ORIGIN OF SPECIES i39 



The integrity of a new gene j^rotects it from being 

 lost through crossing with the old type, because 

 there is no blending of the gene with the original one 

 each time the two are brought together. Darwin 

 confused here the characters that may blend in the 

 hybrid with the genes that do not blend. The main- 

 tenance of the gene's integrity overcomes a serious 

 difficulty in Darwin's theory of natural selection as 

 he first formulated it. 



Soon after the appearance of the Origin, Fleming 

 Jenkin — a Scotch engineer — pointed out that single 

 variants would disappear by "swamping" even al- 

 though slightly beneficial, if, as Darwin supposed, 

 blended inheritance is the rule after crossing; for, 

 the new character will lose some of its advantage 

 each time it combines with the original type. The 

 chance is always greater, at first, of a mating with 

 an individual of the original type owing to the larger 

 numbers of such individuals. In later editions of the 

 Origin Darwin acknowledged the force of this ob- 

 jection and tried to meet it by postulating that the 

 new character must be already present in a large 

 number of individuals if it is going to have any- 

 thing like a chance of sur^dval. But one may ask if 

 a new adaptive character can appear in so large a 

 number of individuals that it swamps virtually the 

 original type, what becomes of the theory of natural 

 selection? If the adaptive change has already taken 

 place in so many individuals it is simpler to assume 



