526 GENETICS IN RELATION TO AGRICULTURE 
data which have been collected are of the observational type, the conclu- 
sions which have been drawn are inferential, and many of them are 
still in dispute among skilled investigators, nevertheless the results 
which have been reached have a high degree of probable validity. 
Whether it is desirable from a sociological standpoint to reject all de- 
fective individuals from reproduction, and to exclude in addition those 
individuals which while themselves normal may transmit some defect, 
is a grave question which should be considered very carefully. It is 
not, however, a question of genetics, the geneticist can only point out the 
remedy. It is a matter of grave concern to any nation that 30 per 
cent. of its population should carry hereditary taints, and yet that is 
about the proportion which Rosanoff estimates on the basis of data 
from certain localities in the United States. 
An example nearer home might be taken, but that of the cretins of 
Aosta described by Whymper is perhaps one of the most striking cases 
of the baneful effects which may follow an improper social treatment of 
defectives. These horrible examples of human deformity, often goitrous 
and almost devoid of intelligence and common decency, had been the 
objects of such pity and charity on the part of society that the condition 
had actually been favored and preserved rather than weeded out. Under 
the old regime the cretins were given the best of care and attention, 
intermarriage between them was sanctioned by the church, and such a 
premium paid upon the deformity that it was multiplied from generation 
to generation. The disease was known to reappear in successive genera- 
tions, yet no attempt was made to stamp it out in the perfectly obvious 
way by preventing reproduction by cretins. Later, however, when this 
method of dealing with the problem was applied, the prevalence of 
cretinism was soon strikingly decreased. 
Whether or not the rate of reproduction in cretins is greater or less 
than that in normal stocks is a question. It is, however, known that 
many families which carry the taint of feeblemindedness are astonish- 
ingly prolific. None but a positive method, therefore, can deal with 
cases of this kind under modern conditions; for there is no assurance 
whatever that such families under present day conditions will tend to 
run out on account of differential survival when compared with normal 
stocks. The student who wishes to carry this subject further will find 
abundant confirmation of these statements in the records of the Juke 
family, the Nam family, the Hill folk, and the Kallikak family. 
Defects in Domestic Animals.—Curiously enough, if it be desired 
to trace the inheritance of defects in animals, man himself provides some 
of the most interesting and best investigated cases. The reason for 
this is very obvious; the animal breeder does not propagate his defectives, 
he rigidly culls them out of the herd. As a consequence although a few 
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