Following the Unification of Italy (1861), when confronted with the underdevelopment problems of the south that had given rise to the so-called "southern question," some Italian anthropologists and psychologists began to study the populations of the south from the psycho-anthropological point of view. These scientists, at times subject to preconceived ideas toward the southerners, conveyed observations and descriptions of the southern character traits that, in general, were considered different, in a negative sense, with respect to those of the northern peoples. To explain such diversity in the "psychological" characteristics between the north and south of the country (presumed cause also of the south's backwardness), various hypotheses were advanced related to the kind of heredity theory adopted, which could be of, more or less, an "innatist" or "transformist" or "environmentalist" kind. The distinction proposed in this article between at least 2 different "hereditarian" theories formulated by the Italian scientists, and the confrontation of these theories with the hypotheses expressed by the "southernist" sociologists, contrary to the idea of "racial varieties" present in the Italian population, allows one to understand in what way and in what sense, at the threshold of the 20th century, there arose the ideology of "Nordicism" and the roots of racism were planted.