436 ON THE ORIGIN OF SPECIES 



affects plants and animals ; or that the poison secreted 

 by the gall-fly produces monstrous growths on the 

 wild rose or oak-tree. Therefore 1 should infer from 

 analogy that probably all the organic beings which have 

 ever lived on this earth have descended from some one 

 primordial form, into which life was first breathed by 

 the Creator. 



When the views advanced by me in this volume, 

 and by Mr. Wallace in the Linnean Journal, or when 

 analogous views on the origin of species are generally 

 admitted, we can dimly foresee that there will be a con- 

 siderable revolution in natural history. Systematists 

 will be able to pursue their labours as at present ; but 

 they will not be incessantly haunted by the shadowy 

 doubt whether this or that form be in essence a species. 

 This I feel sure, and I speak after experience, will be 

 no slight relief. The endless disputes whether or not 

 some fifty species of British brambles are true species 

 will cease. Systematists will have only to decide (not 

 that this will be easy) whether any form be sufficiently 

 constant and distinct from other forms, to be capable 

 of definition ; and if definable, whether the differences 

 be sufficiently important to deserve a specific name. 

 This latter point will become a far more essential con- 

 sideration than it is at present ; for differences, how- 

 ever slight, between any two forms, if not blended by 

 intermediate gradations, are looked at by most natural- 

 ists as sufficient to raise both forms to the rank of 

 species. Hereafter we shall be compelled to acknow- 

 ledge that the only distinction between species and 

 well-marked varieties is, that the latter are known, 

 or believed, to be connected at the present day by in- 

 termediate gradations, whereas species were formerly 

 thus connected. Hence, without rejecting the con- 

 sideration of the present existence of intermediate gra- 

 dations between any two forms, we shall be led to weigh 

 more carefully and to value higher the actual amount 

 of difference between them. It is quite possible that 

 forms now generally acknowledged to be merely varieties 



