Turnover shapes evolution of birth and death rates

A truly predictive evolutionary theory must be derived self-consistently from the underlying stochastic population dynamics, where the environment and ecology are not treated merely as confounders and mediators of evolutionary dynamics. By explicitly decomposing fitness to its birth and death components as well as accounting for how evolution and ecology respectively might affect them, we show how a fundamental asymmetry between reproduction and survival emerges. First, we derive a stochastic replicator equation from a general birth-death process and demonstrate the importance of the demographic turnover rate (defined as the sum of birth and death rates) on mutant fixation. Then, we show how the turnover rate shapes the distribution of evolutionary trajectories causing a systematic turnover bias in the mutant substitution dynamics in favour of less volatile low-turnover strategies. Finally, we provide theory for predicting how organismal growth strategies evolve in response to different population regulation mechanisms and show how the resulting life-history evolution has a clear direction where the pace of life becomes either slower or faster depending on the ecological context and mutational supply. Overall, our results highlight the importance of demographic turnover in evolution and underline the perils of quantifying fitness with a single parameter.