116 
NATUEAL SELECTION. 
Chap. IV. 
Edwards. No physiologist doubts that a stomach adapted 
to digest vegetable matter alone, or flesh alone, draws 
most nutriment from these substances. So in the gene¬ 
ral 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 ani¬ 
mals, with their organisation but little diversified, 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 repre¬ 
senting, as Mr. Waterhouse and others have remarked, 
our carnivorous, ruminant, and rodent mammals, could 
successfully compete with these well-pronounced or¬ 
ders. 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 benefit being derived from divergence of 
character, combined with the principles of natural selec¬ 
tion 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, 
