Theorizing epigenesis in a time of preexistence: From the end of the seventeenth century to the 1720s.

According to a classic periodization in the history of science, biological thought as it emerged in France from the last decades of the seventeenth century to the 1740s was strongly committed to the doctrine of the preexistence of germs. Nicolas Malebranche's role in disseminating this paradigm, particularly in the milieu of the Académie Royale des Sciences during the years when Bernard Le Bouyer de Fontenelle was its secretary, has been studied in detail, especially by Jacques Roger. However, much less has been said about the authors who argued against this doctrine prior to the appearance of the relevant pieces by Pierre-Louis Moreau de Maupertuis, Georges-Louis Leclerc, Comte de Buffon, and Denis Diderot. I aim to examine a series of French medical treatises and clandestine manuscripts that outlined a mechanist theory of epigenesis, between the end of the seventeenth century and the 1720s, to bring to light the strategies-often quite original-that allowed them to achieve this result. One interesting case is the heterodox readers of Malebranche, which use some of his own arguments (notably on the physiology of brain traces and the laws of nature) both against preexistence and to support epigenesis. I inquire into the historical worth of the positions defended by these authors as well as into the connections existing between the history of epigenesis and that of materialism in the early modern era.