 In addition to Comte’s philosophy, Mexican intellectuals applied Spencer’s social evolutionism to theories about Mexican history and society, as can be seen in the works of Justo Sierra (1848–1912) and Francisco Bulnes (1847–1924). According to social evolutionism, nations are like animal species: their organs have evolved to fulfill specific purposes, primarily survival. In his book El porvenir de las naciones hispanoamericanas (1899), Bulnes claimed that Mexico would have to make major changes to survive in its struggle against the Anglo-Saxons. From a political point of view, Spencer’s social evolutionism was the foundation of the view that progress in Mexico would result from a slow, deliberately planned evolution, not another revolution. For instance, Justo Sierra’s Evolución política del pueblo mexicano (1902) was used by some to justify the ongoing dictatorship of General Porfirio Díaz, who ruled Mexico for almost three decades leading up to the Mexican Revolution of 1910.