The infamous Steve Sailer has written a lot about cousin marriage , which, in practice, seems to be correlated with arranged marriage in many cultures (including the European royals in past centuries). Perhaps a lot of arranged marriages in practice may lead to inbreeding, with the genetic dangers that follow.

I'm also wondering about the effects of anonymous sperm banks, where relatively well-off women may pay to choose a biological father on the basis of -- whatever available information they may choose to consider. What factors, in a man they will never meet, do they choose for their offspring?