VARIATIONS, DUE TO REVERSION. 19 



improvements or variations which arise, are due to re- 

 version. Darwin has noted this disposition, on the 

 part of individuals of a species, to develop all of the 

 characters of the given species, and refers it, as he 

 should, to the fact of these characters having once been 

 lost, and to the capacity, in each of the individuals, to 

 regain such characters. As if fearful, that the signifi- 

 cance of the phenomenon, should thrust itself upon 

 the reader's attention, to the prejudice of his hypothe- 

 sis of development without a limit, he assures his 

 readers, that he is " concerned not as hitherto with the 

 causes of variation, but with the results!' He concerns 

 himself about the causes of variation, only when he is 

 engaged upon an enumeration of the conditions of 

 variation (such as food, and climate, and exercise, &c.) 

 which he is able to demonstrate, can furnish no ade- 

 quate explanation of the appearance of the improve- 

 ments. When, however, he trenches upon a well- 

 known, scientific law, such as is reversion, he hastens 

 to add, that all discussion upon causes, has been closed ! 

 On page 417, Vol. ii, Animals and Plants, &c, under 

 the heading, "Analogous or Parallel Variation," he 

 says: 



" By this term I wish to express that similar char- 

 acters occasionally make their appearance in the sev- 

 eral varieties or races descended from the same species. 

 * * * We are here concerned, not as hitherto with 

 the causes of variation, but with the results ; but this 

 discussion could not have been more conveniently in- 

 troduced elsewhere." 



All of the individuals, of a species, are lacking in 



