In his work, Durkheim focused on "totemism", the religion of the Aboriginal Australians and Native Americans. Durkheim saw this religion as the most ancient religion, and focused on it as he believed its simplicity would ease the discussion of the essential elements of religion. As such, he wrote:Now the totem is the flag of the clan. It is therefore natural that the impressions aroused by the clan in individual minds—impressions of dependence and of increased vitality—should fix themselves to the idea of the totem rather than that of the clan: for the clan is too complex a reality to be represented clearly in all its complex unity by such rudimentary intelligences.Durkheim's work on religion was criticized on both empirical and theoretical grounds by specialists in the field. The most important critique came from Durkheim's contemporary, Arnold van Gennep, an expert on religion and ritual, and also on Australian belief systems. Van Gennep argued that Durkheim's views of primitive peoples and simple societies were "entirely erroneous". Van Gennep further argued that Durkheim demonstrated a lack of critical stance towards his sources, collected by traders and priests, naively accepting their veracity, and that Durkheim interpreted freely from dubious data. At the conceptual level, van Gennep pointed out Durkheim's tendency to press ethnography into a prefabricated theoretical scheme.