ABSTRACT
In the “Summary” that concludes chapter 6 of the Origin of Species, Charles Darwin raises a very general question, which involves the main alternative set by the biology of the time, and anticipates some of the major current theoretical cleavages. He mentions the “two great laws of biology.” They are the “principle of conditions of existence,” formulated by Georges Cuvier, and the “unity of type,” then defended by Etienne Geoffroy Saint-Hilaire. Both zoologists worked in the Muséum National d’Histoire Naturelle in Paris, and they fought a notorious academic battle at this Museum in 1830, about the extension of the unity of type. This phrase means that animals are built on the same organizational plan, and Geoffroy Saint-Hilaire extended such unity even beyond the vertebrates, thus generalizing Goethe’s intuition about the unity of the type “vertebrate” (studied in the previous chapter).
