296 Darwin, and after Darwin. 



portant organs.' That is to say, the rudimentary organ finally 

 disappears, not because the force of heredity is finally exhausted, 

 but because natural selection has begun to utilize this force 

 against the continuance of the organ always picking out those 

 congenital variations of the organ which are of smallest size, and 

 thus, by its now reversed action, reversing the force of heredity 

 as regards the organ. 



" Now the oversight here is in not perceiving that the smaller 

 the disappearing structure becomes, the less hold must 'this 

 principle' of reversed selection retain upon it. As above 

 observed, during the earlier stages of reduction (or while co- 

 operating with the cessation of selection) the reversal of selec- 

 tion will be at its maximum of efficiency ; and, as the process 

 of diminution continues, a point must eventually be reached at 

 which the reversal of selection can no longer act. Take the 

 original mass of a now obsolescent organ in relation to that 

 of the entire organism of which it then formed a part to be 

 represented by the ratio I : 100. For the sake of argument we 

 may assume that the mass of the organism has throughout 

 remained constant, and that by * mass ' in both cases is meant 

 capacity for absorbing nutriment, causing weight, occupying 

 space, and so forth. Now, we may further assume that when 

 the mass of the organ stood to that of its organism in the ratio 

 of 1 : 100, natural selection was strongly reversed with respect 

 to the organ. But when this ratio fell to I : 1000, the activity of 

 such reversal must have become enormously diminished, even 

 if it still continued to exercise any influence at all. For we must 

 remember, on the one hand, that the reversal of selection can 

 only act as long as the presence of a diminishing organ con- 

 tinues to be so injurious that variations in its size are matters of 

 life and death in the struggle for existence ; and, on the other 

 hand, that natural selection in the case of the diminishing organ 

 does not have reference to the presence and the absence of the 

 organ, but only to such variations in its mass as any given 

 generation may supply. Now, the process of reduction does 

 not end even at I : 1000. It goes on to 1 : 10,000, and eventually 

 I : oc. Consequently, however great our faith in natural selec- 

 tion may be, a point must eventually come for all of us at which 

 we can no longer believe that the reduction of an obsolescent 



