Slow Gompertzian aging in long-lived <i>C. elegans</i> results from expansion of decrepitude, not decelerated aging

The Gompertz equation describes exponential age-increases in animal mortality rate arising from biological aging. Its parameters, α and β , are widely used to evaluate lifespan-extending interventions and human mortality patterns: it is assumed that reduction in β corresponds to deceleration of aging rate, and reduction in α to reduced aging-independent mortality. However, this view has never been empirically validated. We therefore investigated the biological basis of α and β , by simultaneous quantification of mortality and age-related health in long-lived populations of the nematode Caenorhabditis elegans . We show that reduction in β arises not from decelerated aging but expansion of decrepitude in longer-lived individuals, whereas reduction in α arises from decelerated aging. This empirical re-evaluation of Gompertzian aging inverts and challenges long-standing ideas in the biodemography of aging.