DISTRIBUTION OF INHERITABLE TRAITS 187 





<''*^ 



:^ 



-> 



"- "V ... . 



.^^^^ 



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

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

 which self-fert.ihzation 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. 



