Ethnography and historical disciplines report on different kinds of folk or premodern societies’ ideas and superstitions regarding shadows that are not to find among the collective representations of modern, industrial societies. Shadows were seen as material substances and as doubles of persons and objects, as mystical beings capable to exert all kinds of magical influences. After certain time, however, these ideas were replaced by the rational view that seems so self-evident to every modern adult person. The article shows that developmental psychology has found the same mystical ideas among children. Only older children, due to their psychological development, discover the rational explanation of the origin and nature of shadows. It is argued that the strict parallel of the ontogenetic and historical development of the understanding of shadows is by no means an exception but reflects the same parallel concerning the development of the complete understanding of nature and world, physics and cosmos. Overall, developmental psychology delivers a key to understanding the historical development of humankind, thus forming a basis for ethnology or cultural anthropology specifically, or the human disciplines in general. This in former times widely demonstrated view was replaced by the currently prevailing ideas of “cultural relativism” and “universalism of mankind” especially after 1980. However, the empirical data do not support relativism and universalism but rather the developmental approaches of the previous generations of the human disciplines.