CHAP. XIV.] CLASSIFICATION. 



it is notorious how commonly members of even the same sub- 

 group have different habits. In the second and fourth chapters, 

 on Variation and on Natural Selection, I have attempted 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 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 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 

 principles ; 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 sub-family, distinct from that con- 

 taining the next two genera on the right hand, which diverged 

 from a common parent at the fifth stage of descent. These five 

 genera have also much in common, though less than when grouped 

 in sub-families ; and they form a family distinct from that con- 

 taining the three genera still farther to the right hand, which 

 diverged at an 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 into sub-families, 

 families, and orders, all under one great class. The grand fact of 

 the natural subordination of organic beings in groups under 

 groups, which, from its familiarity, does not always sufficiently 

 strike us, is in my judgment thus explained. No doubt organic 

 beings, like all other objects, can be classed in many ways, either 

 artificially by single characters, or more naturally by a number of 



