Consanguineous Marriages in the American Population - George B. Louis Arner

TABLE XXXII.
Class of Deaf Relatives.	Total.	Consanguinity of Parents.		Per cent.
Class of Deaf Relatives.	Total.	Cousins	Not Cousins	Total	Cousins	Not 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 class of deaf relatives, as shown by Table XXXIII.

TABLE XXXIII.
Class of Deaf Relatives.	Percentage having deaf children.
Class of Deaf Relatives.	Total.	Totally deaf.	Partially deaf.	Congenitally 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]]

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.
Consanguineous Marriages of the Deaf.	Number of marriages	Marriages resulting in deaf offspring		Deaf children
Consanguineous Marriages of the Deaf.	Number of marriages	Number	Per Cent	Number	Number Deaf	Per Cent Deaf
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.
Not consanguineous, 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]]

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.