Étienne Geoffroy Saint-Hilaire and the First Embryological Evolutionary Model on the Origin of Vertebrates.

Historiographical accounts typically place the formulation of the first embryological theory of the evolutionary origin of vertebrates after the publication of Darwin's On the Origin of Species (1859). However, the French naturalist Étienne Geoffroy Saint-Hilaire developed an embryological evolutionary model in the 1820s that followed the Lamarckian theory. Geoffroy was the first to establish a direct embryological relationship between vertebrates and invertebrates. This idea was not forgotten, and the embryologists Anton Dohrn and Carl Semper subsequently updated it in their annelid theory as part of a debate about the origin of vertebrates that occurred during the latter part of the nineteenth century. This paper reviews the traditional historiography, analyzing and integrating Geoffroy's model into the current body of ideas.