The relationship of new market exchange systems to indigenous non-market exchange remained a perplexing question for anthropologists. Paul Bohannan argued that the Tiv of Nigeria had three spheres of exchange, and that only certain kinds of goods could be exchanged in each sphere; each sphere had its own different form of special purpose money. However, the market and universal money allowed goods to be traded between spheres and thus served as an acid on established social relationships.[32]