Sam Hwang, Deaglan Jakob, and Munir Squires at SSRN:
Cousin marriage rates are high in many countries today. We provide the first estimate of the effect of such marriages on the life expectancy of offspring. By studying couples married over a century ago, we observe their offspring across the lifespan. Using US genealogical data to identify children whose parents were first cousins, we compare their years of life to the offspring of their parents’ siblings. We find that marrying a cousin leads to more than a three-year reduction in offspring life expectancy. This effect is strikingly stable across time, despite large changes in life expectancy and economic environment.
More here.