VI. 

 NATURAL SELECTION. 



The theory of " Natural Selection " has been most 

 elaborately argued pro and con, by Mr. Darwin, in 

 " The Origin of Species," and on this theory he, for 

 the most part, relies to explain the evolution of 

 organic forms. 



The general facts concerning it are the following: 

 The earth can produce but a limited supply of food 

 for living beings. Every species of plants and of 

 animals multiplies its kind in a geometrical ratio, so 

 that if all the young of any species of organism could 

 live to the average age of those of its kind that arrive 

 at the age of maturity, the earth would in a few gen- 

 erations be filled by the individuals of that species. 

 As a matter of fact this is not the case, for the earth 

 is occupied by hundreds of thousands of organic 

 forms. 



The whole possible number of organisms that can 

 live on the earth at one time, is limited by the pos- 

 sible quantity of food at their disposal. Taking the 

 birth-rate of organisms and the quantity of food at 

 their disposal, it is evident that most of them must 

 perish before arriving at the age of maturity, for lack 

 of food, if for no other reason. 



In many cases the number of animals living is much 

 less than the food will support, there being frequent- 

 ly a superabundance of food that goes to waste. 



It is, therefore, evident that nature has some means 

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