Page:Popular Science Monthly Volume 27.djvu/31

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19
CAN MAN BE MODIFIED BY SELECTION?


47 pupils had one or more parents deaf and dumb.
38 " " " uncles or aunts deaf and dumb.
29 " " " children "
48 " " " distant relatives "
5 " " " grandparents "
1 " " " great-grandparent "
1 " " " great uncle or aunt "

That this is not peculiar to the pupils of this particular institution, and that it holds true of deaf-mutes in general, is shown by the following table, compiled from the records of six institutions:

INSTITUTIONS. Total
number of
pupils.
Number of pupils
having deaf-mute
relatives.
Percentage of pupils
having deaf-mute
relatives.
American Asylum 2,106 693 32·9
New York Institution 1,165 380 32·6
Ohio Institution 560 166 29·6
Indiana Institution 283 103 36·4
Illinois Institution 1,620 356 21·7
Texas Institution 89 21 23·6
 Total 5,823 1,719 29·5

The table shows that, among 5,823 deaf-mutes taken from different parts of the country, 1,719, or 2912 per cent, are known to have had deaf-mute relatives, and that this is due to the influence of heredity is well shown when we contrast those who were born deaf with those who had afterward lost their hearing. Many of those who lose their hearing by accident or disease have no hereditary tendency to deafness, but a considerable number of those who lose their hearing at some time after birth are born with an hereditary predisposition to deafness. If, therefore, we contrast the congenitally deaf with those who have become deaf, we should expect the latter class to have a much smaller percentage of deaf relatives than the former class, but a greater percentage than the community at large.

Professor Bell has compiled the following two tables from the one which is given above, and they show that, while only about 13 per cent of the pupils which were not born deaf have deaf relatives, more than 54 per cent of the congenitally deaf pupils are recorded as having such relatives:

Table II.Proportion of the Non-congenitally Deaf who have Deaf Relatives.

INSTITUTIONS. Number of
non-congenital
deaf-mutes.
Number
having deaf mute
relatives.
Percentage
having deaf-mute
relatives.
American Asylum 1,040 131 12·6
New York Institution 432 74 17·1
Ohio Institution 268 32 11·9
Indiana Institution 124 31 25· 
Illinois Institution 947 120 12·7
Texas Institution 53 8 15· 
 Total 2,864 396 13·8