To bring back nothing at all would be to cast oneself as an exploiter or a parasite. To bring back an exact equivalent would be to suggest that one no longer wishes to have anything to do with the neighbor. Tiv women, she learned, might spend a good part of the day walking for miles to distant homesteads to return a handful of okra or a tiny bit of change, “in an endless circle of gifts to which no one ever handed over the precise value of the object last received”

These networks of trust, in turn, were largely responsible for the spread of Islam over the caravan routes of Central Asia and the Sahara, and especially across the Indian Ocean, the main conduit of medieval world trade. ... At the same time, Islam gained a toehold in trade emporia from Aden to the Moluccas because Islamic courts were so perfectly suited to provide those functions that made such ports attractive: means of establishing contracts, recovering debts, creating a banking sector capable of redeeming or transferring letters of credit. The level of trust thereby created between merchants in the great Malay entrepôt Malacca, gateway to the spice islands of Indonesia, was legendary.