CONSANGUINEOUS MARRIAGESIN THEAMERICAN POPULATION

STUDIES IN HISTORY, ECONOMICS AND PUBLIC LAW

EDITED BY THE FACULTY OF POLITICAL SCIENCE OF COLUMBIA UNIVERSITY

[Volume XXXI] [Number 3]

CONSANGUINEOUS MARRIAGESIN THEAMERICAN POPULATION

BYGEORGE B. LOUIS ARNER, Ph. D. _University Fellow in Sociology_

1908

PREFACE

This monograph does not claim to treat exhaustively, nor to offer afinal solution of all the problems which have been connected with themarriage of kin. The time has not yet come for a final work on thesubject, for the systematic collection of the necessary statistics, which can only be done by governmental authority, has never beenattempted. The statistics which have been gathered, and which arepresented in the following pages, are fragmentary, and usually bearupon single phases of the subject, but taken together they enable usbetter to understand many points which have long been in dispute. 

The need for statistics of the frequency of occurrence ofconsanguineous marriages has been strongly felt by many far-sightedmen. G. H. Darwin and A. H. Huth have tried unsuccessfully to have thesubject investigated by the British Census, and Dr. A. G. Bell hasrecently urged that the United States Census make such aninvestigation. [1] Another motive for undertaking this present work, aside from the desire to study the problems already referred to, hasbeen to test the widely prevalent theory that consanguinity is afactor in the determination of sex, the sole basis of which seems tobe the Prussian birth statistics of Düsing, which are open to otherinterpretations. 

[Footnote 1: Cf. Bell, "A Few Thoughts Concerning Eugenics. " In_National Geographic Magazine_, March, 1908. ]

The stock illustrations from isolated communities have been omitted astoo difficult to verify, and little space has been given to theresults of the inbreeding of domestic animals, for although suchresults are of great value to Biology, they are not necessarilyapplicable to the human race. 

The writer regrets that it is impossible here to acknowledge all hisobligations to those who have assisted him in the preparation of thiswork. Such acknowledgement is due to the many genealogists and otherfriends who have kindly furnished detailed cases of consanguineousmarriage. For more general data the writer is especially indebted toDr. Alexander Graham Bell, to Dr. Martin W. Barr, to Professor WilliamH. Brewer of Yale University, and to Dr. Lee W. Dean of the Universityof Iowa. In the preparation of the manuscript the suggestions andcriticisms of Professors Franklin H. Giddings and Henry L. Moore havebeen invaluable. 

G. B. L. A. 

MARCH, 1908. 

CONTENTS

CHAPTER I

INTRODUCTION

Problems to be Treated--Degrees of Consanguinity--Literature of theSubject--Noah Webster--Bemiss--Dally--G. H. Darwin--Huth--Bell--LegalStatus in the United States--Methods ofInvestigation--Genealogical--Personal--Isolated Communities

CHAPTER II

RATIO OF THE CONSANGUINEOUS TO ALL MARRIAGES

Previous Estimates--Mayo-Smith--Mulhall--Darwin--Application ofDarwin's Method to American Data--Direct Method--ConsanguinealAttraction--Same-name and Different-name Cousin Marriages--Summary

CHAPTER III

MASCULINITY

Constancy of the Sex-ratio--Consanguinity and Masculinity--Theory ofWestermarck and Thomas--Duesing--Gache--Negroes in the UnitedStates--Genealogical Material--Other Compilations--Summary

CHAPTER IV

CONSANGUINITY AND REPRODUCTION

Theories of the Effect of Consanguinity upon Offspring--ComparativeFertility--Statistics from Darwin and Bemiss--GenealogicalStatistics--Youthful Death-rate--Degeneracy--Fallacies in the Work ofBemiss--Isolated Communities--_The Jukes_--Other DegenerateFamilies--Scrofula

CHAPTER V

CONSANGUINITY AND MENTAL DEFECT

Idiocy and Insanity--Inheritability of Mental Defect--IntensifiedHeredity--Barr's Investigations--Other American and EnglishData--Mayet's Prussian Statistics--Genealogical Data

CHAPTER VI

CONSANGUINITY AND THE SPECIAL SENSES

United States Census Data--The Blind--Consanguinity of Parents--BlindRelatives--Degree of Blindness--Causes of Blindness--RetinitisPigmentosa--European Data--Probability of Blind Offspring ofConsanguineous Marriages--The Deaf--Irish Census--Scotland andNorway--United States Census--Consanguinity of Parents--DeafRelatives--Causes of Deafness--Degree of Deafness--Direct Inheritanceof Deafness--Intensification through Consanguinity--Dr. Fay'sStatistics--Personal Data--Probability of Deaf Offspring fromConsanguineous Marriages--Opinion of Dr. Bell

CHAPTER VII

SUMMARY AND CONCLUSION

Summary of Results--Inbreeding and Evolution--Effects of CloseInbreeding--Crossing and Variation--"Difference ofPotential"--Resemblance and Intensification--Coefficient ofCorrelation between Husband and Wife--Between Cousins--BetweenBrothers and Sisters--Consanguinity and Eugenics--Consanguinity andSocial Evolution--Conclusion

CHAPTER I

INTRODUCTION

The purpose of this essay is to present in a concise form and withoutbias or prejudice, the most important facts in regard toconsanguineous marriages, their effects upon society, and moreparticularly their bearing upon American social evolution. Theproblems to be considered are not only those which relate primarily tothe individual and secondarily to the race, such as the supposedeffect of blood relationship in the parents upon the health andcondition of the offspring; but also the effect, if any, which suchmarriages have upon the birth-rate, upon the proportion of the sexesat birth, and the most fundamental problem of all, the relativefrequency with which consanguineous marriages take place in a givencommunity. 

No thorough and systematic study of the subject has ever been made, and could not be made except through the agency of the census. Thestatistical material here brought together is fragmentary and notentirely satisfactory, but it is sufficient upon which to base somegeneralizations of scientific value. The sources of these data arelargely 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 inconnection with the general subject of consanguineous marriages arehere ignored as having no scientific interest, as for instance that ofthe so-called "marriages of affinity, " which has been so warmlydebated for the past fifty years in the British Parliament. 

For obvious reasons it will often be impossible to distinguish betweenthe different degrees of consanguinity, but wherever possible thedegree will be specified. It is probable that where a number ofmarriages are vaguely given as consanguineous, few are more distantthan second cousins, for in the United States especially, distantrelationships are rarely traced except by genealogists. In designatingdegrees of relationship the common terminology will be used, as in thefollowing table, expressing, however, the rather clumsy expression, "first cousin once removed" by the simpler form "1-1/2 cousin. "

[Illustration]

By far the greater part of the literature of consanguineous marriageis of a controversial rather than of a scientific nature, and a searchfor statistical evidence for either side of the discussion revealssurprisingly little that is worthy of the name. Yet men of highscientific standing have repeatedly made most dogmatic assertions inregard to the results of such unions, and have apparently assumed thatno proof was necessary. For example, Sir Henry Sumner Maine "cannotsee why the men who discovered the use of fire, and selected the wildforms of certain animals for domestication and of vegetables forcultivation, should not find out that children of unsound constitutionwere 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, " andfrequent appeals are made to Scripture, wrongly assuming that themarriage of cousins is prohibited in the Mosaic Law. 

The origin of "prohibited degrees" is only conjectural. The ChristianChurch apparently borrowed its prohibitory canons from the RomanLaw, [3] and a dispensation is still necessary before a Catholic canmarry his first cousin. However, such dispensations have always beeneasy to obtain, especially by royal families, and even the marriage ofuncle and niece sometimes occurs, as among the Spanish Habsburgs, andas 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 inEngland by the Marriage Act of 1540, [4] but by this time the idea ofthe harmfulness of kinship marriage was so thoroughly impressed uponthe people that they were very prone to look askance at such unions, and if they were followed by any defective progeny, the fact would benoted, and looked upon as a chastisement visited upon the parents fortheir sin. Naturally the idea became proverbial, and in some places ithas 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 fromthe pen of Noah Webster, in an essay which should be as interesting tothe spelling reformer as to the sociologist. [5] He writes: "It iz nocrime for brothers and sisters to intermarry, except the fatalconsequences to society; for were it generally practised, men wouldbecome a race of pigmies. It iz no crime for brothers' and sisters'children to intermarry, and this iz often practised; but such nearblood connections often produce imperfect children. The common peeplehav hence drawn an argument to proov such connections criminal;considering weakness, sickness and deformity in the offspring azjudgements upon the parents. Superstition iz often awake when reezoniz asleep. "

[Footnote 5: Webster, _Collection of Essays and Fugitiv Writings onMoral, Historical, Political and Religious Subjects_, 1790, p. 322. ]

From about 1855 to 1880 much was written about the effect ofconsanguineal interbreeding. One of the first contributions came fromAmerica. In 1858 Dr. S. M. Bemiss, of Louisville, Kentucky, reported tothe American Medical Association the results of his investigation of833 cases of consanguineous marriage. [6] His compilation remains tothis day the largest single piece of direct statistical work on thesubject. Unfortunately, however, his statistics have a strong, ifunintentional, bias which seriously affects their value. In France oneof the earliest discussions was by M. Boudin, [7] who evidentlyobtained the Bemiss report (attributing it to Dr. O. W. Morris, who hadquoted freely from Bemiss), [8] and enlarged greatly upon itsfallacies. He also collected statistics of the deaf-mutes in Paris, and, by an amazing manipulation of figures, "demonstrated" thatconsanguinity of the parents was the cause of nearly one-third of thecases of congenital deafness. The savants of the Sociétéd'Anthropologie took sides and the debate became very entertaining. Finally M. Dally came to the rescue, and published some very sane andlogical articles which avoided both extremes, and first advanced thetheory that any ill effects of consanguineous marriage should beattributed 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 Sociétéd'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 Société 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 andlong-suffering "deceased wife's sister. " The best of the English workhas been the statistical study by George H. Darwin, [10] and theclassic "Marriage of Near Kin" by Alfred H. Huth, a book of 475 pages, including a very complete bibliography to the date of the secondedition, 1885. Although Mr. Huth's book is not free from error, and isencumbered with a large amount of worthless material, it is now afterthirty-three years, by far the best treatment of the subject. 

[Footnote 10: "Marriages of First Cousins in England and theirEffects, " _Journal Statistical Society_, 1875, pp. 153-184. ]

In Italy Dr. Montegazza, [11] in Spain Señor Pastor[12] and others, have made useful contributions. German writers have usually preferredmore general subjects, but many of them have given much space toconsanguineous 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 laReal Academia de Ciencias Morales y Políticas_, vol. Ii, pp. 369-400. ]

Since the appearance of the Bemiss report little has been published inthis country which bears directly upon our subject. The most importantAmerican contribution, however, is to be found in the Special Reporton the Blind and the Deaf, in the Twelfth Census of the United States, prepared by Dr. Alexander Graham Bell. Although American writers havehad little part in the theoretical discussions, our legislators havebeen active, so that the statutes of every state specify degrees ofkinship within which marriage is prohibited. In at least sixteenstates the prohibition is extended to include first cousins. In NewHampshire such marriages are void and the children are illegitimate. Other states in which first-cousin marriage is forbidden arePennsylvania, Ohio, Indiana, Illinois, Michigan, Kansas, North Dakota, South Dakota, Wyoming, Nevada, Washington, Oregon, Missouri, Arkansas, and Louisiana. Since both Oklahoma and Indian Territory had similarlaws, the present State of Oklahoma should probably be added to thislist. In all of these states marriages within the prohibited degreesare incestuous or void or both, except in Ohio, where no expressdeclaration is made in the statute. In Ohio, Indiana, Nevada andWashington the law is made to read: "and not nearer of kin than_second cousins_, " therefore including "1-1/2 cousins" within theprohibited degrees. In many states the marriage of step relatives isforbidden, as also marriage with a mother-in-law or father-in-law. Ofthe territories, Arizona, Alaska, and Porto Rico forbid the marriageof first cousins, but in Porto Rico the court may waive theimpediment. 

These laws probably have some effect in reducing the number ofconsanguineous marriages in these states, but the sentiment back ofthe law is more responsible for the decrease in the number of suchunions than the law itself. For in the nature of things enforcementwould be very difficult, and apparently little real effort is made inthat direction. In Ohio, and probably elsewhere, the question as toconsanguinity is not directly put to the applicants for a marriagelicense. The applicants are required to answer the usual questions inregard to age, parentage, residence, etc. , and are then required toswear that their previous statements have been correct and thatneither of them is "epileptic, imbecile or insane, " that they are "notnearer of kin than second cousins, and not at the time under theinfluence of any intoxicating liquor or narcotic drug. " Undoubtedlyviolations of the consanguinity clause are very frequent, and it islikewise easily evaded by going to another state where the laws aremore liberal. One effect of the law is to provide a painless method ofsevering the marriage bond. A correspondent, who is a District CourtJudge in Kansas, in reporting a case of first cousin marriage, addsthat he "divorced them on the ground of consanguinity. "

In the absence of direct investigation by the Census Bureau, or otherpublic records of consanguineous marriages, perhaps the most promisingfield for research is in the genealogical records of Americanfamilies. Several thousand volumes of such material have beenpublished within the last half-century, and a large number of theseare very carefully and scientifically prepared. The material gatheredfrom such sources is very accurate in regard to the number of births, youthful deathrate etc. , but mental or physical defects are rarelymentioned. The greatest objection to the utilization of this material, however, is the amount of labor necessary in order to glean thedesired facts from the mass of irrelevant data. For example, in orderto find one case of first cousin marriage it is necessary on anaverage, to examine the records of nearly two hundred other marriages. 

The collection of data from personal sources is likewise open to graveobjections. Not only is the informant likely to be biassed, but thecases which he will remember will be those in which something unusualhas occurred. Herein lay the fallacy in the conclusions of Dr. Bemiss. I have endeavored to overcome this bias by restricting my requestsfor information to genealogists and others who would more naturallyappeal to records, but my efforts have been only partially successful. 

The number of cases of consanguineous marriage, embracing all degreesof consanguinity, which I have collected from these two sources, genealogies and correspondence, is 723, a number too small in itselfto establish any definite conclusions; but by using this material inconnection with other related data, I trust I may be able to addsomething to the comparatively small amount of real knowledge whichthe world already possesses in regard to the marriage of kin. 

In the course of my investigations I visited Smith's Island, in theChesapeake Bay, about twelve miles across Tangier Sound, fromCrisfield, Maryland, and nearly opposite the mouth of the Potomac. Here is a community of about seven hundred people, who are principallyengaged in the sea-food industry. Their ancestors have lived on theisland for many generations and there have been comparatively fewaccessions to the population from the mainland. As a naturalconsequence the population is largely a genetic aggregation. Consanguineous marriages have been very frequent, until now nearly allare more or less interrelated. Out of a hundred or more families ofwhich I obtained some record, at least five marriages were betweenfirst cousins. All of these were fertile, and all the children wereliving and apparently healthy. Since over thirty per cent of theinhabitants bear one surname (Evans), and those bearing the first foursurnames in point of frequency (Evans, Brad-shaw, Marsh, and Tyler)comprise about fifty-nine per cent of the population, it will readilybe seen that comparatively few absolutely non-related marriages takeplace. 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 fromthe usual causes. During this period there has not been a single caseof idiocy, insanity, epilepsy, deaf-mutism or even of typhoid fever onthe island. 

The evidence gathered from various other isolated communities is veryconflicting. Huth describes a great many of them which have existedfor many generations without crosses without ill results. Otherwriters quote instances where whole communities have becomedegenerate. Until the antecedents of a community are known it is ofcourse impossible to estimate the effect of consanguinity. Theexceptionally high percentage of deaf-mutism on Martha's Vineyard mayto some extent be due to a high percentage of consanguineous marriage, but that inbreeding is not the primary cause is revealed by therecords showing that among the first settlers were two deaf-mutes, whose defect has been inherited from generation to generation for twohundred and fifty years. [13]

[Footnote 13: See article in Cincinnati _Gazette_, Jan. 22, 1895. ]

CHAPTER II

RATIO OF THE CONSANGUINEOUS TO ALL MARRIAGES

Towards determining the average frequency of occurrence ofconsanguineous marriages, or the proportion which such marriages bearto the whole number of marriages, little has as yet been done in thiscountry. Professor Richmond Mayo-Smith estimated that marriagesbetween near kin constituted less than one per cent of the total, [14]and Dr. Lee W. Dean estimates that in Iowa they comprise only aboutone half of one per cent. [15] But these estimates are little more thanguesses, without any statistical basis. 

[Footnote 14: _Statistics and Sociology_, p. 112. ]

[Footnote 15: _Effect of Consanguinity upon the Organs of SpecialSense_, p. 4. ]

In several European countries such marriages have been registered, though somewhat spasmodically and inaccurately. According toMulhall[16] the ratio of the consanguineous among 10, 000 marriages inthe various countries is as follows:

 TABLE I. -----------------------------------Country. | Ratio. | Country. | Ratio. -----------------------------------Prussia | 67 | Alsace | 107Italy | 69 | France | 126England | 75 | Jews | 230-----------------------------------

[Footnote 16: _Dictionary of Statistics_, p. 383. ]

According to Uchermann the ratio is 690 or 6. 9 per cent, includingmarriages between second cousins and nearer. [17] Dr. Peer says that 4per cent of the marriages in Saxony are consanguineous. [18] The ratioseems to be increasing in France but diminishing in Alsace and Italy, as indicated in Table II. [19]

[Footnote 17: _Les Sourds-muets en Norvège_. Quoted by Feer, p. 9. ]

[Footnote 18: _Der Einfluss der Blutsverwandschaft der Eltern auf dieKinder_, 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 | 126Alsace | 1858-65| 143 | Alsace | 1872-75 | 107Italy | 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 | 117Naples | 30 | Piedmont | 131Lombardy | 100 | Liguria | 183------------------------------------------ [A] Per 10, 000. 

It will be noted that the lowest ratios are in provinces where theurban population is comparatively large. Wherever statistics have beengathered it is the rule that the percentage of consanguineous marriageis greater in rural than in urban districts. Table IV, also fromMulhall, illustrates this point. 

 TABLE IV. ------------------------------------------------- |_Ratio per 10, 000 Marriages_. -------------------------------------------------Country. | Rural. | Urban. | General. -------------------------------------------------England | 79 | 71 | 75France | 130 | 115 | 126Alsace | 121 | 41 | 107Norway[A] (Uchermann)| 810 | 260 | 690------------------------------------------------- [A] Includes second cousins. 

In regard to the degree of consanguinity, it seems very probable thatin the French, German, Italian, and English statistics and estimatesfew if any marriages beyond the degree of first cousins are returnedas consanguineous, so in order to compare the Norwegian figures withthe others they should probably be reduced by one half. Out of 1549consanguineous marriages contracted in Prussia in 1889, 1422 werebetween "cousins" (probably first), 110 between uncles and nieces, and16 between nephews and aunts. [20] The ratio of such marriages to10, 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. 1Uncle 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 consanguineousmarriages 92 per cent were of cousins and 8 per cent were of uncle andniece 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 theyears 1853-62 there were 10, 765 marriages in the _8me arrondissement_of Paris, and of these he finds:

-----------------------------------------Marriages between cousins-german | 141Marriages between uncle and niece | 8Marriages between aunt and nephew | 1Total consanguineous | 150-----------------------------------------

[Footnote 23: "Recherches sur les Mariages Consanguins et sur lesRaces Pures. " in _Bulletins de la Société d'Anthropologie_, 1863, p. 527. ]

This is rather higher than the average for urban districts, accordingto official figures, but Dally seems to consider it as typical. Hegives examples of the carelessness and incompetency of the ruralrecord keepers, and insists that the percentage is really much higherthan the official figures would indicate. He estimates theconsanguineous marriages in France not including second cousins, atfrom four to five per cent. 

A very ingenious method of determining the approximate number offirst-cousin marriages was devised by Mr. George H. Darwin. [24]Noticing that in marriage announcements, some were between persons ofthe same surname, it occurred to him that there might be a constantratio between same-name marriages and first cousin marriages. Somesame-name marriages would of course be purely adventitious; so, toeliminate this element of chance, he obtained from the RegistrarGeneral's Report the frequency of occurrence of the various surnamesin England. The fifty commonest names embraced 18 per cent of thepopulation. One person in every 73 was a Smith, one in every 76 aJones and so on. Then the probability of a Smith-Smith marriage due tomere 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 perthousand. After the fiftieth name the fractions were so small as tohave comparatively little effect upon the total. He thereforeconcluded that about one marriage in a thousand takes place, in whichthe parties have the same surname and have been uninfluenced by anyrelationship between them bringing them together. 

[Footnote 24: "Marriages between First Cousins in England and theirEffects, " in _Journal of the Statistical Society_, June, 1875. Pp. 154_et seq_. ]

The next step was to count the marriages announced in the "_Pall MallGazette_" for the years 1869-72 and a part of 1873. Of the 18, 528marriages there found, 232 or 1. 25 per cent were between persons ofthe same surname. Deducting the percentage of chance marriages atleast 1. 15 per cent were probably influenced directly or indirectly byconsanguinity. 

Mr. Darwin then proceeded by a purely genealogical method. He foundthat out of 9, 549 marriages recorded in "Burke's _Landed Gentry_, " 144or 1. 5 per cent were between persons of the same surname, and exactlyhalf 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 cousinmarriages. He then sent out about 800 circulars to members of theupper middle class, asking for records of first cousin marriage amongthe near relatives of the person addressed, and obtained the followingresult:

-----------------------------------------------Same-name first cousin marriages | 66Different-name first cousin marriages | 182Same-name not first cousin marriages | 29-----------------------------------------------

These cases furnished by correspondents he calculated to be 3. 41 percent of all marriages in the families to which circulars were sent. 

From the data collected from all these sources Mr. Darwin obtains thefollowing 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 . 50instead of . 57. By a similar line of reasoning he obtains thisproportion:

 Same-name first cousin marriages 1------------------------------------- = ---Different-name first cousin marriages 3

Here too, he fears that the denominator is too small, for bytheoretical calculation he obtains by one method the ratio 2/7, andby another 1/1. He finally takes 1/4 for this factor. To express theproportion 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 computesthe percentages of first cousin marriages in England with thefollowing results:

---------------------------------------London | 1. 5Other urban districts | 2. Rural districts | 2. 25Middle class and Landed Gentry | 3. 5Aristocracy | 4. 5---------------------------------------

In order to apply this formula to the American population I countedthe names in the New York Marriage License Record previous to1784, [25] and found the number to be 20, 396, representing 10, 198marriages. The fifty commonest names embraced nearly 15 per cent ofthe whole (1526), or three per cent less than the number found byDarwin. [26] Of these, one in every 53 was a Smith, one in 192 aLawrence, 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 theprobability of a chance marriage between persons of the same name waseven less than in England, where Mr. Darwin considered it almost anegligible quantity. 

[Footnote 25: _Names of Persons for whom Marriage Licenses were issuedby 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 personsbearing the same surname. Applying Darwin's formula we would have 5. 9as the percentage of first cousin marriages in colonial New York. This figure is evidently much too high, so in the hope of finding thefallacy, I worked out the formula entirely from American data. Toavoid the personal equation which would tend to increase the number ofsame-name first cousin marriages at the expense of the same-name notfirst cousin marriages, I took only those marriages obtained fromgenealogies, which would be absolutely unbiassed in this respect. Outof 242 marriages between persons of the same name, 70 were betweenfirst 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 inassuming that not more than 1/3 of all same-name marriages are firstcousin marriages. Taking data from the same sources and eliminating asfar as possible those genealogies in which only the male line istraced, 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 whichhe finally changed to 1/4. I am inclined to think that his first ratiowas nearer the truth, for since we have found that the coefficient ofattraction between cousins would be so much greater than betweennon-relatives, why should we not assume that the attraction betweencousins of the same surname should exceed that between cousins ofdifferent surnames? For among a large number of cousins a person islikely to be thrown into closer contact, and to feel better acquaintedwith those who bear the same surname with himself. But since thetheoretical ratio would be about 1/4 it would hardly be safe to putthe probable ratio higher than 1/3, or in other words four firstcousin marriages to every same-name first cousin marriage. Ourrevised formula then is:

All same-name marriages 3 1--------------------------- = --- X --- = . 75All first cousin marriages 1 4

Instead of Mr. Darwin's . 35. 

Taking then the 10, 198 marriages, with their 2. 07 per dent ofsame-name marriages, and dividing by . 75 we have 2. 76 per cent, or 281first cousin marriages. 

In order to arrive at approximately the percentage of first cousinmarriages in a nineteenth-century American community I counted themarriage licenses in Ashtabula County, Ohio, for seventy-five years, (1811-1886). Out of 13, 309 marriages, 112 or . 84 per cent were betweenpersons of the same surname. Applying the same formula as before, wefind 1. 12 per cent of first cousin marriages, or less than half thepercentage found in eighteenth-century New York. This difference mayeasily be accounted for by the comparative newness of the Ohiocommunity, in which few families would be interrelated, and also tothat increasing ease of communication which enables the individual tohave a wider circle of acquaintance from which to choose a spouse. 

Adopting a more direct method of determining the frequency of cousinmarriage, I estimated in each of sixteen genealogical works, thenumber of marriages recorded, and found the total to be 25, 200. Fromthese sixteen families I obtained 153 cases of first cousin marriage, or . 6 per cent. Allowing for the possible cases of cousin marriage inwhich the relationship was not given, or which I may have over-looked, the true percentage is probably not far below the 1. 12 per centobtained by the other method. 

The compiler of the, as yet, unpublished Loomis genealogy writes methat he has the records of 7500 marriages in that family, of which 57or . 8 per cent are same-name marriages. This would indicate that 1. 07per cent were between first cousins. 

In isolated communities, on islands, among the mountains, familiesstill remain in the same locality for generations, and people areborn, marry and die with the same environment. Their circle ofacquaintance is very limited, and cousin marriage is therefore morefrequent. If we exclude such places, and consider only the moreprogressive American communities, it is entirely possible that theproportion 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 farout 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 of1872. |marriages |same-name |first cousin |registered. |marriages. |marriages. ----------------------------------------------------London, | | |Metropolitan | | |Districts | 33, 155 | . 55 | . 73Urban Districts| 22, 346 | . 71 | . 95Rural 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 thanfirst cousins figures are still more difficult to obtain. Thedistribution of 514 cases of consanguineous marriage from genealogieswas 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 | 208Different-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 distributionof consanguineous marriages, since the more distant the degree, themore difficult it is to determine the relationship. However it is veryevident that the coefficient of attraction is at its maximum betweenfirst cousins, and probably there are actually more marriages betweenfirst cousins than between those of any other recognized degree ofconsanguinity. But the two degrees of 1-1/2 cousins and second cousinstaken together probably number more intermarriages than first cousinsalone. Allowing four children to a family, three of whom marry andhave families, the actual number of cousins a person would have oneach 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 doublerelationships, but it will readily be seen that the consanguinealattraction would hardly be perceptible beyond the degree of thirdcousins. [27]

[Footnote 27: See note, _infra_, p. 29. ]

Omitting, as in the discussion on page 24, those genealogies in whichonly 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 | 50Different-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 ofrelationship the ratio of same-name to different-name cousin marriageswould increase in geometrical proportion, viz. First cousins, 1:3;second cousins, 1:9; third cousins, 1:27, etc. , but on the other handthere is the tendency for families of the same name to hold togethereven in migration as may be proved by the strong predominance ofcertain surnames in nearly every community. So that the ratio orsame-name to different-name second cousin marriage may not greatlyexceed 1:4. Beyond this degree any estimate would be pure guesswork. However the coefficient of attraction between persons of the samesurname would undoubtedly be well marked in every degree of kinship, and conversely there are few same-name marriages in which somekinship, 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 generationmarriages of either the next nearer or more remote degrees. Forexample, a man is more likely to marry his first or his second cousinthan either the daughter of his first cousin, or the first cousin ofone of his parents, although such mixed generation marriages oftentake place. 

The conclusions, then, in regard to the frequency of consanguineousmarriage 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 westernstates to 5 per cent, and probably higher, in isolated mountain orisland communities. The average of first cousin marriage in the UnitedStates is probably not greater than one per cent. 

2. The percentage of consanguineous marriages is decreasing with theincreasing ease of communication and is probably less than half asgreat now as in the days of the stage coach. 

3. Although the number of marriageable second cousins is usuallyseveral times as great as that of first cousins, the number ofmarriages between second cousins is probably somewhat less than thenumber of marriages between first cousins, but the number of secondcousin marriages combined with the number of 1-1/2 cousin marriagesprobably exceeds the number of first cousin marriages alone. So thatthe percentage of marriages ordinarily considered consanguineous isprobably between two, and two and a half. 

NOTE. --In an article entitled "Sur le nombre des consanguins dans ungroupe de population, " in _Archives italiennes de biologie_ (vol. Xxxiii, 1900, pp. 230-241), Dr. E. Raseri shows that from one point ofview the actual number of consanguineous marriages is little, if any, greater than the probable number. The average number of children to amarriage he finds to be 5, the average age of the parents 33 and theaverage age at marriage 25. The Italian mortality statistics show that54 per cent of the population lives to the age of 25, of which 15 percent does not marry, leaving an average of 2. 3 children in everyfamily who marry. On this basis a person would have at birth 4, 357relatives within the degree of fourth cousins; at the age of 33 hewould have 4, 547; and at 66, 5, 002. In 1897 out of 229, 041 marriagesin Italy, 1, 046 were between first cousins, giving an average of onein 219. In 1881 the number of men between 18 and 50 and of womenbetween 15 and 45 was 5, 941, 495 in 8, 259 communes with an averagepopulation of 3, 500. In each commune there must be 360 marriageablepersons of each sex, but to marry within his class a man would onlyhave the choice of 180 women and vice versa. Adding the probablenumber who would marry outside the commune, the choice lies within 216of the opposite sex. Of these 25 would be cousins within the tenthdegree (fourth cousins) making the probability of a consanguineousmarriage . 11, reduced by a probable error in excess to . 10. Theprobability of a first cousin marriage would be . 82/216 or . 0038, whereas the actual ratio is 1/219 or . 0045. 

CHAPTER III

MASCULINITY

The predominance of male over female births is almost universal, although varying greatly in different countries and under differentconditions. This fact has given rise to the term Masculinity, whichconveniently expresses the proportion of the sexes at birth. Thedegree of masculinity is usually indicated by the average number ofmale births to every 100 female births. The cause of thispreponderance of males is still a mystery, and will definitely beknown only when the causes of the determination of sex are known. Since, however, it is well known that infant mortality is greateramong males than among females, positive masculinity is necessary tokeep up the balance of the sexes, and therefore seems to be anessential characteristic of a vigorous and progressive race. 

Within recent years the theory has prevailed among certainsociologists that positive masculinity is stronger in the offspring ofconsanguineous marriages than in the offspring of unrelated parents. Professor William I. Thomas in his writings and lectures asserts thisas highly probable. [28] Westermarck, [29] to whom Professor Thomasrefers, quotes authorities to show that certain self-fertilized plantstend to produce male flowers, and that the mating of horses of thesame 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 denPferden. _ Quoted by Westermarck, p. 476. ]

Westermarck continues, quoting from Düsing:[31] "Among the Jews, manyof whom marry cousins, there is a remarkable excess of male births. Incountry districts, where, as we have seen, comparatively more boys areborn than in towns, marriage more frequently takes place betweenkinsfolk. It is for a similar reason that illegitimate unions show atendency to produce female births. "

[Footnote 31: _Die Regulierung des Geschlechtsverhaeltnisses_, pp. 243-244. ]

Westermarck comments: "The evidence for the correctness of hisdeduction is, then, exceedingly scanty--if, indeed it can be calledevidence. Nevertheless, I think his main conclusion holds good. Independently of his reasoning I had come to exactly the same resultin a purely inductive way. " He then quotes a number of travelers tothe effect that marriage between members of different races produce aphenomenal excess of female births. When we consider the extraordinaryproficiency in fiction attained by many travelers in strange lands, weare forced to the belief that Westermarck based his own conclusion onstill more scanty evidence. 

The statistics given by Dr. Düsing for Prussia[32] are as follows:

 TABLE IX. ------------------------------------------------------------ | | | Other | |Evangelical. | Catholic. | Christians. | Jews. ------------------------------------------------------------Male births | 4, 015, 634 | 2, 273, 708 | 12, 283 | 69, 901Female births| 3, 775, 010 | 2, 136, 295 | 11, 548 | 64, 939Masculinity | 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, 958Female births| 149, 205 | 179, 505 | 4. 254 | 2, 850Masculinity | 105. 73 | 105. 70 | 104. 9 | 103. 8--------------------------------------------------------------

In the face of these statistics it is impossible to deny thatendogamy within a great social class or an ethnic race may have sometendency to produce an excess of male births, while exogamy in thisbroad sense may diminish the masculinity. But the perpetuation of acomparatively pure race by marriage within that race, andconsanguineous marriage in the narrower sense are differentpropositions. It may easily be that the marriage of individuals of asimilar type regardless of consanguinity produces a greater excess ofmale offspring. According to the percentage of first cousin marriagesamong the Jews as given by Mulhall, [33] and allowing the averagenumber of children to a marriage, there would be only 3100 children ofsuch marriages among the Jewish births in Prussia, and in order thatthese might raise the masculinity of Jewish births even from 106 to107 the 3100 births would have to have a masculinity of 200. AmongProtestants, or especially among Catholics where the percentage ofcousin marriage is much smaller, it seems hardly reasonable that thegeneral masculinity would be appreciably affected. A much better casecan be made for similarity or difference of race as the cause of thevariation. The difference between Catholic and Protestant is, roughlyspeaking, the difference between the brachycephalic brunette Alpinerace and the dolichocephalic blonde Baltic race. So that a mixedmarriage in Germany would almost always mean the crossing of twodistinct types. 

[Footnote 33: _Dictionary of Statistics, op. Cit. _, p. 383. ]

The investigations of M. Gache in Buenos Ayres covering the periodfrom 1884 to 1894 inclusive, show that cross breeding has had theeffect of _raising_ the masculinity. The births resulting from unionsof Italian, Spanish and French male immigrants with native-bornArgentine females, show a higher masculinity than the births producedeither by pure Argentine alliances or by pure alliances of any ofthese nationalities of Buenos Ayres. Further, the unions of Argentinemales with females of foreign nationality provide a higher masculinitythan is common among Argentines themselves. [34] These facts do notnecessarily contradict the theory that any crossing of great racialgroups diminishes masculinity, for all of the nationalities involvedin this study are predominantly Mediterranean in blood. The theory isborne out by the statistics of the negroes in the United States, alarge proportion of whom are of mixed blood. For taking as a basis thenumber of children of negro descent born during the year ending June1, 1900 reported by the Twelfth Census, the females predominated, giving a negative masculinity of 99. 8. Furthermore, the percentage ofconsanguineous 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 failsto show any correspondence between the percentage of first cousinmarriage and the masculinity:

 TABLE XI. ---------------------------------------Country. |Masculinity. | Per cent 1st | |cousin marriage. ---------------------------------------England | 104. 5 | . 75France | 105. 3 | 1. 26Italy | 107. 0 | . 69Prussia | 105. 8 | . 67U. S. [36] | 104. 9 | 1. 00Jews[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 UnitedStates, for the Census gives the statistics for only one year in tenand even then is untrustworthy on this point. In a few states birthregistration is attempted but the figures thus obtained do notharmonize with the Census and the situation is not greatlyimproved. [38] The masculinity varies considerably in different partsof the country, and is generally higher in states where the ruralpopulation predominates. This fact agrees with European statisticswhich almost universally show a high masculinity in rural districts. Table XII, illustrates this point:

 TABLE XII. _Masculinity in Scotland_. [39]------------------------------------------------------- | | | | Mainland |InsularPeriod. |Principal|Large |Small | rural | rural | towns. |towns. |towns. |districts. |districts. -------------------------------------------------------1855-1861| -- | -- | -- | 105. 6 | 106. 61862-1871| -- | -- | -- | 105. 9 | 105. 61872-1881| 105. 0 | 105. 6| 106. 1| 105. 3 | 108. 01882-1891| 105. 1 | 105. 6| 105. 5| 105. 5 | 108. 71892-1901| 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 byconsanguineous marriage, for consanguineous marriage is more frequentin rural districts, and especially in insular rural districts. Butunless consanguineous marriages can directly be shown to produce anexcess of male births greater than the normal, such indirect evidenceis valueless. 

In the genealogical material previously considered, we have a samplingof the American population throughout its whole history, but the dataso far collected are insufficient for more than an indication of whatmight be expected in further research along the same line. In thefollowing table as before, the figures compiled from printedgenealogies are separated from those obtained through correspondenceand from miscellaneous sources. The "unrelated" marriages fromgenealogies, are marriages of brothers and sisters of the persons whohave married first cousins, and their records were obtained from thesame sources as those in the next previous category. The "children offirst cousins" are the offspring of the first cousin marriages whomarried persons not related to themselves by blood. The last categoryincludes distantly related marriages from correspondence and othersources and marriages between persons of the same surname whoserelationship could not be traced. 

 TABLE XIII. ------------------------------------------------------------------ | | Sex of Children. | |Number |-----------------------|Mascu-Marriages. |Fertile. | Male. |Female. |Unknown. |linity. ------------------------------------------------------------------1st cousin. Gene. | 125 | 318 | 314 | 40 | 101Unrelated. Gene. | 629 | 1561 | 1559 | 64 | 100Ch. Of 1st cousins. Gene. | 170 | 402 | 375 | 48 | 107Other cousin. Gene. | 301 | 736 | 666 | 15 | 1111st Cousin. Cor. | 150 | 316 | 295 | 148 | 107Ch. Of 1st cousins. Cor. | 124 | 192 | 164 | 214 | 111Miscellaneous | 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 mightappreciably change any of the ratios. It will be noticed, however, that the two categories whose masculinity is most similar (100 and101), are derived from cases taken from the same families and from thesame environment, and differing only in that the first is closelyconsanguineous while the second is not. The third and fourth groups, separated from the first two by at least a generation, and probablyliving in a different environment, differ greatly in masculinity fromthem. In the fourth group are included 1-1/2, second, third, and a feweven more distant cousins, all more distantly related than firstcousins, and taken from the same genealogies as these; yet themasculinity is much greater. 

An analysis of the cases collected fifty years ago by Dr. Bemiss, ofcourse 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. 32d and 3rd cousins | 124 | 264 | 240 | 110. 0All consanguineous | 833 | 1509 | 1411 | 106. 9Unrelated | 125 | 444 | 380 | 116. 9----------------------------------------------------------

[Footnote 40: Bemiss, _Report on Influence of Marriages ofConsanguinity_, pp. 420-423. ]

In the "Marriage of Near Kin, " Mr. Huth gives a list of cases ofconsanguineous marriage collected by various persons from all overEurope. [41] He is free to say that they are worse than useless for thepurpose for which they were collected, that of determining whether ornot such marriages produce degeneracy, but in so far as the sex of thechildren is concerned they would not be biassed. 

 TABLE XV. ----------------------------------------------------- |Sex of Children. | |----------------| Marriage. | Male. | Female. | Masculinity. -----------------------------------------------------1st cousins and nearer| 165 | 164 | 100More 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 determiningfactor in sex, its influence is negligible when a small number ofcases is considered. It is interesting accordingly to note that of 100children of incestuous unions and from uncle-niece and aunt-nephewmarriages from Bemiss, Huth and other sources, the sex distributionwas 48 males and 52 females, giving a negative masculinity of 92. 

While in general the evidence presented in this chapter is somewhatconflicting, that which bears most directly upon the problem does notsubstantiate the hypothesis of Westermarck. The evidence in favor ofthe theory is all indirect and is open to other interpretations. It ishardly safe to go to the other extreme and to assert thatconsanguinity diminishes masculinity. The safest, and withal the mostreasonable conclusion is that consanguinity in the parents has noappreciable effect upon the sex of the child. 

CHAPTER IV

CONSANGUINITY AND REPRODUCTION

The principal object of nearly every previous discussion of theintermarriage of kindred, has been either to prove or to disprove somealleged injurious effect upon the offspring. The writers who havetreated the subject may be divided into three groups. First, those whohave maintained in accordance with popular opinion that consanguinity_per se_ is a cause of degeneracy or that in some mysterious waykinship of the parents produces certain diseases in the children. Inthis group Boudin in France and Bemiss in America are typical. Second, those who have flatly contradicted this position and have assertedthat on the whole such marriages are beneficial, and that crossing isin itself injurious to the race. Huth is the chief exponent of thistheory, although he admits that where degenerate conditions exist inthe parents consanguinity in marriage may not be beneficial. The thirdgroup holds that cousin marriages in themselves, especially if notcarried through too many generations, are not harmful, but that if anyhereditary tendency to malformation or disease exists in the family ofthe parents, this tendency, inherited through both parents is stronglyintensified in the offspring, and that consequently an increasedpercentage of the offspring of cousin marriage may be afflicted withhereditary diseases. This group includes a number of the later writerssuch as Feer and Mayet. Among the earlier discussions, those of Dallyin France and George H. Darwin in England take substantially thisposition. On the whole this theory seems to be the most reasonable oneand with a few modifications it will be seen to account for all thefacts herein presented. 

It is undeniable that degeneracy does in some cases follow from themarriage of near kin, and probably with greater frequency than fromnon-related marriages. But it is likewise true that many of theworld's greatest men have been the products of close inbreeding, sometimes continued through several generations. Frederick the Greatof Prussia was the product of three successive cousin marriagesbetween descendants of William the Silent, [42] and among his sevenbrothers and sisters at least three others ranked among the ablest menand women of the generation. Cousin marriage has always been frequentin the "first families of Virginia" which have produced a phenomenalpercentage of able men. In fact, few persons who have traced theirpedigrees back through a number of generations, do not find some namesduplicated, as a result of cousin marriage. 

[Footnote 42: Woods, _Heredity in Royalty_, pp. 74-75. The GreatElector, a great-grandson of William the Silent, married his 1-1/2cousin, a granddaughter of William and also a great-granddaughter ofAdmiral Coligny. Frederick I married his second cousin, daughter ofthe Duchess Sophia of Brunswick, and a descendant of William. Frederick William I married his first cousin, Dorothea, granddaughterof Sophia, and also a descendant of William the Silent. Unfortunatelythe Hohenzollern line was continued by a mediocre brother of FrederickII, but through his sister, Queen Ulrica, the line of genius lastedstill another generation to Gustavus III of Sweden. ]

The ills which have at one time or another been attributed toconsanguineous marriage include nearly all those which cannototherwise be satisfactorily accounted for. But with the progress ofpathology the list has greatly been reduced: for instance, cretinismis now known to be a product of local conditions. The remainingcounts in the indictment against consanguineous marriage may roughlybe classified as: 1. The production of infertility, some forms ofphysical degeneracy, and deformity. 2. The production or aggravationof mental and nervous disorders. 3. The production of certain defectsin the organs of special sense. These three divisions will bediscussed separately. 

1. INFERTILITY AND DEGENERACY

Although there has never been any considerable evidence for the firstof these charges, it has frequently been repeated. ProfessorMontegazza of the University of Pavia collected data in regard to 512cases of consanguineous marriage of which between 8 and 9 per centwere sterile, and with this basis he asserts that sterility is theonly fact which can safely be deduced from his cases, since it cannotbe hereditary. [43] But if in the nature of things absolute sterilityis not inheritable, comparative infertility may be. And even then 8 or9 per cent does not seem to be an excessively high proportion ofsterility, especially if late marriages be counted. Boudin bases hisassertion on this point on even less tenable grounds. [44] On the otherhand some writers assure us that cousin marriages are even moreprolific and less liable to sterility than the average. 

[Footnote 43: See Darwin, "Marriages between First Cousins in Englandand Their Effects, " _Journal of Statistical Society_, June, 1875, p. 178. ]

[Footnote 44: Boudin, "Croisement des familles, de races et desespèces. " In _Memoires de la Société d' Anthropologie_, vol. I, p. 518. ]

The most important statistical investigation was made by G. H. Darwin. [45] From his genealogical data he compiled the followingtable:

 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. 26Parents 1st cousins[A] |97 to 105 |2. 07 to 1. 92|14. 7 to 20. 9| 2. 43One 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 thevariation is slight, but the higher fertility of the cousin marriagesis interesting. 

On the other hand de Lapouge quotes a case of a community founded twocenturies ago by four families and populated almost entirely by theirdescendants, in which from 1862 to 1886 there were 273 marriages ofwhich 63 were consanguineous and 26 were between first cousins. Amongthe non-consanguineous 3 per cent were uniparous, as against 7. 95 percent among the consanguineous. 7. 5 per cent of the non-consanguineouswere sterile as against 16 per cent of the consanguineous. [46] Theimportance of these percentages is impaired by the fact that theyinvolve only five uniparous families and ten sterile ones, and that ofthese 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 sterilityfrom genealogies, for when no children are given in the record, thereis always a strong possibility that there were children of whom thegenealogist has no record. However, of 16 first-cousin marriages ofwhich the record expressly stated "no issue, " or where it waspractically certain that no issue was possible, the average age of thebrides was 34. 3 years and that of the grooms was 39 years, showingthat consanguinity could not have been the only cause of theirsterility. 

In regard to relative fertility the figures are reliable, but theyfail to indicate any effect of consanguinity upon fertility, as willbe noted in Table XVII. 

 TABLE XVII. ------------------------------------------------------------- |No. Of | | Ave. To |fertile | No. Of | fertileParentage. |marriages. |children. |marriage. -------------------------------------------------------------First cousin. Gene. | 125 | 672 | 5. 4First cousin. Cor. | 150 | 759 | 5. 1Double cousins and uncle-niece| 9 | 39 | 4. 3Other consanguineous | 333 | 1605 | 4. 8Non-related | 676 | 3417 | 5. 1Ch. Of 1st cousins | 294 | 1395 | 4. 7All consanguineous | 617 | 3075 | 5. 0All 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 | fertileParentage. |marriages. |children. |marriages. -------------------------------------------------------1st cousins or nearer[A]| 660 | 3363 | 5. 0More distantly related | 119 | 572 | 4. 8Non-consanguineous | 125 | 837 | 6. 7Ohio consanguineous | 155 | 1021 | 6. 6Ohio 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 fromBemiss may easily be accounted for by the fact that the cases werehighly selected so that nearly one-third of the children were in someway defective, and the parents in many cases were far below theaverage in vitality. The "more distantly related" are in a stilllesser degree representative of the class, since out of a greaterpossibility of choice a smaller number were chosen. The"non-consanguineous" were supposed to be near the average in vitalityand fertility. 

In Norway, according to Uchermann, the consanguineous and thenon-consanguineous marriages are equally fertile, averaging 6. 1children per marriage;[49] and in a Black Forest village Tenckhofffound an average of 4. 6 children to each consanguineous marriage asagainst 3. 5 to each non-consanguineous marriage. [50] In regard to theyouthful death-rate among the offspring of consanguineous marriages, comparison with non-related marriages is more feasible. I have countedin each case all those children who are known to have died under theage of twenty. This age was taken for the sake of convenience, and toinclude 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. 7Other cousins | 1417 | 211 | 14. 9Ch. Of 1st cousins| 825 | 103 | 12. 5Non-consanguineous| 3184 | 370 | 11. 6-------------------------------------------------(Correspondence. )-------------------------------------------------First cousins | 759 | 88 | 11. 6Other marriages | 829 | 71 | 8. 6-------------------------------------------------

[Footnote 49: Feer, _Der Einfluss der Blutsverwandschaft der Elternauf 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 thegenealogical cases at least, the youthful death-rate among theoffspring of consanguineous marriages far exceeds the average. Theaverage in the correspondence cases is undoubtedly too low, as manycorrespondents failed to report the deaths. From the fact that acomparatively large percentage of these were reported as defective, weshould expect a higher death-rate than among the unbiased genealogicalcases. 

Dr. Bemiss found a very high death-rate among the children ofconsanguineous marriage, due partly to the fact that his cases werereported by physicians. He reports that of the offspring of marriagesbetween 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, astrong indication of lowered vitality as a result of consanguineousmarriage. 

A determination of even the approximate percentage of degenerateoffspring resulting from marriages of consanguinity by direct inquiryis exceedingly difficult. The average human mind is so constituted asto exaggerate unconsciously the unusual in its experience. Herein liesthe fallacy in the work of Dr. Bemiss. His material was "furnishedexclusively by reputable _physicians_ in various states, " and of the3942 children of consanguineous marriages in the cases thus furnishedhim, 1134 or 28. 8 per cent were in some way "defective. " Of these, 145were deaf and dumb, 85 blind, 308 idiotic, 38 insane, 60 epileptic, 300 scrofulous and 98 deformed. It is evident that a physician inreporting such data to a physician would naturally give cases in whichsomething pathological existed. Even if there were no conscious bias, such cases would be the ones with which a physician would be mostlikely to come in contact. Dr. Bemiss himself recognized thepossibility 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 hisconclusions. 

In order as far as possible to avoid this bias, I sent my owncirculars to genealogists and others who would naturally be moreinterested in the relationships than in pathological conditions. Iasked, however, that all such results be noted. Among 722 children offirst cousins I found 95 or 13 per cent who were defective in thesense in which Bemiss used the term. This is much nearer the actualpercentage, but I have reason to believe, as will be seen hereafter, that even this percentage is far too high. A good illustration of theunconscious bias, which I tried to avoid is afforded by the reports onthe cause of death among children of first cousins. Only 58 replieswere given to this question, and of the 58 deaths 14 or one-fourthwere either accidental or otherwise violent, while only one person wasreported to have succumbed to pneumonia. 

Many efforts have been made to investigate the occurrence ofdegeneracy in the offspring of consanguineous marriages, by studyingcommunities in which such unions have been frequent, but the resultsare untrustworthy. Huth[52] quotes a number of instances wherecommunities have lived for generations without crosses and with noapparent degeneracy, while other writers tell of high percentages ofdegeneracy. Smith's Island, Maryland, as has been said, seemsabsolutely free from serious congenital abnormalities, in spite of thegreat frequency of consanguineous marriages. 

[Footnote 52: _Marriage of Near Kin_, chap. Iv. ]

The causes of degeneracy are so varied, complicated, and obscure thateven if consanguinity is a cause, there can be but few cases in whichit is not complicated by other factors. But for the same reason thatit is so difficult to prove any connection between consanguinity anddegeneracy, it is equally difficult to disprove such a connection. Itis very probable that from the mere operation of the law of heredity, there must be a comparatively large percentage of degenerates amongthe offspring of related parents, for defects which tend to be bredout by crossing are accentuated by inbreeding. This may be the reasonfor the disagreement among investigators of isolated communities. Ifan island, for instance, were settled by a small group of families ineven one of which some hereditary defect was common, in the course ofa few generations that defect would be found in a relatively largepart of the population. While if the same island were settled byperfectly sound families, there would only be a remote chance of anyparticular defect appearing. Thus both classes of investigators may beperfectly conscientious, and yet arrive at diametrically oppositeresults. This theory is at least not to be contradicted by any factswhich have come to light in the present investigation. 

Some interesting points are brought up in Dugdale's well-known studyof the "Jukes. "[53] This family, of about 540 persons living innorthern New York, is descended from five sisters of unknownparentage, who were born between 1740 and 1770. The name "Juke" isfictitious, and is applied to all descendants of these five women, little attempt being made to trace the male lines on account of theexcessive 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 andcould not associate on equal terms with other members of thecommunity. These marriages seem to have been fully as productive asthe average of the family, and the offspring of as high a grade ofintelligence. However, some individual cases are worthy of specialmention 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 andhealthy, and her father had a good reputation, but her mother hadgiven birth to four illegitimate children before marriage, three ofwhom were mulattoes. Thus in this marriage of first cousins, three outof the four parents were of a low moral grade. As a result of thismarriage three sons and three daughters were born. Two sons werelicentious, intemperate and dishonest, two daughters were prostitutes, and the third became such after her husband was sent to prison. Onlyone son turned out fairly well. This son married a second cousin, agranddaughter of Delia Juke, and four out of his seven children wereabove the average of the family. His two elder brothers, however, married prostitutes, and became ancestors of criminals, prostitutesand syphilitics. [54]

[Footnote 54: Ibid. , Chart I. ]

(2) A legitimate son of Ada Juke, whose father was a thief and apauper, married a daughter of Clara Juke, whose antecedents werefairly good. The husband had contracted syphilis before marriage andentail it upon every one of his eight children. Five daughters becameprostitutes and one was idiotic. The only daughter who bore a goodreputation married a grandson of both Clara and Bell Juke. This was aremarkable case of selection. Both husband and wife were grandchildrenof Clara, and so first cousins, and both were the offspring of firstcousins, all within the Juke blood. But, on the other hand, both werethe descendants of Clara, the best of the Juke sisters, and both werethe best of the progeny of their respective parents. The only serioustaint was the secondary syphilis which the wife had inherited from herfather. Six children were born, two males and four females. The eldestson 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 aregiven simply as "unmarried. " This family seems to have had as high anaverage mentally and morally as any family in the whole tribe, onlyone in six being distinctly immoral. In the next generation, theeldest son had two children, the eldest daughter four, and the thirddaughter, who married a first cousin, had one child. It would be ofgreat interest to know more of this last marriage, the thirdgeneration of consanguinity in marriage, and the fourth first-cousinmarriage in three generations, but at the time the book was writtenthe parties were still in their early twenties. [55]

[Footnote 55: Dugdale, op. Cit. , Chart II. ]

Mr. Dugdale makes the following "tentative inductions. " 1. Boyspreponderate in the illegitimate lines. 2. Girls preponderate in theintermarried branches. 3. Lines of intermarriage between Jukes show aminimum of crime. 4. Pauperism preponderates in the consanguineouslines. 5. In the main, crime begins in progeny where Juke bloodcrosses X blood. (Anyone not descended from a Juke, is of "X blood"). 6. The illegitimate lines have chiefly married into X. [56] The thirdand fourth inductions might indicate that a lowered vitality of theconsanguineous lines changed a tendency toward crime into the lessstrenuous channel of pauperism, but I cannot find in Mr. Dugdale'scharts any sufficient basis for the induction. It is true that themost distinctively pauper line is consanguineous, but it is lessclosely inbred than the "semi-successful" branch. As to the fifthinduction, a close examination of the data shows clearly that innearly every case where an X marriage occurred, it was with a personof a distinctly immoral or criminal type. Cousin marriage has alsobeen 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 "ZeroFamily" in Switzerland. [58] Here the first degenerate was the productof two successive consanguineous marriages, both with a branch tainted_with insanity_. In spite of his bad ancestry he lived to the age of106 years. He married an Italian woman of questionable antecedents, and was the father of a large family. Three hundred and ten of hisdescendants are mentioned, of whom many are still young. Of these 310, 74 died in early childhood, 55 are or were vagabonds, 58 wereweak-minded or idiotic and 23 were criminals. Fifty-two were ofillegitimate birth. Although some are counted in more than onecategory, the record is appalling. In this family however, themarriages were nearly all with foreign women, and the effect ofconsanguinity was only the intensification of the neurosis in thefirst 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 ofconsanguineous marriages were subject to scrofula. [59] This is adisease which is almost universally recognized as hereditary, andwhich we should therefore expect to find intensified by doubleheredity. But 7. 7 per cent is obviously too high; otherwise most ofthe scrofulous must be the offspring of marriages of kindred. Aboutone per cent of the children of my own correspondence cases werereported as scrofulous. And while the United States Census reports but3. 9 per cent of the blind as the offspring of consanguineousmarriages, the percentage of the blind from scrofula is 6. 1. [60] Theblind from scrofula of consanguineous parentage were 2. 8 per cent ofall the blind of consanguineous parentage, while all the blind fromscrofula were 1. 8 per cent of all the blind. Consanguinity, then, seems appreciably to intensify scrofula, but there is no indicationthat 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. ]

CHAPTER V

CONSANGUINITY AND MENTAL DEFECT

Idiocy, perhaps more than any other disease or defect, has long beenconnected in the popular mind with the marriage of cousins. This factis not surprising when we consider that until very recent times idiotswere looked upon with a kind of superstitious awe, and the afflictionwas supposed to be a curse of God. For this reason, when idiocy didfollow consanguineous marriage as it sometimes would, it was believedto be the fit punishment of some violation of divine law. Insanityalso frequently has been attributed to consanguineous marriage, butnot so frequently as idiocy, since its occurrence later in life is notso obviously connected with pre-natal conditions. 

The terminology of mental and nervous disorders has been so looselyapplied that some definition may be necessary. By the term "idiocy, "is meant a condition of undeveloped mentality. Idiocy exists invarious degrees, from the complete absence of intellectual facultiesto a condition of mere irresponsibility in which the subject iscapable of self-help, and sometimes of self-support under the carefulguidance 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 fromarrested mental development. 

Insanity, on the other hand, is a disease which destroys or clouds anintellect which has once been developed. It is true that certainconditions of idiocy and imbecility do resemble that phase of insanityknown as dementia--a reversion to the original mental state ofchildhood--in reality a form of second childhood. But the states arenot identical, although one may lapse into the other. One is defect, the other disease; the imbecile in the former being the counterpart ofthe dement in the latter, just as the moral imbecile is the analogueof 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 MindedChildren has published an etiological table embodying the results of acareful examination of 4050 cases of mental defect. Of these, 2651 or65. 45 per cent resulted from causes acting before birth, including1030 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 instancesillustrating the heredity of imbecility, especially where both parentswere imbeciles, and had imbecile relatives. One case in particularforcibly illustrates the disastrous results of the marriage of suchunfortunates. It is taken from the reports of the Connecticut LunacyCommission:

 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 thegrandchildren of the person affected, or the latent tendency may neverreappear unless some disturbing factor such as scarletina, meningitisor other acute disease attacks the weak spot. This possibilitysuggests that the influence of heredity may be vastly greater than theetiological tables would indicate. The apparent causes may be onlyagents which assist in developing the evil really engendered by aninheritance of imbecility. 

It is not at all certain that there is any well marked boundary linebetween genius and some forms of imbecility. Many quite irresponsibleidiots have marvelous verbal memories, and can repeat parrot-like, page after page of books of which they have no comprehension. Dr. Barrtells of cases of prodigies, musical, mathematical and mechanical, whoexcept in their specialty were almost totally deficient mentally. [63]Many of the world's most brilliant musicians, mathematicians and evenmilitary leaders have been men of one-sided mental development, whoseability in other lines was so slight that they were little better thanimbeciles, and it is not at all surprising that their children aresometimes truly idiotic. 

[Footnote 63: Barr, op. Cit. , p. 301 _et seq. _]

The best writers of the present day no longer recognize consanguinityas a cause _per se_, of idiocy. The heredity of neuroses, however, isso strongly established that few would dispute the proposition thatwhere the morbidity is inherited through both parents it appears morefrequently and in a more marked degree than where one parent isentirely free from taint. This is what occurs when a consanguineousmarriage takes place between descendants of a neurotic family. Thepercentage of idiotic children would then be somewhat higher fromconsanguineous marriages than from the average marriage purely throughthe action of the laws of heredity. 

Dr. Barr finds 49 out of 4050 cases of idiocy or 1. 21 per cent, inwhich there was a family history of consanguinity. This is littlehigher than the average frequency of first cousin marriage, and ananalysis of 41 of these cases does not show one case that can beattributed to consanguinity alone. To quote: "Two were the result ofincestuous connection--one of brother and sister, the other of fatherand daughter, and in the others there was an undoubted history, ofgrave neuroses. "[64] "Beach and Shuttleworth find in the considerationof their 100 cases (out of 2, 380 idiots), giving 4. 2 per cent (ofconsanguineous parentage) that the bad effects are due rather to theintensification 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 Scotlandand found that 42 out of 519 or 8. 1 per cent of whom the parentage wasknown, were children of first cousins. [66] Dr. Down found 46 out of852 or 5. 4 per cent to be children of first cousins. [67] Dr. Grabhamof the Earlswood Idiot Asylum in Surrey, England, stated that 53 outof 1388 patients were the offspring of first cousins. The facts, headds, were obtained from the parents and are "therefore tolerablytrustworthy. "[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 thatconsanguinity was a cause of idiocy. Dr. Howe inquired into theparentage of 359 idiots and found that in 17 families the parents werenearly 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 2families 2 each; and in 6 families i each. In all 17 families therewere 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 fairlyhealthy. These of course are selected cases and do not indicate atall, as Dr. Howe supposed, that consanguinity was the cause of thedisasters. He adds that in each case one or both of the parents wereeither intemperate or scrofulous, and that there were also otherpredisposing causes. [70] Dr. Bemiss found that 7. 8 per cent of his3942 children of consanguineous marriages were idiots, while but 0. 7per cent of the children of non-consanguineous parentage wereidiotic. [71] A more detailed examination reveals the fact that in alarge number of these, one or both of the parents were mentallydefective. For example, in a marriage of double cousins the wife was"feeble minded" and the six children were of inferior mentality. In acase of first-cousin marriage the wife became insane and two of thechildren 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 bothparents were feeble-minded and the children idiotic. These are simplytaken at random, and many others might be given. When we find alsothat in a majority of cases no report is given of the ancestry, it isvery obvious that consanguinity alone could not have been the cause ofany 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 cousinmarriage (from correspondence) 26 or 4. 3 per cent are mentallydefective--10 are reported as "idiots, " 13 as "weak-minded" and 3 as"imbeciles. " In at least five of these cases there is evidence of badheredity, in two others the father was intemperate and in two morecauses acting after birth are mentioned. 

The statistics of the insane and idiotic in Prussia presented by Mayetclearly indicate the large part which heredity plays in the productionof mental disorders. Tables XX and XXI set forth the most importantresults of his work. Mayet considers a case hereditary if any nearrelative of the subject suffered from mental or nervous disorder, orwas 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 theoffspring of consanguineous marriages. The term "cousin" in boththese tables probably means first cousins. It will be remembered thatPrussian statistics of consanguineous marriages are very imperfect, but that at least 6. 5 in every thousand are consanguineous (firstcousins or nearer). 

 TABLE XXI. [73]_Parentage of Mental Defectives in Prussia. _----------------------------------------------------- | Consan- | |Uncle and |guineous. |Cousins. | Niece. -----------------------------------------------------1. Insanity (simple) | 6. 5[A] | 5. 8[A]| . 64[A] Hereditary | 14. 2 | 12. 5 | 1. 6 Not hereditary | 3. 0 | 2. 7 | . 22-----------------------------------------------------2. Paralytic Insanity | 4. 1 | 3. 8 | . 35 Hereditary | 11. 1 | 9. 6 | 1. 48 Not hereditary | 2. 9 | 2. 5 | . 11-----------------------------------------------------3. Epileptic Insanity | 5. 6 | 4. 9 | . 64 Hereditary | 11. 7 | 9. 9 | 1. 57 Not hereditary | 3. 5 | 3. 2 | . 29-----------------------------------------------------4. Idiocy and Imbecility| 14. 4 | 12. 8 | 1. 58 Hereditary | 21. 6 | 19. 3 | 2. 12 Not hereditary | 11. 5 | 10. 2 | 1. 37----------------------------------------------------- [A] Per thousand. 

[Footnote 73: Feer, op. Cit. , pp. 13-14. ]

From these tables we may infer that consanguinity influences idiocyfar more than it does insanity, but it is not entirely clear why thenumber of hereditary cases should be relatively smaller among theidiotic. Since insanity is more likely to have some more definitelyassignable cause than idiocy, we should expect the percentage due toheredity to be lower and consequently the influence of consanguinityless. 

It is generally admitted that a tendency toward insanity isinheritable, and it seems probable that this tendency as well as otherneuroses may be intensified through double heredity. A case in pointcan be found in the Shattuck genealogy. [74] For four generations inthe S. Family there is no indication of neurosis. The average numberof children to a family had been eight, few children died young andall were prosperous farmers. But in 1719 J. S. Married E. C. And theirson Z. S. Is thus described: "He was sometimes subject to depression ofspirits; and some peculiar traits of character in a few branches ofhis family seem to have originated with him. " He married A. C. , a nieceof his mother. They both lived to be over 80 and had ten children, ofwhom three were insane; only six married, and of these only two areknown to have left surviving children. One of these a daughter, S. S. , married E. S. , a nephew of her father, and himself the offspring of asecond cousin marriage within the S. Blood. E. S. And S. S. Had fivechildren, all of whom married, and there is no further mention ofinsanity. We may suppose, then, that the C. Stock was neurotic, andthat a consanguineous marriage within that stock, although of the S. Surname, intensified the tendency into insanity, but with a furtherinfusion of the normal S. Blood the morbidity was eliminated. It isvery evident that the heredity and not the consanguinity was the causeof these three cases of insanity. 

[Footnote 74: _Shattuck Memorials_, p. 118. ]

CHAPTER VI

CONSANGUINITY AND THE SPECIAL SENSES

The most important source for this chapter is the special report onthe Blind and the Deaf in the Twelfth Census of the United States. [75]This report was prepared under the direction of Dr. Alexander GrahamBell, as Expert Special Agent of the Census Office. 

[Footnote 75: U. S. Census, 1900, _Special Report on the Blind and theDeaf_. ]

The enumerators of the Twelfth Census reported a total of 101, 123persons as blind, and to each of these Dr. Bell addressed a circularof inquiry. By this method he obtained verified returns of 64, 763cases of blindness in continental United States or 85. 2 per 100, 000 ofthe total population. In the same way he obtained data in regard to89, 287 persons with seriously impaired powers of hearing, or 117. 5 Per100, 000 of the total population. 

In each case the following questions among others were asked: "Werehis (or her) parents first cousins? If not first cousins were theyotherwise related by blood to each other, before their marriage? Wereany of his relatives blind? If yes, what relatives? (Father, mother, grandparents, brothers, sisters, uncles, aunts, and how many of each, so far as known). " The results of this inquiry give us the best andmost reliable statistical material which has ever been compiled on anyphase of the problem of consanguineous marriage. The investigation ofthe deaf was similar to that of the blind, but even more complete. 

I. The Blind. The question as to the relationship of the parents wasanswered in 56, 507 cases, in 2, 527 or 4. 47 per cent of which theparents were reported as cousins. Of the 57, 726 who answered thequestion in regard to blind relatives, 10, 967 or 19 per cent repliedin the affirmative. [76] The blind relatives were divided into twogroups: (a) blind brothers, sisters or ancestors, and (b) blindcollateral relatives or descendants. Table XXII concisely expressesthe results most fundamental for this study. 

[Footnote 76: U. S. Census, 1900, op. Cit. , p. 16. ]

 TABLE XXII. ----------------------------------------------------------------- | |Having |Having | | | |Blind |blind | | | |relatives|relatives|Having |Consanguinity of | |Class |Class |no blind | NotParents. |Totals|(a). [A] |(b). [A] |relatives|Stated. -----------------------------------------------------------------The blind |64, 763| 8, 629 | 2, 338 | 46, 759 | 7, 037-----------------------------------------------------------------Totally blind |35, 645| 4, 378 | 1, 215 | 26, 349 | 3, 703Partially blind |29, 118| 4, 251 | 1, 123 | 20, 410 | 3, 334 | | | | |Parents cousins. | | | | | --The blind | 2, 527| 844 | 149 | 1, 456 | 78-----------------------------------------------------------------Parents cousins. | | | | | --Totally blind | 1, 291| 435 | 78 | 739 | 39Parents cousins. | | | | | --Partially blind | 1, 236| 409 | 71 | 717 | 39 | | | | |Parents not cousins. | | | | | --The blind |53, 980| 7, 395 | 2, 095 | 43, 368 | 1, 122-----------------------------------------------------------------Parents not cousins. | | | | | --Totally blind |29, 892| 3, 720 | 1, 090 | 24, 541 | 541Parents not cousins. | | | | | --Partially blind |24, 088| 3, 675 | 1, 005 | 18, 827 | 581 | | | | |Consanguinity not | | | | | stated. --The blind | 8, 256| 390 | 94 | 1, 935 | 5, 837-----------------------------------------------------------------Consanguinity not | | | | | stated. --Totally | | | | | blind | 4, 462| 223 | 47 | 1, 069 | 3, 123Consanguinity not | | | | | stated. --Partially | | | | | blind | 3, 794| 167 | 47 | 866 | 2, 714----------------------------------------------------------------- [A] Symbols for Blind Relatives--(a) blind brothers, sisters or ancestors; (b) blind collateral relatives or descendants. 

Of the 2527 blind persons whose parents were cousins, 993 or 39. 3 percent have blind relatives, 33. 4 per cent having blind brothers, sisters or ancestors, and 3. 9 per cent having blind collateralrelatives or descendants. And 9 per cent of the blind who have blindrelatives are of consanguineous parentage, while but 3. 1 per cent ofthe blind who have no blind relatives are the offspring of cousins. These figures alone indicate a decided intensification of blindnessthrough consanguinity, although it should be remembered that arelationship "works both ways, " so that when a brother has a blindsister, the sister would have a blind brother. This fact has probablydiminished the apparent number of sporadic cases of blindness. 

Considered with reference to the degree of blindness the table showsthat 1291 or 51. 1 per cent of the blind of consanguineous parentageare totally blind, and 1236 or 48. 9 per cent are partially blind. Among those whose parents were not cousins, 55. 4 per cent were totallyand 44. 6 per cent were partially blind. 

Of the 2527 blind of consanguineous parentage, 632 or 25. 0 per centwere congenitally blind, of whom 350 or 55. 4 per cent also had blindrelatives of the degrees specified. Not counting those who did notanswer the question in regard to blind relatives, we have 615 cases ofwhich 51. 5 per cent had blind relatives of class (a), and 5. 4 per centblind relatives of class (b). Taking the 53, 980 blind whose parentswere not so related the number of congenitally blind was 3666 or but6. 8 per cent, of whom 1023 or 27. 9 per cent had blind relatives. Omitting as before the "blind relatives not stated, " we have 23. 4 percent who had blind relatives of class (a), and 4. 3 per cent relativesof class (b). 

On the hypothesis that consanguinity in the parents intensifies atendency toward blindness we should expect to find among thecongenitally blind a larger proportion of consanguineous parentagethan among those blind from specific causes. In Table XXIII a generalclassification of the causes of blindness is given together with theconsanguinity of parents. Specific causes in which the percentage ofconsanguinity differs in a marked degree from the average, are givenparenthetically. 

 TABLE XXIII. ------------------------------------------------------------------------------- | |Consanguinity of | | | Parents | Percentages | |--------------------------------------------- | | | Not | Not | | Not | NotCause of Blindness. |Total. |Cousins|cousins|stated|Cousins|cousins|stated-------------------------------------------------------------------------------Total |64, 763| 2, 527|53, 980 | 8, 256| 3. 9 | 83. 4 | 12. 7-------------------------------------------------------------------------------Opacity of the eye |33, 930| 1, 000|28, 797 | 4, 133| 2. 9 | 84. 9 | 12. 2-------------------------------------------------------------------------------a. Causes affecting cornea|11, 380| 444|10, 016 | 920| 3. 9 | 88. 0 | 8. 1 (1) Measles | 1, 451| 73| 1, 267 | 111| 5. 0 | 87. 4 | 7. 6 (2) Scrofula | 1, 165| 71| 1, 026 | 68| 6. 1 | 88. 1 | 5. 8b. Causes affecting iris | 1, 307| 33| 1, 093 | 181| 2. 5 | 83. 6 | 13. 9c. Causes affecting lens |11, 769| 228| 9, 467 | 2, 074| 1. 9 | 80. 4 | 17. 7d. Other causes | 9, 474| 235| 8, 221 | 1, 018| 2. 5 | 86. 8 | 10. 7-------------------------------------------------------------------------------Nervous apparatus affected| 7, 944| 276| 6, 980 | 688| 3. 5 | 87. 8 | 8. 7-------------------------------------------------------------------------------Unclassified |14, 885| 938|12, 463 | 1, 484| 6. 3 | 83. 7 | 10. 0------------------------------------------------------------------------------- (1) Congenital | 4, 728| 632| 3, 666 | 430|13. 4 | 77. 5 | 9. 1 (2) Other causes |10, 157| 306| 8, 797 | 1, 054| 3. 0 | 86. 6 | 10. 4-------------------------------------------------------------------------------Unknown | 8, 004| 313| 5, 740 | 1, 951| 3. 9 | 71. 7 | 24. 4-------------------------------------------------------------------------------

To quote from the Report:

 The only specific causes, other than congenital, to which is due a greater proportion of the total cases of blindness among those whose parents were cousins than among those whose parents were not related, are: Catarrh (parents cousins 28. 1, parents not cousins 8. 7 per 1, 000), scarlet fever (parents cousins 10. 7, parents not cousins 10. 1 per 1, 000), scrofula (parents cousins 28. 9, parents not cousins 19 per 1, 000), and measles (parents cousins 28. 9, parents not cousins 23. 5 per 1, 000). The difference in these proportions is but slight, and the relative number of cases of blindness attributed to each of the other causes is greater among those whose parents were not related. [77]

[Footnote 77: U. S. Census, 1900, op. Cit. , p. 17. ]

It will be noted that the greatest proportion is in the case ofscrofula. 

Since it is probable that a part of those who did answer the questionas to consanguinity are in fact the offspring of cousins, thepercentage in each case should be somewhat increased. Allowing forthese the same proportion as for those who did answer the question weshould have of all the blind 4. 47 per cent as the offspring ofcousins; of the totally blind 4. 14 per cent and of the partially blind4. 88. While of the congenitally blind we should have 14. 7 per cent asoffspring of cousins. 

It is interesting to note in this connection that in 1900, Dr. LeeWallace Dean, of the University of Iowa examined the 181 blindchildren in the Iowa College for the Blind, and found that 9 or nearly5 per cent were the offspring of first cousin marriages. [78] Dr. Deancontinues, If we exclude from the list those blind children who were blind because of blennorrhea neonatorum, sympathetic opthalmia, trachoma, etc. , and consider only those who suffered because of congenital conditions, we should find that 14 per cent were the result of consanguineous marriage of the first degree. .. . Among the pupils who have entered the college since 1900 the percentage is about the same. 

[Footnote 78: _Effect of Consanguinity upon the Organs of SpecialSense_, p. 4. ]

This was written in 1903, three years before the publication of Dr. Bell's report. 

Statistics from foreign sources give even larger percentages of theblind as the offspring of consanguineous marriage. Dr. Feer quotesfourteen distinct investigations of the etiology of retinitispigmentosa, embodying in all 621 cases, of which 167 or 27 per centwere the offspring of consanguineous parents. [79] Retinitis pigmentosais perhaps more generally attributed to consanguineous marriage thanany other specific disease of the eye, and it is to be regretted thatthe Census report does not give any data in regard to this cause. Retinitis pigmentosa in known to be strongly inheritable, as isalbinism and congenital cataract. 

[Footnote 79: _Der Einfluss der Blutsverwandschaft der Eltern auf dieKinder_, p. 14. ]

Looking now at the other side of the problem, that of the probabilityof consanguineous marriages producing blind offspring, we have as ourdata the 2527 blind whose parents were cousins, and a conservativeestimate which may be made from the data in Chapter II that 1, 000, 000persons in continental United States are the offspring of cousinswithin the degrees included in the Census report. [80] In the generalpopulation 852 per million are reported as blind, and 63 per millionas congenitally blind. The actual figures for the offspring of cousinmarriages are 2527 per million for all blind and 632 per million forthe congenitally so. In other words only 0. 25 per cent of theoffspring of cousin marriages are blind and only 0. 05 per cent arecongenitally blind. Although the probability that a child of relatedparents will be born blind is ten times as great (632 per million vs. 63 per million) as when the parents are not related, the numbers areso small that there seems to be very little basis for a belief thatconsanguinity does more than to intensify an inherited tendency, especially since over one half of the congenitally blind ofconsanguineous parentage are known to have blind relatives. 

[Footnote 80: From 1-1/2 to 2 per cent of all marriages were found tobe between cousins within the degree of second cousins, and cousinmarriages were found to be normally fertile. ]

2. The Deaf. The extent to which the connection between consanguineousmarriage and deaf-mutism has been studied is indicated by a tablegiven by Mr. Huth, in which are set forth the results of fiftydistinct investigations. [81] In this table the percentages ofdeaf-mute offspring of consanguineous marriage to the total number ofdeaf-mutes investigated, varies from 30 per cent to none at all. Ofthese studies not more than ten or eleven have the slighteststatistical value, and four of these--the most reliable--are from thereports of the Census of Ireland in the years 1851, 1861, 1871 and1881. 

[Footnote 81: _Marriage of Near Kin_, p. 229. ]

The Irish censuses of 1891 and 1901 give similar data, though not sodetailed as in 1871 and 1881. Thus we have in these reports a censusinquiry into a phase of the consanguineous marriage problem extendingover the period of six successive censal years. Although we can hardlysuppose that these figures are accurate in all respects, they throw agreat deal of light upon the problem, and are worth quoting in somedetail. The tables as given by Mr. Huth contain a number of errors ofdetail, the correction of which changes the results materially. [82]

[Footnote 82: In a subsequent article Mr. Huth corrects some of theseerrors. See: "Consanguineous Marriage and Deaf-mutism, " _The Lancet_, Feb. 10, 1900. ]

 TABLE XXIV. ------------------------------------------------------------------ | | Congenital deaf-mutes | |----------------------------------------------- | | | | | Parents cousins | | | | |---------------------- | | | |Average | | |Average | | |Number |number | | |numberCensal | Total | |per | to a | |Per | to ayear. |population|Number|million|family[A]|Number|cent. |family[A]------------------------------------------------------------------1851[B]| 6, 574, 278| 4, 127| 628 | ---- | 242 | 5. 86| 1. 661861 | 5, 798, 967| 4, 096| 706 | 1. 22 | 362 | 8. 84| 1. 721871 | 5, 412, 377| 3, 503| 647 | 1. 30 | 287 | 7. 35| 1. 761881 | 5, 174, 836| 3, 163| 611 | 1. 32 | 191 | 6. 04| 1. 691891 | 4, 706, 448| 2, 570| 546 | 1. 40 | 297 |11. 56| 1. 921901 | 4, 456, 546| 2, 179| 489 | 1. 40 | 249 |11. 43| 1. 73------------------------------------------------------------------ [A] From Table XXV. 

 [B] 1851 data from Huth, "Consanguineous Marriage and Deaf-mutism. " _The Lancet_, 1900. 

Table XXIV summarizes the most important points in the Irish data. Itwill be seen that while there has been an absolute diminution in thenumber of deaf-mutes in Ireland with the decrease in population, therehas been a relative increase of deaf-mutism. There are two possibleexplanations for this phenomenon, both of which may have operated inpart; first that in the great emigration the deaf-mutes have been leftbehind, and second that with the introduction of improved methods ofcensus taking, the returns are more complete than a half century ago. Mr. Huth believes that there is still room for improvement in Irishcensus methods, and thinks there is reason to believe that in theenumeration of the deaf all children born deaf in a family areincluded whether living or not. 

Since Ireland is strongly Roman Catholic, the proportion ofconsanguineous marriages is probably small, so that the percentage ofdeafmutes derived from consanguineous marriages, varying from 5. 86 to11. 56 is very much greater than the percentage of these marriages inthe general population. The average number of deaf children to afamily in Table XXIV varies less than any other part of the table, andclearly shows a much higher average number of deaf children where theparents were cousins. They reveal the interesting fact that theoccurrence of two or more deafmutes in a family is more than twice asprobable where the parents are related as where they are not. TableXXV still better illustrates this point. Of the families where therewas but one deaf-mute, only 4. 3 per cent were the offspring of cousinmarriages; where there were two in a family 12. 9 per cent were ofconsanguineous parentage; three in a family, 13. 3 per cent; four in afamily, 19. 0 per cent; more than four in a family, 21. 1 per cent. 

 TABLE XXV. _Number of Congenital Deaf mutes to a Family in Ireland. _---------------------------------------------------------------- | | Families in which deaf-mutes numbered. | |----------------------------------------Year. | Parentage. | 1. | 2. | 3. |4. |5. |6. |7. |8. |9. |10. |11. ----------------------------------------------------------------1851 | Parents cousins | 127| 45 | 20 |10| 5| 2|. . | 1|. . |. . |. . 1871 | Parents cousins | 91| 38 | 24 | 5| 3| 1| 1|. . |. . |. . |. . 1881 | Parents cousins | 63| 30 | 13 | 6| 1|. . |. . |. . |. . |. . |. . 1891 | Parents cousins | 82| 38 | 19 | 9| 1| 3| 1| 2|. . |. . |. . 1901 | Parents cousins | 79| 34 | 23 | 7| 1|. . | 1|. . |. . |. . |. . 1851 | All families[A] |2963|347 |158 |35|13| 5|. . | 1|. . |. . |. . 1871 | All families[A] |2460|305 |167 |47|20| 5| 1|. . |. . |. . |. . 1881 | All families[A] |2080|281 |162 |39|18| 6|. . |. . |. . | 1 |. . 1891 | All families[A] |1473|273 |134 |40|12| 6| 1| 2|. . |. . | 11901 | All families[A] |1219|231 |122 |34|10| 4| 2|. . |. . |. . |. . ---------------------------------------------------------------- [A] Number of the "Deaf and Dumb" to a family, "as far as could be ascertained. "

In 1871 and 1881 the inquiry was more minute and the degrees ofconsanguinity were specified. Mr. Huth quotes some of the figures forthese years, probably derived from the same sources as Table XXVI, andcomments as follows: "An examination of this table will show that thestatistics so much relied upon as proving the causation of deaf-mutismby consanguineous marriages show nothing of the sort. In 1871 fourthcousins produced more deaf-mutes per marriage than any nearerrelationship. In 1881 third cousins produced more than any nearerrelationship. "[83] Mr. Huth forgets that he is basing these statementson five and nine families respectively, and does not take intoconsideration the probability that if the returns are biased, as hesuspects, this bias would affect the more distantly related, relatively more than the first cousin marriages, for the same reasonthat this would be true of the cases collected by Dr. Bemiss. [84]Combining the figures of the two censal years helps to correct theseaverages, and the distantly related show approximately the sameaverage as the first cousin marriages in spite of the vastly greaterselection which must have obtained in the distantly related cases. 

[Footnote 83: Huth, _Marriage of Near Kin_, p. 227. ]

[Footnote 84: _Cf. Supra_, p. 42. ]

In Table XXVI it will be seen that 52. 5 per cent of the deaf-muteoffspring of consanguineous parents were the offspring of first cousinmarriages. On the assumption that this percentage is fairly typical ofeach set of returns we may say that from three to six per cent of theIrish deaf-mutes are the offspring of first cousin marriages. If, then, the proportion of first cousin marriages is no greater than inEngland, the percentage of deaf-mute offspring is several times asgreat as in the average non-related marriage. 

 TABLE XXVI. -------------------------------------------------------------------------- | 1871 | 1881 | 1871 and 1881 |----------------------------------------------------------- | |Number| | |Number| | |Number| | | of |Aver | | of |Aver | | of |Aver |Number|conge-|age |Number|conge-|age |Number|conge-|ageConsanguinity | of |nital |per | of |nital |per | of |nital |per of |mar- |deaf- |mar- |mar- |deaf- |mar- |mar- |deaf- |mar- Parents. |riages|mutes |riage|riages|mutes |riage|riages|mutes |riage--------------------------------------------------------------------------First cousins | 72 | 128 | 1. 78| 74 | 123 | 1. 66| 146 | 251 | 1. 72Second cousins| 50 | 89 | 1. 78| 29 | 46 | 1. 58| 79 | 135 | 1. 71Third cousins | 24 | 40 | 1. 67| 9 | 21 | 2. 33| 33 | 61 | 1. 85Fourth cousins| 5 | 11 | 2. 20| 1 | 1 | -- | 6 | 12 | 2. 00Fifth and | | | | | | | | |sixth cousins | 12 | 19 | 1. 58| not stated | 12 | 19 | 1. 58--------------------------------------------------------------------------Total | 163 | 287 | 1. 76| 113 | 191 | 1. 69| 276 | 478 | 1. 73No | | | | | | | | |relation- | | | | | | | | |ship[A] |2, 842 |3, 609 | 1. 27|2, 474 |3, 229 | 1. 31|5, 316 |6, 838 | 1. 29--------------------------------------------------------------------------Grand total |3, 005 |3, 896 | 1. 30|2, 587 |3, 420 | 1. 32|5, 592 |7, 316 | 1. 31-------------------------------------------------------------------------- [A] See Table XXV. 

In Scotland Dr. Arthur Mitchell made inquiry of the superintendents ofa number of deaf-mute asylums, and found that of 544 deaf-mutes, 28were the offspring of 24 consanguineous marriages. [85] There were 504families represented in all, so that the average per family was 1. 17among the consanguineous to 1. 07 among the non-consanguineous. 

[Footnote 85: Huth, op. Cit. , p. 226. ]

In Norway, according to Uchermann, while 6. 9 per cent of all marriagesare consanguineous within and including the degree of second cousins, and in single cantons the percentages range as high as 31. 0, only inone single district does the number of the deaf-mutes harmonize withthat of the marriage of cousins. The district of Saeterdalen has thegreatest number of consanguineous marriages (201 out of 1250), but nota single case of deaf-mutism. Hedemarken, which has the fewestconsanguineous marriages has a great many deaf-mutes. Wheredeaf-mutism exists it seems to be intensified by consanguinity, butwhere it is not hereditary it is not caused by consanguinity. Of the1841 deaf-mutes in Norway, 919 were congenitally deaf, and of these212 or 23 per cent were of consanguineous parentage. [86]

[Footnote 86: _Les Sourds-muets en Norvège_. Quoted by Feer, _DerEinfluss der Blutsverwandschaft der Eltern auf die Kinder_, p. 22. ]

Dr. Feer gives a table containing the results of a number of studiesof deaf-mutism, which shows an average of 20 per cent as ofconsanguineous origin. Four investigations give the number of childrento a family. Table XXVII from Feer seems to indicate that the Irishcensus is fairly accurate at this point. [87]

[Footnote 87: Feer, op. Cit. , p. 22. ]

 TABLE XXVII. _Average Number of Children to a Family. _------------------------------------------------- |Consanguineous|"Crossed"Observer. | marriages. |marriages. -------------------------------------------------Huth (Irish Census) | 1. 68 | 1. 17Wilhelmi | 1. 71 | 1. 26Mygind | 1. 53 | 1. 20Uchermann | 1. 41 | 1. 19-------------------------------------------------

In the American Census the instructions to enumerators have been sodiverse that statistics of the deaf have been very poor until recentyears. Not until the Twelfth Census was the inquiry put upon a reallyscientific basis. 

This reform, as also the more intelligent attitude of the Americanpeople in general towards the affliction of deafness, is due largelyto the work of Dr. Alexander Graham Bell. An enumeration of Dr. Bell'sservices directly, and through the agency of the Volta Bureau, in thiscause, cannot be given here. For our purpose the most important of hiscontributions is embodied in the Special Report of the Twelfth Censusof the United States already referred to. 

As in the investigation of the Blind, the circular letter sent to eachperson reported by the enumerators as deaf contained questions inregard to parentage and the existence of deaf relatives. It isunfortunate that in these returns it is impossible to distinguishbetween degrees of relationship, but in such an extensive compilationit was doubtless impracticable to attempt to unravel the intricaciesof consanguinity. Judging from the returns of the Census of Ireland wemay assume that about half of the cases returned as "cousins" werefirst cousins. 

The replies to the inquiry as to deaf relatives were more carefullyanalyzed, and were divided into four groups, which are referred tothroughout as (a), (b), (c) and (d) relatives. These groups are: (a), deaf brothers, sisters or ancestors; (b), deaf uncles, aunts, cousinsor other relatives not (a), (c) or (d); (c), deaf children, (sons ordaughters); (d), deaf husbands or wives. Thus a large proportion ofthe hereditary cases would be included in the first two categories, (a) and (b). [88]

[Footnote 88: U. S. Census _Report on the Blind and the Deaf_, p. 127. ]

The causes of deafness are given in detail, but as might be expectedthe returns are not as definite or as accurate as we should desire. The causes given have been grouped under five main heads; these againare subdivided, often into divisions numerically too minute for realstatistical value. Table XXVIII includes the main groups and thosespecific causes which number more than 3000 cases. The extremevariation in the percentages of those who are the offspring ofconsanguineous marriages cannot be attributed to mere chance. There isclearly some fundamental connection between consanguinity andcongenital deafness if 11. 8 per cent of all the congenitally deaf arethe offspring of consanguineous marriages, while of the adventitiouslydeaf but 3. 1 per cent are the offspring of such marriages. In fact weare tempted to jump at the conclusion that consanguinity is in itselfa cause of deaf-mutism. Furthermore 42. 1 per cent of the deaf whoseparents were cousins were congenitally deaf, while this was true ofbut 15 per cent of those whose parents were unrelated. 

 TABLE XXVIII. ------------------------------------------------------------------------- | | | | | Consanguinty | | | of Parents. | Per cent. | |--------------------|----------------- | | | | | | | Cause of Deafness. | | | Not | Not | | Not | Not |Total. |Cous- |Cous- | Sta- |Cous-|Cous-| Sta- | | ins. | ins. | ted. | ins. | ins. | ted. ---------------------------|------|------|------|------|-----|-----|----- | | | | | | | Total |89, 287| 4, 065|75, 530| 9, 692| 4. 5| 84. 6| 10. 9---------------------------|------|------|------|------|-----|-----|-----Affections of external ear | 871| 29| 760| 82| 3. 3| 87. 3| 9. 4Affections of middle ear |34, 801| 1, 238|30, 824| 2, 739| 3. 5| 88. 6| 7. 9Affections of internal ear |12, 295| 343|11, 121| 831| 2. 8| 90. 4| 6. 8Unclassified |31, 205| 2, 183|25, 281| 3, 741| 7. 0| 81. 0| 12. 0Unknown |10, 115| 272| 7, 544| 2, 299| 2. 7| 74. 6| 22. 7 | | | | | | |Scarlet fever | 7, 424| 285| 6, 647| 492| 3. 9| 89. 5| 6. 6Disease of ear | 4, 210| 222| 3, 683| 305| 5. 3| 87. 5| 7. 2Catarrh |11, 702| 304|10, 450| 948| 2. 6| 89. 3| 8. 1Colds | 3, 074| 81| 2, 666| 327| 2. 6| 86. 7| 10. 7Meningitis | 3, 991| 83| 3, 741| 167| 2. 1| 93. 7| 4. 2Old age | 3, 361| 38| 2, 369| 954| 1. 1| 70. 5| 28. 4Military service | 3, 242| 40| 2, 897| 305| 1. 2| 89. 4| 9. 4Congenital |14, 472| 1, 710|11, 322| 1, 440| 11. 8| 78. 2| 10. 0-------------------------------------------------------------------------

But on the other hand, 53. 4 per cent of the deaf whose parents werecousins had deaf relatives of the (a) and (b) groups, while of thosewhose parents were not cousins, only 29. 9 per cent in these groups haddeaf relatives. In Table XXIX the close connection between deafrelatives of these groups and consanguinity is shown. For the sake ofsimplicity no account is taken of (c) relatives (deaf children), and(d) relatives (deaf husbands or wives), for in the first case only 370deaf are reported as having deaf children and at the same time no (a)or (b) relatives, and in the Second case (d) relatives are notordinarily blood relatives at all. 

 TABLE XXIX. ----------------------------------------------------------------------- | | | | | Consanguinty | | | of Parents. | Per cent. | |--------------------|----------------- | | | | | | |Class of Deaf | | | Not | Not | | Not | NotRelative. [A] |Total. | Cous-| Cous-| Sta- |Cous-|Cous-| Sta- | | ins. | ins. | ted. | ins. | ins. | ted. ----------------------------------------------------------------------- | | | | | | | Total |89, 287| 4, 065|75, 530| 9, 692| 4. 5| 84. 6| 10. 6-----------------------------------------------------------------------Stated |80, 481| 3, 911|73, 639| 2, 931| 4. 9| 91. 5| 3. 6Not stated | 8, 806| 154| 1, 891| 6, 761| 1. 7| 21. 5| 76. 8 | | | | | | |(a) relatives |21, 660| 1, 850|18, 838| 972| 8. 5| 87. 0| 4. 5No (a) relatives |58, 821| 2, 061|54, 801| 1, 959| 3. 5| 93. 2| 3. 3 | | | | | | |(a) or (b) relatives |25, 851| 2, 171|22, 552| 1, 128| 8. 4| 87. 2| 4. 4(a) and (b) relatives | 4, 117| 412| 3, 587| 118| 10. 0| 87. 1| 2. 9(a) but no (b) relatives |17, 543| 1, 438|15, 251| 854| 8. 2| 86. 9| 4. 2(b) but no (a) relatives | 4, 191| 321| 3, 714| 156| 7. 7| 88. 6| 3. 7No (a) or (b) relatives |54, 630| 1, 740|51, 087| 1, 803| 3. 2| 93. 5| 3. 3----------------------------------------------------------------------- [A] Symbols for deaf relatives: (a) deaf brothers, sisters and ancestors; (b) deaf uncles, aunts, cousins, etc. 

Table XXIX shows unmistakably that the connection betweenconsanguinity and hereditary deafness is very close. Where there isthe largest amount of deafness in the family the percentage ofconsanguinity is the highest. That is, of those who had both (a) and(b) relatives ten per cent were the offspring of cousins, while ofthose who had neither (a) nor (b) relatives only three per cent werethe offspring of cousins. It is natural to assume that as a rule wherethe deaf have either (a) or (b) deaf relatives, deafness ishereditary, for the probability of two cases of deafness occurring inthe same family, uninfluenced by heredity would be very small. It islikely also that a great many of the deaf who stated that they had nodeaf relatives were mistaken, for few people are well enough informedin regard to their ancestry to answer this question definitely. Notone man in thousands can even name all of his great-grandparents, tosay nothing of describing their physical or mental traits. Others mayhave understood the inquiry to refer only to living relatives andtherefore have omitted almost all reference to their ancestors. Thesepossible errors might easily explain all the excess of the percentageof consanguinity among those reported as having no deaf relatives overthe probable percentage of consanguineous marriage in the generalpopulation. But this very probability that comparatively few deafancestors have been reported increases the probability that thegreater part of the (a) relatives were brothers and sisters ratherthan ancestors. Now of the 26, 221 deaf having deaf relatives, 17, 345have only (a) relatives, and if these are largely living brothers andsisters the relationship would "work both ways, " so that if there weretwo deaf children in a family, each would have an (a) deaf relative. In the Census of Ireland figures above quoted it will be rememberedthat among families which were the offspring of cousins the proportionhaving two or more deaf children was three times as great as amongthose who were not the offspring of consanguineous unions. If thisfollows in America, it largely accounts for the high percentage of thecongenitally deaf who are the offspring of cousin marriages, andespecially of those who have (a) deaf relatives. 

 TABLE XXX. ------------------------------------------------------------------------ | | Consanguinity | | | of Parents. | Per Cent. | |----------------------------------------------Class of Deaf | | | Not | Not | | Not | Not Relatives. [A] |Total. |Cousins|Cousins|stated |Cousins|Cousins|stated------------------------------------------------------------------------Total |14, 472 | 1, 710 | 11, 322| 1, 440 | 11. 8 | 78. 2 |10. 0------------------------------------------------------------------------Stated |13, 428 | 1, 647 | 11, 110| 671 | 12. 3 | 82. 7 | 5. 0Not stated | 1, 044 | 63 | 212| 769 | 6. 0 | 20. 3 |76. 7(a) relatives | 5, 295 | 986 | 3, 961| 48 | 18. 6 | 74. 8 | 6. 6(b) and (c) but | | | | | | | no (a) relatives| 860 | 126 | 686| 48 | 14. 6 | 79. 8 | 5. 6No (a), (b) or | | | | | | | (c) relatives | 7, 273 | 535 | 6, 463| 275 | 7. 3 | 88. 9 | 3. 8------------------------------------------------------------------------ [A] Symbols for deaf relatives: (a) deaf brothers, sisters or ancestors; (b) deaf uncles, aunts, cousins, etc. ; (c) deaf children. 

A further analysis of the congenitally deaf according to consanguinityof parents and deaf relatives, as in Table XXX, helps to determine towhat extent the greater number of deaf children to a family among theoffspring of consanguineous marriages has influenced the totals. Fromthe report it cannot be determined how many of the congenitally deafhad (a), (b) or (c) relatives alone, but the existence of (b) and (c)relatives would almost certainly indicate that the deafness washereditary. Of these 14. 6 per cent were the offspring of cousins, while of those having (a) relatives 18. 6 per cent were the offspringof consanguineous unions. Thus it would seem to be a more reasonableconclusion that where two or more deaf-mutes appear in the samefamily, at least a tendency toward deaf-mutism is hereditary in thefamily and is intensified by the marriage of cousins, rather than thatconsanguineous marriage is in itself a cause. The fact that in manycases the relationship would "work both ways" would not greatly affectthe percentage of the offspring of cousins having (b) and (c)relatives, for the chance would be slight that the (b) or (c) relativewould be himself the offspring of a consanguineous marriage. Among thecongenitally deaf who reported no deaf relatives, the percentage ofconsanguineous parentage is still high, (7. 3 per cent), but thisexcess can easily be accounted for by the ignorance of deaf relativeson the part of the informant, without contradicting the hypothesis ofheredity. 

Basing now our percentages on the totals of consanguineous andnon-consanguineous parentage respectively, and including only thosewho answered the inquiry as to deaf relatives, it will be seen (TableXXXI) that while of all the deaf less than one third are returned ashaving deaf relatives, of the deaf who were the offspring of cousinsover one half (55. 5 per cent) were returned as having (a) or (b) deafrelatives. 

Again taking into consideration only the congenitally deaf the resultsare still more striking. Table XXXII shows that 66. 5 per cent of thecongenitally deaf who are of consanguineous parentage are known tohave deaf relatives. 

 TABLE XXXI. ---------------------------------------------------------------------- | |Consanguinity | | | of Parents. | Per cent. | |------------------------------------- | | |Not | | |NotClass of Deaf Relatives. |Total. |Cousins|Cousins|Total|Cousins|Cousins----------------------------------------------------------------------Deaf relatives stated |80, 481| 3, 911 |73, 639 |100. 0|100. 00 |100. 00----------------------------------------------------------------------(a) relatives |21, 660| 1, 850 |18, 838 | 26. 9| 47. 3 | 25. 5No (a) relatives |58, 821| 2, 061 |54, 801 | 73. 1| 52. 7 | 74. 5 | | | | | |(a) or (b) relatives |25, 851| 2, 171 |22, 552 | 32. 1| 55. 5 | 30. 6(a) and (b) relatives | 4, 117| 412 | 3, 587 | 5. 1| 10. 5 | 4. 8(a) and no (b) relatives |17, 543| 1, 438 |15, 251 | 21. 8| 36. 8 | 20. 7(b) and no (a) relatives | 4, 191| 321 | 3, 714 | 5. 2| 8. 2 | 5. 1No (a) or (b) relatives |54, 630| 1, 740 |51, 087 | 67. 9| 44. 5 | 69. 4----------------------------------------------------------------------Symbols for deaf relatives: (a) deaf brothers, sisters or ancestors; (b) deaf uncles, aunts, cousins, etc. ; (c) deaf children; (d) deaf husbands or wives. 

 TABLE XXXII. ------------------------------------------------------------------------- | |Consanguinity | | |of Parents. | Per cent. | |------------------------------------- | | |Not | | |NotClass of Deaf Relatives |Total. |Cousins|Cousins|Total|Cousins|Cousins-------------------------------------------------------------------------Deaf relatives stated |13, 428| 1, 647 |11, 110 |100. 0|100. 0 |100. 0-------------------------------------------------------------------------(a) relatives | 5, 295| 986 | 3, 961 | 39. 5| 59. 9 | 35. 6(b) or (c), no (a) relatives| 860| 126 | 686 | 6. 4| 7. 6 | 6. 2No (a), (b) or (c) relatives| 7, 273| 535 | 6, 463 | 54. 2| 32. 5 | 58. 2-------------------------------------------------------------------------Symbols for deaf relatives: (a) deaf brothers, sisters or ancestors; (b) deaf uncles, aunts, cousins, etc. ; (c) deaf children. 

The percentage having (a) relatives, including brothers, and sisters, is nearly twice as great among the deaf of consanguineous parentage asamong the offspring of unrelated parents. This is not inconsistentwith the Irish returns which show the average number of deaf childrento a family to be so much greater where the parents were cousins, thanwhere they were not. 

The statistics of the (c) relatives, or deaf sons and daughters of thedeaf, are not very full. Of the 31, 334 married deaf who answered theinquiry in regard to deaf relatives, 437 or 1. 4 per cent reported deafchildren and 30, 897 or 98. 6 per cent reported no deaf children. Of thetotally deaf 2. 4 per cent had deaf children, and of the congenitallydeaf 5. 0 per cent. The percentage of deaf children varied greatlyaccording to the number and class of deaf relatives, as shown by TableXXXIII. 

 TABLE XXXIII. ------------------------------------------------------------------- | Percentage having deaf children. |---------------------------------------Class of Deaf Relatives. | |Totally |Partially |Congenitally |Total. |deaf. |deaf. |deaf. ---------------------------|------|--------|----------|------------(a), (b) or (d) | 1. 4 | 2. 4 | 1. 1 | 5. 0(d) | 3. 2 | 3. 3 | 2. 6 | 6. 4No (d) | 1. 1 | 1. 4 | 1. 0 | 2. 5(a) and (d) | 6. 3 | 6. 7 | 4. 3 | 7. 8(d), but no (a) | 2. 2 | 2. 2 | 2. 0 | 4. 9(a), but no (d) | 1. 4 | 2. 3 | 1. 3 | 2. 6No (a) or (d) | 0. 9 | 1. 0 | 0. 9 | 2. 3(a), (b) and (d) | 9. 5 | 9. 9 | [A] | 9. 0(a), (d), but no (b) | 5. 5 | 5. 9 | 3. 6 | 7. 4(b), (d), but no (a) | 2. 5 | 2. 4 | [A] | [A](d), but no (a) or (b) | 2. 2 | 2. 2 | 2. 0 | 5. 2(a), (b), but no (d) | 1. 9 | 3. 1 | 1. 7 | [A](a), but no (b) or (d) | 1. 3 | 2. 1 | 1. 2 | 2. 8(b), but no (a) or (d) | 1. 0 | 1. 6 | 1. 0 | [A]No (a), (b) or (d) | 0. 9 | 1. 0 | 0. 9 | 2. 6---------------------------------------------------------------- [A] Percentages not given where base is less than 100. 

 Symbols: (a) deaf brothers, sisters or ancestors; (b) deaf uncles, aunts, cousins, etc. ; (d) deaf husbands or wives. 

The striking feature of these percentages is the regularity withwhich they increase in proportion as the number of deaf relativesincreases, until among the 242 persons who have (a), (b) and (d)relatives, 23 or 9. 5 per cent also have (c) relatives. Aconsanguineous marriage within a family tainted with deafness wouldhave the same effect as doubling the number of deaf relatives, whichas we have seen greatly increases the percentage having deaf children. 

It would seem that the number of the married deaf reported as havingdeaf children is much too small, especially since Dr. Fay[89] producesstatistics of 4471 marriages of the deaf of which 300 produced deafoffspring. Counting only the 3, 078 marriages of which information inregard to offspring was available these figures show an average of alittle less than one such marriage in ten as productive of deafoffspring. The total number of children of these marriages was 6, 782, of which 588 were deaf. These 3, 078 marriages represented 5, 199 deafmarried persons as compared with the 31, 334 reported in the TwelfthCensus, or about one sixth. Increasing the 300 families who had deafchildren in the same ratio we have 1800 as compared with the 437reported by the census. But as it was inevitable that Dr. Fay's casesshould be selected somewhat, he has probably collected records of morethan one sixth of all the cases where deaf children were born of deafparents. But we can hardly believe that he found three-fourths of suchcases. The true number therefore must be considerably greater than437, but less than 1800. [90]

[Footnote 89: _Marriages of the Deaf in America_, chap. V. ]

[Footnote 90: Of the 17 children of first cousins reported on mycirculars as either totally or partially deaf, 9 are known to have haddeaf ancestors. ]

Dr. Fay found that 31 out of the 4, 471 marriages of the deaf wereconsanguineous, but he expresses the belief that the actual numberand percentage of consanguineous marriages of the deaf are larger. Thefollowing table which combines several of Dr. Fay's tables sets forththe main results of his work. In each instance one or both parties tothe marriage were deaf. The totals include only those of whominformation as to the offspring was available. 

 TABLE XXXIV. ---------------------------------------------------------- | | Marriages | | | resulting | | | in deaf | | | offspring | Deaf children |Number|-----------|------------------ Consanguineous |of | | | |Per Marriages |mar- | |Per | |Number|Cent of the Deaf. |riages|Number|Cent|Number|Deaf |Deaf----------------------------------------------------------First cousins | 7 | 4 | 57. | 26 | 7 | 27. Second cousins | 5 | 3 | 60. | 25 | 10 | 40. Third cousins | 1 | 1 | -- | 1 | 1 | --"Cousins" | 14 | 3 | 21. | 36 | 7 | 19. Nephew and aunt | 1 | 1 | -- | 4 | 3 | 75. Distantly related | 3 | 2 | 67. | 8 | 2 | 25. ----------------------------------------------------------Total consanguineous| 31 | 14 | 45. | 100 | 30 | 30. Not consanguineous, | | | | | | or no information |3, 047 | 286 | 9. |6, 682 | 558 | 8. ----------------------------------------------------------Grand total |3, 078 | 300 | 10. |6, 782 | 588 | 9. ----------------------------------------------------------

Obviously percentages based on these figures are of little value ofthemselves, especially since Dr. Fay's cases are not entirely typical, but in general this table points us to the same conclusion that wehave reached by other means, namely that where a tendency towarddeafness exists, a consanguineous marriage is more likely to producedeaf children than a non-consanguineous marriage. If more figures wereavailable the percentage of deaf children would probably increase withthe nearness of consanguinity and the number of deaf relatives, butwith the present data a further analysis has no significance. [91]

[Footnote 91: Mr. Edgar Schuster (_Biometrika_, vol. Iv, p. 465) findsfrom Dr. Fay's statistics that the average parental correlation(parent and child) of deafness is: paternal, . 54; maternal, . 535. English statistics of deafness give: paternal correlation, . 515;maternal, . 535. The fraternal correlation from the American data is. 74 and from the English . 70. See _infra_, p. 92. ]

If, then, consanguineous marriages where relatives are deaf have agreater probability of producing deaf offspring, and also a greaterprobability of producing plural deaf offspring, than ordinarymarriages, and two thirds of the congenitally deaf offspring ofconsanguineous marriages do have deaf relatives, it does not seemnecessary to look beyond the law of heredity for an explanation of thehigh percentage of the congenitally deaf who are of consanguineousparentage. 

In those cases of deafness which, in the Census returns, are ascribedto specific causes, the factor of consanguinity is still noticeable, although the percentage of the non-congenitally deaf who are theoffspring of cousins never exceeds 5. 3 (Table XXVIII). But theinfluence of heredity is not removed by the elimination of thecongenitally deaf. Many instances are known where successivegenerations in the same family have developed deafness in adult life, often at about the same age and from no apparent cause. The followingcase well illustrates this point. It is furnished me by acorrespondent in whom I have great confidence. The facts are these:A---- aged 28 married B---- aged 19, his first cousin who bore thesame surname as himself. Both lived to old age and were the parents ofeight children, two of whom died in infancy. My informant furtherstates:

 Having personally known very well all of the surviving six children of this family, I can truthfully state that all were unusually strong, active and vigorous people and all the parents of healthy children. A---- was troubled with deafness as long as I can remember, and this physical trait he transmitted to all of his children, though some of them did not develop the same till well along in life. C---- (the youngest son), however, began to indicate deafness quite early. No one of his four children is in the least deaf. 

It will be noticed here that whereas in the case of the cousinmarriage the trait was so strongly inherited, it disappeared entirelyin the next generation with a non-consanguineous marriage. Theinheritance of tendencies or weaknesses may be more common than theactual inheritance of defects. Dr. Bell's words on this point aresuggestive:

 Where a tendency toward ear trouble exists in a family, it may lie dormant and unsuspected until some serious illness attacks some member of the family, when the weak spot is revealed and deafness is produced. We are not all built like that wonderful one-horse shay that was so perfectly made in all its parts that when at last it broke down it crumbled into dust. When an accident occurs it is the weak spot that gives way, and it would be incorrect to attribute the damage to the accident alone and ignore the weakness of the part; both undoubtedly are contributing causes. 

 In the case, then, of a deaf person who has deaf relatives, the assigned cause of deafness may not be the only cause involved, or indeed the true cause at all. It may be the cause simply in the same sense that the pulling of a trigger is the cause of the expulsion of a bullet from a rifle, or a spark the cause of the explosion of a gunpowder magazine; hereditary influences may be involved. [92]

[Footnote 92: U. S. Census _Report on the Blind and the Deaf_, p. 127. ]

It is thus possible to account for the large proportion of deafnessamong persons of consanguineous parentage by the simple action of thelaws of heredity. Why then should we go out of our way to look for acause of the defect in consanguinity itself? When two explanations arepossible, the simpler explanation is the more probable, other factorsbeing equal; but in the present problem the factors are not equal, forthe evidence points strongly toward the simpler hypothesis ofintensified heredity, while there is little or no evidence thatconsanguinity is a cause _per se_. 

As to the probability then of a consanguineous marriage producing deafoffspring, it will readily be seen to be very slight, and in thosecases where there is actually no trace of hereditary deafness in thefamily, perhaps no greater than in non-related marriages. While thecensus figures in regard to the deaf are not complete they probablyinclude a great majority of the deaf in the United States. The 89, 287deaf would mean an average of 12 deaf persons to every 10, 000inhabitants and the 14, 472 congenitally deaf, 2 persons to every10, 000. Assuming then, as before[93] that 1, 000, 000 persons incontinental United States are the offspring of consanguineousmarriages within the limits of the term "cousins" as used in theCensus report, 41 out of every 10, 000 persons of consanguineousparentage would be deaf, and 17 congenitally so. Thus less than onehalf of one per cent of the offspring of consanguineous marriages inthe United States are deaf, and only one sixth of one per cent aredeaf-mutes in the commonly accepted sense of the term. 

[Footnote 93: _Supra_, p. 64. ]

It is interesting here to quote an opinion given by Dr. Bell in 1891, as to the probable results of the consanguineous marriage of deafpersons. [94]

[Footnote 94: _Marriage--An Address to the Deaf_, second edition, Appendix. ]

 1. A deaf person, not born deaf, who has no deaf relatives, will probably not increase his liability to have deaf offspring by marrying a blood relative. 

 2. A deaf person, born deaf, who has no deaf relatives, will probably increase his liability to have deaf offspring by marrying a blood relative. 

 3. A deaf person, whether born deaf or not, who has deaf relatives, will probably increase his liability to have deaf offspring by marrying a blood relative, especially if that relative should happen to be on the deaf side of the family. For example: If his father has deaf relatives and his mother has none, he will be more likely to have deaf offspring if he marries a relative of his father than if he marries a relative of his mother. 

 The laws of heredity seem to indicate that a consanguineous marriage increases or intensifies in the offspring whatever peculiarities exist in the family. If a family is characterized by the large proportion of persons who enjoy good health and live to old age with unimpaired faculties, then a consanguineous marriage in such a family would probably be beneficial, by increasing and intensifying these desirable characteristics in the offspring. On the other hand, if a large proportion of the members of a family betray weakness of constitution--for example: if many of the children die in infancy, and a large proportion of the others suffer from ill health, only a few living to old age with unimpaired faculties--then a consanguineous marriage in such a family would probably be hurtful to the offspring. A large proportion of the children would probably die in infancy, and the survivors be subject to some form of constitutional weakness. 

 As there are few families entirely free from constitutional defects of some kind, a prudent person would do well to avoid consanguineous marriage in any case--not necessarily on account of deafness, but on account of the danger of weakening the constitution of the offspring. Remoteness of blood is eminently favorable to the production of vigorous offspring, and those deaf persons who have many deaf relatives would greatly diminish their liability to have deaf offspring by marrying persons very remote in blood from themselves. 

 Children, I think, tend to revert to the type of the common ancestors of their parents. If the nearest common ancestors are very far back in the line of ancestry, the children tend to revert to the common type of the race. Deafness and other defects would be most likely to disappear from a family by marriage with a person of different nationality. English, Irish, Scotch, German, Scandinavian and Russian blood seems to mingle beneficially with the Anglo-Saxon American, apparently producing increased vigor in the offspring. 

CHAPTER VII

SUMMARY AND CONCLUSION

Having thus considered the more important problems which have beenconnected with the marriage of near kin, we have only to discuss thebearing of the conclusions thus formed upon the social aggregate, andthe effect which consanguineous marriages have upon the evolution andimprovement of the human species. 

It has been shown that the frequency with which consanguineousmarriages occur varies greatly with the physical and socialenvironments; that such marriages are more frequent in isolated and inrural communities than in cities; and that with the increasing rangeof individual activity and acquaintance the relative frequency ofconsanguineous marriage is decreasing. 

Consanguinity in the parents has no perceptible influence upon thenumber of children or upon their masculinity, and has little, if any, direct effect upon the physical or mental condition of the offspring. 

The most important physiological effect of consanguineous marriage isto intensify any or all inheritable family characteristics orpeculiarities by double inheritance. The degree of intensificationprobably varies with the nature of the characteristic; degenerateconditions of the mind, and of the delicate organs of special sensebeing the most strongly intensified. 

It is probable also that in the absence of degenerative tendenciesthe higher qualities of mind and body are similarly intensified bymarriage between highly endowed members of the same family. Dr. Reibmayr believes that inbreeding is necessary to the higher evolutionof the race: "A settled abode, natural protection from race mixtureand the development of a closely inbred social class are the basicconditions of every culture period. " But inbreeding must not becarried too far: "In the course of generations the ruling class beginsto degenerate mentally and physically, until not only is the classdestroyed, but for lack of capable leadership the people (Volk) itselfis subjugated and a crossing of blood again takes place. "[95]

[Footnote 95: Trans. From _Insucht und Vermischung beim Menschen_, p. 46. ]

In the breeding of animals the closest inbreeding is frequentlyresorted to in order to improve the stock, and many examples can begiven of the closest possible inbreeding for generations withoutapparent detriment, but it is universally admitted that the animalsselected for such inbreeding must be sound constitutionally, and freefrom disease. After a certain number of generations however, degeneration apparently sets in. The number of generations throughwhich inbreeding may be carried varies with the species, and thepurpose for which the animals are bred. Where they are bred primarilyfor their flesh, as for beef, mutton or pork, it can be pursuedfarther and closer than where they are bred for achievement in which aspecial strength is required--for instance in the breeding of racehorses. This would indicate that the more delicate brain and nervoussystem is sooner affected than the lower bodily functions. 

In man, however, freedom from hereditary taint cannot so easily besecured. Individuals cannot be selected scientifically for breedingpurposes. Furthermore, the human body is more delicately constructedthan that of the lower animals, and the nervous system is more highlydeveloped and specialized, so that it is reasonable to suppose that inman degeneration would set in earlier in the process of inbreeding, and that it would be impossible to breed as closely as with the loweranimals. Instances are well known, however, where incestuous unionshave been productive of healthy offspring, and successive generationsof offspring of incestuous connection are not unknown; but, althoughstatistics are lacking, it seems to be very often true that childrenof such unions are degenerate. It may be that the reason for this isthat with the laws and social sentiments now prevailing in allcivilized communities, only degenerates ever contract incestuousalliances. Desirable as it may be from a social point of view thatthis strong sentiment against incest should continue, it is not yet_proven_ that even the closest blood relationship between the parentsis directly injurious to the offspring. The "instinctive horror ofincest" is a myth, for although a horror of incest does very properlyexist in civilized, and in some tribal societies, it is purely amatter of custom and education, and not at all a universal law. 

Double heredity may account for all the observed ill effects ofconsanguineous marriage, including the high youthful death-rate, thehigher percentage of idiocy, deafness and blindness, and probably alsothe scrofulous and other degenerate tendencies; nevertheless, theremay be in some instances a lowering of vitality which this hypothesisdoes not fully explain. 

The tendency of inbreeding in animals, it is well known, is to fix thetype, the tendency of crossing, to variation. Inbreeding then, tendsto become simple repetition with no natural variations in anydirection, a stagnation which in itself would indicate a comparativelylow vitality. Variation and consequent selection is necessary toprogress. "Sex, " according to Ward[96] "is a device for keeping up adifference of potential, " and its object is not primarilyreproduction, but variation. [97]

[Footnote 96: _Pure Sociology_, p. 232. ]

[Footnote 97: Pearson (_Grammar of Science_, p. 373) points out thatvariation does occur in asexual reproduction. But that sex is at leasta powerful stimulus to variation can hardly be questioned. ]

 It is organic differentiation, higher life, progress, evolution. .. . But difference of potential is a social as well as a physiological and physical principle, and perhaps we shall find the easiest transition from the physiological to the social in viewing the deteriorating effects of close inbreeding from the standpoint of the environment instead of from that of the organism. A long-continued uniform environment is more deteriorating than similarity of blood. Persons who remain for their whole lives, and their descendants after them, in the same spot, surrounded by precisely the same conditions, and intermarry with others doing the same, and who continue this for a series of generations, deteriorate mentally at least, and probably also physically, although there may not be any mixing of blood. Their whole lives, physical, mental, and moral, become fixed and monotonous, and the partners chosen for continuing the race have nothing new to add to each other's stock. There is no variation of the social monotony, and the result is socially the same as close consanguineal interbreeding. On the other hand, a case in which a man should, without knowing it, marry his own sister, after they had been long separated and living under widely different skies, would probably entail no special deterioration, and their different conditions of life would have produced practically the same effect as if they were not related. [98]

[Footnote 98: Ward, op. Cit. , pp. 234-235. ]

Professor Ward's idea of "difference of potential, " or contrast, asessential to the highest vigor of the race as well as to that of theindividual offspring, offers an alternative explanation of theobserved results of consanguineous marriages, and one which does notnecessarily conflict with the explanation already given. All thephenomena of intensification are simply due to a resemblance betweenhusband and wife in particular characteristics, such as a commontendency toward deafness or toward mental weakness. This resemblance, which may or may not be the result of a common descent, renders moreprobable the appearance of the trait in the offspring. If the parentsclosely resembled each other in many respects they would be morelikely to "breed true" and the children would resemble one another intheir inherited traits, thus accounting for the high average ofdeaf-mutes to the family, observed in the Irish statistics. [99]

[Footnote 99: _Cf. Supra_, p. 66. ]

The theory of contrast and resemblance supplements that of intensifiedheredity where the resemblance is general, rather than in particulartraits or characteristics. In such a case the absence of thestimulating effects of contrast might result in a lowering ofvitality, which in turn would react upon the youthful death-rate. 

Where then related persons differ greatly in mental and physicaltraits, and generally speaking, belong to different types, it is veryimprobable that there would be any ill effects resulting from the merefact of consanguinity. A case in point is furnished me by acorrespondent. A first cousin marriage which turned out exceedinglywell was between strongly contrasted individuals; the husband was"short, stocky and dark complexioned" while the wife was "tall, slightof figure, and of exceedingly light complexion. " In other cases inwhich the results were not so good the husband and wife bore a closeresemblance to one another, physically and mentally. 

This, however, does not agree with the results obtained by ProfessorKarl Pearson. Basing his conclusions on the correlation of staturebetween husband and wife, he believes that homogamy is a factor offertility. Taking 205 marriages from Mr. Francis Galton's _FamilyRecords_, Professor Pearson found the correlation between husband andwife to be . 0931 ± . 0467, while weighted by their fertility thecorrelation was . 1783 ± . 0210, practically doubling the intensity ofassortative mating. [100] The value of these correlations, however, isimpaired, as he says, by the insufficient number of observations, andby the fact that absolutely taller mothers are the more fertile. 

[Footnote 100: _Royal Society Proceedings_, vol. 66, p. 30. ]

In a subsequent investigation of from 1000 to 1050 pairs of parents ofadult children, Professor Pearson found the correlation in stature tobe . 2804 ± . 0189; of span . 1989 ± . 0204; and of forearm . 1977 ± . 0205;with cross coefficients varying from . 1403 to . 2023. If, as hebelieves, "The parents of adult children are on the average more alikethan first cousins, then it follows that any evils which may flow fromfirst cousin marriage depend not on likeness of characters, but onsameness of stock. "[101]

[Footnote 101: _Biometrika_, vol. Ii, p. 373. ]

But even if it were true, as is very improbable, that parents of adultchildren are more alike than first cousins, it would still be likelyto follow that first cousins who married would be more alike thanfirst cousins in general. A certain degree of resemblance isundoubtedly necessary to complete fertility: husband and wife must bephysically compatible, and must both enjoy a certain degree of healthand physical strength. These facts are admitted by all, but it doesnot follow that resemblance beyond a certain point is not in itselfdetrimental. 

Professor Pearson's own experiments in this line, however, do notgive consistent results, for in correlating eyecolor with fertility, heterogamy seems to increase fertility. The highest average fertility(4. 57) is in those cases where the father is dark-eyed and the motherlight-eyed, while the lowest is where both parents have blue-green orgray eyes. [102]

[Footnote 102: _Phil. Trans. Of the Royal Society_, vol. 195 A, p. 150. ]

In a recent study an attempt has been made to measure the coefficientof correlation between cousins. [103] In the characteristics of health, success, temper and intelligence the coefficients ranged between . 25and . 30. These values differ but little from those found to obtain forthe resemblance between avuncular relatives for eye color (. 265), orbetween grandparent and grandchild for the same characteristic(. 3164). [104] Positive results were also found, with one doubtfulexception, for the occurrence of insanity and tuberculosis in cousins. The writer concludes: "The grandparent, the uncle and aunt, and thecousin are on practically the same footing with regard to relationshipor intensity of kinship as measured by degree of likeness ofcharacter; and it seems probable that any scientific marriageenactments would equally allow or equally forbid marriage betweengrandparent and grandchild, uncle and niece, aunt and nephew, andbetween first cousins. "[105]

[Footnote 103: Elderton and Pearson, "On the Measure of theResemblance of First Cousins. " _Eugenics Laboratory Memoirs IV. _Reviewed in _Br. Med. Journal_, Feb. 15, 1908. ]

[Footnote 104: _Phil. Trans. Of the Royal Society_, vol. 195 A, p. 106. ]

[Footnote 105: Elderton and Pearson, op. Cit. ]

As we should expect the resemblance between near relatives has beenfound to be much greater. From a measurement of from 4000 to 4886pairs, the average correlation of the characteristics of stature, span, forearm length and eyecolor between parent and child was . 4695. By similar computations and measuring the same characteristics, thefraternal correlation was found to be . 508. [106] From measurements ofa greater variety of characteristics in school children the meanfraternal correlation was . 539. [107] In athletic power the coefficientwas still higher, . 72 between brothers, . 75 between sisters and. 49 between brothers and sisters. Measurements of mentalcharacteristics--vivacity, assertiveness, introspection, popularity, conscientiousness, temper, ability and handwriting proved to be aseasily correlated, the mean coefficients being; brothers, . 52, sisters . 51, brothers and sisters . 52. [108]

[Footnote 106: Pearson and Lee, "On the Laws of Inheritance in Man, "_Biometrika_, vol. Ii, p. 387. ]

[Footnote 107: Ibid. , p. 388. ]

[Footnote 108: Pearson, "On the Laws of Inheritance in Man, " part 2, _Biometrika_, vol. Iii, p. 154. ]

The relative amount of degeneracy and disease among the offspring ofconsanguineous marriages has been enormously exaggerated, and thedanger is by no means as great as is popularly supposed. Nevertheless, since it is undoubtedly true that on the average such marriages do notproduce quite as healthy offspring as do non-consanguineous unions, and since public sentiment is already opposed to the marriage ofcousins, it is perhaps just as well that existing laws on the subjectshould remain in force. From the standpoint of eugenics however, it ismuch more important that the marriage of persons affected withhereditary disease should be prevented. Dr. Bell has pointed out thedanger of producing a deaf-mute race by the intermarriage ofcongenitally deaf persons, [109] and this warning should be made toapply to other congenital defects as well. Some states alreadyprohibit the marriage of the mentally defective, and persons under theinfluence of intoxicants. Such provisions are wise, and are the mostpractical means of achieving eugenic ideals--by preventing thepropagation of the unfit. The interests of society demand that thementally and physically defective should not propagate their kind. 

[Footnote 109: "Memoir upon the Formation of a Deaf Variety of theHuman Race. " _Memoirs of the National Academy of Sciences_, vol. Ii, pp. 177-262. ]

From the broader viewpoint of social evolution the problems ofinbreeding or crossing of stocks merge into the discussion of theendogamous and exogamous types of society. Whatever may have been theorigin of exogamy, the survival of the exogamous type in progressivesocieties may easily be explained on the ground of superioradaptability, variability and plasticity, which enables such societiesto survive a change of environment while the more rigid structure ofthe endogamous clan brings about its extermination. 

Inbreeding leads to caste formation and a rigid and stratified socialstructure, which is in the end self-destructive, and cannot survive achange of environment. The governing caste may, as Reibmayr says, favor the growth of culture, but it is usually the culture of thatcaste, and not of the people at large. The ruling caste is usually theresult of selection of the strongest and ablest, but after it becomesa caste, the individuals are selected on account of hereditary socialposition and not primarily on account of ability. Now biologicalexperiments show that although artificial selection may be carried toa point where animals will breed true to a characteristic to within 90per cent, yet if selection is stopped, and the descendants of theselected individuals are allowed to breed freely among themselves, they will in a very few generations revert to the original type. Thisis what happens in a social caste, unless, as in the case of theEnglish aristocracy, it is continually renewed by selection of theablest of the other classes. 

The superposition and crossing of cultures, the development ofsecondary civilization, is necessary to social evolution in itsbroadest sense, and this usually involves crossing of blood as well ascrossing of cultures. As a result of the unprecedented migrations ofthe last half-century we have in the United States the greatestvariety of social types ever brought so closely together. Anopportunity is offered either for the perpetuation of each racial typeby inbreeding, with the prospect of an indefinite stratification ofsociety, or for the amalgamation of all cultural and racial elementsinto a homogeneous whole, and the development of a race more versatileand adaptable than any the world has yet known. The general tendencywill undoubtedly be toward amalgamation, but there are decidedtendencies in the other direction, as for instance in the "firstfamilies of Virginia, " and in that large element of the New Englandpopulation which prides itself upon its exclusively Puritan ancestry, and which has inherited from its progenitors that intolerance whichcharacterized the early settlers of New England more than the pioneersof the other colonies. The dynamic forces of modern civilization are, however, opposed to caste--the West has long ago obliterated thedistinction between the Pennsylvania German and the Puritan, theScotch-Irish and the Knickerbocker Dutch. These same dynamic forces, which have prevented the formation of caste have at the same time beendiminishing the percentage of consanguineous marriage and willundoubtedly continue to operate in the same way for some time to come. And when rational laws prohibit the marriage of the diseased and thedegenerate, the problem of consanguineous marriage will cease to be ofvital importance. 

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GENEALOGIES CONSULTED. 

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Family. Author. Place and Date of Publication. -----------------------------------------------------------------Augur, E. P. Augur, Middletown, Conn. 1904. Banta, T. M. Banta, New York, 1893. Bent, A. H. Bent, Boston, 1900. Bolton, H. C. And R. P. Bolton, New York, 1895. Champion, F. B. Trowbridge, New Haven, 1891. Dewey, L. M. Dewey, Westfield, Mass. , 1898. Faxon, G. L. Faxon, Springfield, Mass. , 1880. Foster, F. C. Pierce, Chicago, 1899. Gates, C. O. Gates, New York, 1898. Giddings, M. S. Giddings, Hartford, 1882. Goodwin, J. J. Goodwin, Hartford, 1891. Hurlbut, H. H. Hurlbut, Albany, 1888. Kneeland, S. F. Kneeland, New York, 1897. Lee, E. J. Lee, Philadelphia, 1895. Mather, H. E. Mather, Hartford, 1890. Mead, S. P. Mead, New York, 1901. Potts, T. M. Potts, Canonsburg, Pa. , 1901. Shattuck, L. Shattuck Boston, 1855. Tenney, M. J. Tenney, Boston, 1891. Udall, G. B. L. Arner, In _Genealogical Exchange_, Buffalo 1904-5. Varnum, J. M. Varnum, Boston, 1907. Wood, C. W. Holmes, Elmira, 1901.