The chapter presents a philosophical discussion of human nature as a complex concept designed to serve as a heuristic basis for comparative studies and explanations of the behavioral and psychological characteristics of different human populations. The author proposes the concept of flexible essentialism, in which entities are complex realities of evolution and social and cultural interactions that scientists cite to criticize and reject the very notion of “human nature”. After mentioning some common features of humans with animals, he considers three types of uniquely human characteristics: reason (language, consciousness, thinking, creativity), features of anatomy and psychophysiology, and “fruits of reason” that encompass all the technical, social, and cultural structures of human niches. There is a spectrum of options for defining the boundaries of human nature: from a narrow understanding with only innate traits to a broad interpretation that considers the interactions of individuals and groups with elements of their niches in material, social, and cultural aspects. Progress in the productive economy, population growth, and administrative control led to the “civilization trap,” a rut of further expansion of societies burdened by inequality, exploitation, and war. The tumultuous and creative history of populations formed the multifaceted depth of human niches. The diversity and variability of human traits always depend on actual niches and social learning. Thus, human capacities and abilities change throughout history as niches change. But they are not completely plastic. It is acceptable to speak of shifting “natures” in the course of anthropogenesis and subsequent social, cultural evolution. The author proposes a model with “layers” of innate assignments corresponding to long past epochs during which different human populations developed. In a person's psyche and behavior, “inner primate”, “primitive man”, “inner barbarian or Neolithic man”, “traditional man” can coexist with the innate tasks of one or another pre-modern civilization. A special logic of comparative research makes it possible to test these ideas. The proposed definition of human nature takes into account the main semantic components presented.