under unusual conditions would such elements be identical 
in the two systems. Along with this tendency toward decreased pro- 
duction of defectives, however, there is the ever present possibility of 
dissipating the elements characteristic of the ideal family type, of ming- 
ling them with others not so productive or desirable. The tendency is 
by no means so strong as it is in out-breeding, but it is stronger than 
in inbreeding. It serves again to emphasize the fact that any system of 
breeding must be based upon matings of superior individuals. 
Out-breeding.—Out-breeding is merely a system of breeding best to 
best, at the same time avoiding relationship in the animals which are 
mated. While it may tend to avoid completely the disasters which often 
attended inbreeding, it is subject to all the defects of the old system of 
phenotypic selection. Chief among these is its tendency toward lack 
of uniformity in the herd. The harm which it does, however, depends 
largely upon the breed in which it is practised. Thus among Shorthorns 
the extraordinary multiplication of individuals of certain families leaves 
a wide field for the selection of superior individuals distantly related and 
of the same type, so that in this breed, a form of out-breeding which is 
really not out-breeding at all, but a very mild form of line-breeding, 
may be adopted without much danger. Out-breeding, however, is in a 
sense a harking-back to methods which have been discarded, and although 
the new breeder may do well to start his operations by avoiding too close 
affinities, he should steadily endeavor to master the problem of dealing 
with consanguineous matings sanely and effectively. 
Other Systems of Breeding.—Under the chapter on the utilization 
of hybrids in animal breeding, we have discussed at some length grading 
and cross-breeding. The former of these methods of breeding provides 
a simple and practical method for improving livestock on a large scale, 
and its practice is to be commended. Grading is not to becontrasted with 
any of the systems of breeding which have been described, but it may be 
compared on the one hand with pure breeding and on the other hand with 
aimless scrub breeding. In grading, any of the systems of breeding 
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