106 THE ORIGIN OF SPECIES 



class, which vary most; and these tend to transmit to their modi- 

 fied offspring 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 

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

 nature of the affinities, 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 man- 

 ner which we everywhere 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 dif- 

 ferent degrees, forming sub-families, families, orders, sub-classes, 

 and classes^ The several subordinate 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, as we have seen illustrated 

 in the diagram. 



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

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

 speaks the truth. The green and budding twigs may represent 

 existing species ; and those produced during former years may rep- 

 resent the long succession of extinct species. At each period of 

 growth all the growing twigs have tried to branch out on all sides, 

 and to overtop and kill the surrounding twigs and branches, in the 

 same manner as species and groups of species have at all times 

 overmastered other species in the great battle for life. The limbs 

 divided into great branches, and these into lesser and lesser 

 branches, were themselves once, when the tree was young, bud- 

 ding twigs; and this connection of the former and present buds, 

 by ramifying branches, may well represent the classification of all 

 extinct and living species in groups subordinate to groups. Of the 

 many twigs which flourished when the tree was a mere bush, only 

 two or three, now grown into great branches, yet survive and bear 

 the other branches; so with the species which lived during long- 

 past geological periods, very few have left living and modified 

 descendants. From the first growth of the tree, many a limb and 



