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.
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.
The most important statistical investigation was made by G.H. Darwin.[[45]] From his genealogical data he compiled the following table:
| TABLE XVI. | ||||
|---|---|---|---|---|
| Number of marriages. | Average number sons to marriages. | Per cent sterile marriages. | Ave. no. sons to fertile 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. | ||||
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.
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. | |||
|---|---|---|---|
| Parentage. | No. of fertile marriages. | No. of children. | Ave. to fertile 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. | |||
|---|---|---|---|
| Parentage. | No. of fertile marriages. | No. of children. | Ave. to fertile 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. | |||
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. (Genealogies.) | No. of Children. | No. dying 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 |
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]]
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.
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.
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]]
(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]]
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]]
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.
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.