Chap. XIV.] CLASSIFICATION. 203 



to show that within each country it is the widely 

 ranging, the much diffused and common, that is the 

 dominant species, belonging to the larger genera in each 

 class, which vary most. The varieties, or incipient 

 species, thus produced, ultimately become converted 

 into new and distinct species ; and these, on the prin- 

 ciple 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 observing the great diversity 

 of forms which, in any small area, come into the closest 

 competition, and by certain facts in naturalisation. 



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 

 together one class, for all are descended from one ancient 

 parent, and, consequently, have inherited something in 

 common. But the three genera on the left hand have, 

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



