1508 THE STORY OF THE UNIVERSE 



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 organization but little diversified, could 

 hardly compete with a set more perfectly diversi- 

 fied in structure. It may be doubted, for instance, 

 whether the Australian marsupials, which are di- 

 vided 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 diversification in an 

 early and incomplete stage of development. 



If under changing conditions of life organic beings 

 present individual differences in almost every part 

 of their structure, and this can not be disputed; if 

 there be, owing to their geometrical rate of increase, 

 a severe struggle for life at some age, season, or year, 

 and this certainly can not be disputed ; then, consid- 

 ering the infinite complexity of the relations of all 

 organic beings to each other and to their conditions of 

 life, causing an infinite diversity in structure, consti- 

 tution, and habits, to be advantageous to them, it 

 would be a most extraordinary fact if no variations 

 had ever occurred useful to each being's own welfare, 

 in the same manner as so many variations have oc- 

 curred useful to man. But if variations useful to 



