CHAPTER VI_Consanguineous Marriages in the American Population

CONSANGUINITY AND THE SPECIAL SENSES

The most important source for this chapter is the special report on

the Blind and the Deaf in the Twelfth Census of the United States.[75]

This report was prepared under the direction of Dr. Alexander Graham

Bell, as Expert Special Agent of the Census Office.

[Footnote 75: U.S. Census, 1900, _Special Report on the Blind and the

Deaf_.]

The enumerators of the Twelfth Census reported a total of 101,123

persons as blind, and to each of these Dr. Bell addressed a circular

of inquiry. By this method he obtained verified returns of 64,763

cases of blindness in continental United States or 85.2 per 100,000 of

the total population. In the same way he obtained data in regard to

89,287 persons with seriously impaired powers of hearing, or 117.5 Per

100,000 of the total population.

In each case the following questions among others were asked: "Were

his (or her) parents first cousins? If not first cousins were they

otherwise related by blood to each other, before their marriage? Were

any of his relatives blind? If yes, what relatives? (Father, mother,

grandparents, brothers, sisters, uncles, aunts, and how many of each,

so far as known)." The results of this inquiry give us the best and

most reliable statistical material which has ever been compiled on any

phase of the problem of consanguineous marriage. The investigation of

the deaf was similar to that of the blind, but even more complete.

I. The Blind. The question as to the relationship of the parents was

answered in 56,507 cases, in 2,527 or 4.47 per cent of which the

parents were reported as cousins. Of the 57,726 who answered the

question in regard to blind relatives, 10,967 or 19 per cent replied

in the affirmative.[76] The blind relatives were divided into two

groups: (a) blind brothers, sisters or ancestors, and (b) blind

collateral relatives or descendants. Table XXII concisely expresses

the results most fundamental for this study.

[Footnote 76: U.S. Census, 1900, op. cit., p. 16.]

TABLE XXII.

-----------------------------------------------------------------

-----------------------------------------------------------------

The blind |64,763| 8,629 | 2,338 | 46,759 | 7,037

-----------------------------------------------------------------

Totally blind |35,645| 4,378 | 1,215 | 26,349 | 3,703

Partially blind |29,118| 4,251 | 1,123 | 20,410 | 3,334

| | | | |

--The blind | 2,527| 844 | 149 | 1,456 | 78

-----------------------------------------------------------------

--Totally blind | 1,291| 435 | 78 | 739 | 39

--Partially blind | 1,236| 409 | 71 | 717 | 39

| | | | |

--The blind |53,980| 7,395 | 2,095 | 43,368 | 1,122

-----------------------------------------------------------------

--Totally blind |29,892| 3,720 | 1,090 | 24,541 | 541

--Partially blind |24,088| 3,675 | 1,005 | 18,827 | 581

| | | | |

stated.--The blind | 8,256| 390 | 94 | 1,935 | 5,837

-----------------------------------------------------------------

blind | 4,462| 223 | 47 | 1,069 | 3,123

blind | 3,794| 167 | 47 | 866 | 2,714

-----------------------------------------------------------------

[A] Symbols for Blind Relatives--(a) blind brothers, sisters or

ancestors; (b) blind collateral relatives or descendants.

Of the 2527 blind persons whose parents were cousins, 993 or 39.3 per

cent have blind relatives, 33.4 per cent having blind brothers,

sisters or ancestors, and 3.9 per cent having blind collateral

relatives or descendants. And 9 per cent of the blind who have blind

relatives are of consanguineous parentage, while but 3.1 per cent of

the blind who have no blind relatives are the offspring of cousins.

These figures alone indicate a decided intensification of blindness

through consanguinity, although it should be remembered that a

relationship "works both ways," so that when a brother has a blind

sister, the sister would have a blind brother. This fact has probably

diminished the apparent number of sporadic cases of blindness.

Considered with reference to the degree of blindness the table shows

that 1291 or 51.1 per cent of the blind of consanguineous parentage

are totally blind, and 1236 or 48.9 per cent are partially blind.

Among those whose parents were not cousins, 55.4 per cent were totally

and 44.6 per cent were partially blind.

Of the 2527 blind of consanguineous parentage, 632 or 25.0 per cent

were congenitally blind, of whom 350 or 55.4 per cent also had blind

relatives of the degrees specified. Not counting those who did not

answer the question in regard to blind relatives, we have 615 cases of

which 51.5 per cent had blind relatives of class (a), and 5.4 per cent

blind relatives of class (b). Taking the 53,980 blind whose parents

were not so related the number of congenitally blind was 3666 or but

6.8 per cent, of whom 1023 or 27.9 per cent had blind relatives.

Omitting as before the "blind relatives not stated," we have 23.4 per

cent who had blind relatives of class (a), and 4.3 per cent relatives

of class (b).

On the hypothesis that consanguinity in the parents intensifies a

tendency toward blindness we should expect to find among the

congenitally blind a larger proportion of consanguineous parentage

than among those blind from specific causes. In Table XXIII a general

classification of the causes of blindness is given together with the

consanguinity of parents. Specific causes in which the percentage of

consanguinity differs in a marked degree from the average, are given

parenthetically.

TABLE XXIII.

-------------------------------------------------------------------------------

| |Consanguinity of |

| | Parents | Percentages

| |---------------------------------------------

| | | Not | Not | | Not | Not

-------------------------------------------------------------------------------

Total |64,763| 2,527|53,980 | 8,256| 3.9 | 83.4 | 12.7

-------------------------------------------------------------------------------

Opacity of the eye |33,930| 1,000|28,797 | 4,133| 2.9 | 84.9 | 12.2

-------------------------------------------------------------------------------

a. Causes affecting cornea|11,380| 444|10,016 | 920| 3.9 | 88.0 | 8.1

(1) Measles | 1,451| 73| 1,267 | 111| 5.0 | 87.4 | 7.6

(2) Scrofula | 1,165| 71| 1,026 | 68| 6.1 | 88.1 | 5.8

b. Causes affecting iris | 1,307| 33| 1,093 | 181| 2.5 | 83.6 | 13.9

c. Causes affecting lens |11,769| 228| 9,467 | 2,074| 1.9 | 80.4 | 17.7

d. Other causes | 9,474| 235| 8,221 | 1,018| 2.5 | 86.8 | 10.7

-------------------------------------------------------------------------------

Nervous apparatus affected| 7,944| 276| 6,980 | 688| 3.5 | 87.8 | 8.7

-------------------------------------------------------------------------------

Unclassified |14,885| 938|12,463 | 1,484| 6.3 | 83.7 | 10.0

-------------------------------------------------------------------------------

(1) Congenital | 4,728| 632| 3,666 | 430|13.4 | 77.5 | 9.1

(2) Other causes |10,157| 306| 8,797 | 1,054| 3.0 | 86.6 | 10.4

-------------------------------------------------------------------------------

Unknown | 8,004| 313| 5,740 | 1,951| 3.9 | 71.7 | 24.4

-------------------------------------------------------------------------------

To quote from the Report:

The only specific causes, other than congenital, to which is

due a greater proportion of the total cases of blindness among

those whose parents were cousins than among those whose parents

were not related, are: Catarrh (parents cousins 28.1, parents

not cousins 8.7 per 1,000), scarlet fever (parents cousins

10.7, parents not cousins 10.1 per 1,000), scrofula (parents

cousins 28.9, parents not cousins 19 per 1,000), and measles

(parents cousins 28.9, parents not cousins 23.5 per 1,000). The

difference in these proportions is but slight, and the relative

number of cases of blindness attributed to each of the other

causes is greater among those whose parents were not

related.[77]

[Footnote 77: U.S. Census, 1900, op. cit., p. 17.]

It will be noted that the greatest proportion is in the case of

scrofula.

Since it is probable that a part of those who did answer the question

as to consanguinity are in fact the offspring of cousins, the

percentage in each case should be somewhat increased. Allowing for

these the same proportion as for those who did answer the question we

should have of all the blind 4.47 per cent as the offspring of

cousins; of the totally blind 4.14 per cent and of the partially blind

4.88. While of the congenitally blind we should have 14.7 per cent as

offspring of cousins.

It is interesting to note in this connection that in 1900, Dr. Lee

Wallace Dean, of the University of Iowa examined the 181 blind

children in the Iowa College for the Blind, and found that 9 or nearly

5 per cent were the offspring of first cousin marriages.[78] Dr. Dean

continues,

If we exclude from the list those blind children who were blind

because of blennorrhea neonatorum, sympathetic opthalmia,

trachoma, etc., and consider only those who suffered because of

congenital conditions, we should find that 14 per cent were the

result of consanguineous marriage of the first degree....

Among the pupils who have entered the college since 1900 the

percentage is about the same.

[Footnote 78: _Effect of Consanguinity upon the Organs of Special

Sense_, p. 4.]

This was written in 1903, three years before the publication of Dr.

Bell's report.

Statistics from foreign sources give even larger percentages of the

blind as the offspring of consanguineous marriage. Dr. Feer quotes

fourteen distinct investigations of the etiology of retinitis

pigmentosa, embodying in all 621 cases, of which 167 or 27 per cent

were the offspring of consanguineous parents.[79] Retinitis pigmentosa

is perhaps more generally attributed to consanguineous marriage than

any other specific disease of the eye, and it is to be regretted that

the Census report does not give any data in regard to this cause.

Retinitis pigmentosa in known to be strongly inheritable, as is

albinism and congenital cataract.

[Footnote 79: _Der Einfluss der Blutsverwandschaft der Eltern auf die

Kinder_, p. 14.]

Looking now at the other side of the problem, that of the probability

of consanguineous marriages producing blind offspring, we have as our

data the 2527 blind whose parents were cousins, and a conservative

estimate which may be made from the data in Chapter II that 1,000,000

persons in continental United States are the offspring of cousins

within the degrees included in the Census report.[80] In the general

population 852 per million are reported as blind, and 63 per million

as congenitally blind. The actual figures for the offspring of cousin

marriages are 2527 per million for all blind and 632 per million for

the congenitally so. In other words only 0.25 per cent of the

offspring of cousin marriages are blind and only 0.05 per cent are

congenitally blind. Although the probability that a child of related

parents will be born blind is ten times as great (632 per million vs.

63 per million) as when the parents are not related, the numbers are

so small that there seems to be very little basis for a belief that

consanguinity does more than to intensify an inherited tendency,

especially since over one half of the congenitally blind of

consanguineous parentage are known to have blind relatives.

[Footnote 80: From 1-1/2 to 2 per cent of all marriages were found to

be between cousins within the degree of second cousins, and cousin

marriages were found to be normally fertile.]

2. The Deaf. The extent to which the connection between consanguineous

marriage and deaf-mutism has been studied is indicated by a table

given by Mr. Huth, in which are set forth the results of fifty

distinct investigations.[81] In this table the percentages of

deaf-mute offspring of consanguineous marriage to the total number of

deaf-mutes investigated, varies from 30 per cent to none at all. Of

these studies not more than ten or eleven have the slightest

statistical value, and four of these--the most reliable--are from the

reports of the Census of Ireland in the years 1851, 1861, 1871 and

1881.

[Footnote 81: _Marriage of Near Kin_, p. 229.]

The Irish censuses of 1891 and 1901 give similar data, though not so

detailed as in 1871 and 1881. Thus we have in these reports a census

inquiry into a phase of the consanguineous marriage problem extending

over the period of six successive censal years. Although we can hardly

suppose that these figures are accurate in all respects, they throw a

great deal of light upon the problem, and are worth quoting in some

detail. The tables as given by Mr. Huth contain a number of errors of

detail, the correction of which changes the results materially.[82]

[Footnote 82: In a subsequent article Mr. Huth corrects some of these

errors. See: "Consanguineous Marriage and Deaf-mutism," _The Lancet_,

Feb. 10, 1900.]

TABLE XXIV.

------------------------------------------------------------------

| | Congenital deaf-mutes

| |-----------------------------------------------

| | | | |----------------------

Censal | Total | |per | to a | |Per | to a

------------------------------------------------------------------

1851[B]| 6,574,278| 4,127| 628 | ---- | 242 | 5.86| 1.66

1861 | 5,798,967| 4,096| 706 | 1.22 | 362 | 8.84| 1.72

1871 | 5,412,377| 3,503| 647 | 1.30 | 287 | 7.35| 1.76

1881 | 5,174,836| 3,163| 611 | 1.32 | 191 | 6.04| 1.69

1891 | 4,706,448| 2,570| 546 | 1.40 | 297 |11.56| 1.92

1901 | 4,456,546| 2,179| 489 | 1.40 | 249 |11.43| 1.73

------------------------------------------------------------------

[A] From Table XXV.

[B] 1851 data from Huth, "Consanguineous Marriage and

Deaf-mutism." _The Lancet_, 1900.

Table XXIV summarizes the most important points in the Irish data. It

will be seen that while there has been an absolute diminution in the

number of deaf-mutes in Ireland with the decrease in population, there

has been a relative increase of deaf-mutism. There are two possible

explanations for this phenomenon, both of which may have operated in

part; first that in the great emigration the deaf-mutes have been left

behind, and second that with the introduction of improved methods of

census taking, the returns are more complete than a half century ago.

Mr. Huth believes that there is still room for improvement in Irish

census methods, and thinks there is reason to believe that in the

enumeration of the deaf all children born deaf in a family are

included whether living or not.

Since Ireland is strongly Roman Catholic, the proportion of

consanguineous marriages is probably small, so that the percentage of

deafmutes derived from consanguineous marriages, varying from 5.86 to

11.56 is very much greater than the percentage of these marriages in

the general population. The average number of deaf children to a

family in Table XXIV varies less than any other part of the table, and

clearly shows a much higher average number of deaf children where the

parents were cousins. They reveal the interesting fact that the

occurrence of two or more deafmutes in a family is more than twice as

probable where the parents are related as where they are not. Table

XXV still better illustrates this point. Of the families where there

was but one deaf-mute, only 4.3 per cent were the offspring of cousin

marriages; where there were two in a family 12.9 per cent were of

consanguineous parentage; three in a family, 13.3 per cent; four in a

family, 19.0 per cent; more than four in a family, 21.1 per cent.

TABLE XXV.

_Number of Congenital Deaf mutes to a Family in Ireland._

----------------------------------------------------------------

| | Families in which deaf-mutes numbered.

| |----------------------------------------

Year.| Parentage. | 1. | 2. | 3. |4.|5.|6.|7.|8.|9.|10.|11.

----------------------------------------------------------------

1851 | Parents cousins | 127| 45 | 20 |10| 5| 2|..| 1|..|.. |..

1871 | Parents cousins | 91| 38 | 24 | 5| 3| 1| 1|..|..|.. |..

1881 | Parents cousins | 63| 30 | 13 | 6| 1|..|..|..|..|.. |..

1891 | Parents cousins | 82| 38 | 19 | 9| 1| 3| 1| 2|..|.. |..

1901 | Parents cousins | 79| 34 | 23 | 7| 1|..| 1|..|..|.. |..

1851 | All families[A] |2963|347 |158 |35|13| 5|..| 1|..|.. |..

1871 | All families[A] |2460|305 |167 |47|20| 5| 1|..|..|.. |..

1881 | All families[A] |2080|281 |162 |39|18| 6|..|..|..| 1 |..

1891 | All families[A] |1473|273 |134 |40|12| 6| 1| 2|..|.. | 1

1901 | All families[A] |1219|231 |122 |34|10| 4| 2|..|..|.. |..

----------------------------------------------------------------

[A] Number of the "Deaf and Dumb" to a family, "as far as

could be ascertained."

In 1871 and 1881 the inquiry was more minute and the degrees of

consanguinity were specified. Mr. Huth quotes some of the figures for

these years, probably derived from the same sources as Table XXVI, and

comments as follows: "An examination of this table will show that the

statistics so much relied upon as proving the causation of deaf-mutism

by consanguineous marriages show nothing of the sort. In 1871 fourth

cousins produced more deaf-mutes per marriage than any nearer

relationship. In 1881 third cousins produced more than any nearer

relationship."[83] Mr. Huth forgets that he is basing these statements

on five and nine families respectively, and does not take into

consideration the probability that if the returns are biased, as he

suspects, this bias would affect the more distantly related,

relatively more than the first cousin marriages, for the same reason

that this would be true of the cases collected by Dr. Bemiss.[84]

Combining the figures of the two censal years helps to correct these

averages, and the distantly related show approximately the same

average as the first cousin marriages in spite of the vastly greater

selection which must have obtained in the distantly related cases.

[Footnote 83: Huth, _Marriage of Near Kin_, p. 227.]

[Footnote 84: _Cf. supra_, p. 42.]

In Table XXVI it will be seen that 52.5 per cent of the deaf-mute

offspring of consanguineous parents were the offspring of first cousin

marriages. On the assumption that this percentage is fairly typical of

each set of returns we may say that from three to six per cent of the

Irish deaf-mutes are the offspring of first cousin marriages. If,

then, the proportion of first cousin marriages is no greater than in

England, the percentage of deaf-mute offspring is several times as

great as in the average non-related marriage.

TABLE XXVI.

--------------------------------------------------------------------------

| 1871 | 1881 | 1871 and 1881

|-----------------------------------------------------------

| | of |Aver | | of |Aver | | of |Aver

Consanguinity | of |nital |per | of |nital |per | of |nital |per

of |mar- |deaf- |mar- |mar- |deaf- |mar- |mar- |deaf- |mar-

--------------------------------------------------------------------------

First cousins | 72 | 128 | 1.78| 74 | 123 | 1.66| 146 | 251 | 1.72

Second cousins| 50 | 89 | 1.78| 29 | 46 | 1.58| 79 | 135 | 1.71

Third cousins | 24 | 40 | 1.67| 9 | 21 | 2.33| 33 | 61 | 1.85

Fourth cousins| 5 | 11 | 2.20| 1 | 1 | -- | 6 | 12 | 2.00

sixth cousins | 12 | 19 | 1.58| not stated | 12 | 19 | 1.58

--------------------------------------------------------------------------

Total | 163 | 287 | 1.76| 113 | 191 | 1.69| 276 | 478 | 1.73

No | | | | | | | | |

ship[A] |2,842 |3,609 | 1.27|2,474 |3,229 | 1.31|5,316 |6,838 | 1.29

--------------------------------------------------------------------------

Grand total |3,005 |3,896 | 1.30|2,587 |3,420 | 1.32|5,592 |7,316 | 1.31

--------------------------------------------------------------------------

[A] See Table XXV.

In Scotland Dr. Arthur Mitchell made inquiry of the superintendents of

a number of deaf-mute asylums, and found that of 544 deaf-mutes, 28

were the offspring of 24 consanguineous marriages.[85] There were 504

families represented in all, so that the average per family was 1.17

among the consanguineous to 1.07 among the non-consanguineous.

[Footnote 85: Huth, op. cit., p. 226.]

In Norway, according to Uchermann, while 6.9 per cent of all marriages

are consanguineous within and including the degree of second cousins,

and in single cantons the percentages range as high as 31.0, only in

one single district does the number of the deaf-mutes harmonize with

that of the marriage of cousins. The district of Saeterdalen has the

greatest number of consanguineous marriages (201 out of 1250), but not

a single case of deaf-mutism. Hedemarken, which has the fewest

consanguineous marriages has a great many deaf-mutes. Where

deaf-mutism exists it seems to be intensified by consanguinity, but

where it is not hereditary it is not caused by consanguinity. Of the

1841 deaf-mutes in Norway, 919 were congenitally deaf, and of these

212 or 23 per cent were of consanguineous parentage.[86]

[Footnote 86: _Les Sourds-muets en Norvège_. Quoted by Feer, _Der

Einfluss der Blutsverwandschaft der Eltern auf die Kinder_, p. 22.]

Dr. Feer gives a table containing the results of a number of studies

of deaf-mutism, which shows an average of 20 per cent as of

consanguineous origin. Four investigations give the number of children

to a family. Table XXVII from Feer seems to indicate that the Irish

census is fairly accurate at this point.[87]

[Footnote 87: Feer, op. cit., p. 22.]

TABLE XXVII.

_Average Number of Children to a Family._

-------------------------------------------------

|Consanguineous|"Crossed"

Observer. | marriages. |marriages.

-------------------------------------------------

Huth (Irish Census) | 1.68 | 1.17

Wilhelmi | 1.71 | 1.26

Mygind | 1.53 | 1.20

Uchermann | 1.41 | 1.19

-------------------------------------------------

In the American Census the instructions to enumerators have been so

diverse that statistics of the deaf have been very poor until recent

years. Not until the Twelfth Census was the inquiry put upon a really

scientific basis.

This reform, as also the more intelligent attitude of the American

people in general towards the affliction of deafness, is due largely

to the work of Dr. Alexander Graham Bell. An enumeration of Dr. Bell's

services directly, and through the agency of the Volta Bureau, in this

cause, cannot be given here. For our purpose the most important of his

contributions is embodied in the Special Report of the Twelfth Census

of the United States already referred to.

As in the investigation of the Blind, the circular letter sent to each

person reported by the enumerators as deaf contained questions in

regard to parentage and the existence of deaf relatives. It is

unfortunate that in these returns it is impossible to distinguish

between degrees of relationship, but in such an extensive compilation

it was doubtless impracticable to attempt to unravel the intricacies

of consanguinity. Judging from the returns of the Census of Ireland we

may assume that about half of the cases returned as "cousins" were

first cousins.

The replies to the inquiry as to deaf relatives were more carefully

analyzed, and were divided into four groups, which are referred to

throughout as (a), (b), (c) and (d) relatives. These groups are: (a),

deaf brothers, sisters or ancestors; (b), deaf uncles, aunts, cousins

or other relatives not (a), (c) or (d); (c), deaf children, (sons or

daughters); (d), deaf husbands or wives. Thus a large proportion of

the hereditary cases would be included in the first two categories,

(a) and (b).[88]

[Footnote 88: U.S. Census _Report on the Blind and the Deaf_, p. 127.]

The causes of deafness are given in detail, but as might be expected

the returns are not as definite or as accurate as we should desire.

The causes given have been grouped under five main heads; these again

are subdivided, often into divisions numerically too minute for real

statistical value. Table XXVIII includes the main groups and those

specific causes which number more than 3000 cases. The extreme

variation in the percentages of those who are the offspring of

consanguineous marriages cannot be attributed to mere chance. There is

clearly some fundamental connection between consanguinity and

congenital deafness if 11.8 per cent of all the congenitally deaf are

the offspring of consanguineous marriages, while of the adventitiously

deaf but 3.1 per cent are the offspring of such marriages. In fact we

are tempted to jump at the conclusion that consanguinity is in itself

a cause of deaf-mutism. Furthermore 42.1 per cent of the deaf whose

parents were cousins were congenitally deaf, while this was true of

but 15 per cent of those whose parents were unrelated.

TABLE XXVIII.

-------------------------------------------------------------------------

| | |

| | Consanguinty |

| | of Parents. | Per cent.

| |--------------------|-----------------

| | | | | | |

Cause of Deafness. | | | Not | Not | | Not | Not

| | ins. | ins. | ted. | ins.| ins.| ted.

---------------------------|------|------|------|------|-----|-----|-----

| | | | | | |

Total |89,287| 4,065|75,530| 9,692| 4.5| 84.6| 10.9

---------------------------|------|------|------|------|-----|-----|-----

Affections of external ear | 871| 29| 760| 82| 3.3| 87.3| 9.4

Affections of middle ear |34,801| 1,238|30,824| 2,739| 3.5| 88.6| 7.9

Affections of internal ear |12,295| 343|11,121| 831| 2.8| 90.4| 6.8

Unclassified |31,205| 2,183|25,281| 3,741| 7.0| 81.0| 12.0

Unknown |10,115| 272| 7,544| 2,299| 2.7| 74.6| 22.7

| | | | | | |

Scarlet fever | 7,424| 285| 6,647| 492| 3.9| 89.5| 6.6

Disease of ear | 4,210| 222| 3,683| 305| 5.3| 87.5| 7.2

Catarrh |11,702| 304|10,450| 948| 2.6| 89.3| 8.1

Colds | 3,074| 81| 2,666| 327| 2.6| 86.7| 10.7

Meningitis | 3,991| 83| 3,741| 167| 2.1| 93.7| 4.2

Old age | 3,361| 38| 2,369| 954| 1.1| 70.5| 28.4

Military service | 3,242| 40| 2,897| 305| 1.2| 89.4| 9.4

Congenital |14,472| 1,710|11,322| 1,440| 11.8| 78.2| 10.0

-------------------------------------------------------------------------

But on the other hand, 53.4 per cent of the deaf whose parents were

cousins had deaf relatives of the (a) and (b) groups, while of those

whose parents were not cousins, only 29.9 per cent in these groups had

deaf relatives. In Table XXIX the close connection between deaf

relatives of these groups and consanguinity is shown. For the sake of

simplicity no account is taken of (c) relatives (deaf children), and

(d) relatives (deaf husbands or wives), for in the first case only 370

deaf are reported as having deaf children and at the same time no (a)

or (b) relatives, and in the Second case (d) relatives are not

ordinarily blood relatives at all.

TABLE XXIX.

-----------------------------------------------------------------------

| | |

| | Consanguinty |

| | of Parents. | Per cent.

| |--------------------|-----------------

| | | | | | |

Class of Deaf | | | Not | Not | | Not | Not

| | ins.| ins.| ted. | ins.| ins.| ted.

-----------------------------------------------------------------------

| | | | | | |

Total |89,287| 4,065|75,530| 9,692| 4.5| 84.6| 10.6

-----------------------------------------------------------------------

Stated |80,481| 3,911|73,639| 2,931| 4.9| 91.5| 3.6

Not stated | 8,806| 154| 1,891| 6,761| 1.7| 21.5| 76.8

| | | | | | |

(a) relatives |21,660| 1,850|18,838| 972| 8.5| 87.0| 4.5

No (a) relatives |58,821| 2,061|54,801| 1,959| 3.5| 93.2| 3.3

| | | | | | |

(a) or (b) relatives |25,851| 2,171|22,552| 1,128| 8.4| 87.2| 4.4

(a) and (b) relatives | 4,117| 412| 3,587| 118| 10.0| 87.1| 2.9

(a) but no (b) relatives |17,543| 1,438|15,251| 854| 8.2| 86.9| 4.2

(b) but no (a) relatives | 4,191| 321| 3,714| 156| 7.7| 88.6| 3.7

No (a) or (b) relatives |54,630| 1,740|51,087| 1,803| 3.2| 93.5| 3.3

-----------------------------------------------------------------------

[A] Symbols for deaf relatives: (a) deaf brothers, sisters and

ancestors; (b) deaf uncles, aunts, cousins, etc.

Table XXIX shows unmistakably that the connection between

consanguinity and hereditary deafness is very close. Where there is

the largest amount of deafness in the family the percentage of

consanguinity is the highest. That is, of those who had both (a) and

(b) relatives ten per cent were the offspring of cousins, while of

those who had neither (a) nor (b) relatives only three per cent were

the offspring of cousins. It is natural to assume that as a rule where

the deaf have either (a) or (b) deaf relatives, deafness is

hereditary, for the probability of two cases of deafness occurring in

the same family, uninfluenced by heredity would be very small. It is

likely also that a great many of the deaf who stated that they had no

deaf relatives were mistaken, for few people are well enough informed

in regard to their ancestry to answer this question definitely. Not

one man in thousands can even name all of his great-grandparents, to

say nothing of describing their physical or mental traits. Others may

have understood the inquiry to refer only to living relatives and

therefore have omitted almost all reference to their ancestors. These

possible errors might easily explain all the excess of the percentage

of consanguinity among those reported as having no deaf relatives over

the probable percentage of consanguineous marriage in the general

population. But this very probability that comparatively few deaf

ancestors have been reported increases the probability that the

greater part of the (a) relatives were brothers and sisters rather

than ancestors. Now of the 26,221 deaf having deaf relatives, 17,345

have only (a) relatives, and if these are largely living brothers and

sisters the relationship would "work both ways," so that if there were

two deaf children in a family, each would have an (a) deaf relative.

In the Census of Ireland figures above quoted it will be remembered

that among families which were the offspring of cousins the proportion

having two or more deaf children was three times as great as among

those who were not the offspring of consanguineous unions. If this

follows in America, it largely accounts for the high percentage of the

congenitally deaf who are the offspring of cousin marriages, and

especially of those who have (a) deaf relatives.

TABLE XXX.

------------------------------------------------------------------------

| | Consanguinity |

| | of Parents. | Per Cent.

| |----------------------------------------------

Class of Deaf | | | Not | Not | | Not | Not

------------------------------------------------------------------------

Total |14,472 | 1,710 | 11,322| 1,440 | 11.8 | 78.2 |10.0

------------------------------------------------------------------------

Stated |13,428 | 1,647 | 11,110| 671 | 12.3 | 82.7 | 5.0

Not stated | 1,044 | 63 | 212| 769 | 6.0 | 20.3 |76.7

(a) relatives | 5,295 | 986 | 3,961| 48 | 18.6 | 74.8 | 6.6

no (a) relatives| 860 | 126 | 686| 48 | 14.6 | 79.8 | 5.6

------------------------------------------------------------------------

[A] Symbols for deaf relatives: (a) deaf brothers, sisters or

ancestors; (b) deaf uncles, aunts, cousins, etc.; (c) deaf children.

A further analysis of the congenitally deaf according to consanguinity

of parents and deaf relatives, as in Table XXX, helps to determine to

what extent the greater number of deaf children to a family among the

offspring of consanguineous marriages has influenced the totals. From

the report it cannot be determined how many of the congenitally deaf

had (a), (b) or (c) relatives alone, but the existence of (b) and (c)

relatives would almost certainly indicate that the deafness was

hereditary. Of these 14.6 per cent were the offspring of cousins,

while of those having (a) relatives 18.6 per cent were the offspring

of consanguineous unions. Thus it would seem to be a more reasonable

conclusion that where two or more deaf-mutes appear in the same

family, at least a tendency toward deaf-mutism is hereditary in the

family and is intensified by the marriage of cousins, rather than that

consanguineous marriage is in itself a cause. The fact that in many

cases the relationship would "work both ways" would not greatly affect

the percentage of the offspring of cousins having (b) and (c)

relatives, for the chance would be slight that the (b) or (c) relative

would be himself the offspring of a consanguineous marriage. Among the

congenitally deaf who reported no deaf relatives, the percentage of

consanguineous parentage is still high, (7.3 per cent), but this

excess can easily be accounted for by the ignorance of deaf relatives

on the part of the informant, without contradicting the hypothesis of

heredity.

Basing now our percentages on the totals of consanguineous and

non-consanguineous parentage respectively, and including only those

who answered the inquiry as to deaf relatives, it will be seen (Table

XXXI) that while of all the deaf less than one third are returned as

having deaf relatives, of the deaf who were the offspring of cousins

over one half (55.5 per cent) were returned as having (a) or (b) deaf

relatives.

Again taking into consideration only the congenitally deaf the results

are still more striking. Table XXXII shows that 66.5 per cent of the

congenitally deaf who are of consanguineous parentage are known to

have deaf relatives.

TABLE XXXI.

----------------------------------------------------------------------

| |Consanguinity |

| | of Parents. | Per cent.

| |-------------------------------------

| | |Not | | |Not

----------------------------------------------------------------------

Deaf relatives stated |80,481| 3,911 |73,639 |100.0|100.00 |100.00

----------------------------------------------------------------------

(a) relatives |21,660| 1,850 |18,838 | 26.9| 47.3 | 25.5

No (a) relatives |58,821| 2,061 |54,801 | 73.1| 52.7 | 74.5

| | | | | |

(a) or (b) relatives |25,851| 2,171 |22,552 | 32.1| 55.5 | 30.6

(a) and (b) relatives | 4,117| 412 | 3,587 | 5.1| 10.5 | 4.8

(a) and no (b) relatives |17,543| 1,438 |15,251 | 21.8| 36.8 | 20.7

(b) and no (a) relatives | 4,191| 321 | 3,714 | 5.2| 8.2 | 5.1

No (a) or (b) relatives |54,630| 1,740 |51,087 | 67.9| 44.5 | 69.4

----------------------------------------------------------------------

Symbols for deaf relatives: (a) deaf brothers, sisters or ancestors;

(b) deaf uncles, aunts, cousins, etc.; (c) deaf children;

(d) deaf husbands or wives.

TABLE XXXII.

-------------------------------------------------------------------------

| |Consanguinity |

| |of Parents. | Per cent.

| |-------------------------------------

| | |Not | | |Not

-------------------------------------------------------------------------

Deaf relatives stated |13,428| 1,647 |11,110 |100.0|100.0 |100.0

-------------------------------------------------------------------------

(a) relatives | 5,295| 986 | 3,961 | 39.5| 59.9 | 35.6

(b) or (c), no (a) relatives| 860| 126 | 686 | 6.4| 7.6 | 6.2

No (a), (b) or (c) relatives| 7,273| 535 | 6,463 | 54.2| 32.5 | 58.2

-------------------------------------------------------------------------

Symbols for deaf relatives: (a) deaf brothers, sisters or ancestors;

(b) deaf uncles, aunts, cousins, etc.; (c) deaf children.

The percentage having (a) relatives, including brothers, and sisters,

is nearly twice as great among the deaf of consanguineous parentage as

among the offspring of unrelated parents. This is not inconsistent

with the Irish returns which show the average number of deaf children

to a family to be so much greater where the parents were cousins, than

where they were not.

The statistics of the (c) relatives, or deaf sons and daughters of the

deaf, are not very full. Of the 31,334 married deaf who answered the

inquiry in regard to deaf relatives, 437 or 1.4 per cent reported deaf

children and 30,897 or 98.6 per cent reported no deaf children. Of the

totally deaf 2.4 per cent had deaf children, and of the congenitally

deaf 5.0 per cent. The percentage of deaf children varied greatly

according to the number and class of deaf relatives, as shown by Table

XXXIII.

TABLE XXXIII.

-------------------------------------------------------------------

| Percentage having deaf children.

|---------------------------------------

Class of Deaf Relatives. | |Totally |Partially |Congenitally

|Total.|deaf. |deaf. |deaf.

---------------------------|------|--------|----------|------------

(a), (b) or (d) | 1.4 | 2.4 | 1.1 | 5.0

(d) | 3.2 | 3.3 | 2.6 | 6.4

No (d) | 1.1 | 1.4 | 1.0 | 2.5

(a) and (d) | 6.3 | 6.7 | 4.3 | 7.8

(d), but no (a) | 2.2 | 2.2 | 2.0 | 4.9

(a), but no (d) | 1.4 | 2.3 | 1.3 | 2.6

No (a) or (d) | 0.9 | 1.0 | 0.9 | 2.3

(a), (b) and (d) | 9.5 | 9.9 | [A] | 9.0

(a), (d), but no (b) | 5.5 | 5.9 | 3.6 | 7.4

(b), (d), but no (a) | 2.5 | 2.4 | [A] | [A]

(d), but no (a) or (b) | 2.2 | 2.2 | 2.0 | 5.2

(a), (b), but no (d) | 1.9 | 3.1 | 1.7 | [A]

(a), but no (b) or (d) | 1.3 | 2.1 | 1.2 | 2.8

(b), but no (a) or (d) | 1.0 | 1.6 | 1.0 | [A]

No (a), (b) or (d) | 0.9 | 1.0 | 0.9 | 2.6

----------------------------------------------------------------

[A] Percentages not given where base is less than 100.

Symbols: (a) deaf brothers, sisters or ancestors; (b) deaf

uncles, aunts, cousins, etc.; (d) deaf husbands or wives.

The striking feature of these percentages is the regularity with

which they increase in proportion as the number of deaf relatives

increases, until among the 242 persons who have (a), (b) and (d)

relatives, 23 or 9.5 per cent also have (c) relatives. A

consanguineous marriage within a family tainted with deafness would

have the same effect as doubling the number of deaf relatives, which

as we have seen greatly increases the percentage having deaf children.

It would seem that the number of the married deaf reported as having

deaf children is much too small, especially since Dr. Fay[89] produces

statistics of 4471 marriages of the deaf of which 300 produced deaf

offspring. Counting only the 3,078 marriages of which information in

regard to offspring was available these figures show an average of a

little less than one such marriage in ten as productive of deaf

offspring. The total number of children of these marriages was 6,782,

of which 588 were deaf. These 3,078 marriages represented 5,199 deaf

married persons as compared with the 31,334 reported in the Twelfth

Census, or about one sixth. Increasing the 300 families who had deaf

children in the same ratio we have 1800 as compared with the 437

reported by the census. But as it was inevitable that Dr. Fay's cases

should be selected somewhat, he has probably collected records of more

than one sixth of all the cases where deaf children were born of deaf

parents. But we can hardly believe that he found three-fourths of such

cases. The true number therefore must be considerably greater than

437, but less than 1800.[90]

[Footnote 89: _Marriages of the Deaf in America_, chap. v.]

[Footnote 90: Of the 17 children of first cousins reported on my

circulars as either totally or partially deaf, 9 are known to have had

deaf ancestors.]

Dr. Fay found that 31 out of the 4,471 marriages of the deaf were

consanguineous, but he expresses the belief that the actual number

and percentage of consanguineous marriages of the deaf are larger. The

following table which combines several of Dr. Fay's tables sets forth

the main results of his work. In each instance one or both parties to

the marriage were deaf. The totals include only those of whom

information as to the offspring was available.

TABLE XXXIV.

----------------------------------------------------------

| | Marriages |

| | resulting |

| | in deaf |

| | offspring | Deaf children

|Number|-----------|------------------

Consanguineous |of | | | |Per

----------------------------------------------------------

First cousins | 7 | 4 | 57.| 26 | 7 | 27.

Second cousins | 5 | 3 | 60.| 25 | 10 | 40.

Third cousins | 1 | 1 | -- | 1 | 1 | --

"Cousins" | 14 | 3 | 21.| 36 | 7 | 19.

Nephew and aunt | 1 | 1 | -- | 4 | 3 | 75.

Distantly related | 3 | 2 | 67.| 8 | 2 | 25.

----------------------------------------------------------

Total consanguineous| 31 | 14 | 45.| 100 | 30 | 30.

or no information |3,047 | 286 | 9.|6,682 | 558 | 8.

----------------------------------------------------------

Grand total |3,078 | 300 | 10.|6,782 | 588 | 9.

----------------------------------------------------------

Obviously percentages based on these figures are of little value of

themselves, especially since Dr. Fay's cases are not entirely typical,

but in general this table points us to the same conclusion that we

have reached by other means, namely that where a tendency toward

deafness exists, a consanguineous marriage is more likely to produce

deaf children than a non-consanguineous marriage. If more figures were

available the percentage of deaf children would probably increase with

the nearness of consanguinity and the number of deaf relatives, but

with the present data a further analysis has no significance.[91]

[Footnote 91: Mr. Edgar Schuster (_Biometrika_, vol. iv, p. 465) finds

from Dr. Fay's statistics that the average parental correlation

(parent and child) of deafness is: paternal, .54; maternal, .535.

English statistics of deafness give: paternal correlation, .515;

maternal, .535. The fraternal correlation from the American data is

.74 and from the English .70. See _infra_, p. 92.]

If, then, consanguineous marriages where relatives are deaf have a

greater probability of producing deaf offspring, and also a greater

probability of producing plural deaf offspring, than ordinary

marriages, and two thirds of the congenitally deaf offspring of

consanguineous marriages do have deaf relatives, it does not seem

necessary to look beyond the law of heredity for an explanation of the

high percentage of the congenitally deaf who are of consanguineous

parentage.

In those cases of deafness which, in the Census returns, are ascribed

to specific causes, the factor of consanguinity is still noticeable,

although the percentage of the non-congenitally deaf who are the

offspring of cousins never exceeds 5.3 (Table XXVIII). But the

influence of heredity is not removed by the elimination of the

congenitally deaf. Many instances are known where successive

generations in the same family have developed deafness in adult life,

often at about the same age and from no apparent cause. The following

case well illustrates this point. It is furnished me by a

correspondent in whom I have great confidence. The facts are these:

A---- aged 28 married B---- aged 19, his first cousin who bore the

same surname as himself. Both lived to old age and were the parents of

eight children, two of whom died in infancy. My informant further

states:

Having personally known very well all of the surviving six

children of this family, I can truthfully state that all were

unusually strong, active and vigorous people and all the

parents of healthy children. A---- was troubled with deafness

as long as I can remember, and this physical trait he

transmitted to all of his children, though some of them did not

develop the same till well along in life. C---- (the youngest

son), however, began to indicate deafness quite early. No one

of his four children is in the least deaf.

It will be noticed here that whereas in the case of the cousin

marriage the trait was so strongly inherited, it disappeared entirely

in the next generation with a non-consanguineous marriage. The

inheritance of tendencies or weaknesses may be more common than the

actual inheritance of defects. Dr. Bell's words on this point are

suggestive:

Where a tendency toward ear trouble exists in a family, it may

lie dormant and unsuspected until some serious illness attacks

some member of the family, when the weak spot is revealed and

deafness is produced. We are not all built like that wonderful

one-horse shay that was so perfectly made in all its parts that

when at last it broke down it crumbled into dust. When an

accident occurs it is the weak spot that gives way, and it

would be incorrect to attribute the damage to the accident

alone and ignore the weakness of the part; both undoubtedly are

contributing causes.

In the case, then, of a deaf person who has deaf relatives, the

assigned cause of deafness may not be the only cause involved,

or indeed the true cause at all. It may be the cause simply in

the same sense that the pulling of a trigger is the cause of

the expulsion of a bullet from a rifle, or a spark the cause of

the explosion of a gunpowder magazine; hereditary influences

may be involved.[92]

[Footnote 92: U.S. Census _Report on the Blind and the Deaf_, p. 127.]

It is thus possible to account for the large proportion of deafness

among persons of consanguineous parentage by the simple action of the

laws of heredity. Why then should we go out of our way to look for a

cause of the defect in consanguinity itself? When two explanations are

possible, the simpler explanation is the more probable, other factors

being equal; but in the present problem the factors are not equal, for

the evidence points strongly toward the simpler hypothesis of

intensified heredity, while there is little or no evidence that

consanguinity is a cause _per se_.

As to the probability then of a consanguineous marriage producing deaf

offspring, it will readily be seen to be very slight, and in those

cases where there is actually no trace of hereditary deafness in the

family, perhaps no greater than in non-related marriages. While the

census figures in regard to the deaf are not complete they probably

include a great majority of the deaf in the United States. The 89,287

deaf would mean an average of 12 deaf persons to every 10,000

inhabitants and the 14,472 congenitally deaf, 2 persons to every

10,000. Assuming then, as before[93] that 1,000,000 persons in

continental United States are the offspring of consanguineous

marriages within the limits of the term "cousins" as used in the

Census report, 41 out of every 10,000 persons of consanguineous

parentage would be deaf, and 17 congenitally so. Thus less than one

half of one per cent of the offspring of consanguineous marriages in

the United States are deaf, and only one sixth of one per cent are

deaf-mutes in the commonly accepted sense of the term.

[Footnote 93: _Supra_, p. 64.]

It is interesting here to quote an opinion given by Dr. Bell in 1891,

as to the probable results of the consanguineous marriage of deaf

persons.[94]

[Footnote 94: _Marriage--An Address to the Deaf_, second edition,

Appendix.]

1. A deaf person, not born deaf, who has no deaf relatives,

will probably not increase his liability to have deaf offspring

by marrying a blood relative.

2. A deaf person, born deaf, who has no deaf relatives, will

probably increase his liability to have deaf offspring by

marrying a blood relative.

3. A deaf person, whether born deaf or not, who has deaf

relatives, will probably increase his liability to have deaf

offspring by marrying a blood relative, especially if that

relative should happen to be on the deaf side of the family.

For example: If his father has deaf relatives and his mother

has none, he will be more likely to have deaf offspring if he

marries a relative of his father than if he marries a relative

of his mother.

The laws of heredity seem to indicate that a consanguineous

marriage increases or intensifies in the offspring whatever

peculiarities exist in the family. If a family is

characterized by the large proportion of persons who enjoy

good health and live to old age with unimpaired faculties,

then a consanguineous marriage in such a family would probably

be beneficial, by increasing and intensifying these desirable

characteristics in the offspring. On the other hand, if a

large proportion of the members of a family betray weakness of

constitution--for example: if many of the children die in

infancy, and a large proportion of the others suffer from ill

health, only a few living to old age with unimpaired

faculties--then a consanguineous marriage in such a family

would probably be hurtful to the offspring. A large

proportion of the children would probably die in infancy, and

the survivors be subject to some form of constitutional

weakness.

As there are few families entirely free from constitutional

defects of some kind, a prudent person would do well to avoid

consanguineous marriage in any case--not necessarily on account

of deafness, but on account of the danger of weakening the

constitution of the offspring. Remoteness of blood is eminently

favorable to the production of vigorous offspring, and those

deaf persons who have many deaf relatives would greatly

diminish their liability to have deaf offspring by marrying

persons very remote in blood from themselves.

Children, I think, tend to revert to the type of the common

ancestors of their parents. If the nearest common ancestors are

very far back in the line of ancestry, the children tend to

revert to the common type of the race. Deafness and other

defects would be most likely to disappear from a family by

marriage with a person of different nationality. English,

Irish, Scotch, German, Scandinavian and Russian blood seems to

mingle beneficially with the Anglo-Saxon American, apparently

producing increased vigor in the offspring.