In this paper, I analyze a momentous change in eighteenth century French life sciences. Whereas in the first half of the century the conception of natural history as the systematic collection of facts had been most successful, at mid-century a new approach emerged. This approach was characterized by an accent on general philosophical themes rather than on observation and experiment. I study the grounds and features of this historical shift through the work of Maupertuis, who published papers in institutional (or (...) Baconian) natural history in his early years, but then adopted a more speculative approach to the life sciences. (shrink)