Coutumes sexuelles des îles Trobriand

" Although an understanding of reproduction and modern medicine is widespread in Trobriand Society, their traditional beliefs have been remarkably resilient, The real cause of pregnancy is always a baloma, who is inserted into or enters the body of a woman, and without whose existence a woman could not become pregnant; all babies are made or come into existence (ibubulisi) in Tuma. These tenets form the main stratum of what can be termed popular or universal belief. If you question any man, woman, or even an intelligent child, you will obtain from him or her this information. In the past, many held this traditional belief because the yam, a major food of the island, included chemicals (phytoestrogens and plant sterols) whose effects are contraceptive, so the practical link between sex and pregnancy was not very evident."

http://en.wikipedia.org/wiki/Trobriand_Islands

http://en.wikipedia.org/wiki/The_Sexual_Life_of_Savages_in_North-Western_Melanesia