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Reliability theory of aging and longevity
is a scientific approach aimed to gain theoretical insights into mechanisms of biological aging and species survival patterns by applying a general theory of systems failure, known as reliability theory
Reliability theory describes the probability of a system completing its expected function during an interval of time. It is the basis of reliability engineering, which is an area of study focused on optimizing the reliability, or probability of successful functioning, of systems, such as airplanes,...
Reliability theory allows researchers to predict the age-related failure kinetics for a system of given architecture (reliability structure) and given reliability of its components. Applications of reliability-theory approach to the problem of biological aging and species longevity lead to the following conclusions:
In engineering, redundancy is the duplication of critical components or functions of a system with the intention of increasing reliability of the system, usually in the case of a backup or fail-safe....
is a key for understanding aging and the systemic nature of aging in particular. Systems, which are redundant in numbers of irreplaceable elements, do deteriorate (that is, age) over time, even if they are built of non-aging elements.
- Paradoxically, the apparent aging rate or expression of aging (measured as relative differences in failure rate
Failure rate is the frequency with which an engineered system or component fails, expressed for example in failures per hour. It is often denoted by the Greek letter λ and is important in reliability engineering....
s between compared age groups) is higher for systems with higher redundancy levels.
- Redundancy exhaustion over the life course explains the observed 'compensation law of mortality
The compensation law of mortality states that the relative differences in death rates between different populations of the same biological species decrease with age, because the higher initial death rates in disadvantaged populations are compensated by lower pace of mortality increase with age...
' (mortality convergence at later life, when death rates are becoming relatively similar at advanced ages for different populations of the same biological species), as well as the observed late-life mortality deceleration, leveling-off, and mortality plateaus.
- Living organisms seem to be formed with a high initial load of damage (HIDL hypothesis), 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.
- Reliability theory explains why mortality rates increase exponentially with age (the Gompertz law) in many species, by taking into account the initial flaws (defects) in newly formed systems. It also explains why organisms "prefer" to die according to the Gompertz law, while technical devices usually fail according to the Weibull (power) law. Theoretical conditions are specified when organisms die according to the Weibull law: organisms should be relatively free of initial flaws and defects. The theory makes it possible to find a general failure law applicable to all adult and extreme old ages, where the Gompertz and the Weibull laws are just special cases of this more general failure law.
- Reliability theory helps evolutionary theories to explain how the age of onset of deleterious mutations could be postponed during evolution, which could be easily achieved by a simple increase in initial redundancy levels. From the reliability perspective, the increase in initial redundancy levels is the simplest way to improve survival at particularly early reproductive ages (with gains fading at older ages). This matches exactly with the higher fitness priority of early reproductive ages emphasized by evolutionary theories. Evolutionary and reliability ideas also help in understanding why organisms seem to "choose" a simple but short-term solution of the survival problem through enhancing the systems' redundancy, instead of a more permanent but complicated solution based on rigorous repair (with the potential of achieving negligible senescence
Negligible senescence refers to the failure of a few select animals to display symptoms of aging. More specifically, negligibly senescent animals do not have measurable reductions in their reproductive capability with age, or measurable functional decline with age. Death rates in negligibly...
). Thus there are promising opportunities for merging the reliability and evolutionary theories of aging.
Overall, the reliability theory provides a parsimonious explanation for many important aging-related phenomena and suggests a number of interesting testable predictions. Therefore, reliability theory seems to be a promising approach for developing a comprehensive theory of aging and longevity integrating mathematical methods with specific biological knowledge and evolutionary ideas.
Reliability theory of aging provides an optimistic perspective on the opportunities for healthy life-extension. According to reliability theory, human lifespan is not fixed, and it could be further increased through better body maintenance, repair, and replacement of the failed body parts in the future.
- Reliability Theory of Aging and Longevity - Power-Point Presentation of invited lecture at the Buck Institute for Age Research, Novato, California, USA, August 4, 2006.
- Reliability Theory of Aging and Longevity - abstract of invited lecture at the University of California, Santa Cruz. Applied Mathematics & Statistics (AMS) and CSTAR Research Seminars, October 10, 2005.
- Reliability Theory of Aging and Longevity - Power-Point Presentation of invited lecture at the University of Chicago. The Ecology and Evolution Natural History Seminar, Department of Ecology and Evolution, May 10, 2005.
- Reliability-Engineering Approach to the Problem of Biological Aging - invited presentation at the 10th Congress of the International Association of Biomedical Gerontology, Cambridge University, England, September 19-23, 2003.