212 THE OlilGIX OF til'KClHS 



the dominunt species, belonging to the larger geneni m 

 each class, which vary most. The varieties, or incipient 

 species, thus produced, ultimately become converted into 

 new and distinct species; and these, on the principle of 

 inheritance, tend to produce other new and dominant 

 species. Consequently the groups which are now large, 

 and which generally include many dominant species, tend 

 to go on increasing in size. I further attempted to show 

 that from the varying descendants of each species trying 

 to occupy as many and as different places as possible in 

 the economy of nature, they constantly tend to diverge 

 in character. This latter conclusion is supported by ob- 

 serving the great diversity of forms which, in any small 

 area, come into the closest competition, and by certain 

 facts in naturalization. 



I attempted also to show that there is a steady 

 tendency, in the forms which are increasing in number 

 and diverging in character, to supplant and exterminate 

 the preceding, less divergent and less improved forms. 

 I request the reader to turn to the diagram illustrating 

 the action, as formerly explained, of these several prin- 

 ciples; and he will see that the inevitable result is, that 

 the modified descendants proceeding from one progenitor 

 become broken up into groups subordinate to groups. 

 In the diagram each -letter on the uppermost line may 

 represent a genus including several species; and the 

 whole of the genera along this upper line form to- 

 gethe? one class, for all are descended from one ancient 

 parent, and, consequently, have inherited something in 

 commoT>. But the three genera on the left hand have, 

 on thie same principle, much in common, and form a 

 sub-family, distinct from that containing the next two 



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