Swallowing, sucking, and handedness as inferred from fetal thumb sucking

Wide-ranging theories have flourished around fetal nutrition for centuries. The Greeks were somehow more accurate in their intuitions than many of those who followed them. Democritus and Epicurus thought that the unformed fetus ate and drank 'per os', through the mouth [1]. Hippocrates rightly assumed that the maternal blood flow nourished the embryo and even respiration emerged from the cord. Subsequently an almost 'agricultural' view of nutrition prevailed. Fetuses were regarded as passive creatures which simply absorbed nutrients from their mothers, who were equated to the earth and its fertile soil. Albertus Magnus thought that embryos absorbed nutrients 'like a sponge'. Others, like Hildegard of Bingen, believed that retained menstrual blood was the primary source of fetal nourishment [1]. Menstruation ceased in the pregnant woman, and this was taken as a sign that menstrual blood was the fetus's main food. Still others imagined the fetus branching out many vessels into the placenta, the socalled matrix, through which the nourishment was sucked in as from a fertile terrain.