In his introduction, Arthur Wolf surveys the 20th century history of ideas about incest. He looks back at a conference in 1957 and at Westermarck, who was for so long a lone voice in the wilderness. Notable figures with contrary positions included Sigmund Freud, Leslie White, Claude Levi-Strauss, and Rodney Needham. Some claimed there was a natural instinct for sexual relations with family, rather than an aversion; some denied that an incest taboo existed at all; others claimed that it was impossible for that taboo to be derived from a biological aversion.
Alan Bittles surveys rules about consanguineous marriages in different religions and the laws in different Western countries and US states. He also summarises the few attempts there have been to measure the actual biological outcomes of incest.
Looking at the evidence from primates, Anne Pusey finds clear evidence for avoidance of mating with maternal relatives, and a response to paternal relatives that depends on social structure: "the patterns of inbreeding avoidance are consistent with familiarity being the primary mechanism of kin recognition".
Arthur Wolf presents results from his studies of "minor" marriages in Taiwan, in which the wife was adopted by her husband's family as an infant. Examination of their effects on fertility and divorce rates, and the variation of these with the ages of wives and husbands at adoption, suggests a slight modification of the Westermarck hypothesis:
"There is a remarkable absence of erotic feelings between people who live together and play together before age ten. The absence is particularly marked among couples brought together before age three, and, for any given couple, largely depends on the age of the younger partner when they first meet."
One commonly claimed counter-example to a universal incest taboo is sibling marriages in Roman Egypt. Based on analysis of fragments of census records, Walter Scheidel suggests that either large age differences between spouses or upbringing by unrelated wet nurses may have prevented an aversion resulting from childhood association.
Philosopher Neven Sesardic refutes the claim that there is a logical problem with biological aversion to childhood associates producing social sanctions against mating with relatives. He also explains why the case studies that are evidence for the Westermarck Effect — situations where there is avoidance of childhood associates even without social taboos — are necessarily counterexamples to it being the cause of the incest taboo.
William Durham takes a contrary stance to some of the other contributors, presenting ethnographic evidence that suggests incest taboos derive from a rational understanding of the negative effects of inbreeding, rather than or as well as from an innate aversion.
Hill Gates looks back at "anti-Freudian" anthropologist Bronislaw Malinowski's work on incest among the Trobriand Islanders. She also considers the idea that cultural evolution might in some cases run in the opposite direction:
"Where conditions for ranking were auspicious, a family that risked inverting taboo and ignoring aversion set in train a snowballing status improvement for its descendants and an evolutionary leap in social complexity for its society. Somewhere in the history of all early states we might expect to find royal brother-sister incest lurking."
Mark Erickson presents a clinical perspective. Incest disrupts familial affiliation and bonding, which contributes to the trauma of incest and helps to explain why victims of incest are more likely to commit incest themselves.
In the final chapter, Larry Arnhart considers the incest taboo as an illustration of how ethics can be rooted in natural human inclinations. He places Westermarck in an intellectual tradition which goes back to the Socratics, the medieval "natural right" tradition, Adam Smith, and Charles Darwin, and forward to Edward O. Wilson.
Inbreeding, Incest, and the Incest Taboo is an excellent collection: its pieces complement each other nicely, with little repetition, and fit together to make an effective book. As a summary of current knowledge on a topic at the heart of many theoretical debates, it will be helpful to anthropologists; as an accessible presentation of a topic of popular interest, it should command a much broader readership.