Consanguineous Marriages in the American Population

by George B. Louis Arner

TABLE XXVIII.
Cause of Deafness.	Total.	Consanguinity of Parents.			Per cent.
		Cousins.	Not Cousins.	Not Stated.	Cousins.	Not Cousins.	Not Stated.
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.
Class of Deaf Relative.[A]	Total.	Consanguinity of Parents.			Per cent.
		Cousins.	Not Cousins.	Not Stated.	Cousins.	Not Cousins.	Not Stated.
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.
Class of Deaf Relative.[A]	Total.	Consanguinity of Parents.			Per cent.
		Cousins.	Not Cousins.	Not Stated.	Cousins.	Not Cousins.	Not 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 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.
Class of Deaf Relatives.	Total.	Consanguinity of Parents.		Per cent.
		Cousins	Not Cousins	Total	Cousins	Not Cousins
Deaf relatives stated	80,481	3,911	73,639	100.0	100.0	100.0
(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.