Growth rate, evolutionary entropy and ageing across the tree of life

The growth rate of a population serves as a measure of its Darwinian fitness, while its sensitivity indicates the intensity of selection. Generally, the sensitivity of r decreases with age, resulting in an expected increase in population mortality over time. However, this does not hold true for many populations, especially those exhibiting negative senescence. Both evolutionary entropy and its sensitivity serve as complementary measures for assessing fitness and the intensity of selection. The sensitivity of entropy is typically a convex function of age, implying stronger selection pressures in younger and older age groups. We show that the sensitivity functions of entropy exhibit a greater range of behaviours compared to those of the growth rate alone. This strongly suggests that evolutionary entropy offers an extremely valuable measure for capturing the diversity in aging patterns within populations, complementing what can be captured by the growth rate alone.