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.]