“Biology...was a unique science because it could not define its subject matter. Nobody had a definition for life. Nobody knew what it was, really. The old definitions-- an organism that showed ingestion, excretion, metabolism, reproduction, and so on-- were worthless. One could always find exceptions.” –– The Andromeda Strain, Michael Crichton

Life is something we know when we see it, and sometimes don’t. Textbooks and scientists have been trying to define life for ages, attempting to put something so large into a series of categories so we can sort objects to decide whether they are alive or not. It is human nature to want to put things into categories and create the categories themselves, to attempt to make an organized scheme out of a rather chaotic world. It is my firm belief that with concepts as complex as the definition of life that we must allow our categories to leak a bit, and expand what we see as living.

NASA has some definitions of life that seem to correspond with what I remember from my high school biology textbook. In a post called “Life’s Working Definition: Does it Work?” The Astrobiology Magazine staff provides a few accepted definitions. In short-hand, the agreed upon terms of life mentioned are that living things tend to be complex, be highly organized, transform energy and use it for growth and reproduction, have mechanisms for homeostasis, respond to surroundings, learn, reproduce, grow and develop.

In response to this, I pick at the terminology they use: “Living things tend to…” which very clearly shows that even the higher scientific communities do not have a solid definition of what we should consider living. Rather, these variables are guidelines that feed our internal definition of life, which has no set of rules but rather feelings towards certain objects.

For instance, upon seeing a dog run across the room, we would say this thing is alive and it likely satisfies most of the rules set by any textbook or scientific community. We don’t need to read rules to know this, we just do. We could always leave it at that and say that life is whatever we interpret to be alive and continue to make rules that support this, but I believe that this is not enough and that the definition of life is far more complex.

Allow me to speak on the word “alive.” There are many things we call alive. We call the dog running around alive, we call a bird alive. However, we also might call a rainforest, a decaying tree or a seemingly empty night with lots of noise alive. Some might argue that this is merely poetic and not good enough for a scientific definition, but then why are we satisfying some instinctual definitions and not others? Also, any word has the same basic origins and so let us negate this argument for the purposes of this discussion.

To understand where our bias comes from and eliminate it, we need to look at the differences between saying a dog is alive and saying a river is alive. The differences are that we see the dog as something like us (that can communicate (for all intents and purposes), who has bodily organs we understand, etc.), it ends its life within our lifespan (allowing us to observe the difference between dead and alive from an audience's perspective) and we view the system as the dog, just the dog, and nothing but the dog. I will delve into this more later.

Let me first discuss the likeness. We do not completely understand things that are not like us. We may be able to see how they function and discover patterns that allow us to make speculations that are probably true, but we likely do not know the whole story. We look at a dog and see breathing and it’s heart beating, and we look at ourselves (which we know to be alive because we have always defined it as such) and say “hey, our heart beats, it heart beats, we breathe it breathes, it’s alive.”

This may seem simple but we do that with each other all the time. Any first responder can tell you that these are considered “signs of life” and are taken very seriously. Now we also view plants as alive, but we hadn’t truly considered them to react to the same way as animals (at least at the cellular level) until around 1900.

So we started looking at things via the cellular level to determine whether they were considered alive. Plants are now considered just as alive as animals, and so we expanded our definitions to be inclusive of plant life. This restriction once did exist, and it might be existing now with other materials. We consider cells the building blocks of life but what if this view is far too limiting? We have small and single cell organisms that we consider alive, but then why do we consider a dog dead if some of his microorganisms are still alive? Our test of death is not to test if any cells or organisms are alive, rather we look at other things. So what if cells are just one sort of building block?

This brings me to a rock in a river and the conversation of lifespan. I wish to bring in a quote from a favorite author of mine who is the reason I have thought about this so much, and who I also introduced at the beginning of this piece. In The Andromeda Strain, Michael Crichton explores a team of scientists investigating a pathogen that has landed on earth. The organism is completely unfamiliar, and in an attempt to show how limited our view of life is, a character argues how a black cloth, a watch and granite, are all living things. The black cloth converted energy, the watch glowed in the dark showing that decay was taking place. In my personal favorite quote, the character argues for the rock:

“It is living, breathing, walking, and talking. Only we cannot see it, because it is happening too slowly. Rock has a lifespan of three billion years. We have a lifespan of sixty or seventy years. We cannot see what is happening to this rock for the same reason that we cannot make out the tune on a record being played at the rate of one revolution every century. And the rock, for its part, is not even aware of our existence because we are alive for only a brief instant of its lifespan. To it, we are like flashes in the dark” –– The Andromeda Strain, Michael Crichton

So as Crichton so eloquently explained, we are incapable of observing all possible life in this world. He shows that time is certainly a limiting element, but we could also be limited by our vision abilities or our hearing. What if the river could speak to us at certain frequencies? What if the moaning or a splash holds some kind of communication? We simply cannot know, and we are limiting our definition of life based on properties that we cannot always observe.

The last point I aim to make is that the dog is not alone. The dog carries fleas, maybe some parasites, certainly microorganisms that we don’t know about or simply can’t find. When we look at a dog and call it alive, are we calling all of him alive? Are we calling the ecosystem that is the mammal’s body alive, or just the mammal itself?

I truly believe that it is impossible to completely isolate the dog from its’ microorganisms, meaning that the ecosystem that is the dog never truly dies, it merely changes into another sort of body that brings in new sorts of microorganisms. In this way, the same way we might call a busy shopping mall, a rainforest or a night full of sounds alive, we can still call this system alive. Each thing that we look at is an ecosystem, and so things typically seen as just as space can be seen as alive, provided they hold a system of organisms (with a loose definition) that are also alive.

It is based on this that I conclude with my personal definition of life. The textbook definition is all fine and useful, and I can appreciate the scientific value of making complex things much more simple. However, I choose to define life as movement. When the river courses down a riverbed, when microorganisms eat a dog, when the rock decays, when bugs are around and flying but not seen, when the rainforest feels like it is breathing, when a human eats an apple, I consider them to be alive. As someone who has recently stood in the middle of a rainforest at night, I can tell you that we do not always have the ability to observe our surroundings.

A forest floor might seem to be empty dirt and not every animal can be seen, but yet somehow one knows that it is alive. These signs of movement, of flexibility, these things are truly what signifies to us that it is living. I think if we saw a rock move on its own accord one day, we might begin to revisit our definitions, but for now, the textbook definition allows us to simplify our world, and to make it too complex is to limit our ability to discover and understand new things. Breaking definitions is how new discoveries are made, after all.