180 MEMOIRS OF THE NATIONAL ACADEMY OF SCIENCES. 



Such a cou elusion, however, would be incorrect; and I desire to direct attention to the fac^ 

 tliat in this country deaf-mutes marry deaf-mutes. 



An examination of tlie records of some of onr institutions for the deaf and dumb reveals the 

 fact that such marriages are not the exception, but the rule. For the last fifty years there has been 

 some selective influence at work which has caused, and is still causing, the continuous selection of 

 the deaf by the deaf in marriage. 



If the laws of heredity that are linown to hold in the case of animals also apply to man, the 

 intermarriage of congenital deaf-mutes through a number of successive generations should result 

 in the formation of a deaf variety of the human race. 



On the other hand, if it can be shown that congenitally deaf persons many one another 

 without any greater liability to the production of deaf ofl'spriug than is to be found among the 

 people at large, then it will be evident that we cannot safely aijply to man the deductions that 

 have been drawn from experiments upon animals. 



There are good grounds for the belief that a thorough investigation of the marriages of the 

 deaf and the influence of these marriages upon the offspring will afford a solution of the problem, 

 " To what extent is the human race susceptible of variation by selection ?" 



Although the statistics I have been able to collect are very incomplete, I have ventured to 

 bring the subject to the attention of the Academy, in the hope that the publication of the results 

 so far obtained may lead to the completion of the statistics. 



