So, you can look at a person and honestly say with all sincerity, “I’ve completely changed, I really have!” 
“Oh, for the bones of yesteryear”, I’m sure many of us would like to know.
What about my gold tooth?
Next up: what are the chances that my gold filling was originally part of Atahualpa‘s ransom?
ETA: looking back on The Royal Hunt of the Sun, from the room Captain Von Trapp had to fill for Captain Quint, since all the known gold would fill three olympic-sized swimming pools: 7%
Well, that depends on the global mixing time for gold. Yeah, there’s not all that much gold total in the world, and some of it has been melted down and re-worked many times, but some of it has stayed relatively stable for long times.
It’s not hard to do some calculations like this. I looked up the volume of the Pacific ocean, and the volume of one water molecule, multiplied and took the square root. This gives a geometric mean of 4.6 ml, which is quite close to a teaspoon.
Thus, there are as many molecules in a teaspoon of water as there are teaspoons of water in the Pacific Ocean. If somebody dumped a teaspoon of water into the Pacific, and we waited long enough for it to be well mixed, the average number of those original molecules in a newly sampled teaspoon would be one.
Probably the kind of calculation that the factoid was based on …
Problem though is how long does it take to be well mixed? Does it ever get well mixed?
Not all portions of ocean mix the same perhaps? Maybe some hardly mix at all and some quite quickly?
Possibly for the ocean. Don’t know. In the body though some things are likely to stay stuck much more than others. Bone turnover happens lots; it’s constantly remodeling. Muscles, blood, too. Dental enamel not so much so. So on.
Interesting to me that this factoid has had such legs. I wonder what makes for such long factoid life?
It’s kind of cool - the human body version of the Ship of Theseus. I guess it’s attractive to ignore the inconvenient fact that it isn’t really true for the entire body, since that makes the factoid less compelling.
True. Making the point about our identities being based on the continuity of our patterns rather than the constancy of our physical stuff with this “fact” is more appealing than the Ship metaphor to many. Who wants to question a good story that makes a good point?
Has anyone posted this yet?
Or conversely, if you commit a crime and can avoid prosecution for 5 years, you could claim that the ‘now’ you didn’t commit the crime.
If the atom replacement factoid was true…
Perhaps there is a hidden justification for the statute of limitations.
The reasoning and experimental data Aebersold provided is fairly good. Some of the numbers were surprising- the rate of turnover of water in cells is remarkable. I don’t think anyone expected that. The turnover of various elements tested is also high. Half turnover times of two weeks for hydrogen and phosphorus and two months for carbon.
Protein levels in cells are regulated by the balance of degradation and synthesis, with the lysosomal pathway being pretty agnostic to the proteins degraded. Amino acids get degraded similarly. Even bone is maintained as a balance of osteoblasts and osteoclasts doing their work.
Overall the body really is in a state of constant tear down and renewal.
The end products of the degradation pathways all point to paths for elimination from the body. Some will get reworked but lots will be removed. The mere fact of requirements for a range of proteins in our diet is a clue.
Just by chance, I heard Josh saying they did a podcast on this topic (and received the most feedback about). Here’s a link - I haven’t had a chance to listen yet, but I do love those guys.
ETA: Stuff You Should Know.