Vitality-based Intrinsic and Extrinsic Mortality Processes Explain Patterns in Human Survival

Over life, the accumulation of small day-to-day processes associated with behavior, nutrition, health care, stress and other events contribute, in sum, to mortality. A biology-motivated framework is developed to quantify these contributions through two stochastic processes: an intrinsic process defining the survival capacity (i.e. vitality) of an organism declines stochastically to a zero-boundary, and an extrinsic process representing the occurrence of external stresses. Each of the two components is represented parsimoniously using relations that strongly reflect the general mechanisms underlying the killing processes. The model is able to fit the mortality data of entire human life and provides biologically meaningful explanations for the observed anomalies from the classic Gompertz law. Finally, the ability to analyze historical mortality patterns through process-based parameters helps address fundamental questions in demography, such as whether human beings are biologically younger than in the past and how the dynamics of environmental and physiological interactions change over time. This is joint work with James J. Anderson.