One of the most endogenous societies in the world, Japan has approved of incestuous marriages in court circles even in historical times.(152) Preferred sibling, cousin, uncle-niece and aunt-nephew marriages have been so extensive that genetics experts have discovered that the inbreeding has affected their size and health.(153) How often this incestuous marriage system occurred in traditional Japan is still largely unexplored. One indication of what is likely to be found is a 1959 study by Kubo showing that there were still rural areas in Japan where fathers married their daughters when the mother had died or was incapacitated, “in accordance with feudal family traditions.(154) Kubo concluded that incest was considered “praiseworthy conduct” in many traditional rural families. In the 36 incest cases he studied in Hiroshima, he found that there was often community moral disapproval of the families who lived in open incestuous marriages, but that the participants themselves did not think of it as immoral. In fact, when the father was unavailable to head the family, his son often took over his role and had sex with his sister in order “to end confusion in the order of the home.” Other members of the family accepted this incest as normal. <...>

Two recent books on Japanese incest provide new insights into the subject. One of their major findings is that, in addition to the usual father-daughter and sibling incest found in the West, 29 percent of the Japanese calls complained about mother – son incest. This is an extremely high proportion compared to other countries, but about what could be expected considering the common frequency with which Japanese mothers sleep alone with their sons while the father is out having sex with other women – extramarital sex still being the rule for most married men in Japan.(165)

The most commonly reported incest occurs when the mother sees her son masturbate as a teenager and tells him, “It’s not good to do it alone. Your IQ becomes lower. I will help you,” or “You cannot study if you cannot have sex. You may use my body,” or “I don’t want you to get into trouble with a girl. Have sex with me instead.”(166) The researchers found that Japanese mothers and sons often sleep in the same bed and have sex together, although the exact incidence in the population was not investigated. According to the phone interviews, Japanese mothers teach their sons how to masturbate, helping them to achieve first ejaculation in much the same manner as they earlier helped them with toilet training.(167) Most of the sons had no sexual experience with another woman, and became jealous of the mothers’ having sex with their fathers, feeling they should have the right to monopolize the mothers.(168) Mother recent Japanese book, based on one hundred incest reports, confirms these observations, including the unusually high rate of mother – son incest, although it, too, provides no way to determine true national incidence rates.(169)