Saint-Hilaire against Cuvier: On the Degree of Coherence of Biological Architectures
Etienne Geoffroy Saint-Hilaire (1772-1844) and Georges Cuvier (1769-1832) are two great biologists who worked at the Museum of Natural History of Paris. Saint-Hilaire pursued the reflection begun by Lamarck by studying the unfolding of the anatomy of animals, as if all the species were partial manifestations of the same underlying structure. There would be on one side in the world of Ideas or God’s plan a perfect architecture, and on the other side, species that incarnate this plan in a more or less complete way. For him, the theory of evolution shows how the forces of life gradually approach the Ideal architecture.85 In his research, Saint-Hilaire attempted to define the anatomy of each species and the links that can exist between each organ. He was one of those who reinforced the evolutionary theory that anatomical links exist between all of the species. He demonstrated, among other things, that the anatomical similarities between species of mammals are particularly salient when biologists study their respective fetuses.
On a theoretical plane, Saint-Hilaire presents three laws that characterize the relationship between anatomy and evolution:86
1. The law of development is illustrated by the observation that in the history of the species, no organ abruptly appears or disappears. Wallace and Darwin would often refer to this law.
2. The law of compensation postulates that no organ can grow disproportionately unless other organs reduce their size and mass.
3. The law of relative position states that the parts of all animals maintain the same positions relative to each other.