38 THE THEORIES OF EVOLUTION 



are -transmitted through inheritance made him con- 

 ceive the possibility of universal transmutation. The 

 only questions in his mind were the origin of such 

 modifications and the way in which they endow or- 

 ganisms with the means of adapting themselves to 

 their environment. 



Darwin devoted the years which elapsed between 

 his return from his voyage, in 1835, and the publica- 

 tion of his book, to meditating on those problems and 

 collecting the greatest possible number of facts bear- 

 ing upon their solution. As he did not wish to draw 

 any far-reaching conclusions without basing them on 

 irrefutable evidence, he did not publish a single line 

 about his theories. He collaborated to the report on 

 the Beagle's trip, published an essay on "Coral 

 Reefs," and a "Monography on Cirrhipedia," but he 

 reserved: the main question at issue. 



Slowly and patiently, Darwin observed domestic 



/ animals and cultivated plants, until then ignored by 

 scientists, their varieties and the way in which they 



\ were produced. He realised then what power of se- j 



Jection man could wield , 



Maltiius' "Principles of Population," which came 

 accidentally into his possession, suggested t^Hmthe 

 possibility of a similar selection in the animal and 

 vegetable kingdoms. Man tends to_Jncre ase i n 

 geometrical ratio, Malthus said, while the increase of 

 food supply is only in arithmetical ratio. " Hence a 



