The twentieth century is dominated by two great visions: one maintains that human societies tend toward differentiation, the other tells us that they tend, rather, toward homogeneity. Both visions, however, are mainly supported by self-reflection, fleeting observations and little empirical data. The empirical works which have focused on this question speak of a twofold evolution. In this paper, we outline the contradictory postures of the main theoretical frameworks in the human sciences; we attempt to provide an explanation to the dual movement revealed through the above stated empirical works by treating as dialectical its elements; and we discuss some of our works in which we have observed this theorized dialectic.