The authors show how various kinds of qualitative long run demoeconomic behavior depend on household preferences, productivity, and the cost of childbearing. In particular, a dominant trend in growth can be interspersed with periods of fluctuation as slowly moving changes in productivity, preference, and child care costs push nonlinearities past crucial bifurcation points. Moreover, nonperiodic, essentially unpredictable demoeconomic behavior is robust, thus suggesting a possible explanation for persistent and substantial errors in population forecasts.