What do you think is “Earth centric” about it? It is very general and abstract. It does not, for instance, specify any particular sort of chemistry as necessary for life; heck, it does not even specify that life be based on chemistry.
Yes, it is conceivable that one day we might discover something, perhaps in some other part of the universe, that does not share any of the characteristics of life as we know it, but if we did, why would we want to call it life?
The Andromeda Strain’s version of life (PDF; starting at page 195): Leavett presents a black cloth, a watch, and a piece of granite. “I give you three living things.” Of course, Michael Crighton was trying to define life anywhere in the universe.
The human body is a complex collection of interdependent processes, to keep all of the parts “alive”. The brain runs the heart and breathing functions, which in turn supply oxygen and nutrients to the brain. The lungs need blood supply and fresh air. The kidneys and liver flush out used metabolism byproducts from other processes, the brain tells the jaws to chew and the body as a whole to eat so that all the parts get new nutrients to continue the cycle.
Disrupt any of these processes, and parts die - some faster than others. The brain stops working very fast in the absence of oxygen; kidney failure, or insufficient heart function, or insulin problems, OTOH, can mean a loner process before all systems fail. As mentioned, some parts don’t “die” as soon as others; hence organ donation. However, at a certain point damage is sufficiently irreversible that the body as a whole (minus unessential parts) cannot survive. In some cases damage is so complete not even mechanical assistance can keep the rest alive.
When the biochemical activity that keeps the cell9s) in a functioning state stops, the cells are dead (unless they are flash-frozen in such a way that the process is simply suspended.) This can bring up, of course, the question of whether a dormant seed is considered “alive”, “dead” or something inbetween.
To really understand “life”, consider what the simplest form would be - possibly the single cell organism. It does all the essential processes of life within one cell. When those biochemical activities cannot function any longer, the cell is essentially dead.
That merely states, without argument or example, that there are “exceptions” to the “old definitions”, by which it means something like the Seven Characteristics. This is just a novelist bullshitting. Even if there actually are known counterexamples to any of them (and I don’t think there are, unless one insists that viruses are alive, a very questionable claim), that does not make them useless as criteria. We do not necessarily have to have definitions giving necessary and sufficient criteria to know what something is. Not all concepts work like that: some are “family resemblance” concepts. So long as something meets most of the Seven Characteristics, you can make a case that it is alive (as is the case with viruses). If it meets very few of them, you can be confident that it isn’t. If it meets them all, you can be confident that it is.
The cloth, watch, and piece of granite are presented as counterexamples to the suggestion that “energy conversion” is the “hallmark” of life, a stupid suggestion in the first place. Creighton rejects a good characterization of life on no grounds whatsoever, and then gives us a very weak straw-man criterion which he facilely demolishes. It is bullshit: a fiction writer bamboozling you with fallacious arguments to create a fake sense of profundity.
If you stop to think about it, at its core, life is not really a thing but a characteristic of a system - a bias. In general, I think it would be regarded as a bias towards higher and higher states of order and complexity, but I think you can justify any systemic bias.
So a weighted dice is alive? :dubious:
does it progress to higher states of complexity? I’m not sure why you choose to ignore every other parameter, but hey, they’re your blinders, not mine.
Your blinders seem to prevent you from understanding your own words.
As for having a bias toward, or progressing to, higher states of complexity, no, that is just false, life does not have any such bias. Evolution is not progressive. Less complex forms commonly evolve from more complex ones. Or if you are not talking about evolution but individual development, then individual organisms degenerate and die, becoming less ordered and complex (and the degenerative phase is part of life).
You know, it there were a simple and satisfactory one sentence definition of “life”, somebody would almost certainly have thought of it long before you applied your great brain to the matter, and biology teachers would not be wasting their time teaching all the long-winded stuff that they in fact need to deal with.
I presented the criteria as a different way of looking at the question. I didn’t come parading down from a mountain in full beard and robe with 2 stone tablets and I’m pretty sure I made no pretense thereof either.
In terms of missing points, I won’t even both. I’ll just try to explain what I thought would have been obvious.
Thermodynamics dictates that any system not in equilibrium moves toward a greater state of disorder (entropy, technically) assuming no other forces acting upon it. Living things, while they do not of course violate thermodynamics, create localized areas of decreasing entropy.
And while just moving heat from one place to another would qualify as decreasing entropy, it should be obvious that’s not what I mean. The order and complexity that life creates tends to be stable and persistent. It resists adverse changes in its environment and selectively exploits those that are beneficial. IOW, life is something that seems to defy natural forces through specific, persistent and directed reductions in it’s own entropy and that of it’s immediate environment.
You can argue life in a philosophical way all you want, but basically we have one empirical, real-life(?) version of “life”. It consists of an array of biochemical / organic chemical reactions that together allow these processes to continue to function in a cellular organism. Current thought, AFAIK, is that all this “life” can trace itself back to processes that eveolved at one point eons ago in the primordial soup.
Death happens for an organism when these biochemical processes no longer take place. Then, decay can set in, the orgnaic chemicals that make up this life can break down to the point where they are no longer capable or resuming.
We recognize this “life” as something special because it has its own level of (self-sustaining) complexity far beyond what you see with a watch or a robot or a block of granite. But… if you want a precise definition, you aren’t going to see one. There is no black and white line. Virus, for example, maybe straddles the fine line between complex chemical reactions and alive biochemical activity.
If it exists in any of the multi-universes it is alive and has life. Animal, vegetable, mineral and those other things.
What about prions. Are they alive? They are much more simple than a virus yet they self-replicate.
It’d be more accurate to say that they self-catalyze.
I don’t think so, but I’m not sure what you mean. They take another protein with the same chemical structure but different topology and refold it to the pathological form. I’ve usually seen that referred to as self-replicating, but I won’t be dogmatic about it.
Could you say they’re like ice-9? A structure with harmful properties that can induce more of itself.
Sure, but why isn’t it alive? I can say why given the definition I presented earlier, but it meets a lot of the ‘ad hoc’ criteria given here. It’s self-replicating. Prion proteins tend to aggregate into more complex structures which seems to be at least part of the reason they cause damage.
I mean without really thinking about it you know immediately that they’re not alive, but let’s say we send a probe to one of Jupiter’s moons and find something like this and ask the same question. Do we apply the same criteria and get the same answer and if so, how valid is that?
As I said - life is what we call a complex interacting collection of biochemical (organic chemical) reactions that seem to be self-sustaining in the right circumstances.
You can tailor your definition to include or not include prions - a relatively simple chemistry. You might even define life so technically viruses, which are a significantly more complex chemistry, are or are not included. But if you expect to find a solid sharp line - on this side life, on this side non-living - then no. Welcome to the real world, where all lines are grey and fuzzy and all definitions are subject to interpretation; just as when we say the human body, for example, is “dead” there are cells and even whole organs that are still “alive” (or viable) for a while afterwards.
As I understand it: Cow prions and human prions (say) are slightly different. If you introduce a cow prion into a human-protein environment, you can get more prions, but they’ll be human prions, not cow prions. So the molecules aren’t actually copying themselves, so it isn’t really reproduction.
Depending on what you mean, that may not be possible. If the protein in cows doesn’t have the same chemical structure, then the prions don’t add or subtract chemical subunits so it’s not going to change them chemically.
If you mean that they have the same chemical structure in both cows and humans but the prion form has one topology in cows and another in humans and that the BSE (bovine spongiform encephalopathy) prion refolds the normal protein in humans to the human pathological form rather than the BSE form, I’d need to see a cite for that.
edit: I suspect that the prion forms are the same in both cases since with Creutzfeldt–Jakob disease for example, the BSE caused form is just listed as a different variant.
As in, the relevant proteins (in either topology) are chemically different between cows and humans, but that a cow-protein in the prion topology can trigger the human-proteins changing to the prion topology.