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

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[Volume XXXI] [Number 3]


_University Fellow in Sociology_



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 Duesing, which are open to other

[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.


MARCH, 1908.




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



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



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



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



Idiocy and Insanity--Inheritability of Mental Defect--Intensified
Heredity--Barr's Investigations--Other American and English
Data--Mayet's Prussian Statistics--Genealogical Data



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



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



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

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."


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 Societe
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 Societe
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 Societe 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 Senor 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 Politicas_, 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

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.]



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:

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 Norvege_. 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.]

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:

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.

|_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]

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 Societe d'Anthropologie_, 1863, p.

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

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

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

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:

|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:

| First | 1-1/2 |Second | 2-1/2 | Third |Distant|
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

[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:

|First | 1-1/2 |Second | 2-1/2 | Third |Distant|
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.



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 Duesing:[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.

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. Duesing for Prussia[32] are as follows:

| | | 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:

|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.

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:

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:

_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.

| | 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]

| 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.

|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.



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.


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.

[Footnote 44: Boudin, "Croisement des familles, de races et des
especes." In _Memoires de la Societe d' Anthropologie_, vol. i, p.

The most important statistical investigation was made by G.H.
Darwin.[45] From his genealogical data he compiled the following

| | 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

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.

|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]

| 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:

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
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

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

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

[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

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,



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

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.

| 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).

_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

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.]



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

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.]

| |Having |Having | |
| |Blind |blind | |
| |relatives|relatives|Having |
Consanguinity of | |Class |Class |no blind | Not
Parents. |Totals|(a).[A] |(b).[A] |relatives|Stated.

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