Seite - 126 - in The Origin of Species

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