All natural processes proceed from states of order to states of disorder. I am thinking of, for example, the rusting of iron, the decay of monuments and buildings, the erosion of mountains, and putrefaction. Why would living systems be immune to the processes of deterioration? In the early years everything works well but as we age our arteries start to plug up, our electrical system begins to misfire, and mistakes in our Biochemical pathways start to happen. This is my view of aging.

In addition to remembering names and numbers, committing new information to memory might take longer. On the other hand you will likely remember how to ride a bike and how to tie your shoes.  Working memory typically declines, like remembering passwords and where you parked your car. The ability to tune out distractions and focus (selective attention) can decline. My wife, Eleanor, says I am still pretty good at this. Carrying on a conversation while driving can become more difficult (divided attention). However, research shows that we can learn new things throughout our lives.

Many credit Leonardo da Vinci with first identifying the process of arteriosclerosis as one ages. He was born in 1452 and died in 1519 CE. There were two periods in his life when he performed numerous autopsies. He used autopsies to study the structure of muscles to aid his career as a painter. The second period happened as a result of his interest in science and his genius of observation. He compared the vascular system of a recently passed centenarian with that of a two year old boy who had also recently died. He recorded that the walls of the old man’s arteries were “thickened and stiffened by the accumulation of plaque-like substances.” He found the organs fed by these arteries to be “very dry, shrunken and withered.” He found the young boy’s arteries to be “supple and unconstricted.” Medical historians say that Leonardo’s description is the first of “arteriosclerosis as a function of time.”

What about the brain in particular? Our brains tend to shrink beginning in our thirties and forties and their decline accelerates in later years. Some areas shrink faster than others. As it turns out the areas that were formed last, in adolescence, are the first to begin shrinking. The number of connections between brain cells also drops. The formation of new neurons (neurogenesis) also declines with age. Neurogenesis is thought to be rare in adults or it is undetectable.

Aging is complex and probably consist of some or all of the molecular level processes listed below, plus more.

  1. The Gene Theory posits that there is a programmed process over which we have no control. As we grow older destructive genes begin to dominate and the processes of deterioration begin.
  2. The Running-Out Program Theory says that “human cells are programmed to reproduce a certain number of times and then die”. For example, people say that the brain creates few neurons after birth, but loses many. Some experiments have been done that support this idea.
  3. The Somatic Mutation Theory that says that “aging is a time-dependent process resulting in increased chromosomal mutations”. There are lab results that support that mutations do occur as time passes.
  4. The Cross-Linkage Theory says that long molecules bond with each other decreasing their ability to “slide” over one another. This process reduces flexibility and elasticity in the walls of blood vessels and connective tissue. This theory also says that this process can occur between and within nucleic acid molecules (DNA and RNA) inhibiting their function.
  5. The Free Radical Theory says that free radicals are created in our bodies through the pathways of Oxygen metabolism. Free radicals are molecular fragments with unpaired electrons, electrons seeking partners. They are therefore very reactive species with very short lives.  They can destructively react with DNA creating defective cells, for example.  The body makes antioxidants to quench these free radicals before they do their damage. Also, people take antioxidants like Vitamin C and Vitamin E to help the natural quenching process.
  6. The Accumulation Theory suggests that more and more substances build up in a cell’s cytoplasm over time eventually causing cell death. Examples of these substances are aldehydes, histones, quinones, chlorinated hydrocarbons and free radicals. This cell “garbage” can just inhibit natural processes or react with cellular components in destructive ways.
  7. The Error Theory says that random errors can occur as RNA is synthesized from DNA and as proteins are produced through the reading of RNA. These processes are catalyzed by enzymes which are themselves proteins.
  8. The Autoimmune Theory says that with aging the body’s immune systems loses its ability to distinguish foreign invaders (bacteria, virus) from its own cells and begins to attack both. There are a number of diseases now thought of as caused by immune system breakdown.
  9. The Wear and Tear theory posits that the body is like a machine and eventually wears out.

According to Joao Pedro de Megalhaes, Professor, Institute of Ageing and Chronic Disease, University of Liverpool, “Aging is a largely mysterious process”. The World Health Organization states that “At the biological level, ageing results from the impact of the accumulation of a wide variety of molecular and cellular damage over time. This leads to a gradual decrease in physical and mental capacity, a growing risk of disease, and ultimately, death. But these changes are neither linear nor consistent, and they are only loosely associated with a person’s age in years.”

The World Health Organization article also speaks of “factors influencing healthy ageing.”  Included are genetics, a person’s physical and social environment (homes, neighbourhoods, and communities), personal character traits, sex, ethnicity and socioeconomic status. “The environments that people live in as children, or even as developing foetuses, combined with their personal characteristics, have long-term effects on how they age.”

Here we are back at “The Early Years”.

References Consulted:
  1. Leonardo da Vinci, Walter Isaacson, Simon and Schuster, 2017.
  2. Contemporary Health Issues, Eric W. Banister, Murray Allen, Samia Fadl, Gordon Bhakthan, Dawn Howard, Jones and Bartlett Publishers, 1988.
  3. (Aging Theories by Joao Pedro de Megalhaes.)
  4. Aging: What to Expect,
  5. How the Brain Changes With Age,
  6. Aging and Health, 5 February 2018, World Health Organization,