In this paper we analysed the concept of motivation pointing to the two broader conceptual frames that can comprise it and enable us to understand its theoretical meaning. Two paradigms of scientific reasoning--the dynamic conceptualization of the world and the theory of evolution--have been used in the explanation of human behavior since the very beginning of the scientific dealing with the problem. The difference between these two metatheoretical positions is rich in consequences. The object of research of the same problem--the reason (cause) of human behavior--in the two metatheoretical conceptualizations is situated at adjacent but completely different strata of reality. The object of research of motivation as a dynamic explanation of behavior is contained in the psychic layer of reality. On the other hand, the conception of behavior as an adaptation to the biological heritage understands investigations of the objects situated at the organic or biological stratum. We also pointed to a complementary relation of the two research approaches to human behavior.