| Summary: | Question: How can the limitations and potential of biological repair processes be reconciled with evolutionary theory to understand patterns of ageing? Approach: Current mathematical models of ageing under conditions of biological repair are drawn from a limited range of engineering analogies that implicitly assume repair is perfect and/or harmless, with the only constraint being its cost to a common energy budget. Other analogies suggest new models which may be (and in some cases are being) fruitfully developed. A useful guiding principle is the engineer's 'total quality management', which imposes a balance between high-level and low-level design. Key point: Reparability itself may impose trade-offs against, for instance, reliability and efficiency, and may not always be advantageous, even when cost-free. Conclusions: Because the repair of damage is often incomplete or imperfect, the accumula-tion of repair increases the disorder within the system over time, decreasing the effectiveness of the local controls over repair. Asymmetry and sequestration appear to be ways of channelling the disorder to parts of the systems that are reparable. © 2006 David Steinsaltz.
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