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. Davenport6 found the following classes excluded from marriage:
- Sibs (i.e., full brothers and sisters) in all states, and half sibs in most states.
- Parent and child in all states, and parent and grandchild in all states except Pennsylvania.
- Child and parent's sibs (i.e., niece and uncle, nephew and aunt). Prohibited in all but four states.
- First cousins. Marriages of this type are prohibited in over a third of