25 years ago we first applied the reliability theory to explain aging of biological species (Gavrilov, 1978, PMID: 624242; Gavrilov et al., 1978, PMID: 716614). Since that time we continued the development of this theory (Gavrilov and Gavrilova, 2001, Journal of Theoretical Biology 213(4): 527-545, http://www.longevity-science.org/JTB-01.pdf) and came to the following conclusions:
(1) Redundancy is a key notion for understanding aging and the systemic nature of aging in particular. Systems, which are redundant in numbers of irreplaceable elements, do deteriorate (i.e., age) over time, even if they are built of non-aging elements.
(2) An apparent aging rate or expression of aging (measured as age differences in failure rates, including death rates) is higher for systems with higher redundancy levels.
(3) Redundancy exhaustion over the life course explains the observed 'compensation law of mortality' (mortality convergence at later life) as well as the observed late-life mortality deceleration, leveling-off, and mortality plateaus.
(4) Living organisms seem to be formed with a high load of initial damage, and therefore their lifespan and aging patterns may be sensitive to early-life conditions that determine this initial damage load during early development. The idea of early-life programming of aging and longevity may have important practical implications for developing early-life interventions promoting health and longevity.
The theory also suggests that aging research should not be limited to studies of qualitative changes (like age changes in gene expression), because changes in quantity (numbers of cells and other functional elements) could be more important driving force of aging process.