SUMMARY AND CONCLUSION
Having thus considered the more important problems which have been
connected with the marriage of near kin, we have only to discuss the
bearing of the conclusions thus formed upon the social aggregate, and
the effect which consanguineous marriages have upon the evolution and
improvement of the human species.
It has been shown that the frequency with which consanguineous
marriages occur varies greatly with the physical and social
environments; that such marriages are more frequent in isolated and in
rural communities than in cities; and that with the increasing range
of individual activity and acquaintance the relative frequency of
consanguineous marriage is decreasing.
Consanguinity in the parents has no perceptible influence upon the
number of children or upon their masculinity, and has little, if any,
direct effect upon the physical or mental condition of the offspring.
The most important physiological effect of consanguineous marriage is
to intensify any or all inheritable family characteristics or
peculiarities by double inheritance. The degree of intensification
probably varies with the nature of the characteristic; degenerate
conditions of the mind, and of the delicate organs of special sense
being the most strongly intensified.
It is probable also that in the absence of degenerative tendencies
the higher qualities of mind and body are similarly intensified by
marriage between highly endowed members of the same family. Dr.
Reibmayr believes that inbreeding is necessary to the higher evolution
of the race: "A settled abode, natural protection from race mixture
and the development of a closely inbred social class are the basic
conditions of every culture period." But inbreeding must not be
carried too far: "In the course of generations the ruling class begins
to degenerate mentally and physically, until not only is the class
destroyed, but for lack of capable leadership the people (Volk) itself
is subjugated and a crossing of blood again takes place."[95]
[Footnote 95: Trans. from _Insucht und Vermischung beim Menschen_, p.
46.]
In the breeding of animals the closest inbreeding is frequently
resorted to in order to improve the stock, and many examples can be
given of the closest possible inbreeding for generations without
apparent detriment, but it is universally admitted that the animals
selected for such inbreeding must be sound constitutionally, and free
from disease. After a certain number of generations however,
degeneration apparently sets in. The number of generations through
which inbreeding may be carried varies with the species, and the
purpose for which the animals are bred. Where they are bred primarily
for their flesh, as for beef, mutton or pork, it can be pursued
farther and closer than where they are bred for achievement in which a
special strength is required--for instance in the breeding of race
horses. This would indicate that the more delicate brain and nervous
system is sooner affected than the lower bodily functions.
In man, however, freedom from hereditary taint cannot so easily be
secured. Individuals cannot be selected scientifically for breeding
purposes. Furthermore, the human body is more delicately constructed
than that of the lower animals, and the nervous system is more highly
developed and specialized, so that it is reasonable to suppose that in
man degeneration would set in earlier in the process of inbreeding,
and that it would be impossible to breed as closely as with the lower
animals. Instances are well known, however, where incestuous unions
have been productive of healthy offspring, and successive generations
of offspring of incestuous connection are not unknown; but, although
statistics are lacking, it seems to be very often true that children
of such unions are degenerate. It may be that the reason for this is
that with the laws and social sentiments now prevailing in all
civilized communities, only degenerates ever contract incestuous
alliances. Desirable as it may be from a social point of view that
this strong sentiment against incest should continue, it is not yet
_proven_ that even the closest blood relationship between the parents
is directly injurious to the offspring. The "instinctive horror of
incest" is a myth, for although a horror of incest does very properly
exist in civilized, and in some tribal societies, it is purely a
matter of custom and education, and not at all a universal law.
Double heredity may account for all the observed ill effects of
consanguineous marriage, including the high youthful death-rate, the
higher percentage of idiocy, deafness and blindness, and probably also
the scrofulous and other degenerate tendencies; nevertheless, there
may be in some instances a lowering of vitality which this hypothesis
does not fully explain.
The tendency of inbreeding in animals, it is well known, is to fix the
type, the tendency of crossing, to variation. Inbreeding then, tends
to become simple repetition with no natural variations in any
direction, a stagnation which in itself would indicate a comparatively
low vitality. Variation and consequent selection is necessary to
progress. "Sex," according to Ward[96] "is a device for keeping up a
difference of potential," and its object is not primarily
reproduction, but variation.[97]
[Footnote 96: _Pure Sociology_, p. 232.]
[Footnote 97: Pearson (_Grammar of Science_, p. 373) points out that
variation does occur in asexual reproduction. But that sex is at least
a powerful stimulus to variation can hardly be questioned.]
It is organic differentiation, higher life, progress,
evolution.... But difference of potential is a social as well
as a physiological and physical principle, and perhaps we shall
find the easiest transition from the physiological to the
social in viewing the deteriorating effects of close inbreeding
from the standpoint of the environment instead of from that of
the organism. A long-continued uniform environment is more
deteriorating than similarity of blood. Persons who remain for
their whole lives, and their descendants after them, in the
same spot, surrounded by precisely the same conditions, and
intermarry with others doing the same, and who continue this
for a series of generations, deteriorate mentally at least, and
probably also physically, although there may not be any mixing
of blood. Their whole lives, physical, mental, and moral,
become fixed and monotonous, and the partners chosen for
continuing the race have nothing new to add to each other's
stock. There is no variation of the social monotony, and the
result is socially the same as close consanguineal
interbreeding. On the other hand, a case in which a man should,
without knowing it, marry his own sister, after they had been
long separated and living under widely different skies, would
probably entail no special deterioration, and their different
conditions of life would have produced practically the same
effect as if they were not related.[98]
[Footnote 98: Ward, op. cit., pp. 234-235.]
Professor Ward's idea of "difference of potential," or contrast, as
essential to the highest vigor of the race as well as to that of the
individual offspring, offers an alternative explanation of the
observed results of consanguineous marriages, and one which does not
necessarily conflict with the explanation already given. All the
phenomena of intensification are simply due to a resemblance between
husband and wife in particular characteristics, such as a common
tendency toward deafness or toward mental weakness. This resemblance,
which may or may not be the result of a common descent, renders more
probable the appearance of the trait in the offspring. If the parents
closely resembled each other in many respects they would be more
likely to "breed true" and the children would resemble one another in
their inherited traits, thus accounting for the high average of
deaf-mutes to the family, observed in the Irish statistics.[99]
[Footnote 99: _Cf. supra_, p. 66.]
The theory of contrast and resemblance supplements that of intensified
heredity where the resemblance is general, rather than in particular
traits or characteristics. In such a case the absence of the
stimulating effects of contrast might result in a lowering of
vitality, which in turn would react upon the youthful death-rate.
Where then related persons differ greatly in mental and physical
traits, and generally speaking, belong to different types, it is very
improbable that there would be any ill effects resulting from the mere
fact of consanguinity. A case in point is furnished me by a
correspondent. A first cousin marriage which turned out exceedingly
well was between strongly contrasted individuals; the husband was
"short, stocky and dark complexioned" while the wife was "tall, slight
of figure, and of exceedingly light complexion." In other cases in
which the results were not so good the husband and wife bore a close
resemblance to one another, physically and mentally.
This, however, does not agree with the results obtained by Professor
Karl Pearson. Basing his conclusions on the correlation of stature
between husband and wife, he believes that homogamy is a factor of
fertility. Taking 205 marriages from Mr. Francis Galton's _Family
Records_, Professor Pearson found the correlation between husband and
wife to be .0931 ± .0467, while weighted by their fertility the
correlation was .1783 ± .0210, practically doubling the intensity of
assortative mating.[100] The value of these correlations, however, is
impaired, as he says, by the insufficient number of observations, and
by the fact that absolutely taller mothers are the more fertile.
[Footnote 100: _Royal Society Proceedings_, vol. 66, p. 30.]
In a subsequent investigation of from 1000 to 1050 pairs of parents of
adult children, Professor Pearson found the correlation in stature to
be .2804 ± .0189; of span .1989 ± .0204; and of forearm .1977 ± .0205;
with cross coefficients varying from .1403 to .2023. If, as he
believes, "The parents of adult children are on the average more alike
than first cousins, then it follows that any evils which may flow from
first cousin marriage depend not on likeness of characters, but on
sameness of stock."[101]
[Footnote 101: _Biometrika_, vol. ii, p. 373.]
But even if it were true, as is very improbable, that parents of adult
children are more alike than first cousins, it would still be likely
to follow that first cousins who married would be more alike than
first cousins in general. A certain degree of resemblance is
undoubtedly necessary to complete fertility: husband and wife must be
physically compatible, and must both enjoy a certain degree of health
and physical strength. These facts are admitted by all, but it does
not follow that resemblance beyond a certain point is not in itself
detrimental.
Professor Pearson's own experiments in this line, however, do not
give consistent results, for in correlating eyecolor with fertility,
heterogamy seems to increase fertility. The highest average fertility
(4.57) is in those cases where the father is dark-eyed and the mother
light-eyed, while the lowest is where both parents have blue-green or
gray eyes.[102]
[Footnote 102: _Phil. Trans. of the Royal Society_, vol. 195 A, p.
150.]
In a recent study an attempt has been made to measure the coefficient
of correlation between cousins.[103] In the characteristics of health,
success, temper and intelligence the coefficients ranged between .25
and .30. These values differ but little from those found to obtain for
the resemblance between avuncular relatives for eye color (.265), or
between grandparent and grandchild for the same characteristic
(.3164).[104] Positive results were also found, with one doubtful
exception, for the occurrence of insanity and tuberculosis in cousins.
The writer concludes: "The grandparent, the uncle and aunt, and the
cousin are on practically the same footing with regard to relationship
or intensity of kinship as measured by degree of likeness of
character; and it seems probable that any scientific marriage
enactments would equally allow or equally forbid marriage between
grandparent and grandchild, uncle and niece, aunt and nephew, and
between first cousins."[105]
[Footnote 103: Elderton and Pearson, "On the Measure of the
Resemblance of First Cousins." _Eugenics Laboratory Memoirs IV._
Reviewed in _Br. Med. Journal_, Feb. 15, 1908.]
[Footnote 104: _Phil. Trans. of the Royal Society_, vol. 195 A, p.
106.]
[Footnote 105: Elderton and Pearson, op. cit.]
As we should expect the resemblance between near relatives has been
found to be much greater. From a measurement of from 4000 to 4886
pairs, the average correlation of the characteristics of stature,
span, forearm length and eyecolor between parent and child was .4695.
By similar computations and measuring the same characteristics, the
fraternal correlation was found to be .508.[106] From measurements of
a greater variety of characteristics in school children the mean
fraternal correlation was .539.[107] In athletic power the coefficient
was still higher, .72 between brothers, .75 between sisters and
.49 between brothers and sisters. Measurements of mental
characteristics--vivacity, assertiveness, introspection, popularity,
conscientiousness, temper, ability and handwriting proved to be as
easily correlated, the mean coefficients being; brothers, .52,
sisters .51, brothers and sisters .52.[108]
[Footnote 106: Pearson and Lee, "On the Laws of Inheritance in Man,"
_Biometrika_, vol. ii, p. 387.]
[Footnote 107: Ibid., p. 388.]
[Footnote 108: Pearson, "On the Laws of Inheritance in Man," part 2,
_Biometrika_, vol. iii, p. 154.]
The relative amount of degeneracy and disease among the offspring of
consanguineous marriages has been enormously exaggerated, and the
danger is by no means as great as is popularly supposed. Nevertheless,
since it is undoubtedly true that on the average such marriages do not
produce quite as healthy offspring as do non-consanguineous unions,
and since public sentiment is already opposed to the marriage of
cousins, it is perhaps just as well that existing laws on the subject
should remain in force. From the standpoint of eugenics however, it is
much more important that the marriage of persons affected with
hereditary disease should be prevented. Dr. Bell has pointed out the
danger of producing a deaf-mute race by the intermarriage of
congenitally deaf persons,[109] and this warning should be made to
apply to other congenital defects as well. Some states already
prohibit the marriage of the mentally defective, and persons under the
influence of intoxicants. Such provisions are wise, and are the most
practical means of achieving eugenic ideals--by preventing the
propagation of the unfit. The interests of society demand that the
mentally and physically defective should not propagate their kind.
[Footnote 109: "Memoir upon the Formation of a Deaf Variety of the
Human Race." _Memoirs of the National Academy of Sciences_, vol. ii,
pp. 177-262.]
From the broader viewpoint of social evolution the problems of
inbreeding or crossing of stocks merge into the discussion of the
endogamous and exogamous types of society. Whatever may have been the
origin of exogamy, the survival of the exogamous type in progressive
societies may easily be explained on the ground of superior
adaptability, variability and plasticity, which enables such societies
to survive a change of environment while the more rigid structure of
the endogamous clan brings about its extermination.
Inbreeding leads to caste formation and a rigid and stratified social
structure, which is in the end self-destructive, and cannot survive a
change of environment. The governing caste may, as Reibmayr says,
favor the growth of culture, but it is usually the culture of that
caste, and not of the people at large. The ruling caste is usually the
result of selection of the strongest and ablest, but after it becomes
a caste, the individuals are selected on account of hereditary social
position and not primarily on account of ability. Now biological
experiments show that although artificial selection may be carried to
a point where animals will breed true to a characteristic to within 90
per cent, yet if selection is stopped, and the descendants of the
selected individuals are allowed to breed freely among themselves,
they will in a very few generations revert to the original type. This
is what happens in a social caste, unless, as in the case of the
English aristocracy, it is continually renewed by selection of the
ablest of the other classes.
The superposition and crossing of cultures, the development of
secondary civilization, is necessary to social evolution in its
broadest sense, and this usually involves crossing of blood as well as
crossing of cultures. As a result of the unprecedented migrations of
the last half-century we have in the United States the greatest
variety of social types ever brought so closely together. An
opportunity is offered either for the perpetuation of each racial type
by inbreeding, with the prospect of an indefinite stratification of
society, or for the amalgamation of all cultural and racial elements
into a homogeneous whole, and the development of a race more versatile
and adaptable than any the world has yet known. The general tendency
will undoubtedly be toward amalgamation, but there are decided
tendencies in the other direction, as for instance in the "first
families of Virginia," and in that large element of the New England
population which prides itself upon its exclusively Puritan ancestry,
and which has inherited from its progenitors that intolerance which
characterized the early settlers of New England more than the pioneers
of the other colonies. The dynamic forces of modern civilization are,
however, opposed to caste--the West has long ago obliterated the
distinction between the Pennsylvania German and the Puritan, the
Scotch-Irish and the Knickerbocker Dutch. These same dynamic forces,
which have prevented the formation of caste have at the same time been
diminishing the percentage of consanguineous marriage and will
undoubtedly continue to operate in the same way for some time to come.
And when rational laws prohibit the marriage of the diseased and the
degenerate, the problem of consanguineous marriage will cease to be of
vital importance.
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GENEALOGIES CONSULTED.
* * * * *
Family. Author. Place and Date of Publication.
-----------------------------------------------------------------
Augur, E.P. Augur, Middletown, Conn. 1904.
Banta, T.M. Banta, New York, 1893.
Bent, A.H. Bent, Boston, 1900.
Bolton, H.C. and R.P. Bolton, New York, 1895.
Champion, F.B. Trowbridge, New Haven, 1891.
Dewey, L.M. Dewey, Westfield, Mass., 1898.
Faxon, G.L. Faxon, Springfield, Mass., 1880.
Foster, F.C. Pierce, Chicago, 1899.
Gates, C.O. Gates, New York, 1898.
Giddings, M.S. Giddings, Hartford, 1882.
Goodwin, J.J. Goodwin, Hartford, 1891.
Hurlbut, H.H. Hurlbut, Albany, 1888.
Kneeland, S.F. Kneeland, New York, 1897.
Lee, E.J. Lee, Philadelphia, 1895.
Mather, H.E. Mather, Hartford, 1890.
Mead, S.P. Mead, New York, 1901.
Potts, T.M. Potts, Canonsburg, Pa., 1901.
Shattuck, L. Shattuck Boston, 1855.
Tenney, M.J. Tenney, Boston, 1891.
Udall, G.B.L. Arner, In _Genealogical Exchange_,
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Wood, C.W. Holmes, Elmira, 1901.