250 PROBLEMS OF HUMAN EVOLUTION 



IV 



DEFECT 



Deaf- Deaf-dumbness or deaf-mutism, as it is more commonly called, 

 dumbness SU ppij es such strong evidence of the tendency to degenerate, as 

 soon as Natural Selection slackens, and illustrates so strikingly 

 the working of heredity that it is impossible to pass the subject 

 over. But it can only be dealt with in the most meagre fashion 

 in the small space that I can allot to it. For further information 

 I must refer the reader to the best authorities on the subject, to 

 Dr J. K. Love's Deaf Mutism, to Mr E. A. Fay's Marriages of the 

 Deaf in America, to Dr A. G. Bell's Formation of a Deaf Variety 

 of the Human Race (published in the Memoirs of the National 

 Academy of Sciences, Washington, 1883), and to the report of 

 the Royal Commission on the The Blind, the Deaf and Dumb 

 (1889). 



The dumbness of deaf-mutes is due to their deafness, and the 

 deafness is generally due to some abnormality in the labyrinth of 

 the ear. In some cases the defect is congenital, in others it is 

 adventitious, being traceable very often to some disease of the 

 brain, 1 to scarlet fever or measles. " Those two groups of cases, 

 cerebral affections on the one hand and scarlet fever and measles 

 on the other, acccount for 57 per cent, of the acquired surdism 

 in Britain, and scarlet fever alone accounts for 23-5 P er cent - f 

 the whole." 2 In England typhus is disappearing in the presence 

 of improved sanitary conditions, and consequently adds but few 

 to the number of the deaf. Not unfrequently deafness is due to 

 adenoid growths, and there is no reason to suppose that the per- 

 centage due to-this cause is decreasing. 



It is important to distinguish congenital from acquired deaf- 

 ness, but it is no less important to recognise that in a considerable 

 percentage of the cases where deafness is the consequence of 

 disease there is probably some weakness but for which the 



1 Cerebro-spinal meningitis is a frequent cause of deafness in America. 



2 Dr .!. K. Love's Deaf Mutism, p. 143. 



