Abstract: We applied reliability theory to explain aging of biological species 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 nonaging 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 course of life 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 life span and aging patterns may be sensitive to early-life conditions that determine this initial damage load during early development.