Today, many pregnancy guides mention a nesting instinct. According to this, pregnant women would be seized by an urge to create the right environment for their child, for example to buy baby equipment or clean the apartment. The concept of the nesting instinct forms a specific configuration of knowledge: While it is widespread in the popular field, it occupies a marginal position in the scientific field. In this paper, I will investigate the historical epistemology of this form of knowledge. In (...) so doing, the following questions are addressed: How did the knowledge about a nesting instinct during pregnancy form? How was the nest as a specific natural-anthropogenic environment constructed? And to what extent do notions of gender and environment interact here? To answer these questions, the study takes the perspective of a history of knowledge in transit, in the longue durée from the nineteenth century to the present. The investigation reveals a gradual feminization of the concept of environment in the knowledge of the nesting instinct. Whereas in the nineteenth century it was often considered a male behavioral pattern and the nest was an analogy to the house, in the first decades of the twentieth century, the instinct transformed into a primarily female characteristic, with the nest representing the interior of the home. A decisive condition for this circulation of knowledge was that the nest became a ‘metaphorical thing’. As such, the nest did not simply lead to naturalization, but denoted a natural-social in-between space that increasingly became the goal of female care work. (shrink)