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, i. e., 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 



