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Okay so this is a claim that you can see made on the internet that the none of the atoms remain in your body forever. This caught my interest cause this could be used to show that consciousness is not really material. This is like the famous Ship of Theseus argument that Daniel Dennet is mentioning in the audio record I have linked to at the bottom.

Here are some big names that make this claim:

Here is Tor Norretranders (author of 'User Illusion'): https://www.edge.org/response-detail/11492

98 percent of the atoms in the body are replaced every year. 98 percent! Water molecules stays in your body for two weeks (and for an even shorter time in a hot climate), the atoms in your bones stays there for a few months. Some atoms stay for years. But almost not one single atom stay with you in your body from cradle to grave.

Richard Dawkins: https://youtu.be/1APOxsp1VFw?t=630

But here is the bombshell: You weren't there. Not a single atom that is in your body today was there when that event took place.

Here is a claim that says the cell remains but it is repaired not just replaced.

Yes, your body is made up of some of the atoms you were born with. I think the concentration of these "original" atoms would be moderately low since the body not only replaces cells, but also repairs cells continuously. This means that a cell could persist, but its constituents may have been replaced slowly over time.

But on further digging I found many answers contradicting this claim. Here are some:

This audio record that involves Daniel Dennet as a participant says there are a some atoms that remains through the entire course of life: https://www.npr.org/transcripts/11893583?storyId=11893583

"It turns out there are some atoms that are with us fosr our entire life. This comes from a researcher in Sweden and the atoms are actually in some interesting places. They are deep in the DNA of some cells in our brain and in our heart, and also some atoms in our teeth. So brain, heart and teeth. Don't forget to brush."

This paper: https://www.pnas.org/doi/10.1073/pnas.0605605103

The data show that virtually all neurons (i.e., >99%) of the adult human neocortex are generated before the time of birth of the individual, exactly as suggested by Rakic (5), and the inescapable conclusion is that our neocortical neurons, the cell type that mediates much of our cognition, are produced prenatally and retained for our entire lifespan.

https://www.reddit.com/r/askscience/comments/h26f2/how_long_does_it_take_for_complete_cell_turn_over/

the assumption that all your cells die and get replaced is an incorrect assumption.

https://www.reddit.com/r/askscience/comments/6j7r2e/how_do_brain_cells_get_replaced_without_changing/

Neurons, the brain cells that current brain science considers responsible for the vast majority of computation in the brain, (mostly) don't get replaced.

Which of these claims are right? I am confused with all these different takes on the issue. I guess the issue here is there are not enough evidence/research on the issue and most of them claiming this are extrapolating from some incomplete data?

It would be helpful to hear what you guys think of this and who is making the incorrect claim here.

Edit: I went searching for the source for the Richard Dawkins claim and it turns out to be something written by Steve Grand and it looks like Steve Grand is often taken to task by the audience for this exact unsubstantiated claim. It looks like it was just an extrapolation he made and doesn't have a definitive proof for it:

I can’t cite any single definitive authority, although see the last paragraph below. For my part I draw the conclusion from a whole bunch of evidence. The first thing to say, though, is that it ISN’T ABSOLUTELY TRUE. Not quite. Not as an irrefutable and precise fact. I didn’t say it in the first place to declare a free-standing scientific fact but to add emphasis to an important but otherwise hard to believe point, and that point is still true even though I may have exaggerated by an atom or two.

He goes on to substantiate his claim further in his blog: https://stevegrand.wordpress.com/2009/01/12/where-do-those-damn-atoms-go/ but he still doesn't have anything definitive by the end.

I also found this youtube video (there are more) that shows the body replenishing itself completely is a myth, they refer studies based on carbon-14 in human cells from nuclear explosions to claim this: https://www.youtube.com/watch?v=XqJWSyUbmkw.

I haven't found any solid evidence yet to make the contrary claim that the body do replace completely. I tried hunting down Tor's source for his claim but IIRC ended up in a non-english language reference which stopped me from pursuing further. If anyone has different opinion on this feel free to add an answer!

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The significant difference between neurons in the central nervous system and other cells in the body is that function is not the product if a particular type of cell being in the right place, but of the synaptic connections between them (thousands per neuron). For this reason, the body can easily replace a muscle, skin or liver cell while retaining function, but not a neuron: the replacement cell would also need to be rewired in exactly the same way, which is impossible since the wiring is the product of the history of interactions between cells.

This is why brain cells cannot be replaced while retaining existing brain function.

Having said this, the dynamic nature of neural function means that neuron replacement is not entirely forbidden, as discussed in this article

Nottebohm, F. (2002). Neuronal replacement in adult brain. Brain research bulletin, 57(6), 737-749.

https://doi.org/10.1016/S0361-9230(02)00750-5

Furthermore, if you take this down to an atomic level, the active metabolism of living cells means that many of their molecules are continually being produced and replaced. Even without cell replacement there is therefore considerable atomic replacement.

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  • $\begingroup$ From a deeper reduction, all these wiring weights of a neuron over its interaction history at each synapse along the receiving dendrite ultimately mainly depend on the number of excitatory AMPA receptors/channels with Ca2+ ions and inhibitory GABA channels (of course with other biochemical factors too but ignore for now), thus in principle we can clone a same neuronal cell with these exact AMPA/GABA receptors with their corresponding neurotransmitters and Ca2+, sodium and other important elements distributions if technology to manipulate these ions/moleculars are precise and advanced enough. $\endgroup$
    – cinch
    Nov 8, 2022 at 22:04
  • $\begingroup$ I will grant you that 'in principle' such repair (e.g. of neurological damage) could (some day in the distant future) be technologically possible. In practice, with neurodegenerative diseases generally involving a significant percentage of the brain's cells, I think scaling this up as a solution/cure would be entirely unfeasible, so here's hoping for prevention rather than cure! But the question was whether the brain itself replaces its cells (and/or molecules). It is certainly not the case that the brain has such a replication/replacement mechanism. $\endgroup$ Nov 9, 2022 at 6:51

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