The Origin of Species 



we have distinct evidence in their embryological, 

 homologous, and rudimentary structures, that 

 within each kingdom all the members arc de- 

 scended from a single progenitor. 



When the views advanced by me in this volume, 

 and by .Air. Wallace, or when analogous views on 

 the origin of species are generally admitted, we 

 ran dimly foresee that there will be a considerable 

 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 a 

 true species. This, I feel sure and I speak after 

 experience, Mill 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 definable, 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 differences, however slight, 

 between any two forms, if not blended by inter- 

 mediate gradations, are looked at by most natur- 

 alists as sufficient to raise both forms to the rank 

 of species. 



Hereafter we shall be compelled to acknowl- 

 edge that the only distinction between sj 

 and well-marked varieties is. that the latter are 

 known, or believed to be connected at the pr 

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