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Engineering Explains Our Failing Bodies

October 27, 2004

The autumn of our lives comes sooner than we think (it's downhill from age 11). Now, an engineering theory is explaining how and why we age, and how to slow down the process:

At age 11, our bodies are already starting to decline. In fact, if we were somehow able to keep body functions as they are at age 10, we would have an average life expectancy of roughly 5,000 years. But we are expected to live only a fraction of that span because of the simple fact that we fall apart. Fortunately, for the first time in human history, many scientists think that we can now take on human aging and learn to stop it; our understanding of it is that highly developed.

Helping scientists grasp the process of aging is engineering's reliability theory, an approach that was developed in the late 1950s to predict the failure and deterioration of complex electrical and electronic equipment. This approach defines aging as the rising risk of failure. When something is more likely to conk out tomorrow than today, it's aging.

According to reliability theory, human bodies are similar to man-made machines. To be more precise, our bodies can be likened to machines composed of redundant parts, many of which are faulty from the very beginning. In fact, the failure rates for humans and technical devices both follow a curve that resembles a bathtub. The curve can be divided into three stages: 1) working-in or infant-mortality, 2) normal-working and 3) aging.

In the first stage, failure rates are high as both machines and people have a great risk of falling apart at the very beginning of life. The computers and people who make it through the first stage then run smoothly for a while in the second stage. During this normal-working period, failure rates are low and roughly constant. Humans reach this stage at about age 5, but it lasts only 10-15 years.

After the normal-working period, machines and people enter the aging period, during which failure rates increase over time. In humans, this stage stretches from roughly age 20 to 100 years. Then after this third stage, humans and machines enter a fourth epoch, which is characterized by a leveling off of failure rates. This means that if you reach your 110th birthday, your chances of dying are high, but not much higher than when you were 103 years old. The same thing is true for man-made things such as steel, industrial relays, and the thermal insulation of motors.

Because of this phenomenon, no maximum value can be placed on human longevity. In short, there is no biological limit to a life span. The fact that humans are composed of redundant parts helps explain why death rates plateau in people over 100 years old. For most of our lives, system redundancy helps us tolerate damage, but in advanced age, we lose this redundancy and therefore, have a high but constant risk of falling apart. Thus, even in populations where death rates among young people vary significantly, death rates among older people look the same.

Humans not only age like redundant machines but ones that are already damaged to begin with. While new technical devices are assembled out of components that undergo rigorous testing, humans form from cells, which are untested elements. Thus, we have to rely on our redundancy to overcome initial shortcomings. In other words, machines can be assembled to circumvent faults while we are made to endure them.

Through the reliability theory's explanation of aging, scientists have gained powerful insights into how to control the aging process. For starters, we can minimize the cell loss that occurs to our bodies before we are even born through such simple measures as supplying expectant mothers with vitamins (especially folic acid) and other micronutrients. Decreasing the number of flaws we start out with could significantly extend life expectancy.

Another measure that would slow down aging is preventing damage to tissues and organs. By minimizing widespread chronic infections and hidden inflammation, we can stall the development of arthritis, atherosclerosis, diabetes, Alzheimer's disease and some types of cancer. Additionally, learning to mend our bodies completely when we're hurt or ill can boost longevity. For example, if we could learn to control our protective mechanisms—such as the hormesis effect in living organisms which leads to self-repair upon exposure to a small amount of poison—we could potentially curtail the breaking down of cells and systems. Finally, substituting aging organs with healthier ones or replenishing them with stem cells could be the key to prolonging life. In fact, more and more scientists are exploring regenerative medicine and tissue engineering in an effort to replace damaged organs.

Indeed, reliability theory has shed light on how and why we age, and from that knowledge, we can now seriously start plotting ways to derail the process.


Why We Fall Apart
Leonid Gavrilov & Natalia Gavrilova
IEEE Spectrum, September 2004


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