V.] SPECIFIC STABILITY. 137 



large and conspicuous ones. Moreover, it is possible that 

 some of our domestic animals have been in part chosen and 

 domesticated through possessing variability in an eminent 

 degree. 



That each species exhibits certain oscillations of struc- 

 ture is admitted on all hands. Mr. Darwin asserts that 

 this is the exhibition of a tendency to vary which is abso- 

 lutely indefinite. If this indefinite variability does exist, 

 of course no more need be said. But we have seen that 

 there are arguments a priori and a posteriori against it, 

 while the occurrence of variations in certain domestic 

 animals greater in degree than the differences between 

 many wild species, is no argument in favour of its exist- 

 ence, until it can be shown that the causes of variability in 

 the one case are the same as in the other. An argument 

 against indefinite variability, however, may be drawn from 

 the fact, that certain animals, though placed under the 

 influence of those exceptional causes of variation to which 

 domestic animals are subject, have yet never been known 

 to vary, even in a degree equal to that in which certain 

 wild kinds have been ascertained to vary. 



In addition to this immutability of character in some 

 animals, it is undeniable that domestic varieties have little 

 stability, and much tendency to reversion, whatever be the 

 true explanation of such phenomena. 



In controverting the generally received opinion as to 

 " reversion," Mr. Darwin has shown that it is not all breeds 

 which in a few years revert to the original form ; but he 

 has shown no more. Thus, the feral rabbits of Porto Santo, 

 Jamaica, and the Falkland Islands, have not yet so reverted 

 in those several parts of the world. 1 Nevertheless, a Porto 



1 "Animals and Plants under Domestication," vol. i. p. 115. 



