In France, the years 1817-1848 represented a pivotal moment in the development of what was defined then as the "theory” or the “system of races". Works by naturalists on the existence of hereditary natural varieties, showing distinct characters and unequal organic, intellectual and moral capacities, met with some fundamental transformations in the field of moral and political sciences (history, economics, political science), making the question of racial diversity a fundamental element for thinking about the history, development and future of societies. The "point of view of racial diversity" served to renew the way to do the history of nations, to reflect on the factors explaining the unequal development of certain societies as well as to examine the tensions between a horizon turned towards freedom and equality and the effective existence of natural inequalities, or radical struggles fracturing societies between dominated racial groups and oppressors. These discussions gave rise to lively debates in the fields of history, political economy and international politics. They led, in particular, to the formation of the world's first society explicitly dedicated to "the study of human races according to the historical traditions, languages and physical and moral traits of each people": the Société Ethnologique de Paris, created in 1839. Curiously, however, this first moment in the development of the "science of races" has hardly been the subject of in-depth study. The aim of this talk is to examine this moment and, in particular, to try to explain why it was primarily liberal thinkers, socialists and social reformers, who were responsible for these works on human races.