CONSANGUINITY AND MENTAL DEFECT
Idiocy, perhaps more than any other disease or defect, has long been
connected in the popular mind with the marriage of cousins. This fact
is not surprising when we consider that until very recent times idiots
were looked upon with a kind of superstitious awe, and the affliction
was supposed to be a curse of God. For this reason, when idiocy did
follow consanguineous marriage as it sometimes would, it was believed
to be the fit punishment of some violation of divine law. Insanity
also frequently has been attributed to consanguineous marriage, but
not so frequently as idiocy, since its occurrence later in life is not
so obviously connected with pre-natal conditions.
The terminology of mental and nervous disorders has been so loosely
applied that some definition may be necessary. By the term "idiocy,"
is meant a condition of undeveloped mentality. Idiocy exists in
various degrees, from the complete absence of intellectual faculties
to a condition of mere irresponsibility in which the subject is
capable of self-help, and sometimes of self-support under the careful
guidance of other. Under the generic term "idiot" may be included the
"complete idiot," the imbecile, the "feeble-minded" and the
"simpleton," all of whom suffer in a greater or less degree from
arrested mental development.
Insanity, on the other hand, is a disease which destroys or clouds an
intellect which has once been developed. It is true that certain
conditions of idiocy and imbecility do resemble that phase of insanity
known as dementia--a reversion to the original mental state of
childhood--in reality a form of second childhood. But the states are
not identical, although one may lapse into the other. One is defect,
the other disease; the imbecile in the former being the counterpart of
the dement in the latter, just as the moral imbecile is the analogue
of the paranoiac.[61]
[Footnote 61: Barr, _Mental Defectives_, p. 18.]
Of the strong inheritability of idiocy there can be no doubt. Dr.
Martin W. Barr of the Pennsylvania Training School for Feeble Minded
Children has published an etiological table embodying the results of a
careful examination of 4050 cases of mental defect. Of these, 2651 or
65.45 per cent resulted from causes acting before birth, including
1030 or 25.43 per cent with a family history of idiocy and imbecility,
and 529 more (13.06 per cent) with a family history of insanity,
epilepsy and minor neuroses. Dr. Barr gives many instances
illustrating the heredity of imbecility, especially where both parents
were imbeciles, and had imbecile relatives. One case in particular
forcibly illustrates the disastrous results of the marriage of such
unfortunates. It is taken from the reports of the Connecticut Lunacy
Commission:
In one instance, where a pauper female idiot lived in one town,
the town authorities hired an idiot belonging to another town,
and not then a pauper, to marry her, and the result has been
that the town to which the male idiot belongs has for many
years had to support the pair and the three idiot children.[62]
[Footnote 62: Ibid., p. 99.]
Neuroses may remain latent for a generation and reappear in the
grandchildren of the person affected, or the latent tendency may never
reappear unless some disturbing factor such as scarletina, meningitis
or other acute disease attacks the weak spot. This possibility
suggests that the influence of heredity may be vastly greater than the
etiological tables would indicate. The apparent causes may be only
agents which assist in developing the evil really engendered by an
inheritance of imbecility.
It is not at all certain that there is any well marked boundary line
between genius and some forms of imbecility. Many quite irresponsible
idiots have marvelous verbal memories, and can repeat parrot-like,
page after page of books of which they have no comprehension. Dr. Barr
tells of cases of prodigies, musical, mathematical and mechanical, who
except in their specialty were almost totally deficient mentally.[63]
Many of the world's most brilliant musicians, mathematicians and even
military leaders have been men of one-sided mental development, whose
ability in other lines was so slight that they were little better than
imbeciles, and it is not at all surprising that their children are
sometimes truly idiotic.
[Footnote 63: Barr, op. cit., p. 301 _et seq._]
The best writers of the present day no longer recognize consanguinity
as a cause _per se_, of idiocy. The heredity of neuroses, however, is
so strongly established that few would dispute the proposition that
where the morbidity is inherited through both parents it appears more
frequently and in a more marked degree than where one parent is
entirely free from taint. This is what occurs when a consanguineous
marriage takes place between descendants of a neurotic family. The
percentage of idiotic children would then be somewhat higher from
consanguineous marriages than from the average marriage purely through
the action of the laws of heredity.
Dr. Barr finds 49 out of 4050 cases of idiocy or 1.21 per cent, in
which there was a family history of consanguinity. This is little
higher than the average frequency of first cousin marriage, and an
analysis of 41 of these cases does not show one case that can be
attributed to consanguinity alone. To quote: "Two were the result of
incestuous connection--one of brother and sister, the other of father
and daughter, and in the others there was an undoubted history, of
grave neuroses."[64] "Beach and Shuttleworth find in the consideration
of their 100 cases (out of 2,380 idiots), giving 4.2 per cent (of
consanguineous parentage) that the bad effects are due rather to the
intensification of bad heredity common to both parents."[65]
[Footnote 64: Barr, op. cit., p. 94.]
[Footnote 65: Ibid., p. 109.]
Dr. Arthur Mitchell examined all idiots in nine counties of Scotland
and found that 42 out of 519 or 8.1 per cent of whom the parentage was
known, were children of first cousins.[66] Dr. Down found 46 out of
852 or 5.4 per cent to be children of first cousins.[67] Dr. Grabham
of the Earlswood Idiot Asylum in Surrey, England, stated that 53 out
of 1388 patients were the offspring of first cousins. The facts, he
adds, were obtained from the parents and are "therefore tolerably
trustworthy."[68] Other investigations give percentages as follows:
Kerlin, 7; Rogers, 3.6; Brown, 3.5 and C.T. Wilbur, 0.3.[69]
[Footnote 66: Darwin, see _Jour. Stat. Soc._, p. 173.]
[Footnote 67: Huth, _Marriage of Near Kin_, pp. 210-211.]
[Footnote 68: Darwin, op. cit., p. 166.]
[Footnote 69: Barr, op. cit., p. 109.]
The earlier American writers, Drs. Howe and Bemiss, believed that
consanguinity was a cause of idiocy. Dr. Howe inquired into the
parentage of 359 idiots and found that in 17 families the parents were
nearly related; in one of these cases there were 5 idiotic children;
in 5 families there were 4 idiots each; in 3 families 3 each; in 2
families 2 each; and in 6 families i each. In all 17 families there
were 95 children of whom 44 were idiots, 12 were scrofulous and puny,
1 was deaf, 1 dwarf--58 in low health or defective, and only 37 fairly
healthy. These of course are selected cases and do not indicate at
all, as Dr. Howe supposed, that consanguinity was the cause of the
disasters. He adds that in each case one or both of the parents were
either intemperate or scrofulous, and that there were also other
predisposing causes.[70] Dr. Bemiss found that 7.8 per cent of his
3942 children of consanguineous marriages were idiots, while but 0.7
per cent of the children of non-consanguineous parentage were
idiotic.[71] A more detailed examination reveals the fact that in a
large number of these, one or both of the parents were mentally
defective. For example, in a marriage of double cousins the wife was
"feeble minded" and the six children were of inferior mentality. In a
case of first-cousin marriage the wife became insane and two of the
children were idiotic. In a case of the marriage of cousins,
themselves the offspring of cousins the husband was a hypochondriac,
and seven children idiotic. In another marriage of the same class both
parents were feeble-minded and the children idiotic. These are simply
taken at random, and many others might be given. When we find also
that in a majority of cases no report is given of the ancestry, it is
very obvious that consanguinity alone could not have been the cause of
any large proportion of the 308 cases of idiocy in the Bemiss report.
[Footnote 70: Barr, op. cit., p. iii.]
[Footnote 71: Bemiss, op. cit., p. 420.]
My own investigations show that out of 600 children of first cousin
marriage (from correspondence) 26 or 4.3 per cent are mentally
defective--10 are reported as "idiots," 13 as "weak-minded" and 3 as
"imbeciles." In at least five of these cases there is evidence of bad
heredity, in two others the father was intemperate and in two more
causes acting after birth are mentioned.
The statistics of the insane and idiotic in Prussia presented by Mayet
clearly indicate the large part which heredity plays in the production
of mental disorders. Tables XX and XXI set forth the most important
results of his work. Mayet considers a case hereditary if any near
relative of the subject suffered from mental or nervous disorder, or
was intemperate, suicidal, criminal or eccentric.[72]
[Footnote 72: Mayet, _Verwandtenehe and Statistik_, quoted by Feer,
_Der Einfluss der Blutsverwandschaft der Eltern auf die Kinder_, p.
13.]
TABLE XX.
--------------------------------------------------
| No. of |Percentage
| Cases. |hereditary.
--------------------------------------------------
1. Simple Insanity |102,097 | 31.7 = 100
Consanguineous parentage | 664 | 69.0 = 218
Parents cousins | 595 | 68.1 = 215
Parents uncle and niece | 66 | 77.3 = 244
--------------------------------------------------
2. Paralytic Insanity | 22,936 | 17.6 = 100
Consanguineous parentage | 95 | 45.3 = 257
Parents cousins | 87 | 44.8 = 255
Parents uncle and niece | 8 | 75.0 = 426
--------------------------------------------------
3. Epileptic Insanity | 14,067 | 25.6 = 100
Consanguineous parentage | 79 | 53.2 = 208
Parents cousins | 70 | 50.0 = 195
Parents uncle and niece | 9 | 66.7 = 261
--------------------------------------------------
4. Imbecility and Idiocy | 16,416 | 28.7 = 100
Consanguineous parentage | 237 | 43.0 = 150
Parents cousins | 211 | 43.1 = 150
Parents uncle and niece | 26 | 38.5 = 134
--------------------------------------------------
Table XXI gives the proportion of the mentally defective who are the
offspring of consanguineous marriages. The term "cousin" in both
these tables probably means first cousins. It will be remembered that
Prussian statistics of consanguineous marriages are very imperfect,
but that at least 6.5 in every thousand are consanguineous (first
cousins or nearer).
TABLE XXI.[73]
_Parentage of Mental Defectives in Prussia._
-----------------------------------------------------
| Consan- | |Uncle and
|guineous.|Cousins.| Niece.
-----------------------------------------------------
1. Insanity (simple) | 6.5[A] | 5.8[A]| .64[A]
Hereditary | 14.2 | 12.5 | 1.6
Not hereditary | 3.0 | 2.7 | .22
-----------------------------------------------------
2. Paralytic Insanity | 4.1 | 3.8 | .35
Hereditary | 11.1 | 9.6 | 1.48
Not hereditary | 2.9 | 2.5 | .11
-----------------------------------------------------
3. Epileptic Insanity | 5.6 | 4.9 | .64
Hereditary | 11.7 | 9.9 | 1.57
Not hereditary | 3.5 | 3.2 | .29
-----------------------------------------------------
4. Idiocy and Imbecility| 14.4 | 12.8 | 1.58
Hereditary | 21.6 | 19.3 | 2.12
Not hereditary | 11.5 | 10.2 | 1.37
-----------------------------------------------------
[A] Per thousand.
[Footnote 73: Feer, op. cit., pp. 13-14.]
From these tables we may infer that consanguinity influences idiocy
far more than it does insanity, but it is not entirely clear why the
number of hereditary cases should be relatively smaller among the
idiotic. Since insanity is more likely to have some more definitely
assignable cause than idiocy, we should expect the percentage due to
heredity to be lower and consequently the influence of consanguinity
less.
It is generally admitted that a tendency toward insanity is
inheritable, and it seems probable that this tendency as well as other
neuroses may be intensified through double heredity. A case in point
can be found in the Shattuck genealogy.[74] For four generations in
the S. family there is no indication of neurosis. The average number
of children to a family had been eight, few children died young and
all were prosperous farmers. But in 1719 J.S. married E.C. and their
son Z.S. is thus described: "He was sometimes subject to depression of
spirits; and some peculiar traits of character in a few branches of
his family seem to have originated with him." He married A.C., a niece
of his mother. They both lived to be over 80 and had ten children, of
whom three were insane; only six married, and of these only two are
known to have left surviving children. One of these a daughter, S.S.,
married E.S., a nephew of her father, and himself the offspring of a
second cousin marriage within the S. blood. E.S. and S.S. had five
children, all of whom married, and there is no further mention of
insanity. We may suppose, then, that the C. stock was neurotic, and
that a consanguineous marriage within that stock, although of the S.
surname, intensified the tendency into insanity, but with a further
infusion of the normal S. blood the morbidity was eliminated. It is
very evident that the heredity and not the consanguinity was the cause
of these three cases of insanity.
[Footnote 74: _Shattuck Memorials_, p. 118.]