A return to time, cells, systems and aging: II. Relational and reliability theoretic approaches to the study of senescence in living systems.

In this paper, we approach the problem of attempting to understand senescence by understanding the complexity and hierarchical structure of mammalian organisms. To do this, we make use of some concepts from abstract relational biology; in particular, graph theory. We subsequently utilize these concepts to develop the idea of an irreplaceable element in a mammalian system. We then make use of these elements, and some concepts from reliability theory, to show how senescence processes in mammalian systems may be related to the failure of a critical number of irreplaceable elements. Finally, we show how we may derive formulas for the expected number of elements which fail by a given time, and how this time is related to actual lifespan and expected lifespan of the organism. In particular, we relate this to some recent work by Cutler on the evolution of longevity.