Throughout its physical lifetime, our body is continually changing, yet we continue to maintain our core identity and consciousness. Research has shown all living cells in the body have a finite lifespan, ranging from minutes to days to years. A few cells—such as certain brain cells and central nervous system cells—may exist through the duration of the body.
These are the tiny minority of the estimated 200 trillion cells making up the body, however. By far the vast majority of cells in the body will participate in cell division. Following a certain number of divisions, the older cells will timeout. Dead cells are broken down by the immune system and discarded, leaving the newly divided cells in their place.
Using this process the body constantly sloughs off older cells from the body, replacing them with new ones. Different cells in different parts of the body have different lifespans. For example:
- Most intestinal wall cells are replaced about between two and four days
- Stomach lining cells are replaced between two and nine days
- Blood neutrophils and eosinophils are replaced between one and five days
- Lung alveoli cells are replaced within eight days
- Blood platelets are replaced within 10 days
- Skin epidermis cells are replaced within a month
- The entire liver is regenerated within 18 months
- All the cells of the bones are replaced within ten years
- Bone osteoplast cells are replaced within 90 days
- Cells of the heart (cardiomyocytes) are replaced at a rate of up to 10% per year
- Fat cells are all replaced within eight years
- Stem cells are replaced within a few years - often 3-5 years
- The cells of our entire skeleton are replaced within 10 years
Nerve cells and the cells of the lens can live longer—for decades, and some over the lifetime of the body. However, most of the composition of all cells, including many nerve and stem cells, also turnover.
Atoms within cells also turnoverEvery cell in the body is made up of ionic and molecular combinations. The atoms that make up these molecular combinations are constantly being replaced. Each cell's cytoplasm, organelles, and membrane are thus made up of recycled atoms.
These atoms are constantly being replaced with atoms from the matter we take in from breathing, eating and drinking. New atoms enter the body from the environment. Old atoms are expelled through waste and respiration. The processes of each cell - cell membrane diffusion, osmosis and ionic channel conveyance - allow a constant recycling of atomic elements.
Research in the 1950s led by Dr. Paul Aebersold - at the Oak Ridge Atomic Research Center - found that approximately 98 percent of all the atoms in the body are replaced annually.
Consider this carefully. This means that the vast majority of the body's composition is undergoing constant change.
The longest living cellsIn 2005, researchers at the Lawrence Livermore National Laboratory and the Medical Noble Institute at Karolinska Institute utilized carbon-14 analysis to study the lifetimes of cells in the body.
Again they confirmed some of the turnover rates of cells as listed above. They also found that many of the brain's cells are generated (neurogenerative) when the body is young, and many brain and nervous system cells also turnover during our body's lifetime.
Yet they also found a few types of neuron cells are exceptions. These can live without dividing for decades - and can possibly live over the lifetime of the body. These include neuron cells of the occipital cortex.
However, these cells will also turnover molecules and atoms from their cell membranes, cytoplasm, and organelles. The research found that only their genetic matter - the nucleotides of their DNA - appear not to turnover as quickly.
Thus we find that even these longest-living cells in the body still undergo significant change in atomic composition: With the exception of those tiny nucleotides within their genetic matter, which turnover more slowly.
In other words, the research confirms that the vast majority of our body's cells and atoms are undergoing constant recycling. Those neurons that last longer will still turn over the majority of their atomic composition.
A constantly changing bodyWe can see from this information that our physical bodies change nearly every cell within days, weeks or years. And all our body’s atoms and molecules are being replaced from the food we eat, the water we drink and the air we breathe. We can thus accurately make the following statement:
The body we are wearing today is not the same body we were wearing ten years ago.
The vast majority of the cells, molecules, and atoms that made up that body have been replaced by new cells, molecules, and atoms. There may be a few atomic threads of genetic matter remaining - but our body today as a whole is now made of predominantly different composition than the body we had on ten years ago.
This might well be compared to a waterfall. The water within a waterfall is always changing. From moment to moment, the waterfall will be made up of different water. Therefore, the waterfall we see today is not the same waterfall we saw yesterday. Now some of the larger rocks under the waterfall might be the same rocks we saw yesterday, but the waterfall itself - the water making it up - is completely different water.
Since each of us is the same person from moment to moment and year to year within an ever-changing body, logically we must each have a composition that is separate from this temporary fluidic vehicle - the physical body.
Logically, we could not be this body, since most of the body is constantly being recycled while we are still the same person.
For example, should we look at our photograph taken ten years ago, we will be looking at a different body from the one we are wearing today. The face we see in that picture is gone. The face we are wearing now is completely different than the face in the picture. The entire skin of the body we have on now has been replaced. The entire skeleton will be different. The cells of the heart, lungs, liver, digestive tract, blood many other parts will all be new. The vast majority of the atoms that made up our body ten years ago are gone. They've been replaced by new atoms.
Our body has changed but we are still the same person. How can this be? It can only be if we are not the physical body.
Our body contains more bacteria than cellsIn addition to the point that the vast majority of our body's cells and atoms are being constantly replaced, we should understand that our body contains more bacteria than cells: A lot more.
Microbiologists have estimated that the typical human organism contains ten times more bacteria than cells. The typical body will contain about 200 trillion cells. But that same body will contain about 2,000 trillion bacteria units. These will be composed of hundreds of different species.
Each of these bacteria is a single-celled living organism. Yes, like our cells, bacteria have cell walls and cytoplasm and organelles. They also typically have a short lifespan. Our body's bacteria will reproduce by division anywhere from a few minutes to a few hours. So like most of our cells, the precise makeup of our bacteria is also constantly undergoing change.
But unlike our cells, bacteria are also living organisms in themselves.
Research has found that bacteria, in fact, have consciousness. They will communicate with each other using quorum sensing along with biochemical secretion. Indeed, bacteria also communicate with their host (our bodies) utilizing cytokines and other biochemicals. In this way, they can stimulate the body's immune system and also help regulate the body's moods and biorhythms.
In fact, our body cannot survive without these bacteria. They are an important part of the body.
Therefore, not only can we conclude that the human body is constantly undergoing cellular and molecular/atomic change: We can also state with scientific integrity that the human organism is a significant host for numerous other organisms. Thus it might be compared to a planet of sorts - just as the earth hosts and supports so many organisms.
This human organism - constantly undergoing cellular, molecular, atomic and microbiological change - is thus not the solid, stable structure we might imagine it to be.
Rather, it is a fluid structure. It is a complex recycling mechanism that supports life. Not only does it support trillions of microorganisms. This mechanism supports a living entity within - a living being separate from the body's ever-changing cells, molecules, atoms, and bacteria.
This is each of us - the spirit-person within - a life force composed of an altogether different constitution.