Although it is common to assume that monotheism grows naturally from polytheism, each of these religious systems presents, in fact, a distinct and sustainable product of spiritual evolution. The main question that arises in this respect is whether such distinctness and sustainability should result in mutual incompatibility and lack of common grounds or whether the two systems could remain dependent on each other both in substance and in form. In terms of substance, it may be more rewarding to approach the evolution of religion not as a headway progress from inferior to superior but as an evolving response to changes of the scope within which the numinous is perceived by human beings. The author believes that this scope is mostly determined by the predominant social unit within which a given religion is professed and practiced. Thus, animism operates chiefly within the context of extended family; mature polytheism corresponds to the level of clan/tribe, while monotheism proper belongs to the scale of nation/empire. As regards the corresponding evolution of the form, one can say that the above succession/expansion of scope results in a situation where newer religions tend to borrow and assimilate their signs and symbols from their predecessors. This creates a relationship of semiotic interdependence between different systems, which is, however, never perfectly symmetrical due to monotheism's more stronger propensity towards 'religiophagia'. Yet the latter's current tendency towards greater reflection and selfexamination inspires cautious optimism with respect to an improved probability of eventual interreligious harmony.