Wolf tests his own theory with three natural experiments: (cousin) marriage in Morocco, the rarity of marriage within Israeli kibbutz peer groups, and "minor marriages" (in which baby girls were raised by their future mother-in-law to marry an adoptive "brother") in China and Taiwan. These cross-cultural comparisons complete his original and intellectually rich theory of incest, one that marries biology and culture by accounting for both avoidance and taboo.