Riddle argued that the ancient world possessed effective and safe contraceptives and abortifacients; however this knowledge about fertility control, widely held in the ancient world, was gradually lost over the course of the Middle Ages, becoming nearly unavailable by the early modern period. The reasons for this, Riddle argued, was that this knowledge was passed down through the oral and folk tradition, mainly by midwives, and belonged to a distinctly female-centered culture, removed from the male dominated and orientated knowledge of professionally trained physicians.