NATUEAL SELE-CTION. 7 



power of selection. In the one case, as in the other, selection 

 does nothing without variability, and this depends in some 

 manner on the action of the surrounding circumstances on the 

 organism. I have, also, often personified the word Nature ; 

 for I have found it difBcult to avoid this ambiguity ; but 

 I mean by nature only the aggregate action and product 

 of many natural laws, — and by laws only the ascertained 

 sequence of events. 



It has been shown from many facts that the largest amount 

 of life can be supported on each area, by great diversification 

 or divergence in the structure and constitution of its inhabi- 

 tants. AVe have, also, seen that the continued production of 

 new forms through natural selection, which implies that each 

 new variety has some advantage over others, inevitably 

 leads to the extermination of the older and less improved 

 forms. These latter are almost necessarily intermediate^ in 

 structure, as well as in descent, between the last-produced 

 forms and their original parent-species. Now, if we sujipose 

 a species to produce two or more varieties, and these in 

 the course of time to produce other varieties, the principal 

 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 differences character- 

 istic of species, and, by the extermination of the older inter- 

 mediate forms, new species end by being 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 comes into competition with 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 b}^ the preservation of 

 variations which are advantageous under the excessively 

 complex conditions to which each being is exposed, no limit 



