When I was a kid back in the 50s and 60s, it was “common” knowledge that every atom that comprised the cells of your body would eventually be expelled within seven years.
In other words, in seven years you are a completely different person. Over the years this concept repeated pops up in my head, and I’d like to dispel this myth once and for all.
Is there any truth to this?
What I’ve been given to understand is that every cell, with very limited exceptions, reproduces itself by binary fission over that span. So it is not that you have “a brand new body every seven years” but that the next generation of the cells that made up the you of seven years ago are what make up the you of today. Think of an analogy of a small town of 200 years ago, made up of the same six families as had lived there 50 years previous, but most of the 200ya people are the children of the 250ya people.
It would take a cytological physiologist to discuss this at the appropriate level of detail, though. Do we have any Dopers who are?
I would certainly question the ‘seven years’ bit. There is a general rule that works pretty good for such common “knowledge.” The numbers 3 and 7 have long been regarded as magic numbers. Any supposed ‘true fact’ that involves the numbers 3 or 7, and probably 21, should be viewed with skepticism. Most body cells do regenerate and repair damage, but the idea of a different body every seven years of probably a lot of bunk.
I heard the 7 year story too. It’s not true.
Here’s one example wher they measured the isomerization of amino acids in a protein to determine their residence time in the body: