A NATURAL ENVIRONMENT, like a playing field, imposes its own rules. Its physical attributes limit the kinds of survival tactics that can be employed, and they favor certain methods over others. The southern swamps, where the ancestors of the Nunu settled, contained a variety of micro-environments, each with its own rules. Environmental adaptation was essentially a process of learning the rules and discovering which tactics would be successful.

In settling the harsh environments of the southern swamps, the ancestors of the Nunu sought to adapt old techniques and develop new ones so that they could not only survive, but also prosper. The early settlers must have done a great deal of experimenting before settling on certain productive techniques. Once the techniques had been perfected, however, the repertory of tactics available in any given micro-environment stabilized. There was little room for further change without a technological breakthrough.

The diverse micro-environments of the southern swamps shared a common subservience to the rise and fall of the Zaire River. The fluctuations of the Zaire, with a difference of only two meters between the highest and lowest points, were less dramatic than those of the Ubangi, which the settlers had previously experienced. This was in part because south of the equator the Zaire had vast floodplains that absorbed much of the excess water.