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THE AMERICAN NATURALIST [Vol. XL VI 



The method of personal selection has been widely used 

 by the less philosophical breeders. I do not think it fair 

 to Darwin to designate it as the exclusively Darwinian 

 selection. Whether advance can be made by personal 

 selection seems to me still an open question. Granting 

 our inability to reason about genotypical constitution 

 from the pkaenotypical, still, other things being equal, 

 and in the long run and with great numbers of individuals 

 an extremely high variant is more apt to belong to a 

 genotype with a high mean than to one with a low or 

 intermediate mean. Thus a breeder who selects merely 

 the very best somas of a large number will be apt to 

 select any superior biotype that may occur in his mate- 

 rial. This is doubtless the reason why breeders who con- 

 sider only the somas of their breeding stock nevertheless 

 sometimes make progress ; for they are occasionally for- 

 tunate enough to stumble upon a new biotype. 



Fourth, the results of experiments have thrown light 

 on the long-discussed question of the discontinuity be- 

 tween species, of the swamping effects of intercrossing 

 new varieties with the parent species and the necessity 

 for isolation to permit new varieties to become established 

 as distinct species. We now realize that the danger of 

 swamping which formerly seemed so logically necessary 

 is, from our new point of view, not really to be seriously 

 considered. Characters are rarely, if ever, swamped. 

 Apparent swamping by intercrossing occurs when the 

 new character depends on many determiners. But it is 

 not, even in this case, really swamped ; for no true blend 

 occurs but, on the contrary, a segregation of the original 

 extreme conditions takes place. This is well illustrated 

 by the case of human skin color. When the germ cell 

 that carries white skin color unites with the germ cell 

 that carries black skin color the "white" character seems 

 swamped in the offspring; but the swamping is only 

 apparent. Two mulatto parents have children of various 

 tints and, occasionally, one with a clear white skin, as well 

 as one with a black skin like the original negro ancestor. 



