188 HEREDITY IN RELATION TO EUGENICS 



If there is no insanity or albinism in the stock consanguineous 

 marriage will not bring it out; and, strictly, it is not at all 

 consanguinity that brings the trait out but the increasing 

 liability that consanguinity affords to the mating of two 

 similarly defective germ cells. 



The variety of the product of consanguineous marriage is 

 well brought out when we compare localities. Thus con- 

 sanguinity on Martha's Vineyard results in 11 per cent 

 deaf mutes and a number of hermaphrodites; in Point 

 Judith in 13 per cent idiocy and 7 per cent insanity; in an 

 island off the Maine coast the consequence is ''intellectual 

 dullness''; in Block Island loss of fecundity; in some of the 

 ''Banks" off the coast of North Carolina, suspiciousness, 

 and an inability to pass beyond the third or fourth grade 

 of school; in a peninsula on the east coast of Chesapeake 

 Bay the defect is dwarfness of stature: in George Island 

 and Abaco (Bahama Islands) it is idiocy and blindness (G. 

 A. Penrose, 1905). There is thus no one trait that results 

 from the marriage of kin; the result is determined by the 

 specific defect in the germ plasm of the common ancestor. 



The question is often asked, How common are consan- 

 guineous marriages? What proportion of marriages are 

 between kin? This question is so ill-defined that a reply 

 is hardly possible. When we recall the enormous number 

 of our ancestors resulting from the fact that the number 

 (theoretically) doubles in each earlier generation, so that 

 there are more than a million in the twentieth ascending 

 generation, and more than a billion in the thirtieth, then we 

 see that some degree of consanguinity in the parents is to 

 be expected. There are hardly two persons of European 

 origin who are more distantly related than thirtieth cousin 

 — or who do not have a common ancestor of the time of 

 King WilUam I of England. Indeed, how improbable it is 

 that there are many persons of "pure" European stock 



