Starting with the second half of the Eighteenth Century, power relationships between peoples on earth, the growing and dramatic division between dominant nations and nations that were dominated, or even eliminated, and indeed the foundations of social inequalities, were increasingly seen by Western naturalists and intellectuals as inevitable (albeit, to some, unpleasant) features of the order of nature. Racial weakness was regarded as inscribed in the shape of human skulls, individual deficiencies in the traits of human faces. Across the world, as within societies, every human group and individual occupied the place that nature had assigned to it. The attempt to ground political and social phenomena on the authority of nature preceded the advent of Darwinism in the 1860s. It could indeed be claimed that the immediate and chaotic spread of Social Darwinism within the Western world simply reflected the widespread presence of attitudes and beliefs for which Charles Darwin, often unwittingly, appeared to provide authoritative scientific evidence. Darwin himself, in the last analysis, shared many of the presuppositions of his self-appointed and at times extreme followers, and predicted that many peoples on earth would disappear as the inevitable, regrettable consequence of natural laws regulating the relationships between biological populations. Yet, the “natural” triumph of the “civilizing” imperial western powers was not granted. Once again, the struggle for life and natural selection had to be called upon to express anxieties about the stability of the social order. The mounting aggressiveness of the “dangerous classes” and the fertility of the lower orders were jeopardizing the efforts of the “natural” elites that were responsible for civilization and imperial advances. The superior races had to exercise control over the less endowed ones, in the same way as the social elites had to carefully monitor demographic and political transformations that in the long term would endanger the survival of the race itself. Chronic illnesses, moral insensitivity, atavist aggressiveness had to be curbed through a rigid control of immigration and reproduction. New ways to investigate dangerous traits emerging in social groups would have led to scientifically based preventive actions. Racial anthropology found its parallel in criminal anthropology and criminology. Crime was seen as a natural phenomenon for which, often, there was no cure. Individuals as well as crowds often showed the survival of traits that characterized previous stages in the development of society, or in the natural history of man. “Beastly behaviours” and “savage crimes” became expressions that summed up a widespread climate of opinion. The survival of nations depended on their capacity to steer the reproductive flow and to isolate and possibly eliminate the danger that lethal traits would further spread throughout society. To some legislative body, such as the State of Indiana in 1907 and 1927, forced sterilisation appeared as a benign solution capable of stopping the spread of dangerous individual traits. To National Socialist political and scientific leaders in Germany, sterilization had to be accompanied by stronger measures, such as forced isolation and straightforward physical elimination. A strong State had to take strong measures to survive and to lead. Has the tragic lesson of negative eugenics during the 1930s and the early 1940s been learnt? A final lecture will be devoted to the periodic resurgence of attitudes appealing to the authority of nature and of science to explain complex social and historical phenomena. Is intelligence hereditary, geographically and socially distributed, and can “science” prescribe social norms and suggest political measures?