Anthropologists have found considerable evidence suggesting that certain kinds of formal structures recur in widely different traditions of oral and written literature, including myths and folktales. These structures are characterized by binary contrasts, that is by two elements or themes that can be viewed as standing in diametric opposition to each other. Many example of recurring binary contrasts can be found in Western religion, literature, and mythology; good versus bad, up versus down, male versus female, cultural versus natural, young versus old, and so forth.
According to the French anthropologist Levi-Strauss, the founder of the research strategy known as structuralism, the reason these binary contrasts recur so often is that the human brain is wired in such a way as to make binary contrasts especially appealing, or "good to think". From the structuralist point of view, the main task of the anthropological study of literature, mythology, and folklore is contrasts that lie beneath the surface of human thought. However, binary contrasts is due to the way the left cerebral hemisphere works; it is analytical, and hence, it sees the contrasting differences of things in nature (as much as the right hemisphere sees the common features which relate and link every things into one whole) in order to successfully adapt to the environment.