THE APPLICATION TO MAN 233 



and in cousin marriages might subsequently produce 

 some albino children. 



Davenport, in his recent work on "Heredity in Re- 

 lation to Eugenics," brings together a long catalogue 

 of human hereditary defects, although in most 

 instances they are extremely difficult of accurate 

 analysis. This is the case, first, because these defects 

 so often probably depend upon a combination of 

 determiners rather than upon a single one, and, sec- 

 ond, because the available data are usually scattered 

 and incomplete. 



Deafness, for example, is a defect which is heredi- 

 tary though exactly to what degree, it is at present 

 impossible to state. The following table taken from 

 the extensive work of Fay (1898) upon "Marriage of 

 the Deaf in America" gives some idea of the results 

 of different matings lumped together statistically. 





That two parents born deaf do not produce more 

 than 26 per cent of deaf children is probably due to 

 the fact, first, that each parent is in all likelihood heter- 

 ozygous for deafness and that, second, the same com- 



