422 THE ORIGIN OF SPECIES 



genus have been produced, and where they now flourish, these 

 same species should present many varieties; for where the manu- 

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

 rule, to fmd 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 species of 

 smaller genera. The closely allied species also of a larger genera 

 apparently have restricted ranges, and in their affinities they are 

 clustered in little groups round other species — in both respects 

 resembling varieties. These are strange relations on the view that 

 each species was independently created, but are intelligible if 

 each existed first as a variety. 



As each species tends by its geometrical rate of reproduction 

 to increase inordinately in number; and as the modified descend- 

 ants of each species will be enabled to increase by as much as they 

 become more diversified in habits and structure, so as to be able 

 to seize on many and widely different places in the economy of 

 nature, there will be a constant 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 characteristic of the species 

 of the same genus. New and improved varieties will inevitably 

 supplant and exterminate the older, less improved, and intermedi- 

 ate varieties; and thus species are rendered to a large exten; 

 defined and distinct objects. Dominant species belonging to th; 

 larger groups within each class tend to give birth to new and domi • 

 nant forms; so that each large group tends to become still larger, 

 and at the same time more divergent in character. But as all 

 groups cannot thus go on increasing in size, for the world would 

 not hold them, the more dominant groups beat the less dominant.! 

 This tendency in the large groups to go on increasing in size and^ 

 diverging in character, together with the inevitable contingency'' 

 of much extinction, explains the arrangement of all the forms of 

 life in groups subordinate to groups, all within a few great classes, 

 which has prevailed throughout all time. This grand fact of the 

 grouping of all organic beings under what is called the Natural 

 System, is utterly inexplicable on the theory of creation. 



As natural selection acts solely by accumulating slight, succes- 

 sive, favorable variations, it can produce no great or sudden 

 modifications; it can act only by short and slow steps. Hence, the 



