Are we the same person at birth and death?

[Timelord79 (he/him)]

Obvious Question, might have an obvious answer.

What I mean is, Pretty much every cell in our body eventually dies, but can be replaced by another one as long as not to many cells die at once.
Does anybody know if there are also any original molecules and atoms that we begin our life with still left in our body when we die? Assuming we don't die prematurely?
Or will every single atom be replaced with at least another that takes over the same place and function?
Are we just a collection of spare parts when we die?

 

[farmkid]

I remember reading somewhere (I don't remember where, so don't ask for a reference) that it takes about 2 years for everything to be renewed. That renewal isn't always cells being replaced, but individual molecules being replaced. So, as lipids, proteins, etc. wear out they are broken down and replaced with new ones. That happens rather quickly in most cases, but some hang around for a long time. It seems to me that DNA would probably be replaced the slowest in differentiated, non-dividing cells. If the cell isn't dividing, the DNA will only be replaced as it is damaged and repaired, so that would be a slow process.

So, to make a long story short, it takes about 2 years or so to be completely replaced.

 

[Arrqh]

If we are more then the sum of our parts, then why must our identity hinge only on our base makeup?

However, it is said one never crosses the same river twice... unless it's the river Ankh, of course.

 

[Christopher]

I remember reading somewhere (I don't remember where, so don't ask for a reference) that it takes about 2 years for everything to be renewed. That renewal isn't always cells being replaced, but individual molecules being replaced. So, as lipids, proteins, etc. wear out they are broken down and replaced with new ones. That happens rather quickly in most cases, but some hang around for a long time. It seems to me that DNA would probably be replaced the slowest in differentiated, non-dividing cells. If the cell isn't dividing, the DNA will only be replaced as it is damaged and repaired, so that would be a slow process.

I think it's a myth that everything is replaced. After all, some metals and toxins gradually accumulate in our bodies over the decades, contributing to the effects of aging. So that means some stuff is coming in and isn't going out again.

In terms of actual cells, the conventional wisdom is that it takes seven years for every cell to be replaced. But that's total fiction. Some cells, like blood and the intestinal lining, get replaced every couple of weeks, while nerve and heart cells pretty much don't get replaced at all and are with you as long as you live. I'm not sure about the molecules making them up, though. Even if most of the molecules in the body do eventually get replaced, I'm sure that two-years figure is just another fantasy statistic like the seven-years one for cells.

 

[farmkid]

I remember reading somewhere (I don't remember where, so don't ask for a reference) that it takes about 2 years for everything to be renewed. That renewal isn't always cells being replaced, but individual molecules being replaced. So, as lipids, proteins, etc. wear out they are broken down and replaced with new ones. That happens rather quickly in most cases, but some hang around for a long time. It seems to me that DNA would probably be replaced the slowest in differentiated, non-dividing cells. If the cell isn't dividing, the DNA will only be replaced as it is damaged and repaired, so that would be a slow process.

I think it's a myth that everything is replaced. After all, some metals and toxins gradually accumulate in our bodies over the decades, contributing to the effects of aging. So that means some stuff is coming in and isn't going out again.

In terms of actual cells, the conventional wisdom is that it takes seven years for every cell to be replaced. But that's total fiction. Some cells, like blood and the intestinal lining, get replaced every couple of weeks, while nerve and heart cells pretty much don't get replaced at all and are with you as long as you live. I'm not sure about the molecules making them up, though. Even if most of the molecules in the body do eventually get replaced, I'm sure that two-years figure is just another fantasy statistic like the seven-years one for cells.

Actually, most molecules are replaced much faster than that. RNAs and proteins usually have a half life measured in minutes to days. I'm not sure about lipids, but I imagine they have a somewhat longer half life. DNA has a much longer half life, because, as I mentioned above, in non-dividing cells, the individual bases are replaced only as part of the repair process. The minerals in bones are constantly being turned over as bones are remodeled and repaired.

As those molecules are broken down and replaced, some of the components are "refurbished" so to speak, and made into new building blocks, and others are discarded. The metals you mentioned probably stay around a lot longer because there is no mechanism in place to dispose of them, unlike the carbon, hydrogen, oxygen, etc. that make up your body.

 

[V]

oh this is an old philosophical question I believe called the "Theseus' Boat" problem:

the idea was that in ancient Greece, this temple had a perfectly preserved boat that supposedly belonged to Theseus: at any rate the boat was indeed several centuries old, but it had survived so long because incrementally and over the course of centuries, every few decades when a single timber rotted they would replace that one timber.

over the course of decades and centuries, they had, one piece at a time, eventually replaced EVERY timber of wood and there was not a single piece of the actual, original ship left.

Nonetheless, they were certain that it was an EXACT replica at least (they'd used the original wood as a guideline to carve replacement pieces, etc.)....and they only replaced the pieces at a rate of like literally one every decade.

So if you replace only one timber on the boat, would you say it was still the "original"? Probably. What about 2, or 3? Also probably. And what if gradually, it became 50% replacement wood? and what's so different between 49% and 51%?

Needless to say, when the Athens schools of philosophers heard about the boat, it generated intense debate: if something was incrementally replaced so gradually, could it be said to be the same boat? and most importantly...what exactly was the cutoff point?

***they have referrenced this philosophical arguement on Trek in regards to the transporter; in Enterprise season 4 when the guy that invented the transporter comes on the ship and explains that they had all sorts of protests and complaints and stuff when they invented the transporter, like "it gives you brain cancer, or even metaphysical questions, like could the person that left the transporter truly be said to be the same person that went into it?" etc.

 

[Arrqh]

oh this is an old philosophical question I believe called the "Theseus' Boat" problem:

There's also a variant known as Locke's Socks involving Locke's favorite pair of socks with patches over the holes. Rivers are also another example, as I jokingly alluded to before... the water in a river is constantly changing yet the identity of the river remains the same.

Ultimately, before you can talk about if something has changed you have to first decide your criteria for its identity. If the molecules that make up your body are not part of that criteria (and generally its not) then if they change that doesn't necessarily imply a change in identity.

Hey, lets put another Trek spin on it. Is the Enterprise still the same ship after the refit at the beginning of TMP?

 

[FordSVT]

Here's a question involving the same thought process, and it relates to "uploading", the theoretical process by which a person's consciousness is placed into a computer.

Imagine you are a medical patient with a brain problem, and they have to replace a part of your brain with a computer to do the same job. This is already scientific reality. Are they the same person? They would say so, and I think we'd all have to agree they are.

What if you replaced pieces of that brain one by one until the entire brain was a computer? Is that person still "them"? And taking it a step further, what if you took the body out of the equation all-together? Is that entity in a box still "them"?

I wonder whether or not I will be alive long enough to test the hypothesis for myself.