CONSANGUINEOUS MARRIAGES 245 



of the children were feeble-minded, while out of 125 ordi- 

 nary marriages the feeble-minded children were only 0.7 per 

 cent. 



Consanguineous marriages were found by Estabrook and Dav- 

 enport to constitute nearly a quarter of all the matings of the 

 Nam family. Many of the inbred lines of this notorious stock pro- 

 duced a high percentage of feeble-minded offspring. The same 

 is true of the Kallikaks and other families with a large amount of 

 mental defect. It is undeniable that in such cases the marriage 

 of relatives is apt to produce unfortunate results. 



The role of consanguinity in the production of deaf -mutism has 

 been studied especially by Fay and Bell. The precise mode of 

 transmission of congenital deafness is not known. It is appar- 

 ently recessive, but nevertheless the marriage of two congenital 

 deaf mutes produces only about 25 per cent, instead of 100 per 

 cent, of deaf offspring. This may be at least formally explained 

 by assuming that deafness is often the result of different factors 

 in different strains. Fay found that marriages of deaf mute 

 relatives produced 30 per cent of deaf offspring, and that 45 

 per cent of the matings produced at least one deaf child. Bell on 

 the basis of the U. S. census returns estimates that "of the 2,527 

 deaf whose parents were cousins, 632, or 25 per cent, are congeni- 

 tally deaf, of whom 350 or 55.41 per cent also have deaf relatives 

 of the classes specified; while among the 53,980 whose parents 

 were not so related the number of congenitally deaf is 3,666 or 

 but 6.8 per cent, of whom only 1,023, or 27.9 per cent have deaf 

 relatives."^ 



As Davenport states "If one partner be congenitally deaf and 

 the other have no ear defect and knows none in his family the 

 chances for deaf offspring are small. In 72 such marriages con- 

 sidered by Fay only 5 resulted in deaf offspring. It is quite likely 



^ For an interesting attempt to interpret congenital deafness as a simple Mende- 

 lian character see H. Lundborg, Ueber die Erblichkeitsverhaltnisse der konstitu- 

 tionellen (hereditaren) Taubstummheit. Arch. f. Rass. Ges. Biol. 9, 133-149, 1912. 

 Further discussion by the same author will be found in the new journal Heredilas, 

 Vol. I, 35-40, 1920. See also Bergh, E. Studier over dovstumheten i Malmohus 

 Ian. M. D. thesis, Stockholm, 1919. 



