The Janus Model of Life-Course Dynamics

Abstract

In this article, the classic problem of the human life-course, “how can the transition(s) of development into aging be explained?” has been solved. A theoretical model was constructed for the computer simulation of dynamic systems with one or more transitions in biology, psychology, and demography. In constructing the Janus model, it was found that the hypothetical forces of growth and senescence determine the life trajectories of dynamic systems of development and aging in terms of peak time and peak capacity. In validating the model in respect of empirical data, it was found that the Janus model of two coupled systems offers a quite satisfactory explanation for the life-course dynamics of simple and more complex growth and decline functions like general physiological performance, fluid and crystallized intelligence, and US mortality in 1910 and 1970. In conclusion, the interdisciplinary Janus model has therefore proved its validity in respect of the simulation of widely divergent life trajectories in biology, psychology, and demography. As such, the Janus model is fit par excellence for the integration of data and theory in developmental and aging research.