Chap. XIV.] CLASSIFICATION. 203 



to show that within each country it is the widely rang- 

 ing, the much diffused and common, that is the domi- 

 nant species, belonging to the larger genera in each 

 class, which vary most. The varieties, or incipient spe- 

 cies, thus produced, ultimately become converted into 

 new and distinct species; and these, on the principle 

 of inheritance, tend to produce other new and domi- 

 nant species. Consequently the groups which are now 

 large, and which generally include many dominant spe- 

 cies, tend to go on increasing in size. I further at- 

 tempted to show that from the varying descendants 

 of each species trying to occupy as many and as differ- 

 ent 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 tend- 

 ency 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 progeni- 

 tor 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 com- 

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

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



