I recall as a child watching an episode of Star Trek where a malfunction in the transporter created two Captain Kirks. Although I was very young at the time, I recall wondering, if the transporter disassembled and then reassembled matter how could there be two full-sized Captain Kirks? Wouldn’t the best possible outcome be two 50% sized Captains Kirk? Okay, so I was a bit of a science nerd as a kid. Of course, we soon learned that these Kirk’s were not the same. One was the normal Kirk, the other, evil. Even these exact duplicates were not the same, although even then it was puzzling as to why all the evil aspects of a person would be confined to the duplicate.
In reality, how do we know which Kirk was the original? It seemed puzzling, at least to me. And as it turns out, this puzzle was not limited to viewers of Star Trek.
In ancient Greece, the man said to have founded the city of Athens was the legendary king named Theseus. Athens at the time was dependent upon the strength of its ships, and as you might have guessed, Theseus was a great naval tactician who fought, and won, a great many sea battles. As a result, and perhaps to capture the magic, the people honored the memory of their king by putting his great ship, afterwards known as the “Ship of Theseus” on display as a memorial. The ship, we are told, was there for hundreds of years.
As time passed, the wooden ship began to deteriorate. Although Athens is in a very weather-stable area, rain and sun, and the progression of time began to weaken the planks and the substructure, at which time, workers would replace bits and pieces. Now, over a few hundred years, most of this ship of Theseus had to be replaced in order to keep it looking original. The question is, at what point does the ship stop being the Ship of Theseus, and start being just some other ship that was, more or less, LIKE the ship of Theseus?
While the Ship of Theseus probably never actually existed, nevertheless, it has become a philosophical puzzle for thousands of years: the problem of identity. In looking at both Kirk and the ship, what can we truly know about a thing? How do these things change? If the thing changes, can we even agree on what exactly has changed? (After all, the two Kirks looked identical, acted identical, until the one started being evil).
Concerning the ship, how many planks or other bits can be replaced before we no longer have the same ship? Let us suppose, for the same of discussion, that the ship was comprised of 400 pieces or bits. We can agree that replacing one or two bits would make little difference. What if, over time and due to weathering, and other forces, we needed to replace all the deck boards? Is this still the Ship of Theseus? How about after the people had to replace a third of all the bits and pieces? How about half? Lets say that after 400 years, and the ship was so deteriorated over time that, by now, all but the keel had been replaced? Can we say this is still the Ship of Theseus? Would it even matter?
The truth is simply that there is no agreed upon, objective answer. Either to the two Captains Kirk, or to the question of the “Ship of Theseus.” So at this point you may be thinking, okay, this was an interesting thought experiment, but isn’t this a medical blog? And you would be correct, however, there is always method in the madness, or in this case, this digression.
By the time that you reach the age of 68 to 70 years, every single cell in your body will have died and been replaced. You are simply not the same person you were 50 years ago, or even 10 years ago. Like Kirk’s doppelgänger, or the ship replaced over hundreds of year’s bits at a time, you are no longer the original. This is simply a part of aging. But that begs the question, why do we age? Why can’t we, like Captain Kirk, simply replicate our cells in the same condition as the original?
Each time our cells replicate there must also be copies made of our DNA, a complex molecule that is essential for cellular function and reproduction. One theory is that eventually, all this replicating of cells will eventually lead to catastrophic errors that cause cellular death. This is the reason given that our skin begins to lose its elasticity, our muscles begin to atrophy, and our organ systems begin to fail. Maintenance of our biological tissues includes maintenance of the structural integrity of our DNA, critical for cell survival, and just as important, accurate transcription to the daughter cells that replace the original cells.
The concern lay in an enzyme called DNA polymerase alpha. This enzyme constructs DNA molecules by assembling nucleotides. It is essential to the replication of DNA. Generally, these enzymes work in pairs, in order to create two identical DNA strands from each single original DNA molecule. However, if there are any errors in the information transferred during DNA synthesis, it is copied to the new cell’s DNA, another way to look at it, instead of an old cell with original DNA and a new cell with copied DNA, when each double stranded DNA is copied you end up with two double strands, each containing one template strand and one transcribed strand.
When the cells divide, it leads to two 1/2 new cells. Should the original cell have errors, they would be in either or both of the new daughter cells. Alterations in the fidelity of DNA polymerase alpha could result in a progressive degradation in the information transfer during DNA synthesis, eventually affecting a range of cellular components.
Like School children playing telephone, once an error creeps into the story, that error is passed along, and entirely new errors are added to the story based on the original error. The result, much as it was in grammar school, we end up with a message (transcribed in our DNA) that makes no sense at all. When this happens, the daughter cell ceases to function correctly. Eventually this leads to error catastrophe, where the new cell is replicated with such dysfunction that it is essentially useless. At this point, the cell may initiate a process of self-destruction known as apoptosis, or it may be signaled to self-destruct by neighboring cells (Apoptosis is one area of cell death being looked it for certain diseases). Interestingly, cancer cells seem to maintain these DNA errors, yet avoiding apoptosis. No one really understands why, at least right now (Another area of research is looking at errors in the replication of telomeres, but that’s a different post).
In the end, we are all very much like the great ship. We are replaced, bit-by-bit, until the inevitable decay overcomes the ability to replace the parts. If only we could replicate ourselves like Captain Kirk. Of course we would run the risk of stepping off the transporter pad evil.