The clockwork cosmos of early modern science was for the most part a passive and static thing, its shape imposed by an external designer, its movements originating outside itself. The classical mechanists of the seventeenth century mostly evacuated force and agency from the cosmos, often even including from its living inhabitants, to the province of a supernatural Clockmaker. They thereby built a kind of supernaturalism into the very structure of modern science. But not everyone concurred in this banishment. From the late seventeenth century onward, a tradition of dissenters embraced the opposite principle, that agency — a capacity to act, to be self-making and self-transforming — was essential to nature, especially living nature. A crucial member of this dissenting, active-mechanist tradition was the French naturalist Jean-Baptiste Lamarck, professor of natural history at the Muséum national d’histoire naturelle in Paris, and author of the term “biology” as well as of the first theory of what we now call “evolution”. This paper examines his rigorously naturalist approach — which naturalized rather than outsourced agency — and its exile from the halls of mainstream science.