Go Ahead, Kiss Your Cousin

In 2003 Discover Magazine had an article about cousin marriage:

In the United States they are deemed such a threat to mental health that 31 states have outlawed first-cousin marriages. This phobia is distinctly American, a heritage of early evolutionists with misguided notions about the upward march of human societies. Their fear was that cousin marriages would cause us to breed our way back to frontier savagery—or worse. "You can't marry your first cousin," a character declares in the 1982 play Brighton Beach Memoirs. "You get babies with nine heads." So when a team of scientists led by Robin L. Bennett, a genetic counselor at the University of Washington and the president of the National Society of Genetic Counselors, announced that cousin marriages are not significantly riskier than any other marriage, it made the front page of The New York Times. The study, published in the Journal of Genetic Counseling last year, determined that children of first cousins face about a 2 to 3 percent higher risk of birth defects than the population at large. To put it another way, first-cousin marriages entail roughly the same increased risk of abnormality that a woman undertakes when she gives birth at 41 rather than at 30. Banning cousin marriages makes about as much sense, critics argue, as trying to ban childbearing by older women. But the nature of cousin marriage is far more surprising than recent publicity has suggested. A closer look reveals that moderate inbreeding has always been the rule, not the exception, for humans. Inbreeding is also commonplace in the natural world, and contrary to our expectations, some biologists argue that this can be a very good thing. It depends in part on the degree of inbreeding.