The Debate: Cuvier and Geoffroy

This chapter outlines pre-Darwinian ideas in early nineteenth-century French biology. In an epistemic shift, a natural history based on continuity and homology under a unitary body plan, changed to one endorsing a discontinuous taxonomy in which embranchements (phyla) are united by the great functions of life. The old, rational order was seriously challenged. Georges Cuvier was instrumental to this transition, adopting methods of comparative anatomy to develop his theories. Now structures associated with digestion bore a relation to other functions, which taken together reflected the particular conditions of existence of the organism. Disagreements between Cuvier and Etienne Geoffroy Saint-Hilaire, who maintained the thesis of a unitary body plan for all animals, led to a public debate at the French Academy of Sciences in 1830. Rather than structures reflecting their functional purpose, Geoffroy interpreted homologies between animal groups as a rational plan in which structures maintained their relative order, but could be modified for different functions. Laws of composition and balance suggested that structures were rearranged internally with limited resources available for new structures. Cuvier disagreed, proposing that structures were developed for optimal function in the presence of environmental conditions. To Geoffroy, structure preceded function, while Cuvier insisted embranchements were functionally defined by environmental conditions. Cuvier set the stage for Darwin’s account of adaptation.