The chief contributions of Cuvier's great philosophical opponent, Etienne Geoffroy St Hilaire (1772-1844), are to be found in his maintenance with Lamarck of the doctrine of the mutability of species.
He is known as Rouelle the elder, to distinguish him from his younger brother and assistant, Hilaire Marin (1718-1779), who, on his resignation in 1768, succeeded him as demonstrator at the Jardin du Roi.
St Hilaire and afterwards his son Isodore regarded variation as not indefinite but directly evoked by the demands of the environment.
It has been recommended by C. Darwin, and at one of the early meetings of the Societe Zoologique d'Acclimatation, at Paris, Isodore Geoffroy St Hilaire insisted that it was the only method by which acclimatization was possible.
As we have seen, this hypothesis was fathered by Geoffroy St Hilaire in 1830 from his studies of Mesozoic Crocodilia, was sustained by Haldemann, and quite recently has been revived by such eminent palaeontologists as Louis Dollo and A.
Documents subsequently published have somewhat attenuated the responsibility of Ferry and Saint Hilaire for this breach of faith, and have shown that the French forces in Tunisia acted upon secret instructions from General Farre, minister of war in the Ferry cabinet, who pursued a policy diametrically opposed to the official declarations made by the premier and the foreign minister.
Principles of descent and other applications of uniformitarianism which had been struggling for expression in the writings of Lamarck, St Hilaire and de Blainville here found their true interpretation, because the geological succession, the rise, the migrations, the extinctions, were all connected with the grand central idea of evolution from primordial forms.
The last serious attempt of the allies in the centre led to some of the hardest fighting of the day; the Russian Imperial Guard under the grand-duke Constantine pressed closely upon St Hilaire and Vandamme on the plateau, and only gave way when the French Guard and the Grenadiers came into action.