Part I deals with the legacy of ecclesiastical marriage prohibitions of the Middle Ages: Historians dealing with the Reformation have wondered about the political and social implications of theological debates about the incest rules, the Enlightenment opted for sociological considerations of the household and a new anthropology based on the passions, Baroque discourse focused upon sexual relations among kin by marriage , while Enlightenment and Romantic discussions worried the intimacy of siblings.

The first section of Part II deals with the six decades around 1900, during which European and American cultures obsessed about the sexuality of women. Almost everyone concurred in the idea that mother made the family what it was; that she configured the household, kept the lines of kinship vibrant, and stood at the threshold as stern gatekeeper, and many thought that she managed these tasks through her sexuality and an eroticized relationship with sons. Another story line, taken up in the section "Intermezzo," this one about the physical and mental consequences of inbreeding, appeared after 1850. To what extent do close-kin marriages pose risks for progeny? At its center, lay the incest problematic, now restated: Is avoidance of kin genetically programmed? Do all cultures know about risks of consanguinity? As for the twenty-first century, evolutionary and genetic assumptions are challenged by a living world population containing roughly one billion offspring of cousin marriages.

Part III deals with one of the perhaps most remarkable reconfigurations of Western kinship in the aftermath of World War I: The shift from an endogamous to an exogamous alliance system centered on the "nuclear family." An historical anomaly, this family form began to dissolve almost as soon as it came together and, in the process, shifted the focus of incest concerns to a new pairing: father and daughter. By the 1970s, when the father/daughter problematic swept all other considerations of incest aside, that relationship had come to be modeled, for the most part, around power and its abusive potential. As for "incest," its representations in the last three decades of the twentieth century no longer focused on biologically damaged progeny but rather on power abuses in the nuclear family: sexual "abuse." By the mid-1990s, Western culture at least partly redirected its gaze away from father and daughter towards siblings, especially towards brothers and sisters and the sexual boundaries and erotics of their relationships. Correspondingly, siblings became a "model organism" for psychotherapy, evolutionary biology, and the science of genetics.