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Title: Consanguineous Marriages in the American Population
Author: Arner, George B. Louis
Language: English
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CONSANGUINEOUS MARRIAGES
IN THE
AMERICAN POPULATION
STUDIES IN HISTORY, ECONOMICS AND PUBLIC LAW
EDITED BY THE FACULTY OF POLITICAL SCIENCE OF COLUMBIA UNIVERSITY
[Volume XXXI] [Number 3]
CONSANGUINEOUS MARRIAGES
IN THE
AMERICAN POPULATION
BY
GEORGE B. LOUIS ARNER, Ph.D.
_University Fellow in Sociology_
1908
PREFACE
This monograph does not claim to treat exhaustively, nor to offer a
final solution of all the problems which have been connected with the
marriage of kin. The time has not yet come for a final work on the
subject, for the systematic collection of the necessary statistics,
which can only be done by governmental authority, has never been
attempted. The statistics which have been gathered, and which are
presented in the following pages, are fragmentary, and usually bear
upon single phases of the subject, but taken together they enable us
better to understand many points which have long been in dispute.
The need for statistics of the frequency of occurrence of
consanguineous marriages has been strongly felt by many far-sighted
men. G.H. Darwin and A.H. Huth have tried unsuccessfully to have the
subject investigated by the British Census, and Dr. A.G. Bell has
recently urged that the United States Census make such an
investigation.[1] Another motive for undertaking this present work,
aside from the desire to study the problems already referred to, has
been to test the widely prevalent theory that consanguinity is a
factor in the determination of sex, the sole basis of which seems to
be the Prussian birth statistics of Düsing, which are open to other
interpretations.
[Footnote 1: Cf. Bell, "A Few Thoughts Concerning Eugenics." In
_National Geographic Magazine_, March, 1908.]
The stock illustrations from isolated communities have been omitted as
too difficult to verify, and little space has been given to the
results of the inbreeding of domestic animals, for although such
results are of great value to Biology, they are not necessarily
applicable to the human race.
The writer regrets that it is impossible here to acknowledge all his
obligations to those who have assisted him in the preparation of this
work. Such acknowledgement is due to the many genealogists and other
friends who have kindly furnished detailed cases of consanguineous
marriage. For more general data the writer is especially indebted to
Dr. Alexander Graham Bell, to Dr. Martin W. Barr, to Professor William
H. Brewer of Yale University, and to Dr. Lee W. Dean of the University
of Iowa. In the preparation of the manuscript the suggestions and
criticisms of Professors Franklin H. Giddings and Henry L. Moore have
been invaluable.
G.B.L.A.
MARCH, 1908.
CONTENTS
CHAPTER I
INTRODUCTION
Problems to be Treated--Degrees of Consanguinity--Literature of the
Subject--Noah Webster--Bemiss--Dally--G.H. Darwin--Huth--Bell--Legal
Status in the United States--Methods of
Investigation--Genealogical--Personal--Isolated Communities
CHAPTER II
RATIO OF THE CONSANGUINEOUS TO ALL MARRIAGES
Previous Estimates--Mayo-Smith--Mulhall--Darwin--Application of
Darwin's Method to American Data--Direct Method--Consanguineal
Attraction--Same-name and Different-name Cousin Marriages--Summary
CHAPTER III
MASCULINITY
Constancy of the Sex-ratio--Consanguinity and Masculinity--Theory of
Westermarck and Thomas--Duesing--Gache--Negroes in the United
States--Genealogical Material--Other Compilations--Summary
CHAPTER IV
CONSANGUINITY AND REPRODUCTION
Theories of the Effect of Consanguinity upon Offspring--Comparative
Fertility--Statistics from Darwin and Bemiss--Genealogical
Statistics--Youthful Death-rate--Degeneracy--Fallacies in the Work of
Bemiss--Isolated Communities--_The Jukes_--Other Degenerate
Families--Scrofula
CHAPTER V
CONSANGUINITY AND MENTAL DEFECT
Idiocy and Insanity--Inheritability of Mental Defect--Intensified
Heredity--Barr's Investigations--Other American and English
Data--Mayet's Prussian Statistics--Genealogical Data
CHAPTER VI
CONSANGUINITY AND THE SPECIAL SENSES
United States Census Data--The Blind--Consanguinity of Parents--Blind
Relatives--Degree of Blindness--Causes of Blindness--Retinitis
Pigmentosa--European Data--Probability of Blind Offspring of
Consanguineous Marriages--The Deaf--Irish Census--Scotland and
Norway--United States Census--Consanguinity of Parents--Deaf
Relatives--Causes of Deafness--Degree of Deafness--Direct Inheritance
of Deafness--Intensification through Consanguinity--Dr. Fay's
Statistics--Personal Data--Probability of Deaf Offspring from
Consanguineous Marriages--Opinion of Dr. Bell
CHAPTER VII
SUMMARY AND CONCLUSION
Summary of Results--Inbreeding and Evolution--Effects of Close
Inbreeding--Crossing and Variation--"Difference of
Potential"--Resemblance and Intensification--Coefficient of
Correlation between Husband and Wife--Between Cousins--Between
Brothers and Sisters--Consanguinity and Eugenics--Consanguinity and
Social Evolution--Conclusion
CHAPTER I
INTRODUCTION
The purpose of this essay is to present in a concise form and without
bias or prejudice, the most important facts in regard to
consanguineous marriages, their effects upon society, and more
particularly their bearing upon American social evolution. The
problems to be considered are not only those which relate primarily to
the individual and secondarily to the race, such as the supposed
effect of blood relationship in the parents upon the health and
condition of the offspring; but also the effect, if any, which such
marriages have upon the birth-rate, upon the proportion of the sexes
at birth, and the most fundamental problem of all, the relative
frequency with which consanguineous marriages take place in a given
community.
No thorough and systematic study of the subject has ever been made,
and could not be made except through the agency of the census. The
statistical material here brought together is fragmentary and not
entirely satisfactory, but it is sufficient upon which to base some
generalizations of scientific value. The sources of these data are
largely American. Little attempt is made to study European material,
or to discuss phases of the problem which are only of local concern.
Some topics, therefore, which have frequently been treated in
connection with the general subject of consanguineous marriages are
here ignored as having no scientific interest, as for instance that of
the so-called "marriages of affinity," which has been so warmly
debated for the past fifty years in the British Parliament.
For obvious reasons it will often be impossible to distinguish between
the different degrees of consanguinity, but wherever possible the
degree will be specified. It is probable that where a number of
marriages are vaguely given as consanguineous, few are more distant
than second cousins, for in the United States especially, distant
relationships are rarely traced except by genealogists. In designating
degrees of relationship the common terminology will be used, as in the
following table, expressing, however, the rather clumsy expression,
"first cousin once removed" by the simpler form "1-1/2 cousin."
[Illustration]
By far the greater part of the literature of consanguineous marriage
is of a controversial rather than of a scientific nature, and a search
for statistical evidence for either side of the discussion reveals
surprisingly little that is worthy of the name. Yet men of high
scientific standing have repeatedly made most dogmatic assertions in
regard to the results of such unions, and have apparently assumed that
no proof was necessary. For example, Sir Henry Sumner Maine "cannot
see why the men who discovered the use of fire, and selected the wild
forms of certain animals for domestication and of vegetables for
cultivation, should not find out that children of unsound constitution
were born of nearly related parents."[2]
[Footnote 2: Maine, _Early Law and Custom_, p. 228.]
Much space is given to the alleged "innate horror of incest," and
frequent appeals are made to Scripture, wrongly assuming that the
marriage of cousins is prohibited in the Mosaic Law.
The origin of "prohibited degrees" is only conjectural. The Christian
Church apparently borrowed its prohibitory canons from the Roman
Law,[3] and a dispensation is still necessary before a Catholic can
marry his first cousin. However, such dispensations have always been
easy to obtain, especially by royal families, and even the marriage of
uncle and niece sometimes occurs, as among the Spanish Habsburgs, and
as recently as 1889 in the House of Savoy.
[Footnote 3: Luckock, _History of Marriage_, p. 282.]
The prohibition of the marriage of first cousins was removed in
England by the Marriage Act of 1540,[4] but by this time the idea of
the harmfulness of kinship marriage was so thoroughly impressed upon
the people that they were very prone to look askance at such unions,
and if they were followed by any defective progeny, the fact would be
noted, and looked upon as a chastisement visited upon the parents for
their sin. Naturally the idea became proverbial, and in some places it
has influenced the civil law.
[Footnote 4: Child, "On Marriages of Consanguinity," in
_Medico-Chirurgical Review_, April, 1862, p. 469.]
Perhaps the first printed discussion of the subject in America is from
the pen of Noah Webster, in an essay which should be as interesting to
the spelling reformer as to the sociologist.[5] He writes: "It iz no
crime for brothers and sisters to intermarry, except the fatal
consequences to society; for were it generally practised, men would
become a race of pigmies. It iz no crime for brothers' and sisters'
children to intermarry, and this iz often practised; but such near
blood connections often produce imperfect children. The common peeple
hav hence drawn an argument to proov such connections criminal;
considering weakness, sickness and deformity in the offspring az
judgements upon the parents. Superstition iz often awake when reezon
iz asleep."
[Footnote 5: Webster, _Collection of Essays and Fugitiv Writings on
Moral, Historical, Political and Religious Subjects_, 1790, p. 322.]
From about 1855 to 1880 much was written about the effect of
consanguineal interbreeding. One of the first contributions came from
America. In 1858 Dr. S.M. Bemiss, of Louisville, Kentucky, reported to
the American Medical Association the results of his investigation of
833 cases of consanguineous marriage.[6] His compilation remains to
this day the largest single piece of direct statistical work on the
subject. Unfortunately, however, his statistics have a strong, if
unintentional, bias which seriously affects their value. In France one
of the earliest discussions was by M. Boudin,[7] who evidently
obtained the Bemiss report (attributing it to Dr. O.W. Morris, who had
quoted freely from Bemiss),[8] and enlarged greatly upon its
fallacies. He also collected statistics of the deaf-mutes in Paris,
and, by an amazing manipulation of figures, "demonstrated" that
consanguinity of the parents was the cause of nearly one-third of the
cases of congenital deafness. The savants of the Société
d'Anthropologie took sides and the debate became very entertaining.
Finally M. Dally came to the rescue, and published some very sane and
logical articles which avoided both extremes, and first advanced the
theory that any ill effects of consanguineous marriage should be
attributed to the intensification of inherited characteristics.[9]
[Footnote 6: See _Transactions of the American Medical Association_,
1858, pp. 321-425.]
[Footnote 7: "Du Croisement des families," _Mem. de la Société
d'Anthropologie_, vol. i, 1860-63, pp. 505-557.]
[Footnote 8: See Morris: "On Marriages of Consanguinity," in _Amer.
Med. Times_, Mar. 23, 1861.]
[Footnote 9: See _Bulletins de la Société d'Anthropologie_, 1863, pp.
515-575; 1877, pp. 203-213.]
In England similar discussions took place during the same period,
complicated, however, by the presence of the patient and
long-suffering "deceased wife's sister." The best of the English work
has been the statistical study by George H. Darwin,[10] and the
classic "Marriage of Near Kin" by Alfred H. Huth, a book of 475 pages,
including a very complete bibliography to the date of the second
edition, 1885. Although Mr. Huth's book is not free from error, and is
encumbered with a large amount of worthless material, it is now after
thirty-three years, by far the best treatment of the subject.
[Footnote 10: "Marriages of First Cousins in England and their
Effects," _Journal Statistical Society_, 1875, pp. 153-184.]
In Italy Dr. Montegazza,[11] in Spain Señor Pastor[12] and others,
have made useful contributions. German writers have usually preferred
more general subjects, but many of them have given much space to
consanguineous marriage in sociological and biological works.
[Footnote 11: _Studj Sui Matrimonj Consanguinei_. Quoted by Darwin,
op. cit., p. 178.]
[Footnote 12: "De los Matrimonios entre Parientes," Memorias _de la
Real Academia de Ciencias Morales y Políticas_, vol. ii, pp. 369-400.]
Since the appearance of the Bemiss report little has been published in
this country which bears directly upon our subject. The most important
American contribution, however, is to be found in the Special Report
on the Blind and the Deaf, in the Twelfth Census of the United States,
prepared by Dr. Alexander Graham Bell. Although American writers have
had little part in the theoretical discussions, our legislators have
been active, so that the statutes of every state specify degrees of
kinship within which marriage is prohibited. In at least sixteen
states the prohibition is extended to include first cousins. In New
Hampshire such marriages are void and the children are illegitimate.
Other states in which first-cousin marriage is forbidden are
Pennsylvania, Ohio, Indiana, Illinois, Michigan, Kansas, North Dakota,
South Dakota, Wyoming, Nevada, Washington, Oregon, Missouri, Arkansas,
and Louisiana. Since both Oklahoma and Indian Territory had similar
laws, the present State of Oklahoma should probably be added to this
list. In all of these states marriages within the prohibited degrees
are incestuous or void or both, except in Ohio, where no express
declaration is made in the statute. In Ohio, Indiana, Nevada and
Washington the law is made to read: "and not nearer of kin than
_second cousins_," therefore including "1-1/2 cousins" within the
prohibited degrees. In many states the marriage of step relatives is
forbidden, as also marriage with a mother-in-law or father-in-law. Of
the territories, Arizona, Alaska, and Porto Rico forbid the marriage
of first cousins, but in Porto Rico the court may waive the
impediment.
These laws probably have some effect in reducing the number of
consanguineous marriages in these states, but the sentiment back of
the law is more responsible for the decrease in the number of such
unions than the law itself. For in the nature of things enforcement
would be very difficult, and apparently little real effort is made in
that direction. In Ohio, and probably elsewhere, the question as to
consanguinity is not directly put to the applicants for a marriage
license. The applicants are required to answer the usual questions in
regard to age, parentage, residence, etc., and are then required to
swear that their previous statements have been correct and that
neither of them is "epileptic, imbecile or insane," that they are "not
nearer of kin than second cousins, and not at the time under the
influence of any intoxicating liquor or narcotic drug." Undoubtedly
violations of the consanguinity clause are very frequent, and it is
likewise easily evaded by going to another state where the laws are
more liberal. One effect of the law is to provide a painless method of
severing the marriage bond. A correspondent, who is a District Court
Judge in Kansas, in reporting a case of first cousin marriage, adds
that he "divorced them on the ground of consanguinity."
In the absence of direct investigation by the Census Bureau, or other
public records of consanguineous marriages, perhaps the most promising
field for research is in the genealogical records of American
families. Several thousand volumes of such material have been
published within the last half-century, and a large number of these
are very carefully and scientifically prepared. The material gathered
from such sources is very accurate in regard to the number of births,
youthful deathrate etc., but mental or physical defects are rarely
mentioned. The greatest objection to the utilization of this material,
however, is the amount of labor necessary in order to glean the
desired facts from the mass of irrelevant data. For example, in order
to find one case of first cousin marriage it is necessary on an
average, to examine the records of nearly two hundred other marriages.
The collection of data from personal sources is likewise open to grave
objections. Not only is the informant likely to be biassed, but the
cases which he will remember will be those in which something unusual
has occurred. Herein lay the fallacy in the conclusions of Dr. Bemiss.
I have endeavored to overcome this bias by restricting my requests
for information to genealogists and others who would more naturally
appeal to records, but my efforts have been only partially successful.
The number of cases of consanguineous marriage, embracing all degrees
of consanguinity, which I have collected from these two sources,
genealogies and correspondence, is 723, a number too small in itself
to establish any definite conclusions; but by using this material in
connection with other related data, I trust I may be able to add
something to the comparatively small amount of real knowledge which
the world already possesses in regard to the marriage of kin.
In the course of my investigations I visited Smith's Island, in the
Chesapeake Bay, about twelve miles across Tangier Sound, from
Crisfield, Maryland, and nearly opposite the mouth of the Potomac.
Here is a community of about seven hundred people, who are principally
engaged in the sea-food industry. Their ancestors have lived on the
island for many generations and there have been comparatively few
accessions to the population from the mainland. As a natural
consequence the population is largely a genetic aggregation.
Consanguineous marriages have been very frequent, until now nearly all
are more or less interrelated. Out of a hundred or more families of
which I obtained some record, at least five marriages were between
first cousins. All of these were fertile, and all the children were
living and apparently healthy. Since over thirty per cent of the
inhabitants bear one surname (Evans), and those bearing the first four
surnames in point of frequency (Evans, Brad-shaw, Marsh, and Tyler)
comprise about fifty-nine per cent of the population, it will readily
be seen that comparatively few absolutely non-related marriages take
place. Yet in this community from September, 1904, to October, 1907,
or during the residence there of the present physician, Dr. P.H.
Tawes, there have been 87 births and but 30 deaths, the latter from
the usual causes. During this period there has not been a single case
of idiocy, insanity, epilepsy, deaf-mutism or even of typhoid fever on
the island.
The evidence gathered from various other isolated communities is very
conflicting. Huth describes a great many of them which have existed
for many generations without crosses without ill results. Other
writers quote instances where whole communities have become
degenerate. Until the antecedents of a community are known it is of
course impossible to estimate the effect of consanguinity. The
exceptionally high percentage of deaf-mutism on Martha's Vineyard may
to some extent be due to a high percentage of consanguineous marriage,
but that inbreeding is not the primary cause is revealed by the
records showing that among the first settlers were two deaf-mutes,
whose defect has been inherited from generation to generation for two
hundred and fifty years.[13]
[Footnote 13: See article in Cincinnati _Gazette_, Jan. 22, 1895.]
CHAPTER II
RATIO OF THE CONSANGUINEOUS TO ALL MARRIAGES
Towards determining the average frequency of occurrence of
consanguineous marriages, or the proportion which such marriages bear
to the whole number of marriages, little has as yet been done in this
country. Professor Richmond Mayo-Smith estimated that marriages
between near kin constituted less than one per cent of the total,[14]
and Dr. Lee W. Dean estimates that in Iowa they comprise only about
one half of one per cent.[15] But these estimates are little more than
guesses, without any statistical basis.
[Footnote 14: _Statistics and Sociology_, p. 112.]
[Footnote 15: _Effect of Consanguinity upon the Organs of Special
Sense_, p. 4.]
In several European countries such marriages have been registered,
though somewhat spasmodically and inaccurately. According to
Mulhall[16] the ratio of the consanguineous among 10,000 marriages in
the various countries is as follows:
TABLE I.
-----------------------------------
Country.| Ratio. | Country.| Ratio.
-----------------------------------
Prussia | 67 | Alsace | 107
Italy | 69 | France | 126
England | 75 | Jews | 230
-----------------------------------
[Footnote 16: _Dictionary of Statistics_, p. 383.]
According to Uchermann the ratio is 690 or 6.9 per cent, including
marriages between second cousins and nearer.[17] Dr. Peer says that 4
per cent of the marriages in Saxony are consanguineous.[18] The ratio
seems to be increasing in France but diminishing in Alsace and Italy,
as indicated in Table II.[19]
[Footnote 17: _Les Sourds-muets en Norvège_. Quoted by Feer, p. 9.]
[Footnote 18: _Der Einfluss der Blutsverwandschaft der Eltern auf die
Kinder_, p. 9.]
[Footnote 19: Mulhall, _Dictionary of Statistics_, p. 383.]
TABLE II.
---------------------------------------------------------
Country.| Date. |Ratio.[A]| Country.| Date. |Ratio.[A]
---------------------------------------------------------
France | 1853-60| 97 | France | 1861-71 | 126
Alsace | 1858-65| 143 | Alsace | 1872-75 | 107
Italy | 1868-71| 84 | Italy | 1872-75 | 69
---------------------------------------------------------
[A] Per 10,000.
In Italy the ratio varies greatly in different parts of the country.
Mulhall gives the following figures for the years 1872-75:
TABLE III.
------------------------------------------
Province.| Ratio.[A]| Province.| Ratio.[A]
------------------------------------------
Venice | 24 | Sicily | 117
Naples | 30 | Piedmont | 131
Lombardy | 100 | Liguria | 183
------------------------------------------
[A] Per 10,000.
It will be noted that the lowest ratios are in provinces where the
urban population is comparatively large. Wherever statistics have been
gathered it is the rule that the percentage of consanguineous marriage
is greater in rural than in urban districts. Table IV, also from
Mulhall, illustrates this point.
TABLE IV.
-------------------------------------------------
|_Ratio per 10,000 Marriages_.
-------------------------------------------------
Country. | Rural.| Urban. | General.
-------------------------------------------------
England | 79 | 71 | 75
France | 130 | 115 | 126
Alsace | 121 | 41 | 107
Norway[A] (Uchermann)| 810 | 260 | 690
-------------------------------------------------
[A] Includes second cousins.
In regard to the degree of consanguinity, it seems very probable that
in the French, German, Italian, and English statistics and estimates
few if any marriages beyond the degree of first cousins are returned
as consanguineous, so in order to compare the Norwegian figures with
the others they should probably be reduced by one half. Out of 1549
consanguineous marriages contracted in Prussia in 1889, 1422 were
between "cousins" (probably first), 110 between uncles and nieces, and
16 between nephews and aunts.[20] The ratio of such marriages to
10,000 in France during the fifteen years ending in 1875 was:[21]
TABLE V.
-----------------------------------------------
Degree. | Urban.| Rural.| All France.
-----------------------------------------------
Nephew and aunt | 1.6 | 2.4 | 2.1
Uncle and niece | 6.0 | 5.6 | 5.8
"Cousins" | 96.0 | 119.0 | 113.1
-----------------------------------------------
Total | 103.6 | 127.0 | 121.2
-----------------------------------------------
[Footnote 20: Mulhall, op. cit., p. 383.]
[Footnote 21: Ibid., p. 384.]
In Italy during seven years ending in 1874, of all consanguineous
marriages 92 per cent were of cousins and 8 per cent were of uncle and
niece or aunt and nephew.[22]
[Footnote 22: Ibid., p. 384.]
Dally[23] is very skeptical about the accuracy of the French figures,
but says that in Paris the records are well kept. He found that in the
years 1853-62 there were 10,765 marriages in the _8me arrondissement_
of Paris, and of these he finds:
-----------------------------------------
Marriages between cousins-german | 141
Marriages between uncle and niece | 8
Marriages between aunt and nephew | 1
Total consanguineous | 150
-----------------------------------------
[Footnote 23: "Recherches sur les Mariages Consanguins et sur les
Races Pures." in _Bulletins de la Société d'Anthropologie_, 1863, p.
527.]
This is rather higher than the average for urban districts, according
to official figures, but Dally seems to consider it as typical. He
gives examples of the carelessness and incompetency of the rural
record keepers, and insists that the percentage is really much higher
than the official figures would indicate. He estimates the
consanguineous marriages in France not including second cousins, at
from four to five per cent.
A very ingenious method of determining the approximate number of
first-cousin marriages was devised by Mr. George H. Darwin.[24]
Noticing that in marriage announcements, some were between persons of
the same surname, it occurred to him that there might be a constant
ratio between same-name marriages and first cousin marriages. Some
same-name marriages would of course be purely adventitious; so, to
eliminate this element of chance, he obtained from the Registrar
General's Report the frequency of occurrence of the various surnames
in England. The fifty commonest names embraced 18 per cent of the
population. One person in every 73 was a Smith, one in every 76 a
Jones and so on. Then the probability of a Smith-Smith marriage due to
mere chance would be 1/73^2 and of a Jones-Jones marriage 1/76^2.
The sum of fifty such fractions he found to be .0009207 or .9207 per
thousand. After the fiftieth name the fractions were so small as to
have comparatively little effect upon the total. He therefore
concluded that about one marriage in a thousand takes place, in which
the parties have the same surname and have been uninfluenced by any
relationship between them bringing them together.
[Footnote 24: "Marriages between First Cousins in England and their
Effects," in _Journal of the Statistical Society_, June, 1875. pp. 154
_et seq_.]
The next step was to count the marriages announced in the "_Pall Mall
Gazette_" for the years 1869-72 and a part of 1873. Of the 18,528
marriages there found, 232 or 1.25 per cent were between persons of
the same surname. Deducting the percentage of chance marriages at
least 1.15 per cent were probably influenced directly or indirectly by
consanguinity.
Mr. Darwin then proceeded by a purely genealogical method. He found
that out of 9,549 marriages recorded in "Burke's _Landed Gentry_," 144
or 1.5 per cent were between persons of the same surname, and exactly
half of these were first cousins. In the "_English and Irish Peerage_"
out of 1,989 marriages, 18 or .91 per cent were same-name first cousin
marriages. He then sent out about 800 circulars to members of the
upper middle class, asking for records of first cousin marriage among
the near relatives of the person addressed, and obtained the following
result:
-----------------------------------------------
Same-name first cousin marriages | 66
Different-name first cousin marriages | 182
Same-name not first cousin marriages | 29
-----------------------------------------------
These cases furnished by correspondents he calculated to be 3.41 per
cent of all marriages in the families to which circulars were sent.
From the data collected from all these sources Mr. Darwin obtains the
following proportion:
Same-name first cousin marriages 142
-------------------------------- = --- = .57
All same-name marriages 249
He is inclined to think that the ratio should be lower and perhaps .50
instead of .57. By a similar line of reasoning he obtains this
proportion:
Same-name first cousin marriages 1
------------------------------------- = ---
Different-name first cousin marriages 3
Here too, he fears that the denominator is too small, for by
theoretical calculation he obtains by one method the ratio 2/7, and
by another 1/1. He finally takes 1/4 for this factor. To express the
proportion in another form:
Same-name first cousin marriages 1
-------------------------------- = ---
All first cousin marriages 5
The completed formula then becomes:
All same-name marriages 100 1
-------------------------- = ----- X --- = .35 (nearly)
All first cousin marriages 57 5
Applying this formula to the English statistics, Mr. Darwin computes
the percentages of first cousin marriages in England with the
following results:
---------------------------------------
London | 1.5
Other urban districts | 2.
Rural districts | 2.25
Middle class and Landed Gentry | 3.5
Aristocracy | 4.5
---------------------------------------
In order to apply this formula to the American population I counted
the names in the New York Marriage License Record previous to
1784,[25] and found the number to be 20,396, representing 10,198
marriages. The fifty commonest names embraced nearly 15 per cent of
the whole (1526), or three per cent less than the number found by
Darwin.[26] Of these, one in every 53 was a Smith, one in 192 a
Lawrence, and so on. The sum of the fraction 1/53^2, 1/192^2,
etc., I found to be .000757 or .757 per thousand, showing that the
probability of a chance marriage between persons of the same name was
even less than in England, where Mr. Darwin considered it almost a
negligible quantity.
[Footnote 25: _Names of Persons for whom Marriage Licenses were issued
by the Secretary of the Province of New York_.]
[Footnote 26: _Cf. supra_, p. 21.]
Of these 10,198 marriages, 211, or 2.07 per cent were between persons
bearing the same surname. Applying Darwin's formula we would have 5.9
as the percentage of first cousin marriages in colonial New York.
This figure is evidently much too high, so in the hope of finding the
fallacy, I worked out the formula entirely from American data. To
avoid the personal equation which would tend to increase the number of
same-name first cousin marriages at the expense of the same-name not
first cousin marriages, I took only those marriages obtained from
genealogies, which would be absolutely unbiassed in this respect. Out
of 242 marriages between persons of the same name, 70 were between
first cousins, giving the proportion:
Same-name first cousin marriages 70
-------------------------------- = --- = .285
All same-name marriages 242
as compared with Darwin's .57. So that we may be fairly safe in
assuming that not more than 1/3 of all same-name marriages are first
cousin marriages. Taking data from the same sources and eliminating as
far as possible those genealogies in which only the male line is
traced, we have it:
Same-name first cousin marriages 24 1 1
------------------------------------- = -- = -------- = -------
Different-name first cousin marriages 62 (2-7/12) 2.583
This is near the ratio which Darwin obtained from his data, and which
he finally changed to 1/4. I am inclined to think that his first ratio
was nearer the truth, for since we have found that the coefficient of
attraction between cousins would be so much greater than between
non-relatives, why should we not assume that the attraction between
cousins of the same surname should exceed that between cousins of
different surnames? For among a large number of cousins a person is
likely to be thrown into closer contact, and to feel better acquainted
with those who bear the same surname with himself. But since the
theoretical ratio would be about 1/4 it would hardly be safe to put
the probable ratio higher than 1/3, or in other words four first
cousin marriages to every same-name first cousin marriage. Our
revised formula then is:
All same-name marriages 3 1
--------------------------- = --- X --- = .75
All first cousin marriages 1 4
Instead of Mr. Darwin's .35.
Taking then the 10,198 marriages, with their 2.07 per dent of
same-name marriages, and dividing by .75 we have 2.76 per cent, or 281
first cousin marriages.
In order to arrive at approximately the percentage of first cousin
marriages in a nineteenth-century American community I counted the
marriage licenses in Ashtabula County, Ohio, for seventy-five years,
(1811-1886). Out of 13,309 marriages, 112 or .84 per cent were between
persons of the same surname. Applying the same formula as before, we
find 1.12 per cent of first cousin marriages, or less than half the
percentage found in eighteenth-century New York. This difference may
easily be accounted for by the comparative newness of the Ohio
community, in which few families would be interrelated, and also to
that increasing ease of communication which enables the individual to
have a wider circle of acquaintance from which to choose a spouse.
Adopting a more direct method of determining the frequency of cousin
marriage, I estimated in each of sixteen genealogical works, the
number of marriages recorded, and found the total to be 25,200. From
these sixteen families I obtained 153 cases of first cousin marriage,
or .6 per cent. Allowing for the possible cases of cousin marriage in
which the relationship was not given, or which I may have over-looked,
the true percentage is probably not far below the 1.12 per cent
obtained by the other method.
The compiler of the, as yet, unpublished Loomis genealogy writes me
that he has the records of 7500 marriages in that family, of which 57
or .8 per cent are same-name marriages. This would indicate that 1.07
per cent were between first cousins.
In isolated communities, on islands, among the mountains, families
still remain in the same locality for generations, and people are
born, marry and die with the same environment. Their circle of
acquaintance is very limited, and cousin marriage is therefore more
frequent. If we exclude such places, and consider only the more
progressive American communities, it is entirely possible that the
proportion of first cousin marriages would fall almost if not quite to
.5 per cent. So that the estimate of Dr. Dean for Iowa may not be far
out of the way.
Even for England Mr. Darwin's figures are probably much too large.
Applying the corrected formula his table becomes:
TABLE VI.
----------------------------------------------------
|Number |Per cent of|Per cent of
1872. |marriages |same-name |first cousin
|registered.|marriages. |marriages.
----------------------------------------------------
London, | | |
Metropolitan | | |
Districts | 33,155 | .55 | .73
Urban Districts| 22,346 | .71 | .95
Rural Districts| 13,391 | .79 | 1.05
----------------------------------------------------
Total | 68,892 | .64 | .85[A]
----------------------------------------------------
[A] Cf. Mulhall, .75 per cent, _supra_, p. 18.
In regard to the frequency of marriage between kin more distant than
first cousins figures are still more difficult to obtain. The
distribution of 514 cases of consanguineous marriage from genealogies
was as follows:
TABLE VII.
---------------------------------------------------------------------
| First | 1-1/2 |Second | 2-1/2 | Third |Distant|
|cousins|cousins|cousins|cousins|cousins|cousins|Total
---------------------------------------------------------------------
Same-name | 70 | 24 | 49 | 19 | 20 | 26 | 208
Different-name| 96 | 30 | 58 | 22 | 37 | 62 | 305
---------------------------------------------------------------------
Total | 166 | 54 | 107 | 41 | 57 | 88 | 513
---------------------------------------------------------------------
Obviously this cannot be taken as typical of the actual distribution
of consanguineous marriages, since the more distant the degree, the
more difficult it is to determine the relationship. However it is very
evident that the coefficient of attraction is at its maximum between
first cousins, and probably there are actually more marriages between
first cousins than between those of any other recognized degree of
consanguinity. But the two degrees of 1-1/2 cousins and second cousins
taken together probably number more intermarriages than first cousins
alone. Allowing four children to a family, three of whom marry and
have families, the actual number of cousins a person would have on
each degree would be: First, 16; 1-1/2, 80; Second, 96; 2-1/2, 480;
Third, 576; Fourth, 3,456. The matter is usually complicated by double
relationships, but it will readily be seen that the consanguineal
attraction would hardly be perceptible beyond the degree of third
cousins.[27]
[Footnote 27: See note, _infra_, p. 29.]
Omitting, as in the discussion on page 24, those genealogies in which
only the male line is given we have the following table:
TABLE VIII.
--------------------------------------------------------------------
|First | 1-1/2 |Second | 2-1/2 | Third |Distant|
|cousins|cousins|cousins|cousins|cousins|cousins|Total
--------------------------------------------------------------------
Same-name | 24 | 5 | 10 | 4 | 2 | 5 | 50
Different-name| 62 | 15 | 33 | 12 | 23 | 26 | 171
--------------------------------------------------------------------
Total | 86 | 20 | 43 | 16 | 25 | 31 | 221
--------------------------------------------------------------------
It would naturally be supposed that with each succeeding degree of
relationship the ratio of same-name to different-name cousin marriages
would increase in geometrical proportion, viz. first cousins, 1:3;
second cousins, 1:9; third cousins, 1:27, etc., but on the other hand
there is the tendency for families of the same name to hold together
even in migration as may be proved by the strong predominance of
certain surnames in nearly every community. So that the ratio or
same-name to different-name second cousin marriage may not greatly
exceed 1:4. Beyond this degree any estimate would be pure guesswork.
However the coefficient of attraction between persons of the same
surname would undoubtedly be well marked in every degree of kinship,
and conversely there are few same-name marriages in which some
kinship, however remote, does not exist.
The proportion of mixed generation cousin marriages (1-1/2 cousins,
2-1/2 cousins, etc.) is always smaller than the even generation
marriages of either the next nearer or more remote degrees. For
example, a man is more likely to marry his first or his second cousin
than either the daughter of his first cousin, or the first cousin of
one of his parents, although such mixed generation marriages often
take place.
The conclusions, then, in regard to the frequency of consanguineous
marriage in the United States may be summarized as follows:
1. The frequency varies greatly in different communities, from perhaps
.5 per cent of first cousin marriages in the northern and western
states to 5 per cent, and probably higher, in isolated mountain or
island communities. The average of first cousin marriage in the United
States is probably not greater than one per cent.
2. The percentage of consanguineous marriages is decreasing with the
increasing ease of communication and is probably less than half as
great now as in the days of the stage coach.
3. Although the number of marriageable second cousins is usually
several times as great as that of first cousins, the number of
marriages between second cousins is probably somewhat less than the
number of marriages between first cousins, but the number of second
cousin marriages combined with the number of 1-1/2 cousin marriages
probably exceeds the number of first cousin marriages alone. So that
the percentage of marriages ordinarily considered consanguineous is
probably between two, and two and a half.
NOTE.--In an article entitled "Sur le nombre des consanguins dans un
groupe de population," in _Archives italiennes de biologie_ (vol.
xxxiii, 1900, pp. 230-241), Dr. E. Raseri shows that from one point of
view the actual number of consanguineous marriages is little, if any,
greater than the probable number. The average number of children to a
marriage he finds to be 5, the average age of the parents 33 and the
average age at marriage 25. The Italian mortality statistics show that
54 per cent of the population lives to the age of 25, of which 15 per
cent does not marry, leaving an average of 2.3 children in every
family who marry. On this basis a person would have at birth 4,357
relatives within the degree of fourth cousins; at the age of 33 he
would have 4,547; and at 66, 5,002. In 1897 out of 229,041 marriages
in Italy, 1,046 were between first cousins, giving an average of one
in 219. In 1881 the number of men between 18 and 50 and of women
between 15 and 45 was 5,941, 495 in 8,259 communes with an average
population of 3,500. In each commune there must be 360 marriageable
persons of each sex, but to marry within his class a man would only
have the choice of 180 women and vice versa. Adding the probable
number who would marry outside the commune, the choice lies within 216
of the opposite sex. Of these 25 would be cousins within the tenth
degree (fourth cousins) making the probability of a consanguineous
marriage .11, reduced by a probable error in excess to .10. The
probability of a first cousin marriage would be .82/216 or .0038,
whereas the actual ratio is 1/219 or .0045.
CHAPTER III
MASCULINITY
The predominance of male over female births is almost universal,
although varying greatly in different countries and under different
conditions. This fact has given rise to the term Masculinity, which
conveniently expresses the proportion of the sexes at birth. The
degree of masculinity is usually indicated by the average number of
male births to every 100 female births. The cause of this
preponderance of males is still a mystery, and will definitely be
known only when the causes of the determination of sex are known.
Since, however, it is well known that infant mortality is greater
among males than among females, positive masculinity is necessary to
keep up the balance of the sexes, and therefore seems to be an
essential characteristic of a vigorous and progressive race.
Within recent years the theory has prevailed among certain
sociologists that positive masculinity is stronger in the offspring of
consanguineous marriages than in the offspring of unrelated parents.
Professor William I. Thomas in his writings and lectures asserts this
as highly probable.[28] Westermarck,[29] to whom Professor Thomas
refers, quotes authorities to show that certain self-fertilized plants
tend to produce male flowers, and that the mating of horses of the
same coat color tends to produce an excess of males.[30]
[Footnote 28: _Sex and Society_, p. 12.]
[Footnote 29: _History of Human Marriage_, p. 476.]
[Footnote 30: _Goehlert, Ueber die Vererbung der Haarfarben bei den
Pferden._ Quoted by Westermarck, p. 476.]
Westermarck continues, quoting from Düsing:[31] "Among the Jews, many
of whom marry cousins, there is a remarkable excess of male births. In
country districts, where, as we have seen, comparatively more boys are
born than in towns, marriage more frequently takes place between
kinsfolk. It is for a similar reason that illegitimate unions show a
tendency to produce female births."
[Footnote 31: _Die Regulierung des Geschlechtsverhaeltnisses_, pp.
243-244.]
Westermarck comments: "The evidence for the correctness of his
deduction is, then, exceedingly scanty--if, indeed it can be called
evidence. Nevertheless, I think his main conclusion holds good.
Independently of his reasoning I had come to exactly the same result
in a purely inductive way." He then quotes a number of travelers to
the effect that marriage between members of different races produce a
phenomenal excess of female births. When we consider the extraordinary
proficiency in fiction attained by many travelers in strange lands, we
are forced to the belief that Westermarck based his own conclusion on
still more scanty evidence.
The statistics given by Dr. Düsing for Prussia[32] are as follows:
TABLE IX.
------------------------------------------------------------
| | | Other |
|Evangelical.| Catholic. | Christians.| Jews.
------------------------------------------------------------
Male births | 4,015,634 | 2,273,708 | 12,283 | 69,901
Female births| 3,775,010 | 2,136,295 | 11,548 | 64,939
Masculinity | 106.374 | 106.435 | 106.36 | 107.64
------------------------------------------------------------
[Footnote 32: _Das Geschlechtsverhaeltnis der Geburten in Preussen_,
pp. 24-25; in _Staatswissenschaftliche Studien_, vol. iii.]
and for mixed marriages:
TABLE X.
--------------------------------------------------------------
|Evangelical |Catholic and| Other | Jews and
|and Catholic.|Evangelical.| mixed. |Christians.
--------------------------------------------------------------
Male births | 157,755 | 189,733 | 4.464 | 2,958
Female births| 149,205 | 179,505 | 4.254 | 2,850
Masculinity | 105.73 | 105.70 | 104.9 | 103.8
--------------------------------------------------------------
In the face of these statistics it is impossible to deny that
endogamy within a great social class or an ethnic race may have some
tendency to produce an excess of male births, while exogamy in this
broad sense may diminish the masculinity. But the perpetuation of a
comparatively pure race by marriage within that race, and
consanguineous marriage in the narrower sense are different
propositions. It may easily be that the marriage of individuals of a
similar type regardless of consanguinity produces a greater excess of
male offspring. According to the percentage of first cousin marriages
among the Jews as given by Mulhall,[33] and allowing the average
number of children to a marriage, there would be only 3100 children of
such marriages among the Jewish births in Prussia, and in order that
these might raise the masculinity of Jewish births even from 106 to
107 the 3100 births would have to have a masculinity of 200. Among
Protestants, or especially among Catholics where the percentage of
cousin marriage is much smaller, it seems hardly reasonable that the
general masculinity would be appreciably affected. A much better case
can be made for similarity or difference of race as the cause of the
variation. The difference between Catholic and Protestant is, roughly
speaking, the difference between the brachycephalic brunette Alpine
race and the dolichocephalic blonde Baltic race. So that a mixed
marriage in Germany would almost always mean the crossing of two
distinct types.
[Footnote 33: _Dictionary of Statistics, op. cit._, p. 383.]
The investigations of M. Gache in Buenos Ayres covering the period
from 1884 to 1894 inclusive, show that cross breeding has had the
effect of _raising_ the masculinity. The births resulting from unions
of Italian, Spanish and French male immigrants with native-born
Argentine females, show a higher masculinity than the births produced
either by pure Argentine alliances or by pure alliances of any of
these nationalities of Buenos Ayres. Further, the unions of Argentine
males with females of foreign nationality provide a higher masculinity
than is common among Argentines themselves.[34] These facts do not
necessarily contradict the theory that any crossing of great racial
groups diminishes masculinity, for all of the nationalities involved
in this study are predominantly Mediterranean in blood. The theory is
borne out by the statistics of the negroes in the United States, a
large proportion of whom are of mixed blood. For taking as a basis the
number of children of negro descent born during the year ending June
1, 1900 reported by the Twelfth Census, the females predominated,
giving a negative masculinity of 99.8. Furthermore, the percentage of
consanguineous marriage is probably high in the colored population.
[Footnote 34: C.J. & J.N. Lewis, _Natality and Fecundity_, pp.
114-116.]
The following table compiled from Mulhall[35] and other sources fails
to show any correspondence between the percentage of first cousin
marriage and the masculinity:
TABLE XI.
---------------------------------------
Country. |Masculinity.| Per cent 1st
| |cousin marriage.
---------------------------------------
England | 104.5 | .75
France | 105.3 | 1.26
Italy | 107.0 | .69
Prussia | 105.8 | .67
U.S.[36] | 104.9 | 1.00
Jews[37] | 107.6 | 2.30
---------------------------------------
[Footnote 35: Op. cit., p. 92.]
[Footnote 36: Masculinity, _Twelfth Census, Vital Statistics_, Pt. 1.
Per cent of cousin marriage, estimated.]
[Footnote 37: Duesing, op. cit., p. 24.]
It is impossible to obtain the actual masculinity ratio for the United
States, for the Census gives the statistics for only one year in ten
and even then is untrustworthy on this point. In a few states birth
registration is attempted but the figures thus obtained do not
harmonize with the Census and the situation is not greatly
improved.[38] The masculinity varies considerably in different parts
of the country, and is generally higher in states where the rural
population predominates. This fact agrees with European statistics
which almost universally show a high masculinity in rural districts.
Table XII, illustrates this point:
TABLE XII.
_Masculinity in Scotland_.[39]
-------------------------------------------------------
| | | | Mainland |Insular
Period. |Principal|Large |Small | rural | rural
| towns. |towns.|towns.|districts.|districts.
-------------------------------------------------------
1855-1861| -- | -- | -- | 105.6 | 106.6
1862-1871| -- | -- | -- | 105.9 | 105.6
1872-1881| 105.0 | 105.6| 106.1| 105.3 | 108.0
1882-1891| 105.1 | 105.6| 105.5| 105.5 | 108.7
1892-1901| 104.7 | 104.6| 104.9| 105.2 | 107.1
-------------------------------------------------------
Average | 104.9 | 105.3| 105.5| 105.5 | 107.2
-------------------------------------------------------
[Footnote 38: Massachusetts _Census_, 103.1; Reg. 1891-1900, 105.6.
Vermont _Census_, 108.1; Reg. 1890-1896, 105.9. Connecticut _Census_,
103.9; Reg. 1887-1891, 107.2. Rhode Island _Census_, 103.8; Reg.
1854-1901, 104.9.]
[Footnote 39: Lewis and Lewis, op. cit., p. 128.]
This would seem to bear out the theory that masculinity is affected by
consanguineous marriage, for consanguineous marriage is more frequent
in rural districts, and especially in insular rural districts. But
unless consanguineous marriages can directly be shown to produce an
excess of male births greater than the normal, such indirect evidence
is valueless.
In the genealogical material previously considered, we have a sampling
of the American population throughout its whole history, but the data
so far collected are insufficient for more than an indication of what
might be expected in further research along the same line. In the
following table as before, the figures compiled from printed
genealogies are separated from those obtained through correspondence
and from miscellaneous sources. The "unrelated" marriages from
genealogies, are marriages of brothers and sisters of the persons who
have married first cousins, and their records were obtained from the
same sources as those in the next previous category. The "children of
first cousins" are the offspring of the first cousin marriages who
married persons not related to themselves by blood. The last category
includes distantly related marriages from correspondence and other
sources and marriages between persons of the same surname whose
relationship could not be traced.
TABLE XIII.
------------------------------------------------------------------
| | Sex of Children. |
|Number |-----------------------|Mascu-
Marriages. |Fertile.| Male.|Female.|Unknown.|linity.
------------------------------------------------------------------
1st cousin. Gene. | 125 | 318 | 314 | 40 | 101
Unrelated. Gene. | 629 | 1561 | 1559 | 64 | 100
Ch. of 1st cousins. Gene.| 170 | 402 | 375 | 48 | 107
Other cousin. Gene. | 301 | 736 | 666 | 15 | 111
1st Cousin. Cor. | 150 | 316 | 295 | 148 | 107
Ch. of 1st cousins. Cor. | 124 | 192 | 164 | 214 | 111
Miscellaneous | 88 | 210 | 205 | 50 | 102
------------------------------------------------------------------
Total | 1587 | 3735 | 3578 | 578 | 104.4
------------------------------------------------------------------
It is of course impossible to explain all the ratios in this table.
Much variation is here due to chance, and a few additional cases might
appreciably change any of the ratios. It will be noticed, however,
that the two categories whose masculinity is most similar (100 and
101), are derived from cases taken from the same families and from the
same environment, and differing only in that the first is closely
consanguineous while the second is not. The third and fourth groups,
separated from the first two by at least a generation, and probably
living in a different environment, differ greatly in masculinity from
them. In the fourth group are included 1-1/2, second, third, and a few
even more distant cousins, all more distantly related than first
cousins, and taken from the same genealogies as these; yet the
masculinity is much greater.
An analysis of the cases collected fifty years ago by Dr. Bemiss, of
course without thought of masculinity, gives the following result:[40]
TABLE XIV.
----------------------------------------------------------
| Sex of Children. |
|----------------------|
Marriage. |Number.| Male.|Female.|Masculinity.
----------------------------------------------------------
1st cousins and nearer| 709 | 1245 | 1171 | 106.3
2d and 3rd cousins | 124 | 264 | 240 | 110.0
All consanguineous | 833 | 1509 | 1411 | 106.9
Unrelated | 125 | 444 | 380 | 116.9
----------------------------------------------------------
[Footnote 40: Bemiss, _Report on Influence of Marriages of
Consanguinity_, pp. 420-423.]
In the "Marriage of Near Kin," Mr. Huth gives a list of cases of
consanguineous marriage collected by various persons from all over
Europe.[41] He is free to say that they are worse than useless for the
purpose for which they were collected, that of determining whether or
not such marriages produce degeneracy, but in so far as the sex of the
children is concerned they would not be biassed.
TABLE XV.
-----------------------------------------------------
|Sex of Children.|
|----------------|
Marriage. | Male.| Female. | Masculinity.
-----------------------------------------------------
1st cousins and nearer| 165 | 164 | 100
More distant cousins | 95 | 73 | 131
-----------------------------------------------------
[Footnote 41: Huth, _Marriage of Near Kin. Appendix._]
The unusual ratios are of course due principally to a "run of luck,"
and this table only shows that if consanguinity is a determining
factor in sex, its influence is negligible when a small number of
cases is considered. It is interesting accordingly to note that of 100
children of incestuous unions and from uncle-niece and aunt-nephew
marriages from Bemiss, Huth and other sources, the sex distribution
was 48 males and 52 females, giving a negative masculinity of 92.
While in general the evidence presented in this chapter is somewhat
conflicting, that which bears most directly upon the problem does not
substantiate the hypothesis of Westermarck. The evidence in favor of
the theory is all indirect and is open to other interpretations. It is
hardly safe to go to the other extreme and to assert that
consanguinity diminishes masculinity. The safest, and withal the most
reasonable conclusion is that consanguinity in the parents has no
appreciable effect upon the sex of the child.
CHAPTER IV
CONSANGUINITY AND REPRODUCTION
The principal object of nearly every previous discussion of the
intermarriage of kindred, has been either to prove or to disprove some
alleged injurious effect upon the offspring. The writers who have
treated the subject may be divided into three groups. First, those who
have maintained in accordance with popular opinion that consanguinity
_per se_ is a cause of degeneracy or that in some mysterious way
kinship of the parents produces certain diseases in the children. In
this group Boudin in France and Bemiss in America are typical. Second,
those who have flatly contradicted this position and have asserted
that on the whole such marriages are beneficial, and that crossing is
in itself injurious to the race. Huth is the chief exponent of this
theory, although he admits that where degenerate conditions exist in
the parents consanguinity in marriage may not be beneficial. The third
group holds that cousin marriages in themselves, especially if not
carried through too many generations, are not harmful, but that if any
hereditary tendency to malformation or disease exists in the family of
the parents, this tendency, inherited through both parents is strongly
intensified in the offspring, and that consequently an increased
percentage of the offspring of cousin marriage may be afflicted with
hereditary diseases. This group includes a number of the later writers
such as Feer and Mayet. Among the earlier discussions, those of Dally
in France and George H. Darwin in England take substantially this
position. On the whole this theory seems to be the most reasonable one
and with a few modifications it will be seen to account for all the
facts herein presented.
It is undeniable that degeneracy does in some cases follow from the
marriage of near kin, and probably with greater frequency than from
non-related marriages. But it is likewise true that many of the
world's greatest men have been the products of close inbreeding,
sometimes continued through several generations. Frederick the Great
of Prussia was the product of three successive cousin marriages
between descendants of William the Silent,[42] and among his seven
brothers and sisters at least three others ranked among the ablest men
and women of the generation. Cousin marriage has always been frequent
in the "first families of Virginia" which have produced a phenomenal
percentage of able men. In fact, few persons who have traced their
pedigrees back through a number of generations, do not find some names
duplicated, as a result of cousin marriage.
[Footnote 42: Woods, _Heredity in Royalty_, pp. 74-75. The Great
Elector, a great-grandson of William the Silent, married his 1-1/2
cousin, a granddaughter of William and also a great-granddaughter of
Admiral Coligny. Frederick I married his second cousin, daughter of
the Duchess Sophia of Brunswick, and a descendant of William.
Frederick William I married his first cousin, Dorothea, granddaughter
of Sophia, and also a descendant of William the Silent. Unfortunately
the Hohenzollern line was continued by a mediocre brother of Frederick
II, but through his sister, Queen Ulrica, the line of genius lasted
still another generation to Gustavus III of Sweden.]
The ills which have at one time or another been attributed to
consanguineous marriage include nearly all those which cannot
otherwise be satisfactorily accounted for. But with the progress of
pathology the list has greatly been reduced: for instance, cretinism
is now known to be a product of local conditions. The remaining
counts in the indictment against consanguineous marriage may roughly
be classified as: 1. The production of infertility, some forms of
physical degeneracy, and deformity. 2. The production or aggravation
of mental and nervous disorders. 3. The production of certain defects
in the organs of special sense. These three divisions will be
discussed separately.
1. INFERTILITY AND DEGENERACY
Although there has never been any considerable evidence for the first
of these charges, it has frequently been repeated. Professor
Montegazza of the University of Pavia collected data in regard to 512
cases of consanguineous marriage of which between 8 and 9 per cent
were sterile, and with this basis he asserts that sterility is the
only fact which can safely be deduced from his cases, since it cannot
be hereditary.[43] But if in the nature of things absolute sterility
is not inheritable, comparative infertility may be. And even then 8 or
9 per cent does not seem to be an excessively high proportion of
sterility, especially if late marriages be counted. Boudin bases his
assertion on this point on even less tenable grounds.[44] On the other
hand some writers assure us that cousin marriages are even more
prolific and less liable to sterility than the average.
[Footnote 43: See Darwin, "Marriages between First Cousins in England
and Their Effects," _Journal of Statistical Society_, June, 1875, p.
178.]
[Footnote 44: Boudin, "Croisement des familles, de races et des
espèces." In _Memoires de la Société d' Anthropologie_, vol. i, p.
518.]
The most important statistical investigation was made by G.H.
Darwin.[45] From his genealogical data he compiled the following
table:
TABLE XVI.
------------------------------------------------------------------------
| | Average | |Ave. no.
| | number | Per cent |sons to
|Number of | sons to | sterile |fertile
|marriages.| marriage. | marriages. |marriage.
------------------------------------------------------------------------
Not consanguineous | 217 | 1.91 | 15.9 | 2.26
Parents 1st cousins[A] |97 to 105 |2.07 to 1.92|14.7 to 20.9| 2.43
One parent offspring of | | | |
1st cousin marriages. | 93 | 1.93 | 17.2 | 2.34
------------------------------------------------------------------------
[A] Eight cases of doubtful fertility.
[Footnote 45: Op. cit., p. 181.]
It will readily be seen that the conclusion is negative, since the
variation is slight, but the higher fertility of the cousin marriages
is interesting.
On the other hand de Lapouge quotes a case of a community founded two
centuries ago by four families and populated almost entirely by their
descendants, in which from 1862 to 1886 there were 273 marriages of
which 63 were consanguineous and 26 were between first cousins. Among
the non-consanguineous 3 per cent were uniparous, as against 7.95 per
cent among the consanguineous. 7.5 per cent of the non-consanguineous
were sterile as against 16 per cent of the consanguineous.[46] The
importance of these percentages is impaired by the fact that they
involve only five uniparous families and ten sterile ones, and that of
these latter only five were sprung from first cousins.
[Footnote 46: De Lapouge, _Les Selections Societies_, p. 196.]
It is almost impossible to get any accurate statistics of sterility
from genealogies, for when no children are given in the record, there
is always a strong possibility that there were children of whom the
genealogist has no record. However, of 16 first-cousin marriages of
which the record expressly stated "no issue," or where it was
practically certain that no issue was possible, the average age of the
brides was 34.3 years and that of the grooms was 39 years, showing
that consanguinity could not have been the only cause of their
sterility.
In regard to relative fertility the figures are reliable, but they
fail to indicate any effect of consanguinity upon fertility, as will
be noted in Table XVII.
TABLE XVII.
-------------------------------------------------------------
|No. of | | Ave. to
|fertile | No. of | fertile
Parentage. |marriages.|children.|marriage.
-------------------------------------------------------------
First cousin. Gene. | 125 | 672 | 5.4
First cousin. Cor. | 150 | 759 | 5.1
Double cousins and uncle-niece| 9 | 39 | 4.3
Other consanguineous | 333 | 1605 | 4.8
Non-related | 676 | 3417 | 5.1
Ch. of 1st cousins | 294 | 1395 | 4.7
All consanguineous | 617 | 3075 | 5.0
All non-related | 970 | 4812 | 5.0
-------------------------------------------------------------
The report of Dr. Bemiss, and the report of the Ohio commission[47]
which he quotes, give the following figures:[48]
TABLE XVIII.
-------------------------------------------------------
| No. of | | Ave. to
| fertile | No. of | fertile
Parentage. |marriages.|children.|marriages.
-------------------------------------------------------
1st cousins or nearer[A]| 660 | 3363 | 5.0
More distantly related | 119 | 572 | 4.8
Non-consanguineous | 125 | 837 | 6.7
Ohio consanguineous | 155 | 1021 | 6.6
Ohio non-consanguineous | 200 | 1375 | 6.9
-------------------------------------------------------
[A] Includes double-cousins and uncle-niece marriages.
[Footnote 47: Appointed to ascertain the number of the deaf and dumb,
blind, idiotic and insane within the State.]
[Footnote 48: See Bemiss, in _Trans. of Am. Med. Asso._, vol. xi,
1858, pp. 420-425.]
The comparatively low averages of the consanguineous marriages from
Bemiss may easily be accounted for by the fact that the cases were
highly selected so that nearly one-third of the children were in some
way defective, and the parents in many cases were far below the
average in vitality. The "more distantly related" are in a still
lesser degree representative of the class, since out of a greater
possibility of choice a smaller number were chosen. The
"non-consanguineous" were supposed to be near the average in vitality
and fertility.
In Norway, according to Uchermann, the consanguineous and the
non-consanguineous marriages are equally fertile, averaging 6.1
children per marriage;[49] and in a Black Forest village Tenckhoff
found an average of 4.6 children to each consanguineous marriage as
against 3.5 to each non-consanguineous marriage.[50] In regard to the
youthful death-rate among the offspring of consanguineous marriages,
comparison with non-related marriages is more feasible. I have counted
in each case all those children who are known to have died under the
age of twenty. This age was taken for the sake of convenience, and to
include all children indefinitely specified as having "died young."
The results are given in Table XIX:
TABLE XIX.
-------------------------------------------------
Parentage. | No. of |No. dying |
(Genealogies.) |Children.|under 20. |Per cent.
-------------------------------------------------
First cousins | 672 | 113 | 16.7
Other cousins | 1417 | 211 | 14.9
Ch. of 1st cousins| 825 | 103 | 12.5
Non-consanguineous| 3184 | 370 | 11.6
-------------------------------------------------
(Correspondence.)
-------------------------------------------------
First cousins | 759 | 88 | 11.6
Other marriages | 829 | 71 | 8.6
-------------------------------------------------
[Footnote 49: Feer, _Der Einfluss der Blutsverwandschaft der Eltern
auf die Kinder,_ p. 12, _note_.]
[Footnote 50: Ibid.]
If the figures in Table XIX are to be accepted at their face value,
and there seems to be no good reason for not doing so in the
genealogical cases at least, the youthful death-rate among the
offspring of consanguineous marriages far exceeds the average. The
average in the correspondence cases is undoubtedly too low, as many
correspondents failed to report the deaths. From the fact that a
comparatively large percentage of these were reported as defective, we
should expect a higher death-rate than among the unbiased genealogical
cases.
Dr. Bemiss found a very high death-rate among the children of
consanguineous marriage, due partly to the fact that his cases were
reported by physicians. He reports that of the offspring of marriages
between first cousins and nearer relatives, 23 per cent "died young;"
of the offspring of more remote consanguineous marriages, 16 per cent;
and of non-related marriages 16 per cent. There is, therefore, a
strong indication of lowered vitality as a result of consanguineous
marriage.
A determination of even the approximate percentage of degenerate
offspring resulting from marriages of consanguinity by direct inquiry
is exceedingly difficult. The average human mind is so constituted as
to exaggerate unconsciously the unusual in its experience. Herein lies
the fallacy in the work of Dr. Bemiss. His material was "furnished
exclusively by reputable _physicians_ in various states," and of the
3942 children of consanguineous marriages in the cases thus furnished
him, 1134 or 28.8 per cent were in some way "defective." Of these, 145
were deaf and dumb, 85 blind, 308 idiotic, 38 insane, 60 epileptic,
300 scrofulous and 98 deformed. It is evident that a physician in
reporting such data to a physician would naturally give cases in which
something pathological existed. Even if there were no conscious bias,
such cases would be the ones with which a physician would be most
likely to come in contact. Dr. Bemiss himself recognized the
possibility of this bias. To quote him:
It is, natural for contributors to overlook many of the more
fortunate results of family intermarriage, and furnish those
followed by defective offspring and sterility. The mere
existence of either of these conditions would prompt inquiry,
while the favorable cases might pass unnoticed. Contributors
have been particularly requested to furnish without prejudice
or selection all instances of the marriage of consanguinity
within their various circles of observation, whatever their
results.[51]
[Footnote 51: Bemiss. see _Trans. of Am. Med. Asso._, vol. xi, 1858,
p. 323.]
Yet he does not seem to believe that this bias seriously affects his
conclusions.
In order as far as possible to avoid this bias, I sent my own
circulars to genealogists and others who would naturally be more
interested in the relationships than in pathological conditions. I
asked, however, that all such results be noted. Among 722 children of
first cousins I found 95 or 13 per cent who were defective in the
sense in which Bemiss used the term. This is much nearer the actual
percentage, but I have reason to believe, as will be seen hereafter,
that even this percentage is far too high. A good illustration of the
unconscious bias, which I tried to avoid is afforded by the reports on
the cause of death among children of first cousins. Only 58 replies
were given to this question, and of the 58 deaths 14 or one-fourth
were either accidental or otherwise violent, while only one person was
reported to have succumbed to pneumonia.
Many efforts have been made to investigate the occurrence of
degeneracy in the offspring of consanguineous marriages, by studying
communities in which such unions have been frequent, but the results
are untrustworthy. Huth[52] quotes a number of instances where
communities have lived for generations without crosses and with no
apparent degeneracy, while other writers tell of high percentages of
degeneracy. Smith's Island, Maryland, as has been said, seems
absolutely free from serious congenital abnormalities, in spite of the
great frequency of consanguineous marriages.
[Footnote 52: _Marriage of Near Kin_, chap. iv.]
The causes of degeneracy are so varied, complicated, and obscure that
even if consanguinity is a cause, there can be but few cases in which
it is not complicated by other factors. But for the same reason that
it is so difficult to prove any connection between consanguinity and
degeneracy, it is equally difficult to disprove such a connection. It
is very probable that from the mere operation of the law of heredity,
there must be a comparatively large percentage of degenerates among
the offspring of related parents, for defects which tend to be bred
out by crossing are accentuated by inbreeding. This may be the reason
for the disagreement among investigators of isolated communities. If
an island, for instance, were settled by a small group of families in
even one of which some hereditary defect was common, in the course of
a few generations that defect would be found in a relatively large
part of the population. While if the same island were settled by
perfectly sound families, there would only be a remote chance of any
particular defect appearing. Thus both classes of investigators may be
perfectly conscientious, and yet arrive at diametrically opposite
results. This theory is at least not to be contradicted by any facts
which have come to light in the present investigation.
Some interesting points are brought up in Dugdale's well-known study
of the "Jukes."[53] This family, of about 540 persons living in
northern New York, is descended from five sisters of unknown
parentage, who were born between 1740 and 1770. The name "Juke" is
fictitious, and is applied to all descendants of these five women,
little attempt being made to trace the male lines on account of the
excessive prevalence of illegitimacy.
[Footnote 53: R.L. Dugdale, _The Jukes_]
In this family consanguineous marriages have been very frequent,
perhaps partly because the Jukes came to be looked upon as pariahs and
could not associate on equal terms with other members of the
community. These marriages seem to have been fully as productive as
the average of the family, and the offspring of as high a grade of
intelligence. However, some individual cases are worthy of special
mention as illustrative of intensification of hereditary tendencies.
(1) An illegitimate son of Ada Juke married a daughter of Bell Juke.
He was a laborer, honest and industrious. She was reputable and
healthy, and her father had a good reputation, but her mother had
given birth to four illegitimate children before marriage, three of
whom were mulattoes. Thus in this marriage of first cousins, three out
of the four parents were of a low moral grade. As a result of this
marriage three sons and three daughters were born. Two sons were
licentious, intemperate and dishonest, two daughters were prostitutes,
and the third became such after her husband was sent to prison. Only
one son turned out fairly well. This son married a second cousin, a
granddaughter of Delia Juke, and four out of his seven children were
above the average of the family. His two elder brothers, however,
married prostitutes, and became ancestors of criminals, prostitutes
and syphilitics.[54]
[Footnote 54: Ibid., Chart I.]
(2) A legitimate son of Ada Juke, whose father was a thief and a
pauper, married a daughter of Clara Juke, whose antecedents were
fairly good. The husband had contracted syphilis before marriage and
entail it upon every one of his eight children. Five daughters became
prostitutes and one was idiotic. The only daughter who bore a good
reputation married a grandson of both Clara and Bell Juke. This was a
remarkable case of selection. Both husband and wife were grandchildren
of Clara, and so first cousins, and both were the offspring of first
cousins, all within the Juke blood. But, on the other hand, both were
the descendants of Clara, the best of the Juke sisters, and both were
the best of the progeny of their respective parents. The only serious
taint was the secondary syphilis which the wife had inherited from her
father. Six children were born, two males and four females. The eldest
son was at 31 "laborer, industrious, temperate;" the eldest daughter
"good repute, temperate, read and write;" second daughter, "harlot;"
third daughter "good repute, temperate;" and the two youngest are
given simply as "unmarried." This family seems to have had as high an
average mentally and morally as any family in the whole tribe, only
one in six being distinctly immoral. In the next generation, the
eldest son had two children, the eldest daughter four, and the third
daughter, who married a first cousin, had one child. It would be of
great interest to know more of this last marriage, the third
generation of consanguinity in marriage, and the fourth first-cousin
marriage in three generations, but at the time the book was written
the parties were still in their early twenties.[55]
[Footnote 55: Dugdale, op. cit., Chart II.]
Mr. Dugdale makes the following "tentative inductions." 1. Boys
preponderate in the illegitimate lines. 2. Girls preponderate in the
intermarried branches. 3. Lines of intermarriage between Jukes show a
minimum of crime. 4. Pauperism preponderates in the consanguineous
lines. 5. In the main, crime begins in progeny where Juke blood
crosses X blood. (Anyone not descended from a Juke, is of "X blood").
6. The illegitimate lines have chiefly married into X.[56] The third
and fourth inductions might indicate that a lowered vitality of the
consanguineous lines changed a tendency toward crime into the less
strenuous channel of pauperism, but I cannot find in Mr. Dugdale's
charts any sufficient basis for the induction. It is true that the
most distinctively pauper line is consanguineous, but it is less
closely inbred than the "semi-successful" branch. As to the fifth
induction, a close examination of the data shows clearly that in
nearly every case where an X marriage occurred, it was with a person
of a distinctly immoral or criminal type. Cousin marriage has also
been frequent in the middle western counterpart of the Jukes, the
"Tribe of Ishmael."[57]
[Footnote 56: Dugdale, op. cit., p. 16.]
[Footnote 57: McCulloch, _Tribe of Ishmael_.]
A more recent study of hereditary degeneracy is that of the "Zero
Family" in Switzerland.[58] Here the first degenerate was the product
of two successive consanguineous marriages, both with a branch tainted
_with insanity_. In spite of his bad ancestry he lived to the age of
106 years. He married an Italian woman of questionable antecedents,
and was the father of a large family. Three hundred and ten of his
descendants are mentioned, of whom many are still young. Of these 310,
74 died in early childhood, 55 are or were vagabonds, 58 were
weak-minded or idiotic and 23 were criminals. Fifty-two were of
illegitimate birth. Although some are counted in more than one
category, the record is appalling. In this family however, the
marriages were nearly all with foreign women, and the effect of
consanguinity was only the intensification of the neurosis in the
first two generations.
[Footnote 58: Joerger, "Die Familie Zero." Reviewed by Gertrude C.
Davenport, in the _American Journal of Sociology_, Nov., 1907.]
Dr. Bemiss found that 300 or 7.7 per cent of the offspring of
consanguineous marriages were subject to scrofula.[59] This is a
disease which is almost universally recognized as hereditary, and
which we should therefore expect to find intensified by double
heredity. But 7.7 per cent is obviously too high; otherwise most of
the scrofulous must be the offspring of marriages of kindred. About
one per cent of the children of my own correspondence cases were
reported as scrofulous. And while the United States Census reports but
3.9 per cent of the blind as the offspring of consanguineous
marriages, the percentage of the blind from scrofula is 6.1.[60] The
blind from scrofula of consanguineous parentage were 2.8 per cent of
all the blind of consanguineous parentage, while all the blind from
scrofula were 1.8 per cent of all the blind. Consanguinity, then,
seems appreciably to intensify scrofula, but there is no indication
that scrofula is ever caused by parental consanguinity.
[Footnote 59: Bemiss, see _Trans. of Am. Med. Asso._, vol. xi, 1858,
p. 420.]
[Footnote 60: _The Blind and the Deaf._ Special Report of 12th Census,
1906.]
CHAPTER V
CONSANGUINITY AND MENTAL DEFECT
Idiocy, perhaps more than any other disease or defect, has long been
connected in the popular mind with the marriage of cousins. This fact
is not surprising when we consider that until very recent times idiots
were looked upon with a kind of superstitious awe, and the affliction
was supposed to be a curse of God. For this reason, when idiocy did
follow consanguineous marriage as it sometimes would, it was believed
to be the fit punishment of some violation of divine law. Insanity
also frequently has been attributed to consanguineous marriage, but
not so frequently as idiocy, since its occurrence later in life is not
so obviously connected with pre-natal conditions.
The terminology of mental and nervous disorders has been so loosely
applied that some definition may be necessary. By the term "idiocy,"
is meant a condition of undeveloped mentality. Idiocy exists in
various degrees, from the complete absence of intellectual faculties
to a condition of mere irresponsibility in which the subject is
capable of self-help, and sometimes of self-support under the careful
guidance of other. Under the generic term "idiot" may be included the
"complete idiot," the imbecile, the "feeble-minded" and the
"simpleton," all of whom suffer in a greater or less degree from
arrested mental development.
Insanity, on the other hand, is a disease which destroys or clouds an
intellect which has once been developed. It is true that certain
conditions of idiocy and imbecility do resemble that phase of insanity
known as dementia--a reversion to the original mental state of
childhood--in reality a form of second childhood. But the states are
not identical, although one may lapse into the other. One is defect,
the other disease; the imbecile in the former being the counterpart of
the dement in the latter, just as the moral imbecile is the analogue
of the paranoiac.[61]
[Footnote 61: Barr, _Mental Defectives_, p. 18.]
Of the strong inheritability of idiocy there can be no doubt. Dr.
Martin W. Barr of the Pennsylvania Training School for Feeble Minded
Children has published an etiological table embodying the results of a
careful examination of 4050 cases of mental defect. Of these, 2651 or
65.45 per cent resulted from causes acting before birth, including
1030 or 25.43 per cent with a family history of idiocy and imbecility,
and 529 more (13.06 per cent) with a family history of insanity,
epilepsy and minor neuroses. Dr. Barr gives many instances
illustrating the heredity of imbecility, especially where both parents
were imbeciles, and had imbecile relatives. One case in particular
forcibly illustrates the disastrous results of the marriage of such
unfortunates. It is taken from the reports of the Connecticut Lunacy
Commission:
In one instance, where a pauper female idiot lived in one town,
the town authorities hired an idiot belonging to another town,
and not then a pauper, to marry her, and the result has been
that the town to which the male idiot belongs has for many
years had to support the pair and the three idiot children.[62]
[Footnote 62: Ibid., p. 99.]
Neuroses may remain latent for a generation and reappear in the
grandchildren of the person affected, or the latent tendency may never
reappear unless some disturbing factor such as scarletina, meningitis
or other acute disease attacks the weak spot. This possibility
suggests that the influence of heredity may be vastly greater than the
etiological tables would indicate. The apparent causes may be only
agents which assist in developing the evil really engendered by an
inheritance of imbecility.
It is not at all certain that there is any well marked boundary line
between genius and some forms of imbecility. Many quite irresponsible
idiots have marvelous verbal memories, and can repeat parrot-like,
page after page of books of which they have no comprehension. Dr. Barr
tells of cases of prodigies, musical, mathematical and mechanical, who
except in their specialty were almost totally deficient mentally.[63]
Many of the world's most brilliant musicians, mathematicians and even
military leaders have been men of one-sided mental development, whose
ability in other lines was so slight that they were little better than
imbeciles, and it is not at all surprising that their children are
sometimes truly idiotic.
[Footnote 63: Barr, op. cit., p. 301 _et seq._]
The best writers of the present day no longer recognize consanguinity
as a cause _per se_, of idiocy. The heredity of neuroses, however, is
so strongly established that few would dispute the proposition that
where the morbidity is inherited through both parents it appears more
frequently and in a more marked degree than where one parent is
entirely free from taint. This is what occurs when a consanguineous
marriage takes place between descendants of a neurotic family. The
percentage of idiotic children would then be somewhat higher from
consanguineous marriages than from the average marriage purely through
the action of the laws of heredity.
Dr. Barr finds 49 out of 4050 cases of idiocy or 1.21 per cent, in
which there was a family history of consanguinity. This is little
higher than the average frequency of first cousin marriage, and an
analysis of 41 of these cases does not show one case that can be
attributed to consanguinity alone. To quote: "Two were the result of
incestuous connection--one of brother and sister, the other of father
and daughter, and in the others there was an undoubted history, of
grave neuroses."[64] "Beach and Shuttleworth find in the consideration
of their 100 cases (out of 2,380 idiots), giving 4.2 per cent (of
consanguineous parentage) that the bad effects are due rather to the
intensification of bad heredity common to both parents."[65]
[Footnote 64: Barr, op. cit., p. 94.]
[Footnote 65: Ibid., p. 109.]
Dr. Arthur Mitchell examined all idiots in nine counties of Scotland
and found that 42 out of 519 or 8.1 per cent of whom the parentage was
known, were children of first cousins.[66] Dr. Down found 46 out of
852 or 5.4 per cent to be children of first cousins.[67] Dr. Grabham
of the Earlswood Idiot Asylum in Surrey, England, stated that 53 out
of 1388 patients were the offspring of first cousins. The facts, he
adds, were obtained from the parents and are "therefore tolerably
trustworthy."[68] Other investigations give percentages as follows:
Kerlin, 7; Rogers, 3.6; Brown, 3.5 and C.T. Wilbur, 0.3.[69]
[Footnote 66: Darwin, see _Jour. Stat. Soc._, p. 173.]
[Footnote 67: Huth, _Marriage of Near Kin_, pp. 210-211.]
[Footnote 68: Darwin, op. cit., p. 166.]
[Footnote 69: Barr, op. cit., p. 109.]
The earlier American writers, Drs. Howe and Bemiss, believed that
consanguinity was a cause of idiocy. Dr. Howe inquired into the
parentage of 359 idiots and found that in 17 families the parents were
nearly related; in one of these cases there were 5 idiotic children;
in 5 families there were 4 idiots each; in 3 families 3 each; in 2
families 2 each; and in 6 families i each. In all 17 families there
were 95 children of whom 44 were idiots, 12 were scrofulous and puny,
1 was deaf, 1 dwarf--58 in low health or defective, and only 37 fairly
healthy. These of course are selected cases and do not indicate at
all, as Dr. Howe supposed, that consanguinity was the cause of the
disasters. He adds that in each case one or both of the parents were
either intemperate or scrofulous, and that there were also other
predisposing causes.[70] Dr. Bemiss found that 7.8 per cent of his
3942 children of consanguineous marriages were idiots, while but 0.7
per cent of the children of non-consanguineous parentage were
idiotic.[71] A more detailed examination reveals the fact that in a
large number of these, one or both of the parents were mentally
defective. For example, in a marriage of double cousins the wife was
"feeble minded" and the six children were of inferior mentality. In a
case of first-cousin marriage the wife became insane and two of the
children were idiotic. In a case of the marriage of cousins,
themselves the offspring of cousins the husband was a hypochondriac,
and seven children idiotic. In another marriage of the same class both
parents were feeble-minded and the children idiotic. These are simply
taken at random, and many others might be given. When we find also
that in a majority of cases no report is given of the ancestry, it is
very obvious that consanguinity alone could not have been the cause of
any large proportion of the 308 cases of idiocy in the Bemiss report.
[Footnote 70: Barr, op. cit., p. iii.]
[Footnote 71: Bemiss, op. cit., p. 420.]
My own investigations show that out of 600 children of first cousin
marriage (from correspondence) 26 or 4.3 per cent are mentally
defective--10 are reported as "idiots," 13 as "weak-minded" and 3 as
"imbeciles." In at least five of these cases there is evidence of bad
heredity, in two others the father was intemperate and in two more
causes acting after birth are mentioned.
The statistics of the insane and idiotic in Prussia presented by Mayet
clearly indicate the large part which heredity plays in the production
of mental disorders. Tables XX and XXI set forth the most important
results of his work. Mayet considers a case hereditary if any near
relative of the subject suffered from mental or nervous disorder, or
was intemperate, suicidal, criminal or eccentric.[72]
[Footnote 72: Mayet, _Verwandtenehe and Statistik_, quoted by Feer,
_Der Einfluss der Blutsverwandschaft der Eltern auf die Kinder_, p.
13.]
TABLE XX.
--------------------------------------------------
| No. of |Percentage
| Cases. |hereditary.
--------------------------------------------------
1. Simple Insanity |102,097 | 31.7 = 100
Consanguineous parentage | 664 | 69.0 = 218
Parents cousins | 595 | 68.1 = 215
Parents uncle and niece | 66 | 77.3 = 244
--------------------------------------------------
2. Paralytic Insanity | 22,936 | 17.6 = 100
Consanguineous parentage | 95 | 45.3 = 257
Parents cousins | 87 | 44.8 = 255
Parents uncle and niece | 8 | 75.0 = 426
--------------------------------------------------
3. Epileptic Insanity | 14,067 | 25.6 = 100
Consanguineous parentage | 79 | 53.2 = 208
Parents cousins | 70 | 50.0 = 195
Parents uncle and niece | 9 | 66.7 = 261
--------------------------------------------------
4. Imbecility and Idiocy | 16,416 | 28.7 = 100
Consanguineous parentage | 237 | 43.0 = 150
Parents cousins | 211 | 43.1 = 150
Parents uncle and niece | 26 | 38.5 = 134
--------------------------------------------------
Table XXI gives the proportion of the mentally defective who are the
offspring of consanguineous marriages. The term "cousin" in both
these tables probably means first cousins. It will be remembered that
Prussian statistics of consanguineous marriages are very imperfect,
but that at least 6.5 in every thousand are consanguineous (first
cousins or nearer).
TABLE XXI.[73]
_Parentage of Mental Defectives in Prussia._
-----------------------------------------------------
| Consan- | |Uncle and
|guineous.|Cousins.| Niece.
-----------------------------------------------------
1. Insanity (simple) | 6.5[A] | 5.8[A]| .64[A]
Hereditary | 14.2 | 12.5 | 1.6
Not hereditary | 3.0 | 2.7 | .22
-----------------------------------------------------
2. Paralytic Insanity | 4.1 | 3.8 | .35
Hereditary | 11.1 | 9.6 | 1.48
Not hereditary | 2.9 | 2.5 | .11
-----------------------------------------------------
3. Epileptic Insanity | 5.6 | 4.9 | .64
Hereditary | 11.7 | 9.9 | 1.57
Not hereditary | 3.5 | 3.2 | .29
-----------------------------------------------------
4. Idiocy and Imbecility| 14.4 | 12.8 | 1.58
Hereditary | 21.6 | 19.3 | 2.12
Not hereditary | 11.5 | 10.2 | 1.37
-----------------------------------------------------
[A] Per thousand.
[Footnote 73: Feer, op. cit., pp. 13-14.]
From these tables we may infer that consanguinity influences idiocy
far more than it does insanity, but it is not entirely clear why the
number of hereditary cases should be relatively smaller among the
idiotic. Since insanity is more likely to have some more definitely
assignable cause than idiocy, we should expect the percentage due to
heredity to be lower and consequently the influence of consanguinity
less.
It is generally admitted that a tendency toward insanity is
inheritable, and it seems probable that this tendency as well as other
neuroses may be intensified through double heredity. A case in point
can be found in the Shattuck genealogy.[74] For four generations in
the S. family there is no indication of neurosis. The average number
of children to a family had been eight, few children died young and
all were prosperous farmers. But in 1719 J.S. married E.C. and their
son Z.S. is thus described: "He was sometimes subject to depression of
spirits; and some peculiar traits of character in a few branches of
his family seem to have originated with him." He married A.C., a niece
of his mother. They both lived to be over 80 and had ten children, of
whom three were insane; only six married, and of these only two are
known to have left surviving children. One of these a daughter, S.S.,
married E.S., a nephew of her father, and himself the offspring of a
second cousin marriage within the S. blood. E.S. and S.S. had five
children, all of whom married, and there is no further mention of
insanity. We may suppose, then, that the C. stock was neurotic, and
that a consanguineous marriage within that stock, although of the S.
surname, intensified the tendency into insanity, but with a further
infusion of the normal S. blood the morbidity was eliminated. It is
very evident that the heredity and not the consanguinity was the cause
of these three cases of insanity.
[Footnote 74: _Shattuck Memorials_, p. 118.]
CHAPTER VI
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.
-----------------------------------------------------------------
| |Having |Having | |
| |Blind |blind | |
| |relatives|relatives|Having |
Consanguinity of | |Class |Class |no blind | Not
Parents. |Totals|(a).[A] |(b).[A] |relatives|Stated.
-----------------------------------------------------------------
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
| | | | |
Parents cousins. | | | | |
--The blind | 2,527| 844 | 149 | 1,456 | 78
-----------------------------------------------------------------
Parents cousins. | | | | |
--Totally blind | 1,291| 435 | 78 | 739 | 39
Parents cousins. | | | | |
--Partially blind | 1,236| 409 | 71 | 717 | 39
| | | | |
Parents not cousins.| | | | |
--The blind |53,980| 7,395 | 2,095 | 43,368 | 1,122
-----------------------------------------------------------------
Parents not cousins.| | | | |
--Totally blind |29,892| 3,720 | 1,090 | 24,541 | 541
Parents not cousins.| | | | |
--Partially blind |24,088| 3,675 | 1,005 | 18,827 | 581
| | | | |
Consanguinity not | | | | |
stated.--The blind | 8,256| 390 | 94 | 1,935 | 5,837
-----------------------------------------------------------------
Consanguinity not | | | | |
stated.--Totally | | | | |
blind | 4,462| 223 | 47 | 1,069 | 3,123
Consanguinity not | | | | |
stated.--Partially | | | | |
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
Cause of Blindness. |Total.|Cousins|cousins|stated|Cousins|cousins|stated
-------------------------------------------------------------------------------
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
| |-----------------------------------------------
| | | | | Parents cousins
| | | | |----------------------
| | | |Average | | |Average
| | |Number |number | | |number
Censal | Total | |per | to a | |Per | to a
year. |population|Number|million|family[A]|Number|cent.|family[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
|-----------------------------------------------------------
| |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- | | | | | | | | |
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
|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
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
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 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
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 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
Class 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 XXXII.
-------------------------------------------------------------------------
| |Consanguinity |
| |of Parents. | Per cent.
| |-------------------------------------
| | |Not | | |Not
Class 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 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
Marriages |mar- | |Per | |Number|Cent
of the Deaf. |riages|Number|Cent|Number|Deaf |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]
[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.
CHAPTER VII
SUMMARY AND CONCLUSION
Having thus considered the more important problems which have been
connected with the marriage of near kin, we have only to discuss the
bearing of the conclusions thus formed upon the social aggregate, and
the effect which consanguineous marriages have upon the evolution and
improvement of the human species.
It has been shown that the frequency with which consanguineous
marriages occur varies greatly with the physical and social
environments; that such marriages are more frequent in isolated and in
rural communities than in cities; and that with the increasing range
of individual activity and acquaintance the relative frequency of
consanguineous marriage is decreasing.
Consanguinity in the parents has no perceptible influence upon the
number of children or upon their masculinity, and has little, if any,
direct effect upon the physical or mental condition of the offspring.
The most important physiological effect of consanguineous marriage is
to intensify any or all inheritable family characteristics or
peculiarities by double inheritance. The degree of intensification
probably varies with the nature of the characteristic; degenerate
conditions of the mind, and of the delicate organs of special sense
being the most strongly intensified.
It is probable also that in the absence of degenerative tendencies
the higher qualities of mind and body are similarly intensified by
marriage between highly endowed members of the same family. Dr.
Reibmayr believes that inbreeding is necessary to the higher evolution
of the race: "A settled abode, natural protection from race mixture
and the development of a closely inbred social class are the basic
conditions of every culture period." But inbreeding must not be
carried too far: "In the course of generations the ruling class begins
to degenerate mentally and physically, until not only is the class
destroyed, but for lack of capable leadership the people (Volk) itself
is subjugated and a crossing of blood again takes place."[95]
[Footnote 95: Trans. from _Insucht und Vermischung beim Menschen_, p.
46.]
In the breeding of animals the closest inbreeding is frequently
resorted to in order to improve the stock, and many examples can be
given of the closest possible inbreeding for generations without
apparent detriment, but it is universally admitted that the animals
selected for such inbreeding must be sound constitutionally, and free
from disease. After a certain number of generations however,
degeneration apparently sets in. The number of generations through
which inbreeding may be carried varies with the species, and the
purpose for which the animals are bred. Where they are bred primarily
for their flesh, as for beef, mutton or pork, it can be pursued
farther and closer than where they are bred for achievement in which a
special strength is required--for instance in the breeding of race
horses. This would indicate that the more delicate brain and nervous
system is sooner affected than the lower bodily functions.
In man, however, freedom from hereditary taint cannot so easily be
secured. Individuals cannot be selected scientifically for breeding
purposes. Furthermore, the human body is more delicately constructed
than that of the lower animals, and the nervous system is more highly
developed and specialized, so that it is reasonable to suppose that in
man degeneration would set in earlier in the process of inbreeding,
and that it would be impossible to breed as closely as with the lower
animals. Instances are well known, however, where incestuous unions
have been productive of healthy offspring, and successive generations
of offspring of incestuous connection are not unknown; but, although
statistics are lacking, it seems to be very often true that children
of such unions are degenerate. It may be that the reason for this is
that with the laws and social sentiments now prevailing in all
civilized communities, only degenerates ever contract incestuous
alliances. Desirable as it may be from a social point of view that
this strong sentiment against incest should continue, it is not yet
_proven_ that even the closest blood relationship between the parents
is directly injurious to the offspring. The "instinctive horror of
incest" is a myth, for although a horror of incest does very properly
exist in civilized, and in some tribal societies, it is purely a
matter of custom and education, and not at all a universal law.
Double heredity may account for all the observed ill effects of
consanguineous marriage, including the high youthful death-rate, the
higher percentage of idiocy, deafness and blindness, and probably also
the scrofulous and other degenerate tendencies; nevertheless, there
may be in some instances a lowering of vitality which this hypothesis
does not fully explain.
The tendency of inbreeding in animals, it is well known, is to fix the
type, the tendency of crossing, to variation. Inbreeding then, tends
to become simple repetition with no natural variations in any
direction, a stagnation which in itself would indicate a comparatively
low vitality. Variation and consequent selection is necessary to
progress. "Sex," according to Ward[96] "is a device for keeping up a
difference of potential," and its object is not primarily
reproduction, but variation.[97]
[Footnote 96: _Pure Sociology_, p. 232.]
[Footnote 97: Pearson (_Grammar of Science_, p. 373) points out that
variation does occur in asexual reproduction. But that sex is at least
a powerful stimulus to variation can hardly be questioned.]
It is organic differentiation, higher life, progress,
evolution.... But difference of potential is a social as well
as a physiological and physical principle, and perhaps we shall
find the easiest transition from the physiological to the
social in viewing the deteriorating effects of close inbreeding
from the standpoint of the environment instead of from that of
the organism. A long-continued uniform environment is more
deteriorating than similarity of blood. Persons who remain for
their whole lives, and their descendants after them, in the
same spot, surrounded by precisely the same conditions, and
intermarry with others doing the same, and who continue this
for a series of generations, deteriorate mentally at least, and
probably also physically, although there may not be any mixing
of blood. Their whole lives, physical, mental, and moral,
become fixed and monotonous, and the partners chosen for
continuing the race have nothing new to add to each other's
stock. There is no variation of the social monotony, and the
result is socially the same as close consanguineal
interbreeding. On the other hand, a case in which a man should,
without knowing it, marry his own sister, after they had been
long separated and living under widely different skies, would
probably entail no special deterioration, and their different
conditions of life would have produced practically the same
effect as if they were not related.[98]
[Footnote 98: Ward, op. cit., pp. 234-235.]
Professor Ward's idea of "difference of potential," or contrast, as
essential to the highest vigor of the race as well as to that of the
individual offspring, offers an alternative explanation of the
observed results of consanguineous marriages, and one which does not
necessarily conflict with the explanation already given. All the
phenomena of intensification are simply due to a resemblance between
husband and wife in particular characteristics, such as a common
tendency toward deafness or toward mental weakness. This resemblance,
which may or may not be the result of a common descent, renders more
probable the appearance of the trait in the offspring. If the parents
closely resembled each other in many respects they would be more
likely to "breed true" and the children would resemble one another in
their inherited traits, thus accounting for the high average of
deaf-mutes to the family, observed in the Irish statistics.[99]
[Footnote 99: _Cf. supra_, p. 66.]
The theory of contrast and resemblance supplements that of intensified
heredity where the resemblance is general, rather than in particular
traits or characteristics. In such a case the absence of the
stimulating effects of contrast might result in a lowering of
vitality, which in turn would react upon the youthful death-rate.
Where then related persons differ greatly in mental and physical
traits, and generally speaking, belong to different types, it is very
improbable that there would be any ill effects resulting from the mere
fact of consanguinity. A case in point is furnished me by a
correspondent. A first cousin marriage which turned out exceedingly
well was between strongly contrasted individuals; the husband was
"short, stocky and dark complexioned" while the wife was "tall, slight
of figure, and of exceedingly light complexion." In other cases in
which the results were not so good the husband and wife bore a close
resemblance to one another, physically and mentally.
This, however, does not agree with the results obtained by Professor
Karl Pearson. Basing his conclusions on the correlation of stature
between husband and wife, he believes that homogamy is a factor of
fertility. Taking 205 marriages from Mr. Francis Galton's _Family
Records_, Professor Pearson found the correlation between husband and
wife to be .0931 ± .0467, while weighted by their fertility the
correlation was .1783 ± .0210, practically doubling the intensity of
assortative mating.[100] The value of these correlations, however, is
impaired, as he says, by the insufficient number of observations, and
by the fact that absolutely taller mothers are the more fertile.
[Footnote 100: _Royal Society Proceedings_, vol. 66, p. 30.]
In a subsequent investigation of from 1000 to 1050 pairs of parents of
adult children, Professor Pearson found the correlation in stature to
be .2804 ± .0189; of span .1989 ± .0204; and of forearm .1977 ± .0205;
with cross coefficients varying from .1403 to .2023. If, as he
believes, "The parents of adult children are on the average more alike
than first cousins, then it follows that any evils which may flow from
first cousin marriage depend not on likeness of characters, but on
sameness of stock."[101]
[Footnote 101: _Biometrika_, vol. ii, p. 373.]
But even if it were true, as is very improbable, that parents of adult
children are more alike than first cousins, it would still be likely
to follow that first cousins who married would be more alike than
first cousins in general. A certain degree of resemblance is
undoubtedly necessary to complete fertility: husband and wife must be
physically compatible, and must both enjoy a certain degree of health
and physical strength. These facts are admitted by all, but it does
not follow that resemblance beyond a certain point is not in itself
detrimental.
Professor Pearson's own experiments in this line, however, do not
give consistent results, for in correlating eyecolor with fertility,
heterogamy seems to increase fertility. The highest average fertility
(4.57) is in those cases where the father is dark-eyed and the mother
light-eyed, while the lowest is where both parents have blue-green or
gray eyes.[102]
[Footnote 102: _Phil. Trans. of the Royal Society_, vol. 195 A, p.
150.]
In a recent study an attempt has been made to measure the coefficient
of correlation between cousins.[103] In the characteristics of health,
success, temper and intelligence the coefficients ranged between .25
and .30. These values differ but little from those found to obtain for
the resemblance between avuncular relatives for eye color (.265), or
between grandparent and grandchild for the same characteristic
(.3164).[104] Positive results were also found, with one doubtful
exception, for the occurrence of insanity and tuberculosis in cousins.
The writer concludes: "The grandparent, the uncle and aunt, and the
cousin are on practically the same footing with regard to relationship
or intensity of kinship as measured by degree of likeness of
character; and it seems probable that any scientific marriage
enactments would equally allow or equally forbid marriage between
grandparent and grandchild, uncle and niece, aunt and nephew, and
between first cousins."[105]
[Footnote 103: Elderton and Pearson, "On the Measure of the
Resemblance of First Cousins." _Eugenics Laboratory Memoirs IV._
Reviewed in _Br. Med. Journal_, Feb. 15, 1908.]
[Footnote 104: _Phil. Trans. of the Royal Society_, vol. 195 A, p.
106.]
[Footnote 105: Elderton and Pearson, op. cit.]
As we should expect the resemblance between near relatives has been
found to be much greater. From a measurement of from 4000 to 4886
pairs, the average correlation of the characteristics of stature,
span, forearm length and eyecolor between parent and child was .4695.
By similar computations and measuring the same characteristics, the
fraternal correlation was found to be .508.[106] From measurements of
a greater variety of characteristics in school children the mean
fraternal correlation was .539.[107] In athletic power the coefficient
was still higher, .72 between brothers, .75 between sisters and
.49 between brothers and sisters. Measurements of mental
characteristics--vivacity, assertiveness, introspection, popularity,
conscientiousness, temper, ability and handwriting proved to be as
easily correlated, the mean coefficients being; brothers, .52,
sisters .51, brothers and sisters .52.[108]
[Footnote 106: Pearson and Lee, "On the Laws of Inheritance in Man,"
_Biometrika_, vol. ii, p. 387.]
[Footnote 107: Ibid., p. 388.]
[Footnote 108: Pearson, "On the Laws of Inheritance in Man," part 2,
_Biometrika_, vol. iii, p. 154.]
The relative amount of degeneracy and disease among the offspring of
consanguineous marriages has been enormously exaggerated, and the
danger is by no means as great as is popularly supposed. Nevertheless,
since it is undoubtedly true that on the average such marriages do not
produce quite as healthy offspring as do non-consanguineous unions,
and since public sentiment is already opposed to the marriage of
cousins, it is perhaps just as well that existing laws on the subject
should remain in force. From the standpoint of eugenics however, it is
much more important that the marriage of persons affected with
hereditary disease should be prevented. Dr. Bell has pointed out the
danger of producing a deaf-mute race by the intermarriage of
congenitally deaf persons,[109] and this warning should be made to
apply to other congenital defects as well. Some states already
prohibit the marriage of the mentally defective, and persons under the
influence of intoxicants. Such provisions are wise, and are the most
practical means of achieving eugenic ideals--by preventing the
propagation of the unfit. The interests of society demand that the
mentally and physically defective should not propagate their kind.
[Footnote 109: "Memoir upon the Formation of a Deaf Variety of the
Human Race." _Memoirs of the National Academy of Sciences_, vol. ii,
pp. 177-262.]
From the broader viewpoint of social evolution the problems of
inbreeding or crossing of stocks merge into the discussion of the
endogamous and exogamous types of society. Whatever may have been the
origin of exogamy, the survival of the exogamous type in progressive
societies may easily be explained on the ground of superior
adaptability, variability and plasticity, which enables such societies
to survive a change of environment while the more rigid structure of
the endogamous clan brings about its extermination.
Inbreeding leads to caste formation and a rigid and stratified social
structure, which is in the end self-destructive, and cannot survive a
change of environment. The governing caste may, as Reibmayr says,
favor the growth of culture, but it is usually the culture of that
caste, and not of the people at large. The ruling caste is usually the
result of selection of the strongest and ablest, but after it becomes
a caste, the individuals are selected on account of hereditary social
position and not primarily on account of ability. Now biological
experiments show that although artificial selection may be carried to
a point where animals will breed true to a characteristic to within 90
per cent, yet if selection is stopped, and the descendants of the
selected individuals are allowed to breed freely among themselves,
they will in a very few generations revert to the original type. This
is what happens in a social caste, unless, as in the case of the
English aristocracy, it is continually renewed by selection of the
ablest of the other classes.
The superposition and crossing of cultures, the development of
secondary civilization, is necessary to social evolution in its
broadest sense, and this usually involves crossing of blood as well as
crossing of cultures. As a result of the unprecedented migrations of
the last half-century we have in the United States the greatest
variety of social types ever brought so closely together. An
opportunity is offered either for the perpetuation of each racial type
by inbreeding, with the prospect of an indefinite stratification of
society, or for the amalgamation of all cultural and racial elements
into a homogeneous whole, and the development of a race more versatile
and adaptable than any the world has yet known. The general tendency
will undoubtedly be toward amalgamation, but there are decided
tendencies in the other direction, as for instance in the "first
families of Virginia," and in that large element of the New England
population which prides itself upon its exclusively Puritan ancestry,
and which has inherited from its progenitors that intolerance which
characterized the early settlers of New England more than the pioneers
of the other colonies. The dynamic forces of modern civilization are,
however, opposed to caste--the West has long ago obliterated the
distinction between the Pennsylvania German and the Puritan, the
Scotch-Irish and the Knickerbocker Dutch. These same dynamic forces,
which have prevented the formation of caste have at the same time been
diminishing the percentage of consanguineous marriage and will
undoubtedly continue to operate in the same way for some time to come.
And when rational laws prohibit the marriage of the diseased and the
degenerate, the problem of consanguineous marriage will cease to be of
vital importance.
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GENEALOGIES CONSULTED.
* * * * *
Family. Author. Place and Date of Publication.
-----------------------------------------------------------------
Augur, E.P. Augur, Middletown, Conn. 1904.
Banta, T.M. Banta, New York, 1893.
Bent, A.H. Bent, Boston, 1900.
Bolton, H.C. and R.P. Bolton, New York, 1895.
Champion, F.B. Trowbridge, New Haven, 1891.
Dewey, L.M. Dewey, Westfield, Mass., 1898.
Faxon, G.L. Faxon, Springfield, Mass., 1880.
Foster, F.C. Pierce, Chicago, 1899.
Gates, C.O. Gates, New York, 1898.
Giddings, M.S. Giddings, Hartford, 1882.
Goodwin, J.J. Goodwin, Hartford, 1891.
Hurlbut, H.H. Hurlbut, Albany, 1888.
Kneeland, S.F. Kneeland, New York, 1897.
Lee, E.J. Lee, Philadelphia, 1895.
Mather, H.E. Mather, Hartford, 1890.
Mead, S.P. Mead, New York, 1901.
Potts, T.M. Potts, Canonsburg, Pa., 1901.
Shattuck, L. Shattuck Boston, 1855.
Tenney, M.J. Tenney, Boston, 1891.
Udall, G.B.L. Arner, In _Genealogical Exchange_,
Buffalo 1904-5.
Varnum, J.M. Varnum, Boston, 1907.
Wood, C.W. Holmes, Elmira, 1901.
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