We are constantly changing. Our body is in a constant flux. According to researchers, the body replaces itself with a largely new set of cells every seven years to 10 years, and some of our most important parts are revamped even more rapidly. What Frisen found is that the body's cells largely replace themselves every 7 to 10 years. In other words, old cells mostly die and are replaced by new ones during this time span. The cell renewal process happens more quickly in certain parts of the body, but head-to-toe rejuvenation can take up to a decade or so.
The body renews itself at varying paces. Just how long the cells in certain areas last depends on how much work they're asked to do. Red blood cells, for example, enjoy a quick life span of only about four months as a result of their arduous journey through the circulatory system, carting oxygen to tissues throughout the body. Skin sees a fair amount of wear and tear. These skin cells regenerate every two to four weeks. The liver, the human body's detoxifier, remains largely immune to damage from these toxins by renewing itself with new cells every 150 to 500 days. Stomach and Intestines cells are constantly battered by corrosives like stomach acids typically lasting only up to five days. Bone cells regenerate almost constantly; the renewal process slows down as we age. There are also some cells that never leave us. While the eye's cornea can regenerate itself in as little as one day, the lens and other areas don't change. Similarly, neurons in the cerebral cortex stay with us from birth to death. Because they aren't replaced, the loss of these cells over time can cause maladies like dementia. All vital organs begin to lose some function as you age during adulthood. Aging changes occur in all of the body's cells, tissues, and organs, and these changes affect the functioning of all body systems. Despite all this regeneration all the time, the truth is that we still get old and we still die. No one knows for sure how and why people change as they get older, though there are several theories to explain the phenomena. Frisen and others believe that this may be because of DNA mutations, which worsen as they're passed along to new cells over time. Aging is a complex process. It affects different people differently. It is for sure a cumulative effect of the interactions of many lifelong experiences. These influences include heredity, environment, culture, diet, exercise and leisure, past illnesses, and many other factors.
The situation of our body is similar to the philosophical thought experiment the ship of Theseus of Thomas Hobbes. Hobbes is said to have drawn inspiration from Plutarch. A ship is sailing on the sea for quite some time. All its parts are replaced as and when required. At what point does it become a new ship. Is it a new ship when all its parts are replaced, or a part of its parts are replaced? Theseus owned a ship and the ship was entirely made of wood. Every time a piece of the ship needed replacing it was replaced with a metal part. This went on for a few years until eventually it was entirely made of metal. Is the metal ship the same ship as the wooden ship? If the material the ship is made of changes but its purpose doesn’t, does it remain the same? Can a reassembled wooden ship (from the discarded woods) be said to have not changed? It depends upon how we define the change. We may say, it doesn’t change, if it serves our purpose. We may say, any change is a change, and serving our purpose doesn’t change the definition of change. Is gradual change of the parts, and their assimilation with the ship, change? Is it change, if others can’t notice the change?
Coming back to my situation!
Am I the same person I was more than seven decades ago? Can I remain the same person if there are changes in my surroundings? Take for example, I was born and brought up in Kanpur. I left Kanpur when I was 25 years old. In the intervening period, there is almost nothing I was associated with at Kanpur. My parents are no more. My Didima is no more. My bari and mamar bari disintegrated. My childhood schools are non-existent. Most of my brothers and sisters and friends are no longer in Kanpur. There is no excitement that I felt after reaching Kanpur station. I have forgotten (because of want of use) all the bad words that I so meticulously learned while at Kanpur. Most of the cinema halls no longer exist. There is no fear of doing badly in the exams. There is no fear due to uncertainty of the future. Purnendu is no longer Bablu in many senses. Purnendu is Bablu in many other senses. Can Purnendu become Bablu? Should Purnendu become Bablu? Even if the cells are as fresh as they were, can biology be the destiny? Can I live for the future without reliving the past?