2o6 APPENDIX II — INTBNSIVe SEGREGATION. 



on adaptation for overcoming, outdoing, or supplanting others of the 

 same species, should be clearly distinguished and named. We further 

 note that there can be no doubt that dominational selection acting 

 for many generations on sections of a species that are prevented from 

 intercrossing will in all probability follow somewhat different lines. 

 In other words, independent dominational selection will produce diver- 

 gent evolution. 



(14) * Impregnational selection. — The coordination between the pollen of a 

 given species and the stigma and ovules of the same species must be kept up by a 

 process of selection, resulting from the failure to propagate of the individuals whose 

 pollen is least potent, and of those whose ovules are most difficult to fertilize. 

 This we may appropriately call potential selection; and it will be convenient to 

 class it with forms of selection securing other coordinations necessary for success- 

 ful impregnation. These other forms are: dimensional selection, of which we 

 have an example in the coordination between the length of the pollen tubes and 

 of the pistils; also fecundal selection, illustrated by the different degrees of 

 survival secured by variation in the number of the ovules and in the quantity and 

 methods of distribution of the pollen grains; and, as illustrated, in many species 

 of insects, structural selection, due to the success gained through superior coordi- 

 nation of the organs by which males and females clasp each other. Impregnational 

 selection is an important form of reflexive selection. I wish here to call especial 

 attention to the importance of fecundal selection. 



(15) Fecundal selection produces intensive segregation with diver- 

 gence through independent fecundal intension, in isolated sections of 

 a species. It is the form of selection that results from propagation 

 according to degrees of fertility. As it involves not only the superior 

 propagation of the more fertile, but the inferior propagation of the 

 less fertile and the non-propagation of the least fertile, it may be 

 described as the exclusive propagation of the more fertile through 

 the failure to propagate of the less fertile. It would avail nothing in 

 determining the form that is to prevail in succeeding generations if it 

 did not in some degree preclude the crossing of the less fertile with the 

 more fertile; but, as it is evident that, so long as increased fertility is 

 not a disadvantage, the more fertile half of the species will leave a larger 

 number of offspring than the less fertile half, it follows that when the off- 

 spring have come to maturity a larger portion of the fertile will consort- 

 with the fertile than in the previous generation ; and so the fertility of 

 the following generation will be still further increased. The chief check 

 to this law of cumulative fertility is found in the correlative law of 

 cumulative adaptation through adaptational selection. The combined 

 action of these two laws results in the triumphant development of the most 

 fertile of the best fitted or the best fitted of the most fertile. 



*As this paragraph does not occur in the original \ paper it is printed in 

 different form. 



