Consanguineous Marriages in the American Population Part 7

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 relations.h.i.+p. In 1881 third cousins produced more than any nearer relations.h.i.+p."[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 a.s.sumption 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 |----------------------------------------------------------- | |Number| | |Number| | |Number| | | of |Aver | | of |Aver | | of |Aver |Number|conge-|age |Number|conge-|age |Number|conge-|age Consanguinity | of |nital |per | of |nital |per | of |nital |per of |mar- |deaf- |mar- |mar- |deaf- |mar- |mar- |deaf- |mar- Parents. |riages|mutes |riage|riages|mutes |riage|riages|mutes |riage -------------------------------------------------------------------------- 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 Fifth and | | | | | | | | | 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 | | | | | | | | | relation- | | | | | | | | | s.h.i.+p[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 Mitch.e.l.l 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 Norvege_. 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 att.i.tude 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 relations.h.i.+p, 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 a.s.sume that about half of the cases returned as "cousins" were first cousins.

The replies to the inquiry as to deaf relatives were more carefully a.n.a.lyzed, 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 advent.i.tiously 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 |Total.|Cous- |Cous- | Sta- |Cous-|Cous-| Sta- | | 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 Uncla.s.sified |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.

| |--------------------|----------------- | | | | | | | Cla.s.s of Deaf | | | Not | Not | | Not | Not Relative.[A] |Total.| Cous-| Cous-| Sta- |Cous-|Cous-| Sta- | | 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 a.s.sume 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 relations.h.i.+p 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 x.x.x.

------------------------------------------------------------------------ | | Consanguinity | | | of Parents. | Per Cent.

| |---------------------------------------------- Cla.s.s of Deaf | | | Not | Not | | Not | Not Relatives.[A] |Total. |Cousins|Cousins|stated |Cousins|Cousins|stated ------------------------------------------------------------------------ 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 (b) and (c) but | | | | | | | no (a) relatives| 860 | 126 | 686| 48 | 14.6 | 79.8 | 5.6 No (a), (b) or | | | | | | | (c) relatives | 7,273 | 535 | 6,463| 275 | 7.3 | 88.9 | 3.8 ------------------------------------------------------------------------ [A] Symbols for deaf relatives: (a) deaf brothers, sisters or ancestors; (b) deaf uncles, aunts, cousins, etc.; (c) deaf children.

A further a.n.a.lysis of the congenitally deaf according to consanguinity of parents and deaf relatives, as in Table x.x.x, 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 relations.h.i.+p 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 x.x.xI) 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 x.x.xII shows that 66.5 per cent of the congenitally deaf who are of consanguineous parentage are known to have deaf relatives.

TABLE x.x.xI.

---------------------------------------------------------------------- | |Consanguinity | | | of Parents. | Per cent.

| |------------------------------------- | | |Not | | |Not Cla.s.s of Deaf Relatives. |Total.|Cousins|Cousins|Total|Cousins|Cousins ---------------------------------------------------------------------- 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 x.x.xII.

------------------------------------------------------------------------- | |Consanguinity | | |of Parents. | Per cent.

| |------------------------------------- | | |Not | | |Not Cla.s.s of Deaf Relatives |Total.|Cousins|Cousins|Total|Cousins|Cousins ------------------------------------------------------------------------- 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 cla.s.s of deaf relatives, as shown by Table x.x.xIII.

TABLE x.x.xIII.

------------------------------------------------------------------- | Percentage having deaf children.

|--------------------------------------- Cla.s.s 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.]