CHAPTER IV 



DARWIN'S THEORIES OF ARTIFICIAL AND OF NATURAL 



SELECTION 



The Principle of Selection 



Darwin's theory of natural selection is preeminently a theory 

 of adaptation. It appears, in fact, better suited to explain 

 this phenomenon than that of the "origin of species." Dar- 

 win prepared his reader for the ideas contained in the theory 

 of natural selection by a brief consideration of the results of 

 artificial selection; and since the key to the situation is, I 

 believe, to be found in just this supposed resemblance, we 

 cannot do better than examine the theories in the order fol- 

 lowed by Darwin himself. 



One of the means by which the artificial races of animals 

 and plants have been formed by man is selection. The 

 breeder picks out individuals having a certain peculiarity, and 

 allows them to breed together. He hopes to find among 

 the offspring, not only individuals like the parent forms, but 

 also some that have the special peculiarity even more strongly 

 developed. If such are found, they are isolated and allowed 

 to breed, and in the next generation it is hoped to find one or 

 more new individuals that show still more developed the 

 special character that is sought. This process, repeated 

 through a number of generations, is supposed to have led to 

 the formation of many of our various forms of domesticated 

 animals and plants. 



This heaping up as a result of the union of similar individ- 

 uals cannot for a moment be supposed to be the outcome of 

 the addition of the two variations to each other. Such an 



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