Aging Is Not a Genetic Dustbin

Nature designed us to age for a reason.

Harmful genes that cause Huntington’s disease — a disease that attacks the neurons in the brain — only show up between ages 30 to 50, in some cases after the birth of offspring. There are many other diseases that accumulate later on in life, dementia being the main one. In 1952, Peter Brian Medawar tried to explain this by suggestion that older adults accumulate mutations and become a "genetic dustbin."

In Medawar's theory, there is no advantage to aging, nor are there any benefits for older people to live. Aging is simply the result of declining functions before death. This biological interpretation proved popular.

To explain aging, biologist George Williams in 1957 came up with the "antagonistic pleiotropy hypothesis" (named by Michael Rose in 1982). Pleiotropy is the phenomenon where one or a few genes control more than one trait. The antagonism part comes from the negative effect that emerges later on in life. As an example, testosterone in men might result in an attractive, muscular body in youth, as well as masculine features, such a deep voice and facial hair, but it also increases the likelihood of prostate cancer in older age, hence the antagonistic part of the pleiotropy. Although it is the positive aspects of the pleiotropic gene that are selected for in natural selection, the antagonistic aspect also sneaks into the gene pool. Aging is seen as an invisible cloak that sneaks bad genes into the gene pool by cloaking them under positive traits when young. Aging, in this view, has subverted the whole process of natural selection by disguising itself as a positive attribute in early life and then transforming — in a Jekyll-and-Hyde metamorphosis — into an aging liability. Somehow nature has been hoodwinked into allowing people to get old. Aging becomes a problem, a genetic dustbin of humanity. From here, it is fairly easy to see the approach: We need to cure aging, because nature made a mistake. The hubris of judging that nature made a mistake ignores that nature might have a different perspective from ours.

As a species, survival is nature's only ambition.

The only way that successive generations prosper is if they are a good fit with their environment. Each generation must survive long enough to create another generation. Nature keeps our genes immortal, and it has two extreme methods to achieve this single aim. One way is to produce an enormous number of offspring and hope that a few survive to then pass on their genes (known as r-selection). Another approach — one followed by humans — involves having few children whom we nurture until adulthood and beyond (known as K-selection). Therefore nurturing — protecting and supporting others — is our survival strategy, not competition.

Nurturing involves having things to teach and living long enough to be able to teach them. Which is why humans live long and have such a big brain; the two go together. Some 1.6 to 1.9 million years ago, our brain grew very fast; some say — not without contention — that brain expansion mirrors the development of cooking. Cooking, making food more easily digestible, resulted in greater availability of nutrients for the hungriest organ in our body — our brain. Nature engineered us to have both a big brain and longevity; they are intricately intertwined. We can see this through mathematical models that show a leap in predictive value when older people are included in the equation. Whether or not older people have a disease, the presence of older people in the family predicts longer-living children and grandchildren.

In the wild, most mammals die once they lose their ability to reproduce. Humans are different. We continue to live well past our capacity to reproduce, especially females. Is nature wrong again, or does nature have a special role for older people?

What the genetic dustbin proponents do not appreciate is that older people, especially grandmothers, have a statistically positive effect on their community. In 2004 while examining the “grandmother effect,” Mirkka Lahdenperä of the University of Turku, Finland, and her colleagues found statistical evidence that a grandmother has a decidedly beneficial effect on the reproductive success of her children and the survival of her grandchildren. Older adult humans promote the survival of the species. Unlike any other animal, we also transfer wealth, capital, and wisdom to our successive generations way past our reproductive period. When gene survival includes the broader community, then older people have a positive effect on their chances of survival.

By 1973, John Maynard Smith and George Price introduced game theory to evolutionary problems. While classic game theory sees players making rational choices on the basis of individual gain, evolutionary game theory posits an awareness of what others might do and the development of strategies to counter that decision. It is a social decision mode, not a purely individualist one. Maynard Smith argued that since everyone dies, evolution does not benefit individuals. Evolution is designed to benefit the community. In this interpretation, it explains that the strategy humans employ is based on benefits to the community, rather than benefits solely to the individual. Such a model fits the outcomes we see in reality. This insight was revolutionary and transformed the argument from one where aging is seen as a genetic dustbin to one where aging becomes part of a package for survival — a package that includes older adults contributing, in as yet unknown ways, to the promotion of our species.

There are instances where antagonistic pleiotropy of dementia has some really beneficial effects. For example, the Apolipoprotein E Variant 4 that is strongly associated with Alzheimer's disease might have beneficial aspects, such as reducing the rate of age-related macular degeneration, lower testosterone, and although there is no evidence of apoE isoform reducing infectious diseases, there is evidence that apoE could play a role in reducing our susceptibility to viruses, bacteria, and protozoan parasites. Such polymorphisms — having multiple expressions — are abundant in nature.

Despite this insight, in 2002, 51 renowned scientists — including such luminaries as Jay Olshansky, Leonard Hayflick, and Bruce  Carnes — published a position statement in Scientific American stating that “aging is a product of evolutionary neglect, not evolutionary intent.” Again, we are telling nature that it made a mistake, or at least was ignorant of the consequences. When Albert Einstein first confronted quantum physics, he said that “God does not play dice with the cosmos.” What is not reported frequently is the response from Danish physicist Niels Bohr: “Einstein, don't tell God what to do.” It seems that we are telling nature what it should do or how neglectful it is, rather than appreciating the biological system we call life as complete and perfect. We might guess at the intent of evolution — survival of our immortal genes — but we might not understand its methods.

Aging and having a big brain go hand-in-hand. It is nature’s plan for our survival. Older adults improve the survival of both their children and grandchildren. Looking at aging in a broader context allows us to view some of the wonders of nature. We have a lot to learn if we listen.

© USA Copyrighted 2018 Mario D. Garrett

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