The idea of undertaking the research project which has led to the writing of this monograph first came to me in the late 1990s, when I was preparing my MPhil thesis at the Universidad Nacional Autónoma de México (UNAM) on the history of bacteriology in nineteenth-century Mexico. I was told repeatedly by those who supervised my work that the sine qua non for an understanding of this and related topics during the period known as the Porfiriato – that is, the last quarter of the nineteenth century and the first decade of the twentieth – was Leopoldo Zea's work El positivismo en México. Nacimiento, apogeo y decadencia, which clearly established the importance of Positivism as the prevalent ideology which underpinned the political and ideological support given to the president Porfirio Díaz by the powerful group known as ‘The Scientists’. My desire to understand this assumption led me to read Zea's work very carefully and conclude that he argued very forcefully that the supposed Positivism of ‘The Scientists’, and their influence upon Díaz's style of government, resulted from their profound familiarity with the writings and theories of the French and English philosophers Auguste Comte and Herbert Spencer. This assertion surprised me because I was aware of the profound geographical and cultural distance between Mexico and Europe in this period, particularly in the case of Spencer. Moreover, the importance attributed by Zea to ‘The Scientists’ as ideologues of the Díaz regime, and their alleged adhesion to Positivism, seemed to me to be rather forced and sometimes unsustainable, especially in the case of the supposed Spencerianism of Justo Sierra and the Social Darwinism of Francisco Bulnes, two of the most influential commentators upon the political, social, and cultural features of Porfirian Mexico. I was aware, of course, of the influence of Comte in some circles in the period, which could be traced easily through the activities of Gabino Barreda, who had studied under him during the period of his residence in Paris as a student of medicine (1848–51).