We show that deceleration in hazard functions (mortality curves) and the resulting mortality plateaus are an intrinsic property of time-to-event traits that are affected by many underlying genetic and environmental factors. We argue that simply demonstrating that a mortality curve decelerates with age and reaches a plateau provides little information about the underlying biology associated with lifespan and mortality. To test hypotheses about the rate of deceleration of mortality curves and the level of mortality plateaus, observed mortality curves must be compared to mortality curves expected under a null-model, i.e., the deceleration of a mortality curve and the mortality plateau generated from a Normally-distributed trait of the same mean and variance. Comparisons between the observed data and the null models can be achieved with simple statistical tests and the results of these comparisons can be very informative regarding which questions about the shapes of mortality curves will be most informative.
Keywords: lifespan, hazard
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