Chap. XIII. CLASSIFICATION. 373 



siblc in the economy of Nature, there is a constant tendency in 

 their characters to diverge. This latter conclusion is supported 

 by observing tlio 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 constant tendency 

 in the forms -which arc 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- 

 ])lained, of these several jmnciples ; and he will see that the 

 inevitable result is, that tlie modilied 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 sevei'al species ; and the 

 whole of tlie genera along this upper line form together one 

 class, for all arc descended from one ancient parent, and, con- 

 sequentl}', have inherited something in common. But the 

 three genera on the left hand have, on this same principle, 

 nnich in common, and form a sul>family, distinct from that in- 

 cluding the next two genera on the right hand, w^hich diverged 

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

 five genera have also much, though less, in common ; and they 

 form a faniilv distinct from that including the three genera still 

 fartlier to tlie right liand, which diverged at a still earlier 

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

 order distinct from the genera descended from (1). So tliat 

 we here have many species descended from a single progenitor 

 groujied into genera ; and the genera in sub-families, families, 

 and orders, all in one great class. Thus, the grand fact of the 

 natural suliordination of all organic beings in groups under 

 groups, which, from its familiarity^, does not always sulliciently 

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

 lieings, like all other objects, can be classed in many ways, 

 either artificially by single characters or more naturally by a 

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

 and the elemental substances can be thus aiTanged ; in this 

 case there is of course no relation to genealogical succession, 

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

 group.s. But with organic beings the case is different, and the 

 view above given explains their natural an-angement in group 

 under gr(jup ; and no other explanation has ever hccn at- 

 tcm])lc(l. 



