Wear and Tear Theory of Aging

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The Wear and Tear Theory of Aging

The wear and tear theory of aging believes that the effects of aging are caused by damage done to cells and body systems over time. Essentially, these systems "wear out" due to use. Once they wear out, they can no longer function correctly.

The wear and tear theory is deeply ingrained in our thinking, and it is the theory you will often hear expressed in conversation and our culture.

It was first expressed in science by German biologist Dr. August Weismann in 1882. We simply expect that the body, as a mechanical system, is going to break down with use over the years.

What Causes the Wear and Tear Damage that May Lead to Aging?

A range of things can damage body systems. Exposure to radiation, toxins, and ultraviolet light can damage our genes. The effects of our body's own functioning can also cause damage. When the body metabolizes oxygen, free radicals are produced that can cause damage to cells and tissues.

There are some cellular systems that don't replace themselves throughout life, such as the nerve cells of the brain. As these cells are lost, function eventually will be lost. Just like a pair of socks, they can only last so long before becoming threadbare, or getting a hole. While they can patch themselves, like socks they can only be darned so many times before they just don't work anymore.

Within cells that continue to divide, the DNA can sustain damage errors can accumulate. Simply the act of dividing again and again shortens the telomeres of the chromosomes, eventually resulting in a senescent cell that can no longer divide.

Oxidative damage in cells results in cross-linking of proteins, which prevents them from doing the jobs they are intended to do in the cells.

Free radicals inside mitochondria, the powerhouses of our cells, injures their cell membranes so they can't function as well.

The Evidence for and Against Wear and Tear as the Cause of Aging

Not much. While the theory makes some sense if you think of the body as a machine, it doesn't really work when you realize the capacity of the body to repair damage. Of course, not all damage can be repaired fully, and mistakes in repairs may accumulate over time.

Those arguing against the wear and tear theory note that organisms in their growth phase become stronger and stronger. Rather than starting out at the peak of performance, such as a car fresh off the assembly line or a computer new out of the box, living organisms often start life fragile. They build strength and resilience with age. They are able to repair and replace most broken parts themselves.

A more likely explanation is that the decrease of functioning that is seen as "tear" in the "wear and tear" theory is really the result, not the cause, of aging.

More on Why We Age: keep exploring ideas, theories and research into how and why we get old, wear out and show our age.


How and Why Do We Age? The American Federation of Aging Research

Infoaging Guide to Theories of Aging. American Federation for Aging Research. 2011.

Mitteldorf J. "Aging is not a process of wear and tear."  Rejuvenation Res. 2010 Apr-Jun;13(2-3):322-6. doi: 10.1089/rej.2009.0967.

Kunlin Jin "Modern Biological Theories of Aging." Aging Dis. 2010 Oct; 1(2): 72–74.

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