A generalized Dickens-Flynn (2001) model is presented and various simulations undertaken with it to give readers a better sense of the properties of such models. In particular, the inclusion of moderate degrees of persistence of intelligence and intelligence-relevant environment did not have much impact on the overall behavior of the models, although more extreme degrees of persistence did. Even moderate degrees, however, affected the internal relationships in the models. The importance of specifying the time scale and of addressing developmental aspects of the models is emphasized. It is noted that the translation of individual changes to population changes is not a simple matter in resolving the "IQ paradox" of large population gains over time in intelligence test scores.