128 HEREDITY IN RELATION TO EUGENICS 



If one partner be congenitally deaf and the other have 

 no ear defect and knows of none in his family the chances 

 for deaf offspring are small. In 72 such marriages considered 



^ 

 ^ 



cousins 



op 



DDDDNNNNNNN 



'"iioioa 



ana 



Fig. 98. — ^Pedigree of deaf mutism. In the first generation 2 hearing 

 cousins many. They have 14 children of whom 7 are dead. Two of these 

 marry deaf wives belonging to fraternities with other cases of deafness. Of 

 9 children, altogether, all are deaf. Fat, 1898, No. 7. 



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

 that in some even of these five matings the normal parent 

 had unknown deaf relatives. 





2D 



U 



D N 



n 



N N 



Fig. 99. — Pedigree of deaf mutism. Two deaf mutes, first cousins, marry 

 and have 4 children, all deaf mutes. One of these marries a wife whose 

 father, an uncle and two nephews or nieces were deaf mutes, and two out of 

 three children were deaf mutes. Another child of the original pair married a 

 deaf mute and had two hearing children. Fat, 1898. Nos. 3292, 2260 442 

 3290, 3291, 3234. 



But if the hearing partner have deaf relatives then the 

 proportion of resulting fraternities containing deaf mutes 

 increases to 35 per cent. 



