CHARLES DARWIN 243 



acter; for the more organic beings diverge in structure, habits, and 

 constitution, by so much the more can a large number be supported on 

 the area, — of which we see proof by looking to the inhabitants of any 

 small spot, and to the productions naturalised in foreign lands. 

 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 the descendants become, the better 

 will be their chance of success in the battle for life. Thus the small 

 differences distinguishing varieties of the same species, steadily tend 

 to increase, till they 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 within each class, 

 which vary most; and these tend to transmit to their modified off- 

 spring that superiority which now makes them dominant in their 

 own countries. Natural selection, as has just been remarked, leads 

 to divergence of character and to much extinction of the less im- 

 proved and intermediate forms of life. On these principles, the 

 nature of the afifinities, and the generally well-defined distinctions 

 between the innumerable organic beings in each class throughout the 

 world, 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 groups, subordinate to groups, in the manner which we every- 

 where behold — namely, varieties of the same species most closely 

 related, species of the same genus less closely and unequally related, 

 forming sections and sub-genera, species of distinct genera much less 

 closely related, and genera related in different degrees, forming sub- 

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

 ordinate groups in any class cannot be ranked in a single file, but 

 seem clustered round points, and these round other points, and so 

 on in almost endless cycles. If species had been independently 

 created, no explanation would have been possible of this kind of 

 classification ; but it is explained through inheritance and the complex 

 action of natural selection, entailing extinction and divergence of 

 character . . . 



The affinities of all the beings of the same class have sometimes 

 been represented by a great tree. I believe this simile largely speaks 



