i6o Darwin, and after Darwin. 



survival of a peculiarity of type. No one has ever said that 

 an individual is assisted by the possession of selective fer- 

 tility : that is a matter which cannot affect his chance of life. 

 Nor has any one said that the possession of selective fertility 

 in an individual will of itself increase the chance of his having 

 progeny that will survive, and in turn become the progenitors 

 of others that will survive. Taken by itself, the fact that an 

 individual is capable of fertility with some only of the oppo- 

 site sex lessens the chance of his having progeny. Whether 

 or not he is more or less favourably situated than his con- 

 freres for the battle of life must be decided by the total sum 

 of his peculiarities ; and the question whether or not this 

 selective fertility will be a hindrance must be decided by 

 considerations depending on the other peculiarities associated 

 with it. 



But when we come to consider the survival or permanence 

 of a type or peculiarity, the case is quite different. It then 

 becomes not only a favourable circumstance, but, in my opinion, 

 almost a necessary condition, that the peculiarity should be 

 associated with selective fertility'. 



Take the case of the Jews. I don't think that intermarriage 

 with other nations would lessen their fertility, or diminish the 

 number of their progeny ; nor is there any reason to think that 

 this progeny would be unequal to the struggle for existence. 

 But no one doubts that the abandonment of their voluntary 

 isolation (which operates so far as this is concerned as a selec- 

 tive fertility), would lead to the disappearance of the familiar 

 Jewish type. All the world would get some of it ; but as a whole 

 it would be "swamped." 



Now although no doubt Wallace would admit all this, he 

 fails to give it the weight it ought to have. In discussing the 

 question of its operation he considers too exclusively the case 

 of the individual. 



Of course, a type can only be perpetuated through the medium 

 of individuals, and all that his argument amounts to is, that 



' As, for example, in the case of sexuality in general. It is not to 

 the advantage of such individual male Arthropoda as peiish after the 

 performance of the sexual act that they should perform it; but its per- 

 formance is necessary for the perpetuation of their species. — G. J. R. 



