-WALLACE AND DARWIN. 79 



former is, like the latter, operated upon by natural 

 selection. 



Wallace makes a special point of protective 

 resemblances in the colours of insects, etc. 



The important principle of "divergence of char- 

 acter," and the relatively unimportant one of " sexual 

 selection," are both clearly explained by Darwin. 



Neither writer speaks of the direct effect of 

 external conditions except as a cause of plasticity 

 by Darwin or the inherited effects of use and disuse. 

 Lamarck is mentioned only to be dismissed by 

 Wallace. The evolution of the giraffe's long neck is 

 explained by Wallace on the principle of natural 

 selection, which is contrasted with Lamarck's original 

 explanation of the same character. This contrast, 

 which has been so often drawn, was therefore 

 originally contained in the first public statement of 

 natural selection. 



As has been indicated above, Darwin suggested a 

 cause of variation in the direct effect of changed 

 external conditions on the reproductive system. 



In comparing the two essays it is not unnatural 

 to conclude, as Professor Osborn has done ("From 

 the Greeks to Darwin," 1894, p. 245), that the two 

 writers held different views upon the material 

 utilised by natural selection in the production of 

 new species, Darwin relying upon the usual slight 

 differences which separate individuals and upon 

 variations in single characters, Wallace upon fully 

 formed varieties viz. individuals which departed 



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