Yet he does not seem to believe that this bias seriously affects his conclusions.
In order as far as possible to avoid this bias, I sent my own circulars to genealogists and others who would naturally be more interested in the relationships than in pathological conditions. I asked, however, that all such results be noted. Among 722 children of first cousins I found 95 or 13 per cent who were defective in the sense in which Bemiss used the term. This is much nearer the actual percentage, but I have reason to believe, as will be seen hereafter, that even this percentage is far too high. A good illustration of the unconscious bias, which I tried to avoid is afforded by the reports on the cause of death among children of first cousins. Only 58 replies were given to this question, and of the 58 deaths 14 or one-fourth were either accidental or otherwise violent, while only one person was reported to have succumbed to pneumonia.
Many efforts have been made to investigate the occurrence of degeneracy in the offspring of consanguineous marriages, by studying communities in which such unions have been frequent, but the results are untrustworthy. Huth[[52]] quotes a number of instances where communities have lived for generations without crosses and with no apparent degeneracy, while other writers tell of high percentages of degeneracy. Smith's Island, Maryland, as has been said, seems absolutely free from serious congenital abnormalities, in spite of the great frequency of consanguineous marriages.
The causes of degeneracy are so varied, complicated, and obscure that even if consanguinity is a cause, there can be but few cases in which it is not complicated by other factors. But for the same reason that it is so difficult to prove any connection between consanguinity and degeneracy, it is equally difficult to disprove such a connection. It is very probable that from the mere operation of the law of heredity, there must be a comparatively large percentage of degenerates among the offspring of related parents, for defects which tend to be bred out by crossing are accentuated by inbreeding. This may be the reason for the disagreement among investigators of isolated communities. If an island, for instance, were settled by a small group of families in even one of which some hereditary defect was common, in the course of a few generations that defect would be found in a relatively large part of the population. While if the same island were settled by perfectly sound families, there would only be a remote chance of any particular defect appearing. Thus both classes of investigators may be perfectly conscientious, and yet arrive at diametrically opposite results. This theory is at least not to be contradicted by any facts which have come to light in the present investigation.
Some interesting points are brought up in Dugdale's well-known study of the "Jukes."[[53]] This family, of about 540 persons living in northern New York, is descended from five sisters of unknown parentage, who were born between 1740 and 1770. The name "Juke" is fictitious, and is applied to all descendants of these five women, little attempt being made to trace the male lines on account of the excessive prevalence of illegitimacy.
In this family consanguineous marriages have been very frequent, perhaps partly because the Jukes came to be looked upon as pariahs and could not associate on equal terms with other members of the community. These marriages seem to have been fully as productive as the average of the family, and the offspring of as high a grade of intelligence. However, some individual cases are worthy of special mention as illustrative of intensification of hereditary tendencies.
(1) An illegitimate son of Ada Juke married a daughter of Bell Juke. He was a laborer, honest and industrious. She was reputable and healthy, and her father had a good reputation, but her mother had given birth to four illegitimate children before marriage, three of whom were mulattoes. Thus in this marriage of first cousins, three out of the four parents were of a low moral grade. As a result of this marriage three sons and three daughters were born. Two sons were licentious, intemperate and dishonest, two daughters were prostitutes, and the third became such after her husband was sent to prison. Only one son turned out fairly well. This son married a second cousin, a granddaughter of Delia Juke, and four out of his seven children were above the average of the family. His two elder brothers, however, married prostitutes, and became ancestors of criminals, prostitutes and syphilitics.[[54]]
(2) A legitimate son of Ada Juke, whose father was a thief and a pauper, married a daughter of Clara Juke, whose antecedents were fairly good. The husband had contracted syphilis before marriage and entail it upon every one of his eight children. Five daughters became prostitutes and one was idiotic. The only daughter who bore a good reputation married a grandson of both Clara and Bell Juke. This was a remarkable case of selection. Both husband and wife were grandchildren of Clara, and so first cousins, and both were the offspring of first cousins, all within the Juke blood. But, on the other hand, both were the descendants of Clara, the best of the Juke sisters, and both were the best of the progeny of their respective parents. The only serious taint was the secondary syphilis which the wife had inherited from her father. Six children were born, two males and four females. The eldest son was at 31 "laborer, industrious, temperate;" the eldest daughter "good repute, temperate, read and write;" second daughter, "harlot;" third daughter "good repute, temperate;" and the two youngest are given simply as "unmarried." This family seems to have had as high an average mentally and morally as any family in the whole tribe, only one in six being distinctly immoral. In the next generation, the eldest son had two children, the eldest daughter four, and the third daughter, who married a first cousin, had one child. It would be of great interest to know more of this last marriage, the third generation of consanguinity in marriage, and the fourth first-cousin marriage in three generations, but at the time the book was written the parties were still in their early twenties.[[55]]
Mr. Dugdale makes the following "tentative inductions." 1. Boys preponderate in the illegitimate lines. 2. Girls preponderate in the intermarried branches. 3. Lines of intermarriage between Jukes show a minimum of crime. 4. Pauperism preponderates in the consanguineous lines. 5. In the main, crime begins in progeny where Juke blood crosses X blood. (Anyone not descended from a Juke, is of "X blood"). 6. The illegitimate lines have chiefly married into X.[[56]] The third and fourth inductions might indicate that a lowered vitality of the consanguineous lines changed a tendency toward crime into the less strenuous channel of pauperism, but I cannot find in Mr. Dugdale's charts any sufficient basis for the induction. It is true that the most distinctively pauper line is consanguineous, but it is less closely inbred than the "semi-successful" branch. As to the fifth induction, a close examination of the data shows clearly that in nearly every case where an X marriage occurred, it was with a person of a distinctly immoral or criminal type. Cousin marriage has also been frequent in the middle western counterpart of the Jukes, the "Tribe of Ishmael."[[57]]