A stochastic differential equation model is developed to clarify the interaction of debilitation, recuperation, selection and aging. The model yields various insights about lingering mortality consequences of disasters such as wars, famines and epidemics that may weaken the survivors. A key result is that debilitation and selection are interdependent: debilitation that increases population heterogeneity will result in subsequent selection; selection, by altering the distribution of population heterogeneity, will influence the impact of debilitating events.