V.] SPECIFIC STABILITY. 135 



species certainly vary as much as do domestic races ; it is 

 possible that they may do so, but at least this has not been 

 yet shown. Indeed, the much greater degree of variation 

 among domestic animals than among wild ones is asserted 

 over and over again by Mr. Darwin, and his assertions are 

 supported by an overwhelming mass of facts and instances. 



Of course it may be asserted that a tendency to indefi- 

 nite change exists in all cases, and that it is only the circum- 

 stances and conditions of life which modify the effects of 

 this tendency to change so as to produce such different 

 results in different cases. But assertion is not proof, and 

 this assertion has not been proved. Indeed, it may be 

 equally asserted (and the statement is more consonant with 

 some of the facts given), that domestication in certain an- 

 imals induces and occasions a capacity for change which is 

 wanting in wild animals the introduction of new causes 

 occasioning new effects. For, though a certain degree of 

 variability (normally, in all probability, only oscillation) ex- 

 ists in all organisms, yet domestic ones are exposed to new 

 and different causes of variability, resulting in such striking 

 divergencies as have been observed. Not even in this latter 

 case, however, is it necessary to believe that the variability 

 is indefinite, but only that the small oscillations become in 

 certain instances intensified into large and conspicuous ones. 

 Moreover, it is possible that some of our domestic animals 

 have been in part chosen and domesticated through possess- 

 ing variability in an eminent degree. 



That each species exhibits certain oscillations of struct- 

 ure is admitted on all hands. Mr. Darwin asserts that this 

 is the exhibition of a tendency to vary which is absolutely 

 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 thV 

 occurrence of variations in certain domestic animals greater 

 in degree than the differences between many wild species, 



