CHAPTER II 

 Theories of Development 



V. Organic Development. 



The Evolution Theory. The evolution theory is 

 popularly attributed to Darwin. He is more properly 

 said to have demonstrated the truth of the theory of 

 descent by natural selection. This theory of descent, 

 commonly called evolution, was suggested even as 

 early as the ancient Greeks, which is not surprising, 

 since even a child must be able to see that things grow 

 and that one living thing springs from another living 

 thing, as in the case of parent and offspring. It was 

 considerably later that the theory of spontaneous 

 generation was definitely disproved. While the fact 

 of descent seemed so evident within the same group or 

 species, no satisfactory explanation of the origin of 

 species had been given before the appearance of Dar- 

 win's work bearing that title. 



The explanation which Darwin offered was also 

 given by Wallace at about the same time, and is 

 briefly this: By the blending of ancestral characters 

 variations arise. Such of those variations as are use- 

 ful are preserved, because they enable that particular 

 organism to survive in the struggle for existence. 

 Owing to the enormous increase in numbers, which 

 is everywhere apparent in living things, some must 

 perish in the struggle for existence; and those that 

 do perish are those least adapted to the conditions of 



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