Cousin Marriage: The Strange Politics Of Inward-Branching Family Trees

American eyebrows were raised when news broke that the mother of Maine Democrat candidate for U.S. Senate Troy Jackson’s children was his second cousin. The couple shares only 3% of their DNA, but first cousins share over 12% of DNA, and their children are twice as much at risk of genetic defects as children of unrelated couples.

In America, marrying a first cousin is still legal in 16 states and Washington, D.C. But Jerry Lee Lewis notwithstanding, it’s rare: only around 0.1% of marriages.