Evolutionary thinking was prominent during the classical period of sociological theory, but it became increasingly rare as the twentieth century progressed. By the 1960s, stage models of evolutionary thought reappeared, and the onset of the second Darwinian revolution in the mid-1970s marked a resurgence of evolutionary thinking. Currently, a new evolutionary sociology is emerging, and it focuses on sociocultural evolution, the adapted mind, the evolution of the social brain, and cross-species analysis.