Our bodies’
backup systems don’t prevent aging, they make it more certain. This
is one proposition of a new “reliability theory of aging and longevity”
by two researchers at the National Opinion Research Center at the University
of Chicago.
Authors Leonid
Gavrilov and Natalia Gavrilova, in their paper, “The Reliability Theory
of Aging and Longevity,” published in the Journal of Theoretical Biology
(213, 527-545), have offered a comprehensive, groundbreaking theory to
understand why people (and other biological species) deteriorate and die
more often with age. Interestingly, the relative differences in mortality
rates across nations and gender decrease with age. That is, although
people living in the U.S. have longer life spans on average than people
living in countries with poor health and high mortality, those who achieve
the oldest-old age in those countries die at rates relatively similar to
the oldest-old in the U.S.
Humans are built
from the ground up. We start off with a few cells that differentiate and
multiply to form the systems that keep us operating. Even at birth,
the cells that make up our systems are full of faults and defective elements
that would kill primitive organisms that lack the redundancies that are
built into us.
“ It’s as if
we were born with our bodies already full of garbage, “ said author Gavrilov.
“Then, during
our life span we are assaulted by random destructive hits that accumulate
in further damage. Thus we age. At some point one of those
hits causes a critical system without a back-up redundancy to fail, and
we die.”
All those in
the world who have achieved the oldest-old age have very few redundancies
remaining; therefore they can’t accumulate many more defects. They
simply die when the next random shock hits a critical system. Hence,
the mortality rates tend to level off at extreme old ages, and people all
over the world die at relatively similar rates on average. The initial
differences in body reserves (redundancy) eventually disappear.
This fundamental
theory of aging and longevity is grounded in a predictive mathematical
model that accounts for questions raised by previous models that have addressed
the mechanisms of aging, mortality, survival, and longevity.
The authors
are Research Associates at the Center for Aging at the University of Chicago’s
National Opinion Research Center. The research was sponsored by the
National Institute on Aging.
Abstract &
text description of the model
Abstract
Reliability
theory is a general theory about systems failure. It allows researchers
to predict the age-related failure kinetics for a system of given architecture
(reliability structure) and given reliability of its components.
Reliability
theory predicts that even those systems that are entirely composed of non-aging
elements (with a constant failure rate) will nevertheless deteriorate (fail
more often) with age, if these systems are REDUNDANT in irreplaceable
elements. Aging, therefore, is a direct consequence of systems redundancy.
Reliability
theory also predicts the late-life mortality deceleration with subsequent
leveling-off, as well as the late-life mortality plateaus, as an inevitable
consequence of REDUNDANCY EXHAUSTION at extreme old ages.
The 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.
The theory explains
why relative differences in mortality rates of compared populations (within
a given species) vanish with age, and mortality convergence is observed
due to the exhaustion of initial differences in redundancy levels.
Overall, reliability
theory has an amazing predictive and explanatory power with a few, very
general and realistic assumptions. Therefore, reliability theory seems
to be a promising approach for developing a comprehensive theory of aging
and longevity integrating “
Description
of Model
The phenomena
of mortality increase with age and the subsequent mortality leveling-off
are theoretically predicted to be an inevitable feature of all reliability
models that consider aging as a progressive accumulation of random damage.
. . . In short, if the destruction of an organism occurs not in one but
in two or more sequential random stages, this is sufficient for the phenomenon
of aging (mortality increase) to appear and then to vanish at older ages.
Each stage of destruction corresponds to one of the organism's vitally
important structures being damaged. In the simplest organisms with unique,
critical structures, this damage usually leads to their deaths. Therefore
defects in such organisms do not accumulate, and the organisms themselves
do not age - they just die when damaged. In more complex organisms with
many vital structures and significant redundancy, every occurrence of damage
does not lead to death because of this redundancy.
Defects do accumulate, therefore,
giving rise to the phenomenon of aging (mortality increase). Thus, aging
is a direct consequence (trade-off) of systems redundancy that ensures
increased reliability and lifespan of organisms. As defects accumulate,
the redundancy in the number of elements finally disappears. As a result
of this redundancy exhaustion, the organism degenerates into a system with
no redundancy, that is, a system with elements connected in series, with
the result being that any new defect leads to death.
In such a state,
no further accumulation of damage can be achieved, and the mortality rate
levels off.
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Information Provided By
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