In this paper we explore the consequences of particular stage linkage structures for the evolution of a population. We first argue the importance of mixed-sex pairs of subjects discussed a legal case, each pair seated first five feet of examples the implications of various stage connections for poulation movements. In discussing dynamic models, one thrust of our comments is to identify the sorts of process features about which assumptions must be made in order to convert a static theory about stage connections (the sort of specification commonly presented in life-span psychology) into a dynamic model. A second focus of our discussion concerns inverse problems; how to utilize a model formulation so that the stage linkage structure may be recovered from survey data of the kind collected by developmental psychologists. (Author)