DARWIN. 241 



shall change again when I get all my facts under one point of 

 view, and a pretty hard job this will be." 



Fourteen years later, Darwin had positively in- 

 cluded Buffon's factor among the causes of Evolu- 

 tion. In 1876 he wrote to Moritz Wagner: 



" When I wrote the Origin, and for some years afterwards, I 

 could find little good evidence of the direct action of the environ- 

 ment ; now there is a large body of evidence, and your case of 

 the Saturnia is one of the most remarkable of which I have heard." 



In 1878 he fully included 1 Wagner's theory as 

 one cause of origin of species, through the direct 

 action of environment in the same country or 

 through geographical isolation. In 1877 he also 

 wrote to Morse : " I quite agree about the high 

 value of Mr. Allen's works, as showing how much 

 change may be expected apparently through the 

 direct action of the conditions of life." There is 

 thus no doubt that the idea of Natural Selection, 

 as almost the sole factor, came to a climax in Dar- 

 win's mind and then gradually appeared less im- 

 portant and exclusive. In preparing his work on 

 ' Variation,' the importance of the problem of 

 heredity came before him, and in writing to Hux- 

 ley, in i865, 2 he gives a 'brief of his point of view 

 at the time, in concisely stating what a working 

 theory of heredity should embrace : 



"The case stands thus: in my next book I shall publish long 

 chapters on bud and seminal-variation, on inheritance, reversion, 



1 Letter to Semper, Life and Letters, Vol. III., p. 160. 

 * Life and Letters, Vol. III., p. 44. 



