Denis Diderot’s natural philosophy is deeply and centrally ‘biologistic’: as it emerges between the 1740s and 1780s, thus right before the appearance of the term ‘biology’ as a way of designating a unified science of life (McLaughlin), his project is motivated by the desire both to understand the laws governing organic beings and to emphasize, more ‘philosophically’, the uniqueness of organic beings within the physical world as a whole. This is apparent both in the metaphysics of vital matter he puts (...) forth in works such as D’Alembert’s Dream (1769) and the more empirical concern with the mechanics of life in his manuscript Elements of Physiology, on which he worked during the last twenty years of his life. This ‘biologism’ obviously presents the interpreter of Diderot with some difficulties, notably as regards his materialism, given that contemporary forms of materialism have on the contrary strongly rejected notions of emergence, vitalism, teleology and any concepts appealing to unique, irreducible features of organisms. In response, some have described him as a ‘holist’ (Kaitaro) while others have emphasized his materialist, naturalist project (Bourdin, Wolfe). In what follows I examine a little-known aspect of Diderot’s articulation of his biological project: his statement in favour of epigenesis within the short but suggestive Encyclopédie article “Spinosiste.” Diderot was, of course, a partisan of epigenesis (the developmental-biological theory opposed to preformation, according to which beings develop by successive adjunction of layers of matter), but why include a statement in favour of a particular biological (or developmental) theory within an entry dealing with a philosopher, Spinoza, who does not seem to have been concerned at all with the specific properties of living beings, how they grow from embryonic to developed states, and so on? By trying to answer this question I also try and locate Diderot’s biological project in relation to what will become, in the years after his death, the project for a science called ‘biology’, with figures such as Treviranus and Lamarck. For it is not clear that the two can be easily correlated or causally linked: Diderot’s ‘epigenetic Spinozism’ is a different conceptual entity from what we find in histories of biology. (shrink)