Quantifying the role of heterogeneity in aging demographics, late-life mortality plateau, and high early-life mortality

Survivorship studies consistently reproduce two significant deviations from Gompertz-like mortality across a diverse collection of species: high early-life mortality (HELM) and late-life mortality plateau (LLMP). The relation between these demographic observations and the underlying trajectories in biological aging or individual mortality is uncertain. Here we show that both HELM and LLMP can be derived from genetic and environmental heterogeneity. We simulate heterogeneity in two model populations: (1) individuals with mortality following the Gompertz-Makeham Law and (2) individuals with Weibull mortalities. In both model populations, LLMP and HELM is sensitive to the mean and variation of parameter values. Using numerical models, we assess the biological validity of LLMP and HELM from demographic mortality trends for a diverse set of organisms (D. melanogaster, C. elegans, H. sapiens). Together, the results of this investigation suggest that selection bias from genetic heterogeneity and environmental heterogeneity in current methods of calculating mortality estimates in a population may be responsible for the widely reported high early-life mortality and late-life mortality plateau.