128 NATURAL SELECTION. Chap. IV. 



character ; for more living beings can be supported on 

 the same area the more they diverge in structure, habits, 

 and constitution, of which we see proof by looking at 

 the inhabitants of any small spot or at naturalised pro- 

 ductions. Therefore during the modification of the 

 descendants of any one species, and during the incessant 

 struggle of all species to increase in numbers, the more 

 diversified these descendants become, the better will be 

 their chance of succeeding in the battle of life. Thus 

 the small differences distinguishing varieties of the same 

 species, will steadily tend to increase till they come to 

 equal the greater differences between species of the 

 same genus, or even of distinct genera. 



We have seen that it is the common, the widely- 

 diffused, and widely-ranging species, belonging to the 

 larger genera, which vary most ; and these will tend to 

 transmit to their modified offspring that superiority 

 which now makes them dominant in their own coun- 

 tries. Natural selection, as has just been remarked, 

 leads to divergence of character and to much extinction 

 of the less improved and intermediate forms of life. On 

 these principles, I believe, the nature of the affinities 

 of all organic beings may be explained. It is a truly 

 wonderful fact — the wonder of which we are apt to 

 overlook from familiarity — that all animals and all 

 plants throughout all time and space should be related 

 to each other in group subordinate to group, in the 

 manner which we everywhere behold — namely, vari- 

 eties of the same species most closely related together, 

 species of the same genus less closely and unequally 

 related together, forming sections and sub-genera, spe- 

 cies of distinct genera much less closely related, and 

 genera related in different degrees, forming sub-fami- 

 lies, families, orders, sub-classes, and classes. The 

 several subordinate groups in any class cannot be 



