The legal regulation of marriage between close relatives, known as consanguinity laws, has deep historical roots in the United States. These laws draw from a mixture of English common law, religious doctrine, and social customs. While prohibitions on incest have ancient origins, the specific state laws banning cousin marriage in the U.S. began to appear in the mid-19th century. This movement was part of a broader trend to increase state authority over marriage alongside regulations concerning age and medical fitness (Paul & Spencer, 2008). The initial motivations were often related to social and moral standards and a desire to ensure clear lines of inheritance.

As scientific understanding evolved, particularly with the development of genetics in the late 19th and early 20th centuries, a new rationale for these laws emerged. It became understood that children of closely related parents had a higher risk of inheriting recessive genetic disorders. This is because close relatives are more likely to carry identical harmful recessive alleles, and their offspring have an increased chance of inheriting two copies, which can result in serious health conditions (Hamamy, 2012). This scientific evidence provided a strong public health justification for states to enact and maintain laws prohibiting consanguineous marriages, shifting the basis from purely moral grounds to include medical and genetic concerns.

North Carolina’s laws on consanguinity reflect the combination of historical tradition and modern scientific reasoning. The specific regulations are outlined in North Carolina General Statute, which states that all marriages “between any two persons nearer of kin than first cousins” are void. The statute also includes a specific and less common prohibition against marriages “between double first cousins.” While North Carolina generally permits marriage between first cousins, it carves out an exception for this relationship (North Carolina General Assembly, 2025). Double first cousins occur when two siblings from one family marry two siblings from another. Their children have an inbreeding coefficient of 0.125, which is double the risk of typical first cousins and makes them genetically similar to half-siblings (Hamamy, 2012).

North Carolina’s legal framework fits squarely within the broader history of consanguinity laws in the United States. It upholds the widespread prohibition against marriages between very close relatives while allowing for first-cousin marriage, a practice permitted in about 20 states. Including a ban on double first cousins demonstrate a particularly nuanced approach, acknowledging a scenario with elevated genetic risk that many other state laws do not specifically address (Paul & Spencer, 2008). This provision suggests that North Carolina’s legislature has considered the degree of relationship and the specific genetic implications of certain unions.

References

Hamamy, H. (2012). Consanguineous marriages: Preconception consultation in primary health care settings. Journal of Community Genetics, 3(3), 185–192. https://doi.org/10.1007/s12687-011-0072-y

North Carolina General Assembly. (2025, 06 15). Want of capacity; void and voidable marriages. Retrieved from NCLEG: https://www.ncleg.net/enactedlegislation/statutes/html/bysection/chapter_51/gs_51-3.html

Paul DB, Spencer HG (2008) “It’s Ok, We’re Not Cousins by Blood”: The Cousin Marriage Controversy in Historical Perspective. PLoS Biol 6(12): e320. https://doi.org/10.1371/journal.pbio.0060320