V.] SPECIFIC STABILITY. 143 



Thus, then, it seems that a certain normal specific 

 stability in species, accompanied by occasional sudden 

 and considerable modifications, might be expected a priori 

 from what we know of crystalline inorganic forms and 

 from what we may suspect with regard to the lowest 

 organic ones. This presumption is strengthened by the 

 knowledge of the increasing difficulties which beset any 

 attempt to indefinitely intensify any race characteristics. 

 The obstacles to this indefinite intensification, as well as 

 to certain lines of variation in certain cases, appear to be 

 not only external, but to depend on internal causes or an 

 internal cause. We have seen that Mr. Darwin himself 

 implicitly admits the principle of specific stability in 

 asserting the singular inflexibility of the organization of 

 the goose. We have also seen that it is not fair to con- 

 clude that all wild races can vary as much as the most 

 variable domestic ones. It. has been shown besides that 

 there are grounds for believing in a tendency to reversion 

 generally, as it is distinctly present in certain instances ; 

 further, that the doctrine of specific stability is confirmed 

 by the fact that physiological obstacles oppose themselves 

 to any considerable or continued intermixture of species, 

 while no such barriers oppose themselves to the blending 

 of varieties. All these considerations taken together may 

 fairly be looked upon as strengthening the belief that 

 specific manifestations are relatively stable. At the same 

 time the view advocated in this book does not depend 

 upon, and is not identified with, any such stability. All 

 that the author contends for is that specific manifestation 

 takes place along certain lines, and according to law ; and 

 not in an exceedingly minute, indefinite, and fortuitous 



