 As a consequence of the failure of “mechanistic” epigenesis, post-Cartesian mechanists resolved this issue with the theory of “preexistence”. Scientific foundations of this can be traced to the work of the microscopist Jan Swammerdam (1637–80) in the late 1660s on the basis of his microscopic observations on developing insects. The philosophical development of this theory was made by the French Oratorian priest Nicholas Malebranche (1638–1715), whose influential Recherche de la vérité of 1674 recast many Cartesian principles into a framework of “theistic” universal mechanism (Gaukroger 2010: chp.2). In this work Malebranche offered a novel theory of generation which is most accurately termed a “preexistence” theory. On this view, the new organism is not generated in secular time, but has pre-existed since the original creation of the world. This theory, often supported by appeals to Augustine’s theory of the creation of original seeds (see above  Section 1.2),  was to become the paradigmatic theory for nearly a century, and was closely associated with some version of the mechanical philosophy. Various expressions of the preexistence theory can be traced into the public teaching and published works of such influential expositors of academic medicine as Hermann Boerhaave (1668–1738) of the University of Leyden. The theory is also endorsed in numerous scientific treatises of the early eighteenth century. The question of both individual and species origin was by this theory removed to divine action at the first creation of the world (Pyle 2006; Roger 1963 [1997: chp. 6]).