On damage accumulation and biological aging

If biological aging is understood as some process of damage accumulation, it does not necessarily lead to increasing mortality rate. Within the framework of suggested models and relevant examples we show that even for the monotonically increasing degradation, the mortality rate can, at least, ultimately decrease. Aging properties of systems with imperfect repair are also studied. It is shown that for some models of imperfect repair the corresponding age process is monotone and stable. This means that as t -> infinity, degradation slows down, which results in the mortality rate deceleration and its possible convergence to a constant. (C) 2008 Elsevier B.V. All rights reserved.