DEFINITION
A living object is material in an ordered state, which actively maintains its state (at least), and (better yet) is able to rearrange increasing amounts of its environment into something similar to itself, by growth (ok) or replication (best of all).
In detail, it’s an object that is…
- significantly more ordered than its environment (maybe not its immediate environment, as a bacterium living inside an animal, but its broader environment, like the environment that animal lives in), and
- actively maintains its ordered state (when its order is disrupted, energy is involved in (attempting to) return to its previous state), and
- is able to make more of itself or something very similar to itself.
Do we need to specify it replicates on its own, without needing to hijack another living object (like a virus)?
All maintenance, growth and replication happen actively – by processing energy. I guess they could be passive, but not nearly as effective, probably totally ineffective for objects complex enough to be alive. So must be active. But do we need to say that – does it need to be part of the definition? Maybe it’s a side-effect of satisfying other requirements. (Universe doesn’t care, only we do.)
It should probably be specified that it doesn’t just grow larger but results in more individual objects, though also is that necessary? It seems to make a difference to the survival of that life form. But if it can successful grow larger, turn more and more of its environment into itself, that seems good enough, even though it might not be the runaway success of making lots and lots of replicants of itself which can keep repeating the process. Ok it’s a matter of success. In order of increasing effectiveness, it needs to be able to…
- Repair itself. If that’s the best it can do, then it’s surviving but not expanding. An event too big for it to handle will end it.
- Grow larger (convert environment into itself). If this is the best it can do, then it’s only one object expanding (and area increases slower than volume) and only into it’s current environment (which could become depleted or not have enough variety).
- Replicate (convert environment into more objects similar to itself). This is best because exponential: multiple objects now mean more surface area to interact to convert environment into larger objects, and can sample less depleted or wider variety of environments.
EXAMPLES
A crystal is in an ordered state (though not dramatically more ordered than its surroundings). But it doesn’t actively maintain that order, like if it’s cleaved, smashed or melted. It is able to make more of itself, or grow larger anyway (though not more individual objects), since its surfaces are the template for newly deposited atoms to line up on. That’s one of the most important parts of life. Are we being self-centric to think that a living object has to be complicated, or it has to actively repair itself (since most crystals are pretty durable, so not much need to actively repair in order to survive, which is the whole point: survive to grow and make more of your surroundings like you.)? Maybe a crystal, like a tornado, meets the definition of a living object, it’s just a really boring and not very successful one.
The orbit of a planet around a star is an ordered state. But it doesn’t actively maintain it. New orbit is different and doesn’t return to existing orbit.
An electron in an atomic orbital is an ordered state. When disrupted by adding energy, it often returns to its former state. Is it active maintenance though? Energy is involved, but it doesn’t really process it. Also of course an atom can’t replicate itself.
A fire grows, turning more and more of its environment into something similar to itself (as long as it lasts anyway). It can even propagate from burning ashes carried aloft and traveling (though not real far). These are key attributes of living objects. But it is a disordered state and leaves behind a disordered state. Disordered states are very common and not very interesting.
A tornado is an ordered state (though like a crystal not dramatically more ordered than environment), and it actively maintains it! Circular air motion is more ordered than non-moving (well just Brownian motion) air, and it maintains it by energy released from condensing raindrops. This is the example that made me add “able to make more of itself” to the definition. Otherwise a tornado fits the definition for a single living object.
A virus is an ordered state, but it doesn’t actively maintain itself (as far as I know). It does make more of itself, though it has to hijack fully living cells to do that. Similar to when we consider DNA as a living object, below.
A bacterium is an ordered state, it actively maintains its state (repairs broken cell membrane, probably repairs internal stuff), and it replicates itself.
A bacterium that can’t divide, for whatever reason, we would still call a living object, it just has an important feature missing (self-replication) that limits its ultimate survival. Since others like it meet our definition, so we just chalk it up to a defect in this individual one that doesn’t take away from the fact that it’s alive.
Interesting, eh? We take a living object, do something to remove an important attribute according to the definition, and we still call it a living object. It can go on living, it just can’t replicate, so its survivability as its *type* of living thing is limited.
So replication is necessary for living objects is general to keep living. But not for any individual living object to be considered a living object.
A bacterium or other living object that grows bigger and bigger, instead of replicating, I think we have to call that a living object too. So the important thing isn’t replication, exactly, it’s turning more and more of its disordered environmental material into its ordered self. By that definition, a crystal’s ability to grow counts (though it still doesn’t actively repair itself) (and it doesn’t actively grow, but is that important?).
It seems like maintenance and growth are important to be active. Actually for practically living objects, passive isn’t good enough, they have to be active. So it kinda doesn’t matter whether we specify active or not.
The Earth aka Gaiea is an ordered state; like other living objects, it’s far more ordered than its surroundings (space) and probably than the other Solar system planets and star. It has been argued that it actively maintains its order – the Gaia Hypothesis. I think that’s partly true, though it doesn’t seem real good at it – lots of ups and downs, and possibly things it can’t handle (though the latter is true for unquestionably living objects too). Assume for the moment it can’t grow or reproduce. In this sense it’s kinda like a bacterium that can’t divide, and maybe has trouble maintaining its order but manages to well enough to keep living. So living but by some accident that doesn’t seem really important can’t grow or divide.
But what if humans migrate to other planets and terraform them? Then Earth has replicated something similar to itself – the third criterion for life. The humans are like genes that go out into the environment, take control of non-living material, and rework it in their living object’s likeness. I can’t think of a regular living analog: viruses use genes from one type of living object to co-opt another living object, but this uses genes from one living object to co-opt non-living matter.
But in that case, how is the Earth different from a beaver dam complex (the dam, the pond, the lodge, the nearby trees raw material)? A beaver dam complex is more ordered than its environment (not by much maybe, esp if we think of the trees cut down), it actively maintains itself (thanks to the beavers, who act as both genes and mechanics), and it replicates itself using beavers, that like humans in terraforming, go out into the less-ordered environment and replicate the beaver dam complex. Is a beaver dam complex a living organism like the Earth/Gaia?
A beaver dam complex isn’t much more ordered than its surroundings. A little bit, sure, but not dramatically so. But a human city, that would qualify. A human city is much more ordered than its surroundings, maintains the order and actively repairs damage, and makes more of itself – it grows into its surroundings, and humans migrate taking their knowledge and abilities to make new cities with them. Again humans are both the genes and the mechanics.
MORE: Is the Earth – or Could a Planet with Living Things – Be a Living Thing?
HIGHER-LEVEL APPROACH
Seems like we have a higher-level type of living object here. Like the selfish gene could be considered the living object and cells are just its raw materials it organizes for maintaining and propagating itself, and we’re too proud to think that we and our cells are just puppets of semi-living genes, so could beavers and humans be living objects and beaver dams and planets are just our raw materials we organize for maintaining and propagating ourselves, and the beaver dam complex and Earth are too proud to think that they’re just puppets of semi-living beavers and humans. Whereas the beaver dam complex and Earth are just as alive as we are, only on a larger scale, composed of objects alive on a smaller scale.
So, hierarchy of living objects…
- a DNA molecule or gene (can’t do everything in our definition of a living object on its own, but it seems to belong in the hierarchy of living objects at a minimal level as much as a planet does at a maximal level) (even if you think it isn’t living, it’s useful to have in the list as something just over the boundary because it’s too minimal).
- a single-cell organism
- a multi-cellular organism (and to a lesser extent a colony of single-cell organisms); also recognizing that most or all multi-cellular organisms are also colonies or ecosystems
- an ecosystem, like a human city
- a whole planet (an ecosystem of ecosystems, or is that not doing it justice?)
We don’t feel totally right about saying a gene or a planet are living objects because they’re far away from us in size and also don’t entirely fit with the definition of life above, which is pretty compelling. But maybe we’re just self-centric in coming up with a definition of life, and genes and planets qualify if we just think beyond our own scale for a bit.
To handle this expanded definition, that goes outside our species-centric way of thinking, let’s define “Life”. That’s what this article is titled, yet I’ve been more concrete and defined “a living object”, not some universal almost mystical thing called “life”. Yet in our expansive consideration of living things, we want to include genes, which don’t meet all criteria on their own, and cities, which don’t have boundaries so aren’t really objects, and Gaia, which some people would have trouble calling an object ‘cuz it has so many parts (but an atom has parts and so does an animal and we call them objects), and some of those parts are already living objects themselves, and which doesn’t seem concrete enough to call a “living object” yet we could see how we might identify it with the less concrete-sounding term “life.”
Life is ordered stuff (significantly more ordered than its surroundings) that actively (by processing energy) turns more of its surroundings into ordered stuff similar to itself.
NATURE DOESN’T CARE
Nature doesn’t care about life – life isn’t a thing. There are only properties, and when you put the right ones together, you get these complex and amazing things objects. There is certainly a real, qualitative difference between living and non-living things. But the universe doesn’t categorize things into living and non-living; what happens happens and that’s all there is to it.
For humans, we want to categorize things. It helps us function. In this case, once we decide something is living, we feel it’s worth more attention and value than something non-living. We tend to imbue it with additional properties (correctly or incorrectly), mostly of a spiritual, animated, deciding what it’s going to do and how it’s going to affect its world sort.
MORE: The Universe Doesn’t Think Like We Do
DISCUSSION
So descriptively, once you put all characteristics together to achieve full life, what is/are the qualitative difference? Living objects are characterized by high complexity and low entropy, they process energy in order to actively maintain their state, and they contain detailed information for making new objects similar to themselves.
WHY DOES THE DEFINITION OF LIFE – OR A LIVING THING – MATTER?
- As humans it’s helpful to categorize things, so we need a definition or definitions of the category.
- As humans we want to recognize when something is alive that’s a lot different than the life we know. Maybe the plasma inside stars could arrange itself, maybe there could be whole ecosystems of living things inside stars. I doubt it, but maybe, and it’s a concrete example to think of what could be drastically different yet still alive. Maybe galaxies actively maintain their organization, we just haven’t figured that out yet (there are a lot of things we’re still figuring out about galaxies after all: how dark matter affects them and what dark matter is anyway) and are thus alive, and they’re kinda like cells and giant clusters, threads, sheets of galaxies like multicellular organisms.
READ FURTHER
Is the Earth – or could a planet with living things – be a living thing?
Very Universe 