V.] SPECIFIC STABILITY. 141 



Thus, then, it seems that a certain normal specific sta- 

 bility 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 anticipate 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 obsta- 

 cles 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 conclude that all wild 

 races can vary as much as the most variable domestic ones. 

 It has also been shown that there are grounds for believing 

 in a tendency to reversion generally, as it is distinctly pres- 

 ent in certain instances. Also that specific stability is con- 

 firmed by the physiological obstacles which oppose them- 

 selves to any considerable or continued intermixture of 

 species, while no such barriers oppose themselves to the 

 blending of varieties. All these considerations taken to- 

 gether may fairly be considered 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 

 manner. Finally, he cannot but feel justified, from all 

 that has been brought forward, in reiterating the open- 

 ing assertion of this chapter that something is still to be 

 said for the view which maintains that species are stable, 

 at least in the intervals of their comparatively rapid suc- 

 cessive manifestations. 



