Chap. IV.] SUMMARY. 161 



to divergence of character; 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 in- 

 habitants 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 be- 

 come, the better will be their chance of success in the 

 battle for life. Thus the small differences distinguish- 

 ing varieties of the same species, steadily tend, to in- 

 crease, 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 offspring that 

 superiority which, now makes them dominant in their 

 own countries. Natural selection, as has just been re- 

 marked, leads to divergence of character and to much 

 extinction of the less improved and intermediate forms 

 of uf e. On these principles, the nature of the af&nities, 

 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 fa- 

 miliarity — 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 

 everywhere behold — namely, varieties of the same spe- 

 cies most closely related, species of the same genus less 

 closely and unequally related, forming sections and sub- 



