140 EESULTS OF THE ACTION OF [Chap. IV. 



general economy of any land, the more widely and per- 

 fectly the animals and plants are diversified for different 

 habits of life, so will a greater number of individuals be 

 capable of there supporting themselves. A set of animals, 

 with their organisation but little diversified, could hardly 

 compete with a set more perfectly diversified in structure. 

 It mav be doubted, for instance, whether the Australian 

 marsupials, which are divided into groups differing but 

 little from each other, and feebly representing, as Mr. 

 "Waterhouse and others have remarked, our carnivorous, 

 ruminant, and rodent mammals, could successfully 

 compete with these well-developed orders. In the 

 Australian mammals, we see the process of diversifica- 

 tion in an early and incomplete stage of development. 



The Probable Effects of the Action of Natural Selection 

 through Divergence of Character and Extinction, on 

 the Descendants of a Common Ancestor. 



After the foregoing discussion, which has been much 

 compressed, we may assume that the modified descend- 

 ants of any one species will succeed so much the better 

 as they become more diversified in structure, and are 

 thus enabled to encroach on places occupied by other 

 beiiiL N w let us see how this principle of benefit 

 being derived from di ,ence of character, combined 

 with the principles of natural selection and of extinc- 

 tion, tends to act 



The accompanying diagram will aid us in understand- 

 in^ this rather perplexing subject. Let A to L represent 

 the species of a genus large in its own country ; these 

 species are suppossd to resemble each other in unequal 

 degrees, as is so generally the case in nature, and as is 



