The Origin of Species 205 



animals, was, in the year 1858, attacked by fever 

 and confined to his bed. His thoughts wan- 

 dered to the problem he was engaged in solving 

 when, as he writes, " in a sudden flash of in- 

 sight the idea of natural selection presented 

 itself to my mind." After a few hours' thought 

 he noted down the views he had formed on the 

 subject, and forwarded them by the next mail 

 to C. Darwin, requesting him to show this com- 

 munication to Sir C. Lyell. Darwin at once 

 complied with this request, although realising 

 to the full that this paper of Wallace's fore- 

 stalled the ideas contained in a work on " The 

 Origin of Species " he had in hand, and which 

 he published in the year 1859. In this work 

 Darwin proved from facts of the most varied 

 kind, the truth of the idea he had formed regard- 

 ing natural selection or the survival of the 

 fittest. He held that animals have descended 

 from at most only four or five progenitors, and 

 plants from an equal or lesser number, which 

 were gradually modified in structure in response 

 to changes in their environment caused by 

 geological, climatic, and other influences- 

 beneficial or harmful. This led him to the 



