CLASSIFICATION. 403 



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 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 ex- 

 plained, of these several principles ; and he will see that 

 the inevitable result is, that the modified descendants pro- 

 ceeding 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 some- 

 thing 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 containing 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 contain- 

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

 diverged at an earlier period. And all these genera, de- 

 scended 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 sub- 

 ordination 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 num- 

 ber of characters. We know, for instance, that minerals 

 and the elemental substances can be thus arranged. In this 

 case there is of course no relation to genealogical succession, 

 and no cause can at present be assigned for their falling into 

 groups. But with organic beings the case is different, and 

 the view above given accords with their natural arrangement 

 in group under group; and no other explanation has ever 

 been attempted. 



