While the widespread rule that men should not marry under 21 and women under 18 has some justification, then, an ideal law would permit exceptions where there was adequate income and good mating. Laws to prohibit or restrict consanguineous marriages fall within the scope of this chapter, in so far as they are not based on dogma alone, since their aim is popularly supposed to be to prevent marriages that will result in undesirable offspring. Examining the laws of all the United States, C. B. Davenport[91] found the following classes excluded from marriage: 1. Sibs (i.e., full brothers and sisters) in all states, and half sibs in most states. 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."