 The dominance of some form of pre-existence theory of generation between roughly 1670 and the 1740s provides some explanation for the lack of efforts among natural philosophers to develop transformist theories of species origins in the same period. A notable exception to this claim was the Epicurean cosmology resembling some aspects of Lucretius’s poem, developed by the French philosophe Benôit de Maillet (1656–1738) in his privately circulated manuscript Telliamed that was known in French circles for ten years before its publication in 1748. In this work de Maillet offered bold speculations on how sea creatures developed into land forms over time. Nonetheless, the period before the middle of the eighteenth century was dominated by a theory of organic generation that effectively precluded the naturalistic development of species. The development of scientific transformism can be seen to be intimately tied to new theories of generation, and also to the development of “active” rather than “passive” conceptions of matter.