Abstract

In 1859, Darwin proposed a solution for the tension between unity of typeUnity of type and conditions of existencePrincipleconditions of existence that had shaped the growth of pre-evolutionary morphology. The theory developed in On the Origin of Species contemplated and integrated both ideas: the unity of type explained by common descent and the arrangement to the conditions of existence explained by natural selection. That integration, however, was not a presupposition of the argument developed there but rather its most important achievement. The compatibility between the requirements of the principle of the conditions of existence stressed by Georges Cuvier and the Unity of Type highlighted by Étienne Geoffroy Saint-Hilaire was, in fact, the main tour de force of Darwin’s work and maybe its main key of reading. However, despite this, it can also be said that the synthesis that Darwin proposes for the antithesis between unity of type and conditions of existence ends up tipping the balance a little in Geoffroy’s favor. He led us to consider nature as an austere demiurge that tended to work with the same materials, modifying them indefinitely in virtue of the new functions that came to them in virtue of different circumstances and minimizing the production of new structures.