Their oral history corroborates this evidence, indicating that they originally migrated from the area around Lake Chad to the north with their current neighbors, the Ngbaka and Gbaya peoples, to escape slave traders. Their migration was complete by the time Europeans arrived in the late 19th century. The Manja are primarily an agrarian people, growing sorghum, maize, and manioc as staple crops amid the dripping rain forest that surrounds them. Bananas, taro, and yams are also important to the daily diet. The raising of livestock contributes relatively little to the local economy.
Men fish in the local rivers and manage to snare the occasional meal through sporadic hunting.
Regional trade is carried out along the major rivers. Men are responsible for clearing the land using slash and burn techniques, while the remainder of the farming work is done by the women. The Manja live in small clusters of houses which remain relatively isolated and independent of one another. The eldest male member of each extended family is recognized as the leader among them. Men often marry several wives, each of whom is given her own house where she can raise her own children.