There are two modern evolutionary theories of mammal senescence: Programmed theories contend that mammals purposely limit their lifespans because doing so creates an evolutionary advantage. Non-programmed theories contend that each mammal specie only needs a particular lifespan and therefore only evolved and retained the capability for attaining that lifespan. Arguments over the evolutionary nature of aging have now existed for more than 150 years and for reasons described here may never be definitively resolved.
The programmed/ non-programmed question is critical to medical research because the theories have grossly different predictions regarding the biological mechanisms associated with the aging process and therefore, the nature of age-related diseases and conditions.
This article describes and compares two approaches for avoiding the need to obtain resolution on the evolutionary basis of senescence in order to identify and characterize the biological mechanisms responsible for aging and therefore the nature of highly age-related diseases.