The thesis deals with Andrés Molina Enriquez's pro-miscegenation theory. Molina (1868-1940), a Spencirian evolutionist who believed race struggle is history's driving force, departs from the premise that Mexico will not be a cohesive, progressive nation until all Mexicans become Mestizos - i.e., the product of racial intermingling between Spaniards and Indians. Thus, the analysis of this theory is the main objective of the thesis. In order to analyse Molina's theory within its historical context, however, the preliminary section of the thesis briefly describes the thoughts of those Mexican intellectuals who had previously proclaimed ethnic homogeneity -via miscegenation- the key to national stability and development. Similarly, the last part of the thesis presents the ideas of some of Molina's successors, those who were in favor of miscegenation - not only a racial one but also a cultural one - in postrevolutionary Mexico. The first and last parts of the thesis allow us to see pro-miscegenation as a current of the Mexican intelligentsia's quest for national identity. The central part of it - the one devoted to Molina's theory, undoubtedly the most important and sophisticated contribution in the field - gives us a general picture of the contradictory nature of this current of thought. Even though it is clear that a pervasive miscegenation made ever more Mexican intellectuals endorse the idea that Mestizos are the real people of Mexico. The analysis of Molina's writings shows that he attempted to predict the supremacy of Mestizos with a theoretical framework that leads him to the opposite direction. Indeed, no matter how much he twisted it, Spencerian evolutionism did not serve him (or his contemporary pro-miscegenationists) to prove white-racism wrong. The conclusion is that Molina, as most of his fellow "Mestizophilia" supporters, chose to hail the ethnic group that represented an ever-growing majority of the Mexican population, and tried to build a scientific theory to prove the supremacy of that group. But in doing so he had to use the only methodological tools he had learned at the positivist schools of Porfirian Mexico. The result is a contradictory theory that, nevertheless, sheds light on the path to national identity in Mexico.