126 ORIGIN OF SPECIES 



the physiological division of labor in the organs of the same 

 individual body — a subject so well elucidated by Milne Ed- 

 wards. No physiologist doubts that a stomach 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 diversified, could hardly compete with a set more per- 

 fectly diversified in structure. It may be doubted, for in- 

 stance, 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 suc- 

 cessfully compete with these well-developed orders. In the 

 Australian mammals, we see the process of diversification 

 in an early and incomplete stage of development. 



THE PROBABLE EFFECTS OF THE ACTION OF NATURAL SELECTION 

 THROUGH DIVERGENCE OF CHARACTER AND EXTINC- 

 TION, ON THE DESCENDANTS OF A COMMON 

 ANCESTOR 



After the foregoing discussion, which has been much com- 

 pressed, we may assume that the modified descendants of any 

 one species will succeed so much the better as they become 

 more diversified in structure, and are thus enabled to en- 

 croach on places occupied by other beings. Now let us see 

 how this principle of benefit being derived from divergence 

 of character, combined with the principles of natural selec- 

 tion and of extinction, tends to act. 



The accompanying diagram will aid us in understanding 

 this rather perplexing subject. Let A to L represent 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 as we saw in the second chapter, 

 on an average more species vary in large genera than in 



