The sharing of a sexual partner between relatives has always been taboo. In this stunning work, anthropologist Francoise Heritier charts the incest prohibition throughout history, from the strict decrees of Leviticus to modern civil codes, and finds a secondary type of incest, which she calls the incest of two sisters. The term refers not to incest between two sisters, or between two sisters and their mother, but to a love triangle of sorts in which the transfer of bodily fluids among sexual partners, two of whom are related to each other, creates undeniable bonds. Drawing on her field work in West African societies where the bans against two sisters are particularly stringent and on various cultural practices (such as milk kinship), Heritier fashions a complex "mechanics of fluids" in which blood, milk, and semen form the basis for kinship and prohibition. The intricate connections among the social, the natural, and the bodily emerge, fully apparent, and kinship studies are seen in a new light, one that illuminates the primacy of the symbolic.