Consanguineous Marriages in the American Population
by George B. Louis Arner
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[Volume XXXI] [Number 3]


BY GEORGE B. LOUIS ARNER, Ph.D. 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 interpretations.

[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 Families—Scrofula



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 community.

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 impediment.

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:

TABLE I. - 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.]

TABLE II. - 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:

TABLE III. 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.

TABLE IV. - 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]

TABLE V. - 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. 527.]

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 consanguinity.

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 result:

- 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 proportion:

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:

TABLE VI. 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:

TABLE VII. - First 1-1/2 Second 2-1/2 Third Distant cousins cousins cousins cousins cousins cousins Total - 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 cousins.[27]

[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:

TABLE VIII. First 1-1/2 Second 2-1/2 Third Distant cousins cousins cousins cousins cousins cousins Total 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. 243-244.]

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:

TABLE IX. 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:

TABLE X. 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. 114-116.]

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:

TABLE XI. - 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:

TABLE XII. 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.

TABLE XIII. 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]

TABLE XIV. 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.

TABLE XV. - 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. 178.]

[Footnote 44: Boudin, "Croisement des familles, de races et des especes." In Memoires de la Societe 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.]



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.

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