The Nature of Life And Other Trivia

1: The Basic Gist

A few thousand years ago, Greek philosophers came up with an interesting thought experiment that, at the time, probably just seemed like a fun head-scratcher. Eventually, it turned out to be profoundly relevant to biology, the origins of humanity, and all life that ever existed. Pretty standard for the ancient Greeks, I guess. The exercise is known as the Ship of Theseus, and it goes something like this: a ship sets off from port loaded with a bunch of lumber. As it sails along, each individual piece of the ship, one by one, is replaced with an identical but new piece from the cargo hold while the original is cast out to sea. By the time the ship arrives at its destination, every single part of the ship has been replaced with a new one. Is the ship that arrives the same one that departed? Abstract, but definitely something interesting to ponder.

Now, fast-forward a few thousand years. An idea put forth by biologists is eerily similar to the Ship of Theseus: every single atom that makes up your body right now will be replaced or otherwise shed within about 5 years or so. In other words, each one of us- or nearly any living thing- is a biological Ship of Theseus. But, instead of replacing timber, nails, and sails, our biological “ships” replace each of the trillions of atoms in our trillions of cells with identical copies. Just imagine the complexity and scale of such a process. It’s practically unfathomable.

You may now be wondering exactly what I wondered when I first heard this idea. If all the actual stuff I’m made of is replaced, what part of me is me? Where in this squishy sack of flesh and bones am I? I definitely feel like I’m the same me now that I will be in 5 years or that I was 5 years ago. But all my actual parts have been replaced. So where do I live?

The easy answer is the soul, an immaterial entity that inhabits the body and comprises an individual’s true essence but is not defined by the body itself. This is a pleasing idea, but unfortunately it doesn’t stand up to much logical or scientific scrutiny. This explanation does have the benefit of making us feel special, as if somehow a human is above all the harsh realities of the universe. But, being the heathen skeptic that I am, I see no reason to believe that such a thing exists. A more parsimonious answer harkens back to that ship I mentioned. If I am still me 10 years from now, but all my atoms have been replaced, the only thing that doesn’t change much during those years is the relationships between the atoms and the information those relationships represent.

In case that’s not clear, there is a simple natural phenomenon that is another good example of this type of process. We’re all familiar with the piles of water laying around all over the place: puddles, lakes, oceans, etc. When you disturb an otherwise still body of water by dropping a pebble into it, the collision of the pebble with the molecules of water results in a transfer of energy in the form of motion from that pebble to some of the water molecules. They in turn transfer that energy to other molecules in an orderly and fairly predictable way. This is just a detailed way of explaining what we can all sum up with one word: a wave. Here’s a nice animation that demonstrates what goes on at the level of atoms:

Notice that the one molecule highlighted in the animation doesn’t do a whole lot. It just gets tapped by its neighbor, dances around a bit, and then returns to rest. That little dance is enough to tap its next neighbor and pass the energy of the wave on to it. The wave itself is not defined by any one of those individual water molecules, but rather the energy being passed along by them from neighbor to the next. If you were to freeze time at one instant and look at the molecules involved in the wave, they would be an entirely different set of molecules than just a few moments later. But it’s still the same wave. Just like the Ship of Theseus, and just like us, provided you wait enough time to observe.

Almost all biological life operates in a similar manner. We require a constant supply of matter, i.e. food and water, and use those raw materials to maintain or expand our bodies. That matter becomes part of the process of our biological lives. Most individual molecules are eventually shed, excreted, or otherwise replaced, returning to rest in the environment. This pattern is much like a wave. Matter is initially at rest, gets pulled into doing a complicated dance as part of our bodies, then returns to rest. But instead of being a brief, simple, mechanical disturbance, life is a massively complex, highly coordinated process from even the tiniest bacterium all the way up to elephants and whales. And, life propagates not only through water but also through an ocean of many kinds of matter. Like a wave, it seems more appropriate to define life by this propagating set of relationships between molecules than by the matter it happens to consist of at any given moment. You are not the collection of atoms that happen to make up your body right now. You are the coordination between them happening right now. That coordination will be similar to the coordination occurring within future you, albeit between many different atoms.