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This thought experiment is neither just a thought nor an experiment. This is the reality of life - every single cell in the body of a plant or animal is replace

by msiyer 7y ago

This thought experiment is neither just a thought nor an experiment. This is the reality of life - every single cell in the body of a plant or animal is replaced every few months. Essentially, talking about the physical body, we are not what we were a few months ago. EDIT: Agreed, a few types of brain cells do not get replaced, but everything else does. My point still stands. Physically, we are not what we were a few months ago.

msiyer 7y ago
The complexity is mind boggling. Physically, we are not what we were a few months ago. And what exactly is physicality? People were commenting that the idea that every cell is replaced in a living organism is 'laughable'. Brain cells and osteocytes were cited as examples of cells that are never replaced. However, I still think, and more strongly than ever, that brain cells and osteocytes can be examples of unchanging cells if an only if it is proven beyond a shadow of doubt that every single atom constituting such cells remains intact during the lifetime of such cells. Since the human body is subjected to a lot of physical stress and damage and repair is continuous, it is possible that damaged brain cells or osteocytes get replaced with new ones. Need to read more about this, though.
hn_throwaway_99 7y ago
> This is the reality of life - every single cell in the body of a plant or animal is replaced every few months. This is laughably false.
- nojvek 7y ago
  Do you have a source for your claim?
  - beaner 7y ago
    Does the person he's replying to?
  - nickcox 7y ago
    Not sure it's on the GP to provide a source but here's one: https://www.timeshighereducation.com/news/life-span-of-human-cells-defined-most-cells-are-younger-than-the-individual/198208.article https://www.timeshighereducation.com/news/life-span-of-human...
  - nojvek 7y ago
    I like how HN downvotes when asking for a “source”. I was merely expecting a “this is false because of X”. Rather than “this is false” I guess we all have our biases.
- doikor 7y ago
  Outside of some cells in the brain all the cells do get replaced. But there are some that have lifespans of over a year (white blood cells) and some only a few days (cells in a human colon)
  - hn_throwaway_99 7y ago
    Osteocytes in your bone have a half life of 25 years, and many of them don't get "replaced" even after they die.
- fg6hr 7y ago
  It's not just the reality of life, it's the essense of reality. Everything "real" is looks like the Ship of Theseus and if something doesn't look like that ship, it's not real.
jpster 7y ago
“You can never step into the same river twice.”
WoahNoun 7y ago
You think every brain cell is replaced every few months? Please delete this comment and read a biology textbook.
- shreyansj 7y ago
  Are you saying that a brain cell is immortal through one’s life?
  - dmoy 7y ago
    Yea some of them are. Obviously not every cell in the brain, but some types are not replaced.
  - ryanhuff 7y ago
    https://www.nationalgeographic.com/science/phenomena/2013/02/25/neurons-could-outlive-the-bodies-that-contain-them/ https://www.nationalgeographic.com/science/phenomena/2013/02... "New neurons are made in just two parts of the brain—the hippocampus, involved in memory and navigation, and the olfactory bulb, involved in smell (and even then only until 18 months of age). Aside from that, your neurons are as old as you are and will last you for the rest of your life. They don’t divide, and there’s no turnover."
- msiyer 7y ago
  https://www.ncbi.nlm.nih.gov/pubmed/16495940?access_num=16495940&link_type=MED&dopt=Abstract https://www.ncbi.nlm.nih.gov/pubmed/16495940?access_num=1649... Adult neurogenesis or brain plasticity is a fact. Skin cells, blood cells and all types of cells have a finite lifespan - a few days to a few months.
  - hn_throwaway_99 7y ago
    Just because neurogenesis exists, it most definitely does not follow that "every single cell in the body of a plant or animal is replaced every few months", which is what you said. Osteocytes in human bone can live up to 50 years.
mnm1 7y ago
I think this applies to most atoms in the body over time: https://stevegrand.wordpress.com/2009/01/12/where-do-those-damn-atoms-go/ https://stevegrand.wordpress.com/2009/01/12/where-do-those-d... But while it applies to many cells over varied lengths of time (up to many years), it doesn't apply to all cells. https://www.livescience.com/33179-does-human-body-replace-cells-seven-years.html https://www.livescience.com/33179-does-human-body-replace-ce... https://www.snopes.com/fact-check/does-body-replace-itself-seven-years/ https://www.snopes.com/fact-check/does-body-replace-itself-s... So the idea does apply but not exactly as you claim and it's definitely not absolute, even for atoms, let alone cells.
- msiyer 7y ago
  I am not a biologist. One way or the other the body is in a constant state of flux. Even if 90% of body is regenerated over a period of time, it is still a great wonder.

by msiyer 7y ago

msiyer 7y ago

The complexity is mind boggling. Physically, we are not what we were a few months ago. And what exactly is physicality? People were commenting that the idea that every cell is replaced in a living organism is 'laughable'. Brain cells and osteocytes were cited as examples of cells that are never replaced. However, I still think, and more strongly than ever, that brain cells and osteocytes can be examples of unchanging cells if an only if it is proven beyond a shadow of doubt that every single atom constituting such cells remains intact during the lifetime of such cells. Since the human body is subjected to a lot of physical stress and damage and repair is continuous, it is possible that damaged brain cells or osteocytes get replaced with new ones. Need to read more about this, though.

hn_throwaway_99 7y ago

> This is the reality of life - every single cell in the body of a plant or animal is replaced every few months. This is laughably false.

nojvek 7y ago
Do you have a source for your claim?
- beaner 7y ago
  Does the person he's replying to?
- nickcox 7y ago
  Not sure it's on the GP to provide a source but here's one: https://www.timeshighereducation.com/news/life-span-of-human-cells-defined-most-cells-are-younger-than-the-individual/198208.article https://www.timeshighereducation.com/news/life-span-of-human...
- nojvek 7y ago
  I like how HN downvotes when asking for a “source”. I was merely expecting a “this is false because of X”. Rather than “this is false” I guess we all have our biases.
doikor 7y ago
Outside of some cells in the brain all the cells do get replaced. But there are some that have lifespans of over a year (white blood cells) and some only a few days (cells in a human colon)
- hn_throwaway_99 7y ago
  Osteocytes in your bone have a half life of 25 years, and many of them don't get "replaced" even after they die.
fg6hr 7y ago
It's not just the reality of life, it's the essense of reality. Everything "real" is looks like the Ship of Theseus and if something doesn't look like that ship, it's not real.

jpster 7y ago

“You can never step into the same river twice.”

WoahNoun 7y ago

You think every brain cell is replaced every few months? Please delete this comment and read a biology textbook.

shreyansj 7y ago
Are you saying that a brain cell is immortal through one’s life?
- dmoy 7y ago
  Yea some of them are. Obviously not every cell in the brain, but some types are not replaced.
- ryanhuff 7y ago
  https://www.nationalgeographic.com/science/phenomena/2013/02/25/neurons-could-outlive-the-bodies-that-contain-them/ https://www.nationalgeographic.com/science/phenomena/2013/02... "New neurons are made in just two parts of the brain—the hippocampus, involved in memory and navigation, and the olfactory bulb, involved in smell (and even then only until 18 months of age). Aside from that, your neurons are as old as you are and will last you for the rest of your life. They don’t divide, and there’s no turnover."
msiyer 7y ago
https://www.ncbi.nlm.nih.gov/pubmed/16495940?access_num=16495940&link_type=MED&dopt=Abstract https://www.ncbi.nlm.nih.gov/pubmed/16495940?access_num=1649... Adult neurogenesis or brain plasticity is a fact. Skin cells, blood cells and all types of cells have a finite lifespan - a few days to a few months.
- hn_throwaway_99 7y ago
  Just because neurogenesis exists, it most definitely does not follow that "every single cell in the body of a plant or animal is replaced every few months", which is what you said. Osteocytes in human bone can live up to 50 years.

mnm1 7y ago

I think this applies to most atoms in the body over time: https://stevegrand.wordpress.com/2009/01/12/where-do-those-damn-atoms-go/ https://stevegrand.wordpress.com/2009/01/12/where-do-those-d... But while it applies to many cells over varied lengths of time (up to many years), it doesn't apply to all cells. https://www.livescience.com/33179-does-human-body-replace-cells-seven-years.html https://www.livescience.com/33179-does-human-body-replace-ce... https://www.snopes.com/fact-check/does-body-replace-itself-seven-years/ https://www.snopes.com/fact-check/does-body-replace-itself-s... So the idea does apply but not exactly as you claim and it's definitely not absolute, even for atoms, let alone cells.

msiyer 7y ago
I am not a biologist. One way or the other the body is in a constant state of flux. Even if 90% of body is regenerated over a period of time, it is still a great wonder.