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Chapter ii 



The Theory of Natural Selection 



THE publication of Darwin's The Origin of Species in 

 1859 produced a tremendous impression upon the 

 intellectual life of Europe and America. The book 

 accomplished two distinct purposes remarkably well. The 

 first of these was to make the general theory of the transfor- 

 mation of species appear reasonable on the basis of a vast 

 accumulation of facts from comparative anatomy, embry- 

 ology, geography and paleontology. Darwin made it clear 

 at the time that there was no rational explanation of ex- 

 isting species of plants and animals other than the assump- 

 tion that there had been descent xvith ^modifications, Dar- 

 win himself did not use the word evolution. He did make 

 out a good case, however, for what we now call evolution 

 of species, as against the idea that each type was specially 

 created in the first instance. 



The second purpose which the book accomplished was 

 to work out a theory to explain hmv evolution of forms 

 could have taken place through the action of intelligible 

 natural forces. This theory of natural selection seems to 

 furnish a mechanism in accord with common sense and com- 

 mon experience. Many were inclined to accept the gen- 

 eral theory of descent but were prevented by their inability 

 to see clearly just how in the course of generations plants or 

 animals could become differentiated from their ancestors. 

 These were enabled by Darwin's theory to accept whole- 

 heartedly the general idea that evolution had in fact taken 

 place. 



Unfortunately, the two purposes became inextricably 

 confused in the minds of most people. As a result, clear 



