CLASSIFICATION 371 



*nd dominant species. Consequently the groups which 

 Are now large, and which generally include many domi- 

 nant species, tend to go on increasing indefinitely in 

 size. I further attempted to show that from the vary- 

 ing descendants of each species trying to occupy as 

 many and as different places as possible in the economy 

 of nature, there is a constant tendency in their char- 

 acters to diverge. This conclusion was supported by 

 looking at the great diversity of the forms of Life which, 

 in any small area, come into the closest competition, 

 and by looking to certain facts in naturalisation. 



I attempted also to show that there is a constant 

 tendency in the forms which are increasing in number 

 and diverging in character, to supplant and exterminate 

 the less divergent, the less improved, and preceding 

 forms. I request the reader to turn to the diagram 

 illustrating the action, as formerly explained, of these 

 several principles ; and he will see that the inevitable 

 result is that the modified descendants proceeding from 

 one progenitor become broken up into groups subordi- 

 nate to groups. In the diagram each letter on the 

 uppermost line may represent a genus including several 

 species ; and all the genera on this line form together 

 one class, for all have descended from one ancient 

 but unseen 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 sub -family, distinct from that 

 including the next two genera on the right hand, which 

 diverged from a ecunmon parent at the fifth stage of 

 descent. These five genera have also much, though 

 less, in common ; and they form a family distinct from 

 that including the three genera still farther to the 

 right hand, which diverged at a still earlier period. 

 And all these genera, descended from (A), form an 

 order distinct from the genera descended from (I). So 

 that we here have many species descended from a 

 single progenitor grouped into genera ; and the 

 genera are included in, or subordinate to, sub -families, 

 families, and orders, all united into one class. Thus. 



