Many people should have heard of this thought experiment. A large ship composed of wood needs to be replaced every once in a while, and then there will always be a day when all the wood that makes up this big ship will be replaced. So, after all this round of replacement is completed, even if the name of the ship has not changed, is it still the original ship? Similar problems also happen to each of us. Each of our bodies is composed of trillions of cells and . Over time, cells will age or be damaged, and the cells of the body will constantly replicate themselves, thus producing their own substitutes, thereby maintaining the normal physiological activities of various organs and tissues of the body. In other words, the cells you have in your body today are not exactly the same as the cells you have yesterday.
There is a popular saying that the human body's cells will be replaced every 7 years or so. Whether it is the cells that make up the hair, eyelashes or intestines, from the outside to the inside, after 7 years of replication and rotation, the human body's cells will form a new "self". Then the brain-burning problem mentioned above appears again. Every 7 years, are you still the same you as you?
First of all, let’s take a look at whether human cells are replaced every 7 years.
In fact, the cells that make up the human body are divided into many types, such as skin cells, endocrine cells, visceral cells, nerve cells, germ cells, blood cells, etc. Similar cells form tissues, and the organs are composed of multiple tissues. The combination of multiple organs forms different systems, and ultimately the human body is composed of different systems. Among all cells, except for the erythrocyte in the blood, all other cells have an nucleus .
Most cells in the human body have the ability to divide and proliferate. This ability not only promotes the growth and development of the human body, but also repairs and replaces damaged or aging parts. However, the division ability of different types of cells in the human body is still very different. For example, the one with the strongest division ability is epithelial cells and hematopoietic cells. Because these two cells often come into contact with the outside world or come into contact with substances input from the outside world, they are the most likely to be stimulated by external substances, the strongest strength, and the lifespan is also very short. Therefore, the strong division ability can ensure the body's defense system and blood circulation system, and maintain the body's basic physiological functions in the most efficient way.
From the perspective of cell lifespan, cell lifespans such as intestinal cells, taste bud cells, lung cells, white blood cells, , epithelial cells, etc. are shorter, basically no more than 1 month, and intestinal cells on average less than 3 days. There are many people with a lifespan longer than these cells, such as erythrocytes for 4 months and liver cells for 5 months. Cells with longer lifespans include nerve cells, cardiomyocytes and skeletal cells, etc. Their lifespan is generally several years, more than ten years or even longer. Some nerve cells and cardiomyocytes do not divide at all from birth to death, that is, they always remain the same.
Here, one problem needs to be clarified, that is, the lifespan of the cell is not the same concept as the cycle of all replacements. The life cycle of a cell, , is its life span, is the overall stage from the production, development of the individual to the final division until death.
For example, the cycle of a liver cell is 5 months, but it does not mean that the human liver will be completely renewed in 5 months, because different liver cells are produced differently. Under the condition of the same lifespan, the renewal of the human liver is completely a continuous dynamic process, and it is not completely updated at a unified time point. According to relevant research, if all liver cells in the human body are replaced, it will take about 3 years or even longer.
However, like the human body's bone cells, cardiomyocytes, peripheral nerve cells, especially brain neuron cells, the division ability of these cells is relatively weak. For example, bone cells can be completely replicated every 10 years; only 40% of cardiomyocytes are replaced, and the rest are "intact"; some hippocampal neuron cells in the brain will be updated at a rate of about 1.7% per year, but most of the neuron cells will accompany us throughout our lives.
Therefore, the statement that the human body's cells will be updated every 7 years on average is strictly inaccurate. Many cells start from production and have almost never divided or proliferated.
So the key to the problem is, since many cells in have been replaced, are we still the same ones? The core of the problem of is what are our cognitive principles and standards for ourselves, that is, the sense of belonging to personality.
From the perspective of natural persons, the physical body is of course an important aspect of the difference between people, which gives us different height, weight, and appearance characteristics from others, but more importantly, each of us has a different individual consciousness from others.
The formation and maintenance of individual consciousness depends on the control and feedback of our nervous system , especially the central brain system. The basis is the content, quantity and changes of external information we are exposed to to form specific memories and self-modescription of information processing. In a person's life, the number of brain neurons will basically not change, and it will decrease with age, which is also the fundamental reason why people will lose memory to the elderly. Since the carrier of human self-consciousness - brain neurons, which has the sustainability of "from beginning to end", our personality cognition will not change, so we are still the same as us.
Even if we assume that the neuronal cells of the brain will undergo periodic replacement, then due to the acceptance of memory, the original memory and the way of processing external information will be transmitted from old cells to new cells. Therefore, our subjective consciousness will not change with the replacement of cells. We are still ourselves, but we are just a dynamically changing ourselves. Dear readers, do you think this is the reason?
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