146 ON THE ORIGIN OF SPECIES 



bility in a tendency to produce any character being 

 inherited for an endless number of generations, than 

 in quite useless or rudimentary organs being, as we all 

 know them to be, thus inherited. Indeed, we may 

 sometimes observe a mere tendency to produce a rudi- 

 ment inherited : for instance, in the common snap- 

 dragon (Antirrhinum) a rudiment of a fifth stamen so 

 often appears, that this plant must have an inherited 

 tendency to produce it. 



As all the species of the same genus are supposed, on 

 my theory, to have descended from a common parent, 

 it might be expected that they would occasionally vary 

 in an analogous manner ; so that a variety of one species 

 would resemble in some of its characters another 

 species ; this other species being on my view only a 

 well-marked and permanent variety. But characters 

 thus gained would probably be of an unimportant 

 nature, for the presence of all important characters 

 will be governed by natural selection, in accordance 

 with the diverse habits of the species, and will not be 

 left to the mutual action of the conditions of life and of 

 a similar inherited constitution. It might further be 

 expected that the species of the same genus would 

 occasionally exhibit reversions to lost ancestral char- 

 acters. As, however, we never know the exact char- 

 acter of the common ancestor of a group, we could not 

 distinguish these two cases : if, for instance, we did 

 not know that the rock-pigeon was not feather-footed 

 or turn-crowned, we could not have told, whether these 

 characters in our domestic breeds were reversions or 

 only analogous variations ; but we might have inferred 

 that the blueness was a case of reversion, from the 

 number of the markings, which are correlated with 

 the blue tint, and which it does not appear probable 

 would all appear together from simple variation. More 

 especially we might have inferred this, from the blue 

 colourand marks so often appearing when distinct breeds 

 of diverse colours are crossed. Hence, though under 

 nature it must generally be left doubtful, what cases 

 are reversions to an anciently existing character, and 



