RECAPITULATION 295 



cies of a genus, if the other species possess differently 

 colored flowers, than if all possessed the same colored 

 flowers? If species are only well-marked varieties, 

 of which the characters have become in a high de- 

 gree permanent, we can understand this fact; for they 

 have already varied since they branched off from a com- 

 mon progenitor in certain characters, by which they have 

 come to be specifically distinct from each other; therefore 

 these same characters would be more likely again to vary 

 than the generic characters which have been inherited 

 without change for an immense period. It is inexpli- 

 cable on the theory of creation why a part developed in 

 a very unusual manner in one species alone of a genus, 

 and therefore, as we may naturally infer, of great impor- 

 tance to that species, should be eminently liable to varia- 

 tion; but, on our view, this part has undergone, since 

 the several species branched off from a common progeni- 

 tor, an unusual amount of variability and modification, 

 and therefore we might expect the 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 structure, 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 do corporeal structures on 

 the theory of the natural selection of successive, slight, 

 but profitable modifications. We can thus understand 

 why nature moves by graduated steps in endowing dif- 

 ferent animals of the same class with their several in- 



