The incest taboo is a human institution; we universally prohibit having sex with siblings, parents, or grandparents, but vary culturally regarding cousins, uncles, and others on our family tree. We disagree on how far prohibition should go, and why. Indeed, natural selection primed us for cousin marriage as it offers some evolutionary advantage. In this article, which appeared in Skeptic magazine 24.2 (2019), Gabriel Andrade asks: How truly dangerous is cousin marriage, and should it be legalized?
