This chapter examines human thinking from two different perspectives: personal epistemologies and social representations. We first present a developmental model of personal epistemologies, that is, individuals’ assumptions of the nature of knowledge and justification of knowledge claims. After that we introduce the theory of social representations – how people as groups form everyday theories of issues that are interesting, important or new to them. The specific focus of this chapter is on how Finnish people form an everyday understanding of the human species within the frameworks of the evolution theory and creation story – both having a relatively strong position within the Finnish educational system and culture. People’s understanding of the origins of human beings are analysed from the perspectives of personal epistemologies and social representations. The results show that knowledge is polymorphic and social subjects may use contrasting modes of reasoning depending on the context and their needs. We suggest that the concept of cognitive polyphasia helps to understand the use of different kinds, sometimes contradictory, explanatory models in everyday thinking of human species. We conclude by discussing the potential of combining personal epistemologies and social representations in the study of human thinking.