Human nature is a concept that transgresses the boundary between science and society and between fact and value. It is as much a political concept as it is a scientific one. This chapter will cover the politics of human nature by using evidence from history, anthropology and social psychology. The aim is to show that an important political function of the vernacular concept of human nature is social demarcation (inclusion/exclusion): it is involved in regulating who is ‘us’ and who is ‘them.’ It is a folk concept that is used for dehumanization, for denying (a) membership in humankind or (b) full humanness to certain people in order to include or exclude them from various forms of politically relevant aspects of human life, such as rights, power, etc.