48 ARE THE EFFECTS OF USE INHERITED? 



Darwin's earlier sketch of his theory of evolution 

 (1844) he attached more weight to the inheri- 

 tance of acquired habits than he does in his 

 Origin of Species published fifteen years later. 1 

 He appears to have acquired the belief in early 

 life without first questioning and rigorously test- 

 ing it as he would have done had it originated 

 with himself. In later life it appeared to assist his 

 theory of evolution in minor points, and in 

 particular it appeared absolutely indispensable 

 to him as the only explanation of the diminution 

 of disused parts in cases where, as in domestic 

 animals, economy of growth seemed to be prac- 

 tically powerless. He failed to adequately notice 

 the effect of panmixia, or the withdrawal of 

 selection, in causing or allowing degeneracy and 

 dwindling under disuse ; and he hardly attached 

 sufficient importance to the fact that rudiment- 

 ary organs and other supposed effects of use or 



1 Life and Letters, ii. p. 14. 



