Theory of Natural Selection 



The theory of natural selection is so generally 

 understood, that to set it forth in detail in this 

 place would be quite superfluous. 



Darwin, it will be remembered, based his 

 great hypothesis on the following observed 

 facts : 



1. No two individuals of a species are exactly 

 alike. This is sometimes called the law of 

 variation. 



2. All creatures tend in a general way to 

 resemble their parents in appearance more 

 closely than they resemble individuals not re- 

 lated to them. This may be termed the law of 

 heredity. 



3. Each pair of organisms produces in the 

 course of a lifetime, on an average, many more 

 than two young ones. 



4. On an average the total number of each 

 species remains stationary. 



From (3) and (4) follows the doctrine of 

 Malthus, namely, that many more individuals 

 are born than can reach maturity. 



Darwin applied this doctrine to the whole of 

 the animal and the vegetable kingdoms. 



In his introduction to The Origin of Species 

 he writes : " As many more individuals of each 

 species are born than can possibly survive ; and 

 as, consequently, there is a frequently recurring 

 struggle for existence, it follows that any being, 

 if it vary, however slightly, in any manner pro- 



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