EVOLUTION 



341 



work. He was constantly in correspondence with animal breeders, many 

 of his conclusions were drawn from studies of animals and plants under 

 domestication, and he was the first to be willing to use knowledge so 

 gained to argue concerning hving things in nature. Often he asked 

 others to make observations or perform experiments for him. As a 

 result he had a mass of evidence which seemed to him to point strongly 

 to the conclusion that animals and plants are now in the process of 

 evolution, that they have evolved in the past, and that the things 

 which are causing evolution now caused it then. 



His first idea as to the cause of this evolution was gained in 1838 

 from the reading of a book by Malthus, "Essay on Population, " in which 

 it was pointed out that overpopulation led to a struggle for existence. 



mm 



L 



.^^aiiiiiiaiiteitt 



Fig. 234. — Sir Charles Lyell, 1797-1875. {From Schuchert's Hiblorical Geoloay. John 



Wiley and Sons.) 



Darwin was at once struck with the idea that " Under these circumstances 

 favorable variations would tend to be preserved and unfavorable ones to 

 be destroyed. The result of this would be the formation of a new species. 

 Here then I had at last got a theory by which to work, but I was so 

 anxious to avoid prejudice that I determined not for some time to write 

 even the briefest sketch of it. In June, 1842, I first allowed myseK the 

 satisfaction of writing a very brief abstract of my theory in pencil, in 

 thirty-five pages, and this was enlarged during the summer of 1844 into 

 one of 230 pages. " (Quoted from Darwin's Autobiography, in Life and 

 Letters.) During the twenty j'-ears and more in which Darwin was 

 collecting data he had opportunity to test this theory, which has since 

 been called the theory of Natural Selection. 



