What about the community of Batz, on the coast of France, where Voisin found five marriages of first cousins and thirty-one of second cousins, without a single case of mental defect, congenital deafness, albinism, retinitis pigmentosa or malformation? The population was 3,000, all of whom were said to be interrelated.
What about Cape Cod, whose natives are known throughout New England for their ability? "At a recent visit to the Congregational Sunday-School," says a student, "I noticed all officers, many teachers, organist, ex-superintendent, and pastor's wife all Dyers. A lady at Truro united in herself four quarters Dyer, father, mother and both grandmothers Dyers."
And finally, what about the experience of livestock breeders? Not only has strict brother and sister mating—the closest inbreeding possible—been carried on experimentally for twenty or twenty-five generations without bad results; but the history of practically every fine breed shows that inbreeding is largely responsible for its excellence.
The Ptolemies, who ruled Egypt for several centuries, wanted to keep the throne in the family, and hence practiced a system of intermating which has long been the classical evidence that consanguineous marriage is not necessarily followed by immediate evil effects. The following fragment of the genealogy of Cleopatra VII (mistress of Julius Cæsar and Marc Antony) is condensed from Weigall's Life and Times of Cleopatra (1914) and
shows an amount of continued inbreeding that has never been surpassed in recorded history, and yet did not produce any striking evil results. The ruler's consort is named, only when the two were related. The consanguineous marriages shown in this line of descent are by no means the only ones of the kind that took place in the family, many like them being found in collateral lines.
It is certain that consanguineous marriage, being the mating of like with like, intensifies the inheritance of the offspring, which gets a "double dose" of any trait which both parents have in common. If the traits are good, it will be an advantage to the offspring to have a double dose of them; if the traits are bad, it will be a disadvantage. The marriage of superior kin should produce children better than the parents; the marriage of inferior kin should produce children even worse than their parents.
In passing judgment on a proposed marriage, therefore, the vital question is not, "Are they related by blood?" but "Are they carriers of desirable traits?"
The nature of the traits can be told only by a study of the ancestry. Of course, characters may be latent or recessive, but this is also the case in the population at large, and the chance of unpleasant results is so small, when no instance can be found in the ancestry, that it can be disregarded. If the same congenital defect or undesirable trait does not appear in the three previous generations of two cousins, including collaterals, the individuals need not be discouraged from marrying if they want to.
Laws which forbid cousins to marry are, then, on an unsound biological basis. As Dr. Davenport remarks, "The marriage of Charles Darwin and Emma Wedgewood would have been illegal and void, and their children pronounced illegitimate in Illinois, Indiana, Iowa, Kansas, Missouri, Nebraska, New Hampshire, Oklahoma, Oregon, Pennsylvania, South Dakota, Utah, Washington, Wyoming, and other states." The vitality and great capacity of their seven children are well known. A law which would have prevented such a marriage is certainly not eugenic.