It is undeniable that degeneracy does in some cases follow from the marriage of near kin, and probably with greater frequency than from non-related marriages.  But it is likewise true that many of the world’s greatest men have been the products of close inbreeding, sometimes continued through several generations.  Frederick the Great of Prussia was the product of three successive cousin marriages between descendants of William the Silent,[42] and among his seven brothers and sisters at least three others ranked among the ablest men and women of the generation.  Cousin marriage has always been frequent in the “first families of Virginia” which have produced a phenomenal percentage of able men.  In fact, few persons who have traced their pedigrees back through a number of generations, do not find some names duplicated, as a result of cousin marriage.

[Footnote 42:  Woods, Heredity in Royalty, pp. 74-75.  The Great Elector, a great-grandson of William the Silent, married his 1-1/2 cousin, a granddaughter of William and also a great-granddaughter of Admiral Coligny.  Frederick I married his second cousin, daughter of the Duchess Sophia of Brunswick, and a descendant of William.  Frederick William I married his first cousin, Dorothea, granddaughter of Sophia, and also a descendant of William the Silent.  Unfortunately the Hohenzollern line was continued by a mediocre brother of Frederick II, but through his sister, Queen Ulrica, the line of genius lasted still another generation to Gustavus III of Sweden.]

The ills which have at one time or another been attributed to consanguineous marriage include nearly all those which cannot otherwise be satisfactorily accounted for.  But with the progress of pathology the list has greatly been reduced:  for instance, cretinism is now known to be a product of local conditions.  The remaining counts in the indictment against consanguineous marriage may roughly be classified as:  1.  The production of infertility, some forms of physical degeneracy, and deformity. 2.  The production or aggravation of mental and nervous disorders. 3.  The production of certain defects in the organs of special sense.  These three divisions will be discussed separately.

1.  INFERTILITY AND DEGENERACY

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