510 ORIGIN OF SPECIES 



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 differences characteristic of varie- 

 ties 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 ex- 

 terminate the older, less improved, and intermediate vari- 

 eties ; and thus species are rendered to a large extent defined 

 and distinct objects. Dominant species belonging to the 

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

 dominant forms; so that each large group tends to become 

 still larger, and at the same time more divergent in char- 

 acter. 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 Nat- 

 ural System, is utterly inexplicable on the theory of creation. 

 As natural selection acts solely by accumulating slight, 

 successive, favourable variations, it can produce no great or 



' sudden modifications ; it can act only by short and slow steps. 

 Hence, the canon of "Natura non facit saltum," which every 

 fresh addition to our knowledge tends to confirm, is on this 

 theory intelligible. We can see why throughout nature the 

 same general end is gained by an almost infinite diversity of 

 means, for every peculiarity when once acquired is long in- 

 herited, and structures already modified in many different 

 ways have to be adapted for the same general purpose. We 

 can, in short, see why nature is prodigal in variety, though 

 niggard in innovation. But why this should be a law of 

 nature if each species has been independently created no man 

 can explain. 

 Many other facts are, as it seems to me, explicable on 



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