SELECTIVE INFLUENCE. 37 



of eacb. individual. An organ exclusively adapted to a certain 

 medium, or fitted only for one restricted use, must degenerate 

 and at last disappear if it becomes useless by the change of 

 conditions, even though the animal itself does rot suffer from 

 this on the whole. Or, secondly, the animal, though not ex- 

 terminated, may be more or less crippled or altered. An organ 

 no longer needed for its original purpose may adapt itself to 

 the altered circumstances, and alter correspondingly if it con- 

 tains within itself, as I have explained above, the elements of 

 such a change. Then the influence exerted by the changed 

 conditions will be transforming, not selective. 



This last view may seem somewhat bold to those readers 

 who know that Darwin, in his theory of selection. Las almost 

 entirely set aside the direct transforming influence of external 

 circumstances. Yet he seems latterly to be disposed to admit 

 that he had undervalued the transforming as well as the selective 

 influence of external conditions ; and it seems to me that his 

 objection to the idea of such an influence rested essentially on 

 the method of his argument, which seemed indispensable for 

 setting his theory of selection and his hypothesis as to the 

 transformation of species in a clear light and on a firm footing. 

 By a rearrangement of the materials of his argument, however, 

 we obtain, as I conceive, convincing proof that external condi- 

 tions can exert not only a very powerful selective influence, but 

 a transforming one as well, although it must be the more 

 Kmited of the two. We shall presently see that in many indi- 

 vidual cases direct effects of this kind have been actually 

 observed and perfectly established by a systematic series of ex- 

 periments. The discussion of these must naturally be reserved 

 for the chapters to which they belong. 



Finally, I have yet a few words to say on another objection 

 which has already been frequently made to the view which is 

 here brought forward. It is pretty generally supposed — and 

 indeed the facts often seem to bear it out 6— that those changes 

 of organs or of organisms which are brought about by the 

 direct influence of any external cause are neither constant nor 

 hereditary, so that the varieties that have originated in such a 

 manner seem incapable of any share in the process of trans- 



