100 



CHAPTER XV. 



THE ORIGIN OF SPECIES (1859). 



It is very interesting to separate the two arguments 

 which occur interwoven in the " Origin " — the argu- 

 ment for evolution and the argument for natural 

 selection. The paramount importance of Darwin's 

 contributions to the evidences of organic evolution 

 are often forgotten in the brilliant theory which 

 he believed to supply the motive cause of descent 

 with modification. Organic evolution had been 

 held to be true by certain thinkers during many 

 centuries ; but not only were its adherents entirely 

 without a sufficient motive cause, but their evidences 

 of the process itself were erroneous or extremely 

 scanty. It was Darwin who first brought together a 

 great body of scientific evidence which placed the pro- 

 cess of evolution beyond dispute, whatever the causes 

 of evolution may have been. And accordingly we find 

 that, even at first, natural selection was attacked far 

 more generally than the doctrine ot descent with 

 modification. 



In Chapter I., Variation under Domestication and 

 man's power of selection in forming breeds of animals 

 and plants are discussed ; in Chapter II., Variation 

 under Nature ; in Chapter III., the Struggle for 



