44 DARWINISM TO-DAY. 



plants it in the minds of some, in species-forming is pointed 

 out in chapter ix, to which the interested reader may 

 refer. 



But in those cases where the differences or variation 



among individuals may be or obviously are of the character 



The swamping of useful ones, and where by comparing ex- 



or extinguishing tremes o f this variation the life-and-death- 



oi iavourable va- 

 riations by inter- determining worth of this utility might be 



Ceding, conceded, still, what chance is there for the 



perpetuation of this advantage? Nageli long ago pointed 

 out that the extreme variations, that is, the rare variations, 

 would in almost every case be inevitably extinguished by 

 interbreeding. If a certain considerable variation occurred 

 in one individual of a hundred born, in 20,000 individuals of 

 the species 200 would have this worth-while variation. 

 Now if the chances of mating are the same for all there 

 would be 9,801 parings of individuals not showing the 

 variations, 198 pairings between a varying individual and a 

 non-varying one, and a single mating between two indi- 

 viduals both preserving the considerable variation. In fact 

 every rare variation will, as Delage says, be immediately 

 effaced by the dilution of the blood of the varying individual 

 by that of the great mass of individuals not possessed of the 

 particular variation. This inevitable swamping of the ad- 

 vantageous variations of individuals has long ago led to the 

 practical giving up by Darwinians of any claims to species- 

 forming or evolution on the basis of extreme or rare varia- 

 tions and to the restriction of the selecting influence to 

 masses. The species must be changed through the selection 

 of it as a mass or unit rather than through the selection of 

 special scattered individuals of it. 



But for the selection of masses of individuals sufficiently 

 considerable to avoid the extinguishing of the fortunate 

 variations by interbreeding, and to insure a repetition of 

 the advantage and an opportunity for its fostering and 



