PRESENT STATUS OP THE QUESTION 17 



in making useful races of animals and plants. But 

 how selection could be applied to organisms living 

 in a state of nature remained for some time a mystery 

 to me." The key to this mystery was suggested to 

 him by reading Malthus' famous essay on Population. 

 In his own words: "Being well prepared to appre- 

 ciate the struggle for existence which everywhere 

 goes on from long continued observation of the 

 habits of animals and plants, it at once struck me 

 that under these circumstances favourable variations 

 would tend to be preserved, and unfavourable ones 

 to be destroyed. The result of this would be the 

 formation of new species. Here then I had a theory 

 by which to work." , 



Time fails to trace farther the stages of growth 

 in Darwin's opinions. All that can be here at- 

 tempted is a brief outline of the theory which, after 

 nearly twenty strenuous years, he gave to the world 

 in the "Origin of Species," published in 1859. Un- 

 like most other explanations of evolution, Darwin's 

 theory is a chain of reasoning, every link of which is 

 an undisputed fact, the only question being, does 

 the theory afford a sufficient and adequate explana- 

 tion of the phenomena? The attempts to give a 

 definite and conclusive answer, affirmative or nega- 

 tive, to this question have given rise to the many 

 debates of which we have by no means heard the 

 last word. 



4 (1) The first of the undisputed facts upon which 

 Darwin's theory is founded is that of variability. It is 



