DISTRIBUTION OF INHERITABLE TRAITS 187 



Fig. 167. — The piles of ears of corn on the right and left are from seed 

 ears which had been self-fertihzed; the pile in the middle from a seed ear in 

 which self-fertilization had been prevented. This figure and the preceding 

 were contributed by Dr. G. H. Shull. 



tubercular) and 22 per cent are said to have "died young." 

 In some data gathered by Dr. Howe (1853) 17 consanguin- 

 eous marriages produced 50 per cent idiots; in the data of 

 Dr. Mitchell (1866) 7.5 per cent were insane, and 1.4 per cent 

 deaf mutes. Other observers record consanguineous mar- 

 riages without deaf mutism, others without idiocy, others 

 with less than 1 per cent of insanity. Voisin (1865) tells of 

 the isolated community of Batz where 5 marriages of first 

 cousins and 31 of second cousins has occurred without a case 

 of mental disease, deaf mutism, albinism, retinitis pigmentosa 

 or malformation appearing. These varied results are to be 

 expected. Consanguineous marriage per se does not create 

 traits; it permits the defects of the germ plasm, that may not 

 appear in the parents, to reveal themselves in the offspring. 



