116 NATUKAL SELECTION. Chap. IV. 



Milne Edwards. No physiologist doubts that a stomach 

 by being adapted to digest vegetable matter alone, or 

 flesh alone, draws most nutriment from these substances. 

 So in the general economy of any land, the more widely 

 and perfectly 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 diver- 

 sified, could hardly compete with a set more perfectly 

 diversified in structure. It may 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 mam- 

 mals, could successfully compete with these well-pro- 

 nounced orders. In the Australian mammals, we see 

 the process of diversification in an early and incomplete 

 stage of development. 



After the foregoing discussion, which ought to have 

 been much amplified, we may, I think, assume that the 

 modified descendants of any one species will succeed by 

 so much the better as they become more diversified in 

 structure, and are thus enabled to encroach on places 

 occupied by other beings. Now let us see how this 

 principle of great benefit being derived from divergence 

 of character, combined with the principles of natural 

 selection and of extinction, will tend to act. 



The accompanying diagram will aid us in understand- 

 ing this rather perplexing subject. Let A to L repre- 

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

 these species are supposed to resemble each other in 

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

 and as is represented in the diagram by the letters 

 standing at unequal distances. I have said a large 

 genus, because we have seen in the second chapter, 



