426 ON THE ORIGIN OF SPECIES 



breeds of pigeon have descended from the blue and 

 barred rock-pigeon ! 



On the ordinary view of each species having been 

 independently created, why should the specific charac- 

 ters, or those by which the species of the same genus 

 differ from each other, be more variable than the 

 generic characters in which they all agree ? Why, for 

 instance, should the colour of a flower be more likely 

 to vary in any one species of a genus, if the other 

 species, supposed to have been created independently, 

 have differently coloured flowers, than if all the species 

 of the genus have the same coloured flowers ? If species 

 are only well-marked varieties, of which the characters 

 have become in a high degree permanent, we can 

 understand this fact ; for they have already varied 

 since they branched off from a common progenitor 

 in certain characters, by which they have come to be 

 specifically distinct from each other ; and therefore 

 these same characters would be more likely still to be 

 variable than the generic characters which have been 

 inherited without change for an enormous period. It 

 is inexplicable on the theory of creation why a part 

 developed in a very unusual manner in any one species 

 of a genus, and therefore, as we may naturally infer, 

 of great importance to the species, should be eminently 

 liable to variation ; but, on my view, this part has 

 undergone, since the several species branched off from 

 a common progenitor, an unusual amount of variability 

 and modification, and therefore we might expect this 

 part generally to be still variable. But a part may be 

 developed in the most unusual manner, like the wing 

 of a bat, and yet not be more variable than any other 

 staucture, if the part be common to many subordinate 

 forms, that is, if it has been inherited for a very long 

 period ; for in this case it will have been rendered 

 constant by long-continued natural selection. 



Glancing at instincts, marvellous as some are, they 

 offer no greater difficulty than does corporeal structure 

 on the theory of the natural selection of successive, 

 slight, but profitable modifications. We can thuf 



