2. Parent and child in all states, and parent and grandchild in all states except Pennsylvania.
3. Child and parent's sibs (i.e., niece and uncle, nephew and aunt). Prohibited in all but four states.
4. First cousins. Marriages of this type are prohibited in over a third of the states, and tacitly or specifically permitted in the others.
5. Other blood relatives are occasionally prohibited from marrying. Thus, second cousins in Oklahoma and a child and his or her parent's half sibs in Alabama, Minnesota, New Jersey, Texas, and other states.
In the closest of blood-relationships the well-nigh universal restrictions should be retained. But when marriage between cousins—the commonest form of consanguineous marriage—is examined, it is found to result frequently well, sometimes ill. There is a widespread belief that such marriages are dangerous, and in support of this idea, one is referred to the histories of various isolated communities where consanguineous marriage is alleged to have led to "an appalling amount of defect and degeneracy." Without questioning the facts, one may question the interpretation of the facts, and it seems to us that a wrong interpretation of these stories is partly responsible for the widespread condemnation of cousin marriage at the present time.
The Bahama Islands furnish one of the stock examples. Clement A. Penrose writes[92] of them:
"In some of the white colonies where black blood has been excluded, and where, owing to their isolated positions, frequent intermarriage has taken place, as for instance at Spanish Wells, and Hopetown, much degeneracy is present, manifested by many abnormalities of mind and body.... I am strongly of the opinion that the deplorable state of degeneracy which we observed at Hopetown has been in a great measure, if not entirely, brought about by too close intermarrying of the inhabitants."
To demonstrate his point, he took the pains to compile a family tree of the most degenerate strains at Hopetown. There are fifty-five marriages represented, and the chart is overlaid with twenty-three red lines, each of which is said to represent an intermarriage. This looks like a good deal of consanguineous mating; but to test the matter a little farther the fraternity at the bottom of the chart,—eight children, of whom five were idiots,—was traced. In the second generation it ran to another island, and when the data gave out, at the fourth generation, there was not a single case of consanguineous marriage involved.
Another fraternity was then picked out consisting of two men, both idiots and congenitally blind, and a woman who had married and given birth to ten normal children. In the fourth generation this pedigree, which was far from complete, went out of the islands; so far as the data showed there was not a single case of consanguineous marriage. There was one case where a name was repeated, but the author had failed to mark this as a case of intermarriage, if it really was such. It is difficult to share the conviction of Dr. Penrose, that the two pedigrees investigated, offer an example of the nefarious workings of intermarriage.
Finally a fraternity was traced to which the author had called particular attention because three of its eleven members were born blind. The defect was described as "optic atrophy associated with a pigmentary retinitis and choryditis" and "this condition," Dr. Penrose averred, "is one stated by the authorities to be due to the effects of consanguineous marriage."