Étienne Geoffroy Saint-Hilaire as a predecessor of the epigenetic concept of evolution

The contribution of Étienne Geoffroy Saint-Hilaire (1772-1844) to evolutionary biology is reviewed in commemoration of his 250th birthday. Geoffroy's views on saltational changes during embryogenesis of animals characterize him as a predecessor of the epigenetic concept of evolution, which is now developing in the frames of the extended evolutionary synthesis or evo-devo. While Lamarck distinguished between the two modes of evolution, one within the same level of organization and the other characterized by the transition to a more complex organization, Geoffroy Saint-Hilaire attempted to explain the second mode by the changes in embryogenesis triggered by environmental influences. In this regard, he placed the phenomenon of complexification in the centre of the evolutionary context. Geoffroy Saint-Hilaire can be considered also as an early predecessor of the cell theory. His ideas about the unique plan of structure for animal species and of the fundamental connections that establish the homology of anatomical parts represent an important contribution to the evolutionary concept.