78 CHARLES DARWIN. 



originator of either of these hypotheses. He held them both 

 as articles of scientific faith, but they existed before his time, and 

 he never claimed their authorship. Darwin's grand discovery was 

 not ' descent with modification,' but that of ' natural selection,' 

 the age7icy by which, "as he was the first to prove, definite kinds of 

 plants and animals have been slowly evolved from simpler forms, 

 with definite adaptations to the special circumstances by which 

 they are surrounded." An abstract of his theory can be given in 

 half-a-dozen concise sentences : — 



I. — More organisms are produced than can survive. 



2. — The fittest survive, />., in the struggle for existence. 



3. — No two are alike — the tendency is to variation due to 

 sundry causes. 



4. — Variations are transmitted. 



5. — Variations must be in harmony with surroundings. This 

 is the very essence of natural selection. 



6. — Variations repeatedly produced result finally in new 

 species. 



7. — Ages of time must be postulated as necessary for the 

 various changes and developments from the primitive organism up 

 to Man. 



All these steps in the process of descent by modification 

 through the agency of natural selection can be proved from 

 Embryology, Morphology, Geological succession. Geographical 

 distribution, and Classification, as well as by our own application 

 of the theory in the variation of plants and domestic animals. 



Thus Darwin did not discover ' descent by modification,' but 

 he did discover the machinery by which such a result could come 

 about. To quote Grant Allen's way of putting it : "He was not, as 

 most people falsely imagine, the Moses of evolutionism, the prime 

 mover in the biological revolution ; he was the Joshua who led the 

 world of thinkers and workers into full fruition of that promised 

 land which earlier investigators had but dimly descried from the 

 Pisgah-top of conjectural speculation. Darwin raised this theory 

 from the rank of a mere plausible and happy guess to the rank of 

 a highly elaborate and almost universally received biological 

 system." 



The doctrine of the * Fixity and Immutability of Species,' 



