470 CONCLUSION. 



of the lower algae may claim to have first a characteristically 

 animal, and then an unequivocally vegetable existence." 

 Therefore, on the principle of natural selection with 

 divergence of character, it does not seem incredible, that, 

 from some such low and intermediate form; both animals 

 and plants may have been developed ; and, if we admit this, 

 we must likewise admit that all the organic beings which 

 have ever lived on this earth may be. descended from some 

 one primordial form. But this inference is chiefly grounded 

 on analogy, and it is immaterial whether or not it be 

 accepted. No doubt it is possible, as Mr. G. H. Lewes 

 has urged, that at the first commencement of life many 

 different forms were evolved ; but if so, we may conclude 

 that only a very few have left modified descendants. For, 

 as I have recently remarked in regard to the members of 

 each great kingdom, such as the Vertebrata, Articulat^, etc., 

 we have distinct evidence in their embryological, homol- 

 ogous, and rudimentary structures, that within each king- 

 dom all the members are descended from a single progenitor. 



When the views advanced by me in this volume, and by 

 Mr. Wallace, or when analogous views on the origin of 

 species, are generally admitted, we can dimly foresee that 

 there will be a considerable revolution in natural history. 

 Systematists will be able to pursue their labors as at present ,* 

 but they will not be incessantly haunted by the shadowy 

 doubt whether this or that form be a true 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 good 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 defin- 

 able, whether the differences be sufficiently important to 

 deserve a specific name. This latter point will become a far 

 more essential consideration than it is at present ; for differ- 

 ences, however slight, between any two forms, if not blended 

 by intermediate gradations, are looked at by most naturalists 

 as sufficient to raise both forms to the rank of species. 



Hereafter, we shall be compelled to acknowledge 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 intermediate gradations, whereas species 

 were formerly thus connected. Hence, without rejecting 

 the consideration of the present existence of intermediate 



