This chapter argues against the narrative that posits a pre-twentieth century past, where the mother and fetus were one, in contrast with the present, where the fetus is visible and autonomous. I complicate this narrative by showing that the maternal–fetal relationship was redrawn and reinterpreted multiple times in the twentieth century. The ‘fetal parasite’ era was informed by the hereditarianism of the early 1900s. The notion of a developing organism sensitive to external influences was replaced by a remarkably sheltered fetus. In contrast, concerns around the physical and psychological trauma following the Second World War supported the notion of ‘critical’ periods, responsive to external influences mediated by the mother. Yet soon thereafter, the language and imagery of an autonomous, self-sufficient fetus became prevalent amidst political battles over abortion. The notion of the autonomous fetus is linked to evolutionary biology’s 1970s concepts of the ‘selfish gene’ – with the ‘selfish’ fetus pitted against the mother in the struggle over scarce resources. By the 1990s, the rise of DOHaD and epigenetics signalled a return of the maternally mediated environment to the science of human development. While some interpreted this as a return to the pre-modern model, there is a significant difference. Here maternal experiences and surroundings have to be rendered accessible to an experimental, molecular approach and to show evidence of a quantifiable change in observed parameters.