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 réle 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 
1 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 Hereditas, 
Vol. 1, 35-40, 1920. See also Bergh, E. Studier 6ver dévstumheten i Malméhus 
lin. M. D. thesis, Stockholm, 1919. 
