정말 일본에서 이런 일이 1950년도에도 존재 했군요!

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.

In traditional Japan, quite young girls were introduced into sex by older boys who visited their bedrooms at night with the complicity of the girl's parents (called night-prowling, yobai). The boys "assembled in communal huts and instructed slightly younger village males in sex approaches and techniques..." Although they recommended "gentle persuasion,"(155) there was no guarantee that all was so gentle in fact, since the parents "looked the other way" in accordance with custom while the older boys had intercourse with their young daughters.

Western observers even today often notice that Japanese mothers still masturbate their young children during the day in public and at night in the family bed - in order, they say, "to put them to sleep."(156) The average Japanese today sleeps with his or her children until the children are ten or fifteen years old,"(157) - one recent Japanese study found daughters still sleeping with their fathers over 20 percent of the time even after age sixteen.(158) Even when the home contains a dozen rooms or more, parents and grandparents feel "lonely" if they sleep apart from
the children in the family, and therefore go to bed with some child every night (the mean age in one study of children sleeping alone is 12.7 years).(159) Since so many families still practice what is termed dakine co-sleeping - with the parent or grandparent sleeping while physically embracing the child, a practice said to be beneficial to the health of the adult"(160) - and since most Japanese parents still regularly have sexual in-tercourse while the child is in bed with them,(161) one wonders how scholars can continue to maintain that nothing sexual usually happens to the Japanese child in the family bed, particularly since none have yet ask-ed the children themselves about their sexual experiences.

http://www.psychohistory.com/htm/06a1_incest.html