Alfred Russel Wallace 



abundance of new facts and the advocacy of many new 

 and old theories. As it had frequently been considered a 

 weakness on Darwin's part that he based his evidence 

 primarily on experiments with domesticated animals and 

 cultivated plants, Wallace desired to secure a firm founda- 

 tion for the theory in the variation of organisms in a state 

 of nature. It was in order to make these facts intelligible 

 that he introduced a number of diagrams, just as Darwin 

 was accustomed to appeal to the facts of variation among 

 dogs and pigeons. 



Another change which he considered important was that 

 of taking the struggle for existence first, because this is 

 the fundamental phenomenon on which Natural Selection 

 depends. This, too, had a further advantage in that, after 

 discussing variations and the effects of artificial selection, 

 it was possible at once to explain how Natural Selection acts. 



The subjects treated with novelty and interest in their 

 important bearings on the theory of Natural Selection 

 were : (1) A proof that all specific characters are (or once 

 have been) either useful in themselves or correlated with 

 useful characters (Chap. VI.) ; (2) a proof that Natural 

 Selection can, in certain cases, increase the sterility of 

 crosses (Chap. VII.) ; (3) a fuller discussion of the colour 

 relations of animals, with additional facts and arguments 

 on the origin of sexual differences of colour (Chaps. VIII. — 

 X.); (4) an attempted solution of the difficulty presented 

 by the occurrence of both very simple and complex modes 

 of securing the cross-fertilisation of plants (Chap. XI.) ; 

 (5) some fresh facts and arguments on the wind-carriage 

 of seeds, and its bearing on the wide dispersal of many 

 arctic and alpine plants (Chap. XII.) ; (6) some new illus- 

 trations of the non-heredity of acquired characters, and a 

 proof that the effects of use and disuse, even if inherited, 

 must be overpowered by Natural Selection (Chap. XIV.) ; 



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