NATTJEAL SELECTION. 



In the chapter devoted to natural selection I shall show 

 from experiment and from a multitude of facts, that the 

 greatest amount of life can be supported on each spot by 

 great diversification or divergence in the structure and consti- 

 tution of fc its inhabitants. We shall, also, see that the con- 

 tinued production of new forms through natural selection, 

 which implies that each new variety has some advantage over 

 others, almost inevitably leads to the extermination ^of the 

 older and less improved forms. These latter are almost neces- 

 sarily intermediate in structure as well as in descent between 

 the last-produced forms and their original parent- species. 

 Now, if we suppose a species to produce two or more varieties, 

 and these in the course of time to produce other varieties, 

 the principle of good being derived from diversification of 

 structure will generally lead to the preservation of the most 

 divergent varieties; thus the lesser differences characteristic 

 of varieties come to be augmented into the greater differ- 

 ences characteristic of species, and, by the extermination of 

 the older intermediate forms, new species come to be distinctly 

 defined objects. Thus, also, we shall see how it is that organic 

 beings can be classed by what is called a natural method in 

 distinct groups— species under genera, and genera under 

 families.) 



As all the inhabitants of each country may be said, owing 

 to their high rate of reproduction, to be striving to increase 

 in numbers ; as, each form is related to many other forms in 

 the struggle for life,— for destroy any one and its place will be 

 seized by others ; as every part of the organization occasionally 

 varies in some slight degree, and as natural selection acts 

 exclusively by the preservation of variations which are advan- 

 tageous under the excessively complex conditions to which 

 each being is exposed, no limit exists to the number, singu- 

 larity, and perfection of the contrivances and co-adaptations 

 which may thus be produced. A.n animal or a plant may thus 

 slowly become related in its structure and habits in the most 

 intricate manner to many other animals and plants, and to the 

 physical conditions of its home. Variations in the organiza- 

 tion will in some cases be aided by habit, or by the use and 

 disuse of parts, and they will be governed by the direct action 



