Ancient medical writers and biologists elaborated different theories to explain the phenomenon of multiple births. The earliest extant texts are in the Hippocratic collection and in the physiological treatises of Aristotle. They express opposed ideas: for the Hippocratics multiple births are the result of an ideal conception, for Aristotle they are regarded as anomalies associated with notions of monstrosity and excess. These views shed light on ancient collective imagery. Three themes in particular are found in non-medical literature and iconography: twin birth as a model of ideal fecundity, the ambiguous status of twins of different sexes, and the relation of multiple births to monstrosity and animality, as evidenced by the motif of twins born from one egg.
The treatise Des monstres etprodiges (1579,1585) by Ambroise Paré includes a vignette depicting a monstrous embryo in the form of a human head surrounded by snakes. This picture belongs to the iconographic tradition relating to the Graeco-Roman mythology of sexuality and procreation. It derives from the belief in the womb's animal nature, illustrated on magic Graeco-Roman and Byzantine gemstones, where the uterus is shown in turn as a cupping vessel, a scarab-beetle, an octopus or the head of Gorgo.