470 RECAPITULATION. Chap. XIV. 



where many species of a genus have been produced, 

 and where they now flourish, these same species should 

 present many varieties ; for where the manufactory of 

 species has been active, we might expect, as a general 

 rule, to find it still in action ; and this is the case if 

 varieties be incipient species. Moreover, the species of 

 the larger genera, which afford the greater number of 

 varieties or incipient species, retain to a certain degree 

 the character of varieties ; for they differ from each 

 other by a less amount of difference than do the spe- 

 cies of smaller genera. The closely allied species also 

 of the larger genera apparently have restricted ranges, 

 and they are clustered in little groups round other spe- 

 cies — in which resjDects they resemble varieties. These 

 are strange relations on the view of each species having 

 been independently created, but are intelligible if all 

 species first existed as varieties. 



As each species tends by its geometrical ratio of 

 reproduction to increase inordinately in number; and 

 as the modified descendants of each species will be 

 enabled to increase by so much the more as they 

 become more diversified in habits and structure, so as 

 to be enabled to seize on many and widely different 

 places in the economy of nature, there will be a con- 

 stant tendency in natural selection to preserve the most 

 divergent offspring of any one species. Hence during a 

 long-continued course of modification, the slight differ- 

 ences, characteristic of varieties of the same species, 

 tend to be augmented into the greater differences cha- 

 racteristic of species of the same genus. New and im- 

 proved varieties will inevitably supplant and exterminate 

 the older, less improved and intermediate varieties ; and 

 thus species are rendered to a large extent defined and 

 distinct objects. Dominant species belonging to the 

 larger groups tend to give birth to new and dominant 



