DO VARIETIES WEAR OUT? 175 
for. They may be smothered out by the adverse force of 
superior numbers ; they are even more likely to be bred out 
of existence by unprevented cross-fertilization, or to disappear 
from mere change of fashion. The question, however, is not 
so much about reversion to an ancestral state, or the falling 
off of a high-bred stock into an inferior condition. Of such 
cases it is enough to say that, when a variety or strain of 
animal or vegetable is led up to unusual fecundity or size or 
product of any organ, for our good, and not for the good of 
the plant or animal itself, it can be kept so only by high feed- 
ing and exceptional care; and that with high feeding and 
artificial appliances come vastly increased liability to disease, 
which may practically annihilate the race. But then the race, 
like the bursted boiler, could not be said to wear out, while 
if left to ordinary conditions, and allowed to degenerate back 
into a more natural, if less useful state, its hold on life would 
evidently be increased rather than diminished. 
As to natural varieties or races under normal conditions, 
sexually propagated, it could readily be shown that they are 
neither more nor less likely to disappear from any inherent 
cause than the species from which they originated. Whether 
species wear out, 7. ¢., have their rise, culmination, and decline 
from any inherent cause, is wholly a geological and very specu- 
lative problem, upon which, indeed, only vague conjectures can 
be offered. The matter actually under discussion concerns 
cultivated domesticated varieties only, and, as to plants, is 
covered by two questions. 
First: Will races propagated by seed, being so fixed that 
they come true to seed, and purely bred (not crossed with 
any other sort), continue so indefinitely, or will they run out 
in time —not die out, perhaps, but lose their distinguishing 
characters? Upon this, all we are able to say is, that we know 
no reason why they should wear out or deteriorate from any 
inherent cause. The transient existence or the deterioration 
and disappearance of many such races are sufficiently ac- 
counted for otherwise ; as in the case of extraordinarily exuber- 
ant varieties, such as mammoth fruits or roots, by increased 
liability to disease, already adverted to, or by the failure of 
