Evolvability, Population Benefit, and the Evolution of Programmed Aging in Mammals.

Programmed aging theories contend that evolved biological mechanisms purposely limit internally determined lifespans in mammals and are ultimately responsible for most instances of highly age-related diseases and conditions. Until recently, the existence of programmed aging mechanisms was considered theoretically impossible because it directly conflicted with Darwin's survival-of-the-fittest evolutionary mechanics concept as widely taught and generally understood. However, subsequent discoveries, especially in genetics, have exposed issues with some details of Darwin's theory that affect the mechanics of the evolution process and strongly suggest that programmed aging mechanisms in humans and other mammals can and did evolve, and more generally, that a trait that benefits a population can evolve even if, like senescence, it is adverse to individual members of the population. Evolvability theories contend that organisms can possess evolved design characteristics (traits) that affect their ability to evolve, and further, that a trait that increases a population's ability to evolve (increases evolvability) can be acquired and retained even if it is adverse in traditional individual fitness terms. Programmed aging theories based on evolvability contend that internally limiting lifespan in a species-specific manner creates an evolvability advantage that results in the evolution and retention of senescence. This issue is critical to medical research because the different theories lead to dramatically different concepts regarding the nature of biological mechanisms behind highly age-related diseases and conditions.