This article makes the point that aging does not cause any disease. Getting old is not a cause of cardiovascular disease, strokes, high blood pressure, cancer, type 2 diabetes, parkinson’s disease, dementia (including Alzheimer’s), COPD, osteoarthritis, osteoporosis, cataracts, age related macular degeneration or hearing loss. Aging does not cause joint stiffness, ringing in the ears, forgetfulness, or even grey hair. Aging does not cause any of these things because aging is not any one single thing. Aging is a term for many different events, the effects of some of which do cause the above conditions, but we must be specific about these causes to find solutions. Each type of the various individual types of damage, therefore, should be addressed to make aging a curable “disease” or condition.
In 2014 Suresh Rattan published a paper titled “Aging is not a disease: implications for intervention” (PubMed) in which he stated that aging is the common cause of all age-related diseases but that aging itself cannot be considered a disease. Just like radiation sickness is not a disease, aging is an illness resulting from accumulated damage. The illness of each can be repaired, up to the limits of current natural biological mechanisms plus assistance from technology.
Suresh Rattan stated in 2014 that “There are no gerontogenes which have the specific evolutionary function to cause aging.” While “specific evolutionary function” is debatable, “gerontogenes” have been demonstrated to exist. There are genes that cause aging. Scientists have observed that C. elegans nematode worms live twice as long if you damage just one of their genes. One gene change makes the entire animal live twice as long. The worms age more slowly with this one genetic mutation.
Why would aging genes exist? Evolutionary, genetically caused aging can be a strategy for the entire population to better survive. Younger animals–which can reproduce the healthiest offspring–will, this way, get more of the limited resources from the environment.
In any individual, with time, cellular damage due to environmental challenges will accumulate if not repaired or removed. Radiation, for example, damages DNA over time. Killing off damaged cells to keep the entire individual healthy is something our bodies do naturally. Cells will, when they become too damaged, self-destruct (apoptosis) to prevent themselves from damaging surrounding cells. As an extension of this strategy, there can be built-in, genetic mechanisms to degrade an entire individual organism in support of the entire population.
Aging, from this perspective, is an evolutionary strategy, a built in self-destruct-if-highly-compromised mechanism, which, just as it is different for different cell types, is set at different ages for different animals based on things such as their abilities to repair cellular damage. A bat, which is the size of a mouse, can live many years longer than any mouse.
None of this is an answer to aging, it is only the way things are now, not the way things must stay.
The site longlonglife.org has a great functional definition of aging.
“Aging can be defined as the sum of all the mechanisms that alter the functions of a living thing, prevents it from maintaining physiological balance and eventually leads to the death of said organism.” (Link)
The entire article is worth reading.