The ship of Theseus of the human body

The ship of Theseus is an ancient thought experiment, which was first recorded by Plutarch. It describes a ship that can sail at sea for hundreds of years - during such a long voyage, of course, the hull needs to be repaired and replaced. Whenever a piece of wood decays, it will be replaced, and so on. One day, all the parts will not be the first ones. The question is, is the ship that eventually came into being still the original ship of Theseus, or has it become a completely different ship? If it is not the original ship, when will it no longer be the original ship?

If this concept is extended to the human body, it will give us a new angle to understand ourselves. The human body is like a surging river. It is spitting out the old and absorbing the new quickly and persistently. Its metabolism speed is amazing.

Professor Jonas Frisian of the Karolinska research center in Sweden was inspired by archaeology to use the concentration of carbon 14 as a marker of cell age.

With the carbon-14 marker, Professor Frisian began to analyze the age of some cells in the human body. His team can only focus on a limited area of human cells for the time being.

Through analysis, they found that the average age of adult intestinal cells was 10.7 ± 3.6 years. Previous studies have shown that due to the harsh environment, the life span of intestinal epidermal cells is only 5 days. After removing these short-lived epidermal cells, Professor Frisian found that the average age of the remaining intestinal cells was about 15.9 years. In addition, they found that the average age of human skeletal muscle was about 15.1 years. The types of human cells are far more than those studied by Professor Frisian, and there are many cells with high replacement rate. In addition to intestinal epidermal cells, many human cells have strong ability to divide and proliferate, among which epithelial cells and hematopoietic cells have the strongest ability to divide.

The cell cycle of cells in different tissues of the human body is different. For example, the gingiva is updated every 2 weeks and the skin every 4 weeks. The liver cells with a longer life span have a life span of 300 to 500 days, and the seemingly lifelong human skeleton is also updated every 10 years. Taking these different kinds of cells together, the average age of human cells is 7 to 10 years old.

The so-called cell cycle refers to the process from the end of one mitosis to the end of the next division. The cell cycle of red blood cells is 3 months, which does not mean that the blood will be completely renewed within 3 months, because the production time of different cells is different. Under the condition of equal life span, the complete replacement of blood cells is a dynamic process. Moreover, cells will also encounter accidents in the human body. For example, red blood cells may die instantly due to crushing in capillaries.

Brain neurons and cardiomyocytes are relatively lack of division ability. Professor Frisian, a neurobiologist, carried out the study to answer the question of whether neurons in the cerebral cortex regenerate. This study shows that the age of neurons in occipital cortex is basically the same as that of people. This study tells us that almost all neurons in the cerebral cortex exist soon after a person is born. Unless there is damage, there will usually be no new cells. It will not change with the growth of people's age, but it will increase or decrease its connotation with the change of people's contact with external information. The number of brain neurons will not increase, but will decrease with age.

In the journey to the end of life, the human body constantly updates the most basic part - cells. We don't have to worry about the philosophical problem of "I or not I", but we should re understand ourselves from the perspective of biology. Our body is changing every minute. In addition to the daily metabolism and the continuous updating of cells, the indicators and data reflecting our health are also changing, and our daily basic data are not uniform and constant. We should learn to use dynamic thinking to build the self in our hearts and make corrections and adjustments at any time, so as to make the human body, the ship of Theseus, travel more smoothly and for a long time.