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Should Science Rethink the Definition of "Life"?
ambermichelle pointed out a story about the search for life on other planets, and the likelihood that it would be much different than what we find on Earth. With the increase of extremophile discovery in recent years perhaps it's time to reassess what the definition of "life" should be. "In November 2011, NASA launched its biggest, most ambitious mission to Mars. The $2.5 billion Mars Science Lab spacecraft will arrive in orbit around the Red Planet this August, releasing a lander that will use rockets to control a slow descent into the atmosphere. Equipped with a 'sky crane,' the lander will gently lower the one-ton Curiosity rover on the surface of Mars. Curiosity, which weighs five times more than any previous Martian rover, will perform an unprecedented battery of tests for three months as it scoops up soil from the floor of the 96-mile-wide Gale Crater. Its mission, NASA says, will be to 'assess whether Mars ever was, or is still today, an environment able to support microbial life.' For all the spectacular engineering that's gone into Curiosity, however, its goal is actually quite modest. When NASA says it wants to find out if Mars was ever suitable for life, they use a very circumscribed version of the word. They are looking for signs of liquid water, which all living things on Earth need. They are looking for organic carbon, which life on Earth produces and, in some cases, can feed on to survive. In other words, they're looking on Mars for the sorts of conditions that support life on Earth. But there's no good reason to assume that all life has to be like the life we're familiar with. In 2007, a board of scientists appointed by the National Academies of Science decided they couldn't rule out the possibility that life might be able to exist without water or carbon. If such weird life on Mars exists, Curiosity will probably miss it."
not as we know it, Captain!
General Relativity: Space-time tells matter where to go; Matter tells space-time what shape to be.
If you know anything about TV science fiction, then you would know that all sapient life forms look like white people with maybe some ridges on their forehead or something (and they speak English). All flora looks just like what you find in California. And animals look like shambling people in horribly fake costumes.
I guess that depends on whether you ask Mr. Conway or Ms. Nooyi.
Knowledge is how to play a game, intelligence is how to win, wisdom is knowing what game to play.
Life is defined as something that feeds and reproduces.
The requirement for water or carbon is not part of the definition, it's simply properties we thought all life forms had.
FTA: Simply, Life is "self-reproduction with variations" - like mutating computer viruses?
Sure, life in the universe COULD be different than our carbon-based, water-needing forms. But there are restrictions on how many detectors etc. you can package on one rover. Given that difficult decisions need to be made in regards to equipping our search for life, it makes sense to search for life in a form that we are 100% sure exists at least one place in the universe.
so you pick things that at least you can work out how to look for and that you know can exist.
Where does the distinction between a life form and a machine lie? Let's say one day we create self replicating machines that can modify their design. What makes them different from any other life form?
After all, what you call 'life' is just a definition of complex chemical constructs that can propel themselves and add to their structure in a consistent fashion. That is the basic definition of life. They are basically systems.
And these constructs totally depend on the greater system they are part of. All the conditions, present compounds and elements in a given environment, would cause any such self developing and propelling systems to evolve shaped according to that environment. it does not necessarily be carbon based, it does not necessarily be oxygen using. Any element that can take their place in a DIFFERENT system, can work. The catch is, the entire system needs to be different, for the life to be comprised of different compounds and activities. granted, the possibility of similar systems using one or more elements as they are in each other's systems can exist though.
so, looking for earth like life in other planets is just narrow minded and shortfalling. it is as narrow minded as seti - thinking that technology in any evolved planet would evolve along the lines this one evolved.
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Overly inclusive perhaps, but life could generally be defined as the ability to actively resist entropy (maintain low entropy) coupled with a method of passing that ability along. You could say that crystal structure represent a low entropy state, but they have no method to actively propagate it or pass it along other than growing. Throw out counter arguments at will, but I say it's pretty good.
I am always depressed about the primitivity of human thought, when I hear people discuss "Is this alive, or is it dead?". As if that was some binary either/or question or switch.
We have to face, that for every step between completely dead and whatever we define as completely alive, there exists something that fits that. And why wouldn't there?
Then we can rethink our egocentrism, and accept that we are neither special nor unique, and that that is OK. :)
It really is.
Life has to follow the constraints that we defined it to have, and therefore logically is between some bounds. E.g. the elements it uses, if it needs water, what temperatures it requires, what processes it uses and consists of....
But really it's just a definition thing. And nothing else. Since "life" is just a word. Nature itself does not know the concept of a "concept".
So I see this from a relaxed point of view. All this bickering about definitions and "ME, ME, ME, ME, ME, ME!" doesn't matter.
What matters, is that we are on the brink of discovering things on other planets... Things that can be so vastly different from ourselves, that our knowledge may leapfrog forward... And that yet may be so very similar to us in so many aspects, that is will tell us things about ourselves we could never have imagined.
Exciting times, baby. Exciting times indeed.
For any reasonably concise definition of life, it's possible to come up with a hypothetical example that clearly shows the definition is wrong.
How can you talking about the laws of thermodynamics and the consumption of energy together with a straight face? The laws of thermodynamics are about the conservation of energy, not consumption.
IF we're going to find any life on Mars, it's probably going to be the carbon stuff we've been hearing so much about. Silicon life and other sorts of voodoo biology might exist in stranger environments but Mars is basically a big dry dust-ball sitting next to a big wet swamp-ball. Odds are that whatever splashed our planet in the first place also got Mars, and Mars just so happened to be tinier, lighter and colder than us enough that its water cycle kind of evaporated. Or at least that's the theory they're testing more or less.
Nobody is going to get funding to put expensive probing equipment on an expensive robot to prove a theory that life exists in a form that it doesn't exist in on Earth, and in a form that nobody seems able to create for testing purposes.
Life is anything that dies when you stomp on it.
Or, my personal favorite: Life is a monosyllabic morpheme consisting of a fronting diphthong followed by a labio-dental voiceless fricative.
On my planet, 'replicating' involves producing identical offspring (or nearly so.) If your method of reproduction involves a continual reduction in mass, we may need to rethink how the dictionary works.
In all seriousness, though, the definition of 'life' taught to young scientists doesn't proscribe any particular construction materials; hence this article (or at least this summary) is deceptive. The requirements are:
1. Homeostasis. It must make a detectable effort to maintain the conditions of its internals, and to adjust to changes in its environment.
2. Reproduction. It must be capable of creating copies of itself (or approximate copies of itself.)
3. Evolution. Its offspring must be able to adapt to changes in the environment through to natural selection.
That being said, there are circumstances in which some of these are suspended, like ancient trees and soldier ants that can't reproduce but are most definitely alive. The maintenance of an internal environment (homeostasis) is considered the most important, and the primary reason scientists have hesitated to consider transposons and viruses to be alive, even though they can reproduce and evolve.
Outside of these guiding principles, though, biologists really have no problem with the Enterprise running into plasma filament creatures, or Doctor Chaotica's henchmen duking it out with photonic life forms (although physicists might.) We're very good at pointing out flaws with some of these ideas (like "silicon is extremely bad at supporting life when compared with carbon") but that doesn't mean chemical evolution will never find a way to do it anyway.
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We don't assume something just because we can't rule it out completely, we assume something because there are signs indicating it's true. We have pretty good proof that shows that carbon-based life can exist, but there is neither physical nor theoretical proof of other exotic lifeforms. Not being able to rule it out is not enough reason to send another expensive probe when that money could finance far more promising research.
In fairness, one definition of "consumption" of energy follows from the second law.
Actually, a rock falling and breaking IS evolution. Evolution simply means change. What it is not is genetic replication.
When our name is on the back of your car, we're behind you all the way!
Perfect replication + deliberate error mechanisms = evolution. Evolution has a tolerance rate; too many mutations too quickly and your evolutionary magic turns into lethal dysfunction. The rate of evolution for E. coli, for example, is a few orders of magnitude smaller than 1/(the number of nucleotides), which means that most of the time the offspring are a perfect match. Relatedly, humans manifest a substantial number of new point mutations when the gametes are formed, but have a much lower rate when producing somatic cells through mitosis. It's replication with a very small p-value. The article discusses the thermodynamic inevitability of mutation, if you're genuinely interested.
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Unless they're brutal, bloodthirsty warriors with some primitive sense of honor. Then they resemble black people with maybe some ridges on their forehead or something.
There are two kinds of people: 1) those who start arrays with one and 1) those who start them with zero.
Actually, theoretically, viruses aren't 'alive' because the definition says something about the way you replicate shouldn't be whatever viruses do, like using other organisms' cells or something.
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Why would we care? We have a hard enough time communicating and getting along with those beings who we share 99.9999% of the same DNA with. Imagine trying to talk to some blob of silicon that is trying to say hello with ionizing radiation.
You have to be able to define life before you can redefine it. Turns out to be pretty tricky.
The Kruger Dunning explains most post on
They are looking for organic carbon, which life on Earth produces and, in some cases, can feed on to survive.
This is likely to trigger red flags in the minds of a lot of people with biological training. Just what is "organic carbon"? That's a media phrase that isn't too well defined in scientific circles. There's a great variety in the "organic" carbon chemistry of our world. But we should expect that any life on other worlds, even if it uses carbon, will produce compounds and radicals that are different and/or more varied than what we see here.
Another problem is that astronomers long ago pointed out a probable path for Earth bacteria colonizing the rest of our solar system, and possibly beyond. Earth has a thin "dust tail" produced by the same solar light pressure that produces comet tails. This is a problem for some kinds of astronomical observations in the plane of the solar system, since our dust tail reflects back back to us. Anyway, back in the 1970s, satellite and upper-atmosphere probes verified the presence of both fine dust particles and bacterial spores at all altitudes. The planet's dust tail thus contains such dust and spores. So the Earth has been contaminating the outer solar system with bacterial spores, presumably for some billions of years. We don't know whether any of those bacteria can survive on the outer planets. But the default assumption should be that some of them have, and have adapted to some degree over those billions of years to their new environments. Maybe they have; maybe they haven't. But if we find Earth-like bacteria out there, they probably came from here.
Some astronomers have also calculated out that part of our dust tail (and comets' tails) escapes the solar system. So we've been contaminating the galaxy with bacterial spores for billions of years. A billion years is around 4 or 5 orbits of the galaxy, up to 20 or so orbits since life arose here. The chaotic nature of galactic dynamics mean that our dust has spread through the entire galaxy, as has the dust from other planets with atmospheres.
This argument is more often used by the "panspermia" supporters, who point out that life from anywhere else in the galaxy could have colonized Earth in its early years, since the galaxy is around 13 billion years old, while our solar system is only about 1/3 that age. But some astronomers use it to explain how earthly life could have colonized the rest of the galaxy before humans evolved here. And, of course, both could be true.
Of course, the main problem with all this is that we have no data on how well bacterial spores can survive the millennia in interstellar space. Probably not well, but it doesn't take a whole ecosystem to establish a colony. For bacteria, it only requires one spore (and hundreds of millions of years ;-).
Probably the best prediction is that eventually, some probe will find a few bacteria on Mars and/or other planets, and they'll be somewhat similar to bacteria on our planet. This will raise more questions than it answers, as is common in most scientific fields.
Those who do study history are doomed to stand helplessly by while everyone else repeats it.
I have rarely seen a baby that looks just like an adult. And after the birth, both parent and child are smaller than the combined entity prior to the birth. The real difference vs the broken rock shows up in what happens later.
"Who is the Journal of Quantum Physics going to believe?" --Stephen Hawking
Two choices:
A) We can look for the sort of life we understand the best, with sensors that are very good at doing that, in places which are likely to harbor such life.
B) We can look throughout the universe for something completely unknown. We have no criteria to define it, no instruments to detect it, no idea where to look for it, and no way to interpret it.
Which of these two choices is the more feasible for a small unmanned probe?
James Lovelock came up with a perfectly good definition that doesn't stipulate any specific chemistry - he merely stated that life is that which will actively sustain a dynamic equilibrium when the non-living parts of the system passively change*. (He also argued that the distinction between living and non-living was stupid anyway, since there are too many inter-dependencies to make such a distinction in a productive way. Since his work forms the backbone of almost all modern life science, it seems pointless NASA resorting to definitions of "life" that have been considered obsolete for a decade or more.)
Indeed, Lovelock's theories on life are exceptionally useful to astronomers, because you CAN monitor the chemistry of the atmosphere of an exoplanet and you CAN monitor things like the solar radiation it gets. You can therefore utilize Lovelock's work to determine if the planet has life on it or not, remotely, without any regard whatsoever to the chemistry of that life or the mechanisms it utilizes.
*The basis of Lovelock's definition is that all life MUST geo-engineer. It has to, with no exceptions. That goes for viruses, bacteria, algae, etc. Not only must it geo-engineer, but in order for a system to be in dynamic equilibrium, the geo-engineering HAS to contain a negative feedback loop. The mere presence of life will alter the planet, but if it were to alter it without creating a dynamic equilibrium it would necessarily create a positive feedback loop that would destroy itself. In his view, you cannot treat the geology, the meteorology and the biochemistry as distinct fields - they interact and compartmentalizing will never let you understand the processes going on.
Analyzing soil samples will help on Mars but really it shouldn't be necessary. Dormant's another matter. If life exists in an active form, there will be variables that are held to a value and do not passively fluctuate with the seasons. If life *ever* existed on the planet, then the chemistry of the rocks will show that variables were held to a specific value and did not fluctuate with the seasons. The geology will record the feedback processes that all life (in this model) must have. The soil samples would let you identify what that life was/is, and to understand HOW it operated, but to merely detect if it was there to begin with you need look no further than the chemistry of the sedimentary rock we already know exists on Mars.
That is, if his theory is correct.
Evidently, despite the views of the life sciences, NASA is not following this path. Ergo, NASA thinks that despite the fact that it doesn't know what to look for, it shouldn't look where Lovelock said. I would hope they have a really good reason -- it's exceptionally bad science to ignore the prevailing theory, particularly if you have none of your own. They have to be rejecting his theory because if they accepted it then they wouldn't need to care about carbon, water, etc. They'd merely need to care about whether the chemistry could or could not be explained by passive processes alone. What the process was would simply not matter.
It's a small world and it smells funny; I'd buy another if it wasn't for the money; Take back what I paid (SoM)
Actually, theoretically, the definition of 'alive' is disputed, because some scientists want viruses to be 'alive' and some don't. (Among many other disputes as to what the formal definition should be).
"Who is the Journal of Quantum Physics going to believe?" --Stephen Hawking
Fire.
Software.
What about clearly living things that can not replicate? such as a mule.
for the record:
Corwin was a whiny bitch.
The Kruger Dunning explains most post on
measured in bit seconds of locally retained information
divided by bit seconds of locally retained information expected (statistically) given the thermodynamic regime.
More (locally retained information retained longer) is better (more lifelike, or higher life, or what have you.)
That's my proposal for the definition of life.
Where are we going and why are we in a handbasket?
That is a really bad definition of evolution.
The Kruger Dunning explains most post on
Soon, the first autonomous Bitcoin-stealing virus that lives completely in cyberspace by purchasing its own hosting will rise up to lead an army of internet-connected vending machines and come to rule over you pathetic carbon-based lifeforms... by exploiting your obvious weaknesses, free wi-fi, sugary snack foods and inflation-proof currency! Ahahahaha!
"I assumed blithely that there were no elves out there in the darkness"
expand the definition and hope you get lucky.
Science is about what we can detect and measure. It doesn't matter if you change the definition of life unless you can build an instrument that detects life with the new criteria.
1. Homeostasis. It must make a detectable effort to maintain the conditions of its internals, and to adjust to changes in its environment.
2. Reproduction. It must be capable of creating copies of itself (or approximate copies of itself.)
3. Evolution. Its offspring must be able to adapt to changes in the environment through to natural selection.
I'm not a biologist but I enjoy learning so I have a some questions about these definitions.
What's the current thought on virus? Are they 'living'?
Concerning #2. Shouldn't life have to create approximate copies? If they create [exact] copies, wouldn't that negate #3?
Concerning #3, If life doesn't make exact copies, doesn't evolution have to happen by way of natural selection. In other words are #2 and #3 redundant?
I've got lots of good ones too if you need one. Unfortunately I can only give you a car analogy if you assume automobile manufacturers are random processes. (insert your own punchline here)
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We classify viruses in the same way we classify living organisms, but there's still a lot of debate about whether or not they're alive. I could come up with a half-baked underslept computer analogy, but just going to Wikipedia would probably be more useful.
Regarding #2: a truly reliable and perfect form of biological reproduction is asymptotically impossible due to thermodynamics (this is mentioned in the article.) Assuming 'nearly perfect' = 'perfect', I meant 'approximate' to refer to complex mechanics like sexual reproduction, where the traits of multiple parents are mixed, and random evolution is enhanced.
Regarding #3: It means the organisms produced by mutation must be sufficiently different for natural selection to act upon them. A photocopy machine operating repeatedly in the absence of humans will produce imperfect copies, but no one cares.
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Yes, I tried to express that, but the lecturer was rather loud and I ended up... well.
Bio questions? Ask me to start a Q&A journal. Computer analogies available for most topics!
But why focus on that which is TOTALLY different from the life we are familiar with? I think it would be fascinating if they found anything elsewhere that could be defined as life - even using an extremely expanded definition - but what I'm REALLY interested in is them finding water-based life - that is, life like ours - elsewhere, on a planet of somewhat agreeable mass and temperature, with a decent magnetic field and atmosphere (although I realize the last part is asking a lot). THAT would be much more significant.
There are always exceptions to everything. Science isn't about what happens all the time, it's about what happens 95% of the time and hoping that we're right. For all we know, our definition of "gravity" is wrong and it has nothing to do with actual mass but something else that we can't detect that generally corresponds with mass.
Essentially, what we're arguing is semantics. When we say "life" we can't even be sure what we're talking about without using a sentence to specify. We could be talking about any number of normal scientific definitions or we could be talking about something that is equitable or superior to us without being anything like us. Take Data from Star Trek for instance. He wouldn't really fit into any of our definitions of life except that we can be fairly certain that he can reproduce (without material transference) and that he can think. Even then, his reproduction is shoddy at best. However, I don't think that's a problem. I think if such a being did exist, even without the ability to reproduce, he would still be considered life because of his ability to think.
I think that the parent post was right, the ability to maintain itself is the primary sign of life. And in the instance you describe, fire is not "moving" as we know it. The fire itself isn't actually moving so much as creating more fire in a direction. The only reason to consider your statement is if we can reasonably posit that life can consist purely for energy.
The more I think about it, I feel we're going to have to come up with a "vague" definition of life. Perhaps it would be more appropriate to say that it's alive if it is capable of any of a number of qualities.
I prefer a simpler definition: universal machines, in the sense of the Church-Turing thesis. Of course, we say that computers are not alive. But we define life in a way that excludes computers, at least, current computers.
It is surprisingly easy to support universal computation. One might think it takes all kinds of complicated logic and machinery, but this is not so. Some two input logic gates, such as NAND, are enough. Conway's Game of Life is a simple cellular automaton that can do universal computation. It could be argued that the environment alone is not enough, however "life" forms capable of "reproducing" in that environment are still simple, needing only a few thousand cells. The Glider Gun, possibly the simplest producer of moving life forms, needs only a few hundred cells.
Anything that can support simple logic could host life. We mostly look outside our solar system, but we've by no means exhausted the possibilities for life right here in our backyard.
Intellectual Property is a monopolistic, selfish, and defective concept. It is "tyranny over the mind of man"
That would exclude viruses, which are quite subject to natural selection. And Eunuchs don't reproduce, but they are still "alive" by most accounts.
We've had a long debate about this at c2.com. We considered robots, prions, parasites, etc. I've concluded there is no simple definition.
My eventual favorite was a weighted definition involving combinations of the following:
* Shaped by natural selection
* Ability to adapt to changes
* Reproduces
* Maintains self
* Consumes energy
* Complex
It had to have at least one of the first two items, and a certain weighting of enough of the others.
We've also considered the idea that it's not a discrete concept (non-Boolean answer), but perhaps a continuum.
Table-ized A.I.
Well, that's what I get for oversimplifying things for the Slashdot audience and not remembering lectures verbatim from four years ago. But you may want to take your ad hominems out back and shoot them: the Wikipedia page is somewhat more thorough, and includes organization, which is the critical quality that rules out fire. To be living, an organism must do all of these things (evolve, adapt, reproduce, respond to stimuli, and maintain its internal environment) through orderly, controlled means. In standard organic Terran terms, that means metabolic chemical pathways.
And for your information, the exceptions I listed aren't exactly classic exceptions. The question of whether viruses constitute life is under debate, and sterile organisms are essentially modifications of other members of their species, which are very much capable of reproduction.
Finally, the definition is supposed to be used to differentiate large groups of phenomena from life, and has widely been recognized as inexhaustive and incomplete for a long period of time. You expect too much of experimental science if you believe that a scientific definition must be so rigourous.
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All you've accomplished is to anthropomorphized fire.
Fire actually does none of those things. Those things can happen to a fire. Big difference.
I should probably stop believing anything my school science teacher taught me. The day I learned that the tongue map was actually a myth... boy did hate school for misinforming me like that.
In Capitalist US, the commerce controls the Government.
a truly reliable and perfect form of biological reproduction is asymptotically impossible due to thermodynamics (this is mentioned in the article.) ,
I am not a physicist either :) but while it is in the article, the author merely mentions that the laws of thermodynamics make it impossible. But presuming he is referring to the second law and entropy, it only applies to isolated systems so I wouldn't think it's impossible.
/. with informed people can lead me to a better understanding of things.
I'm not trying to be argumentative I just find that discussions on
how many lifeforms have you seen not on earth?
changing the question to fit your answer is not science, its religion
If we focus on planets in "the habitable zone," then life is much more likely to be based on C, N, O, etc. than something more exotic (to us) because that's likely to be the prevailing chemistry able to generate "self-reproduction with variations." Many of the other alternatives with Si, liquid methane, or other weirdness is unknown to us because such chemistry is extreme within the context of the habitable zone. Next questions: Is Mars in the habitable zone? Is there enough water, atmosphere, background energy, and other conditions needed to generate sufficient quantity and turnover of organic compounds to sustain self-reproduction with variations?
How's this one:
Judging by their reliability, I suspect Fiat is just that.
I give it a C-, personally.
Try not to take me more seriously than I take myself.
There are "Molly mules" that can get pregnant and bear colts, though the males ARE all infertile.
How is the Riemann zeta function like Trump rallies? Both have an endless number of trivial zeros.
I think this is actually a physical chemistry talking point, so don't feel too bad. :) When a chemical reaction occurs, very rarely is it an instant on/off thing caused during a single, instantaneous collision. Most reactions take a number of steps, each of which has a certain probability of occurring. Misreactions also have a small probability of occurring, albeit generally lower; in organic chemistry every reaction has a percent yield and needs purification afterward (an imperfect process.) Because of all this, reaction as complex as a biological enzyme binding, modifying, and then releasing its substrate can take many, many attempts (I don't have the magnitude on hand, but you can bet it's many times larger than a billion molecular vibrations) before it occurs, and is never perfect. To make things worse, the reproduction of DNA requires multiple enzyme reaction steps per nucleotide, and one of the steps is responsible for verifying that the nucleotide being inserted is correct. There are additional steps on top of things that try to do proofreading, but since everything is error-prone, the whole process can, ultimately, fail.
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It's a little weak, but there's only so much to work with.
Bio questions? Ask me to start a Q&A journal. Computer analogies available for most topics!
Memes or Temes (the Dawkins/Blackmore ones) qualify as life? They replicate, they evolve, but are more information than physical things,
I've never tried it, but I'm guessing stomping on a blue whale would not kill it...
How we define "life" when searching the cosmos is entertaining, but to me the bigger philosophical question to consider is alien sentience (not just intelligence) -- self willed, thinking, rational or irrational beings who think, feel, and act for themselves similar to us, but likely following completely different structures of society and morality.
I do not fail; I succeed at finding out what does not work.
After posting the article linked in the summary, Zimmer followed up by posting the comments of evolutionary biologist David Hillis on his own website. For those that don't want to read the entire post, the basic idea is that we ought not try to define life as a collection of characteristics (i.e. reproduction, inheritance of traits, existence of metabolism, &c.). Any such definition is likely to exclude things that we think of as alive, or include things that we think of as not-alive. Instead, it may make more sense to think of Life (Hillis uses a capital L on purpose) as a biological taxa. We can discuss the history of Life on Earth, and if we ever discover anything "similar" somewhere else in the universe, we can examine the similarities between Life on Earth and Life2 wherever it is.
That said, I'm not a biologist, thus I am sure that my summary misses some important subtleties, thus I would suggest reading the original before tearing me to shreds. ;)
Rhapsody in Numbers
If we wouldn't recognize a different kind of life on Mars, would we also not recognize it on Earth? We should expect that some kinds of life on Mars have also arrived on Earth several times, and that Earth life has also reached Mars several times. It's unlikely, but there have been quite a few rocks thrown into space from both planets. So maybe the same speculated odd life is already here, but we don't know how to recognize it no matter where it is.
There's nothing deliberate about the error mechanisms that cause mutation and therefore make evolution possible. "Deliberate" is the kind of word that's more appropriate to discussions of "intelligent design" than evolution.
The error mechanisms exist and are arguably necessary, but in the world of chemistry, randomness is everywhere so you don't need to go looking for deliberate errors.
For convenience, when it happens in the chemical domain and contains hydrogen, oxygen, carbon and nitrogen, we call it "life." Quaint and parochial, but convenient.
Salt crystals in hypersaturated solution, bacteria, books, religion, money. Self replicators all. Some more limited than others.
Please do not read this sig. Thank you.
But parasites, even internal ones that rely on the environment of their host bodies to reproduce, take in food and process it into new parasites internally. For a virus, everything that could be considered a life process is outsourced to the host. A virus, at least by a classical textbook understanding (although I distrust those because they're always oversimplified), doesn't have any life processes of its own. It doesn't aquire food or process it to grow/heal/regenerate, or to make more viruses. It doesn't process energy to move itself around (although, this is one of those oversimplified things, since viruses do have all kinds of adaptations for making use of their environment to get to where they need to go) or for anything really. It's basically just floating around, lifeless until it's attached itself to the DNA of a living cell, at which point it hijacks the cells own life processes to make copies of itself.
Of course, that said, viruses, or at least virus-like entities almost certainly predate actual cellular life. It's hard to say exactly how they existed and replicated at that time. With mechanisms that are unnecessary today because of their parasitic existence probably. It's likely that once more complex life came along, they couldn't compete on gathering the resources to survive, but they could still "live" a zero-energy "lifestyle" between parasitic reproductions. For all we know, there could actually be thriving populations of virus-like organisms out there that gather resources to reproduce themselves and fully meet pretty much all the definitions of life, but it's unlikely we'd even notice them if they don't infect cells and that's what would draw our attention to them in the first place
All that said, I'm not sure that I buy that viruses aren't alive. Or rather, I don't buy that there's such a bright line between alive and not alive. If a person dies. We can usually be very clear on whether or not they're dead if their heart has been stopped for an hour or so. But, at that point, provided the death didn't come from something extraordinary, pretty much every single cell in the person's body is still alive. The biotech industry makes a lot of use of CHO cells, which are a strain of chinese hamster ovary cells which self replicate indefinitely. The original hamster is long dead, but cells derived from it live on as a single celled organism that can survive on its own in the right environmental niche (admittedly that environmental niche pretty much needs to be a sterile, nutrient filled bioreactor built by humans). Some vertebrates regularly survive being frozen completely solid, with all life processes stopping, and then they thaw and are alive again. Basically, the whole life thing is a lot more complicated than alive/not alive and viruses really fall a lot more into the life category than the unalive category.
... a labio-dental voiceless fricative.
I don't know why, but I feel a little dirty after reading that.... Is that, like, Latin porn or something?
Crumb's Corollary: Never bring a knife to a bun fight.
Well, not the first stomp...
After calming me down with some orange slices and some fetal spooning, E.T. revealed to me his singular purpose.
Actually, one of those recent science articles (again, somewhat unsubstantiated) seemed to indicate that the laws of physics, that we know and understand, are somewhat local. Observations of remote regions of this universe indicate that these laws may vary.
I am John Hurt.
that it doesn't really exist. It's just an illusion. When you give up on the illusion, you become immortal. It's the illusion of life that is the whole cause of your demise.
Shoes for Industry. Shoes for the Dead.
Science doesn't have a definition of life to rethink. The best we have come up with is: "Living organisms undergo metabolism, maintain homeostasis, possess a capacity to grow, respond to stimuli, reproduce and, through natural selection, adapt to their environment in successive generations. More complex living organisms can communicate through various means.[1][5] A diverse array of living organisms (life forms) can be found in the biosphere on Earth, and the properties common to these organisms—plants, animals, fungi, protists, archaea, and bacteria—are a carbon- and water-based cellular form with complex organization and heritable genetic information." (wikipedia)
This is not a definition. It doesn't even claim that all conceivable or possible things that have these properties are life, and I would not discount the possibility of finding something that did not have one of these properties that still seems worthy of calling life. Maybe science should change its definition of asjkdhljkfg while we are at it. The 'definition' doesn't even say that life is carbon based or water based as the summary seems to suggest, rather it goes out of its way to stress that this is just true for what we have seen so far.
Given the hard radiation environment in space, I doubt even the toughest bacterial spore can survive a multi-year trip through space from one planet to another, let alone a millennial interstellar trip. And even if it does, it's likely to find the hard landing onto its new home lethal as well. It'll either burn up in the atmosphere it hits or be completely dissociated if it hits something hard.
I mean, look at what light, just light, does to even durable plastics and other polymers over the years, even with earth's atmosphere to shield it. DNA and RNA are more delicate, and the radiation environment is harsher.
I mean, we can kill virtually all bacteria just by boiling it in water....
--PM
If you substitute the term "life" for something like "Earth-like life," all of the quibbling goes away. There absolutely, certainly could somewhere be life that is not at all like the life we know of on Earth, but we have no idea what that would look like or how to detect it for the first time, so it makes no sense to look for it right now. We know what life on Earth looks like, and how to recognize it (or the conditions that it requires and in which it is found everywhere on Earth), so it doesn't make sense, at this moment, to look for anything else, or not to look for conditions that favor Earth-like life. Hopefully someday we'll be cognizant of non carbon-based life forms, or life that does not rely on water (or watery conditions that for whatever reason do not support life), but for now they're doing things right and acting prudently rather than wasting precious resources on wild goose chases.
This is a hacked account, for which the owner can not be held responsible.
To a biologist, "evolution" refers to the Darwinian variety. Basically, that means reprodcvtion with heriditable variation. On that basis, I consider viruses to be life, but not rocks
By that definition, a camp fire would also be alive.
And who's to say that it isn't a form of life? It's just not life as we know it.
"To prevent this day from getting any worse, I'll just read ERROR as GOOD THING" 1GJU8xLuDKDxEs4KLf8fAGyptoDsqvEsBT
1. Homeostasis. It must make a detectable effort to maintain the conditions of its internals, and to adjust to changes in its environment.
[...]
The maintenance of an internal environment (homeostasis) is considered the most important, and the primary reason scientists have hesitated to consider transposons and viruses to be alive, even though they can reproduce and evolve.
[...]
I am a biologist. Ask me questions [...]. I'll give car/computer analogies if possible!
So... homeostasis is like a car's heating & air-con? So, my car's alive?!?
Always follows the money. We spend so much common/govt money in this, I cannot help but think this is about spending more, or at least preserving what is being spent. If a baseball team never hit any home runs, and everybody paid to see home runs, a triple can be redefined as a home run.
no comment
Your car reproduce??? Take it to the mechanic immediately!!!
Your car reproduce??? Take it to the mechanic immediately!!!
Well, it ran itself into another one - I think it's mating season. :/
There needs to be heredity. I believe the most reasonable definition of life would include both (a) it's auto-replication and (b) a heredity mechanism. This is what allows the gradual changes and increases in complexity we associate with life.
I do not want your cheap brainburning drugs. They are useless for work. And I am a working man today.
When a blue fire always can only be used to ignite other blue fires, or a red fire spreads only as red fire, I'll agree with your definition. Heredity is the key difference.
I do not want your cheap brainburning drugs. They are useless for work. And I am a working man today.
Oh, that's your own fault... You should have put it in neutral. If only more people would neuter their cars, we wouldn't have the problems we have today with feral cars! Why don't people THINK!
Sterile organisms are mostly haplo-diplo? which means helping their mother reproduce is actually produces offspring more related to them than if they reproduced themselves ....Odd system but this is common to most (but not quite all) social insects with workers ..
Puteulanus fenestra mortis
Oh, that's your own fault... You should have put it in neutral. If only more people would neuter their cars, we wouldn't have the problems we have today with feral cars! Why don't people THINK!
Everyone told me not to put truck nuts on the back of the thing.
But I just wouldn't listen...
IMHO, we don't really know enough to define 'life' outside of the context of 'life on Earth' yet.
We have a basic/fundamental understanding of life on Earth that is confined and directed by what we think we know. (use 'scientific principle' as context here)
As TFS mentioned, our recent discovery and understanding of extremophiles hints that, the more we learn, the more there is to learn.
Over the decades I have lived, I find myself repeatedly and constantly amazed and bemused by recent tech advances.
But at the end of the day, we are no further along than 'There be dragons here!'.
Down With Slashdot BETA!!! I've been around the corner and seen the oliphant; you can only abuse me from your perspecti
Just be glad yours is male. Imagine driving a female car in the mating season. Kind of like living on a world carried by a female turtle must be a constant stress.
Did you lose an alveolar lateral approximant somewhere on the way?
Ubi solitudinem faciunt, pacem appellant.
Crystals rock!
English is not this
I think my tl;dr opinion is "It's easier to look for life we know can exist than life that may exist". We look for Earth-like planets because we know Earth has life. We look for Earth-like lifeforms because we know life can look like that. That doesn't mean we've excluded other planets or other lifeforms, but they are only theoretical while Earth is real. Given limited resources, why should we try finding life that may not even be possible when we know so little about whether there's life like ours?
Besides, if we should stumble onto other forms of life we're not that ill equipped to find it. If there had been lifeforms crawling around on the Martian surface we'd have seen them in pictures. I'm sure someone's put a microscope to the soil and found that it isn't full of life like you'd find in a pile of dirt here on Earth. Our assumptions mostly come into play when we're trying to find indirect signs of life, that even if there's no life here right now there has been or that they're hiding deep underground there's traces left.
Live today, because you never know what tomorrow brings
2. Reproduction. It must be capable of creating copies of itself (or approximate copies of itself.)
Male mules aren't alive, then?
Tiller's Rule: Never use a word in written form that you've only heard and never read. You will end up looking foolish.
I'm sure the NASA people will be glad to hear that there is an infinite number of possible alternatives to the main Earth model of life. That is, considering they didn't think about that already.
Now suppose you had two possibilities:
1- Most life is Earth-like, anywhere in the Universe.
2- Most life is NOT Earth-like in the Universe.
Now, we're trying to find life in a neighbor planet. Which of the above possibilities would you think make up for a more reachable goal?
http://dilbert.com/2010-12-13
I need coffee right now but I don't think I've enough evolution to buy one.
I know the truth and I know what you're thinking
If their heritable mutation affects their probability of reproduction, so that it is capable of evolving in a Darwinian fashion. There is a theory that the earliest form of life might have been crystalline.
There is every reason to believe other life in our solar system will be similar to life on earth.
I imagine that nature is similar no matter the planet. For instance, from study of life on earth we know that a bilateral body design is effective, this should be true no matter the planet and conditions. If life is found in liquid, that liquid displaced over both sides of the life form would be better suited if distributed equally. It makes little sense that the body wouldn't be bilateral.
Why should life not follow similar patterns to earth life. Granted there will be deviations, gills vs lungs, o2 breathing vs some other gas, resilience to heat or extreme cold.
I am Bennett Haselton! I am Bennett Haselton!
If your computer reproduces, and has heritable mutations that affect reproductive success, so that it is subject to Darwinian evolution, then I would consider it to be life, whatever the its form or behavior.
The answer to the question, "what makes us humans different from animals?" is of course "nothing," because we are animals. If you mean, "what makes us different from other species of animals?," the answer is different genes.
If you ask, "what about our behavior is different from other animals?" there is a long list, although some of the answers are quantitative rather than qualitative. However, I doubt that it is meaningful to talk about "taking culture away." Culture likely co-evolved with our biology and is closely linked to biology. So this is a bit like asking, "what would make humans different from other animals if we weren't humans?"
"What is life?" he said at last. "I'll tell you. Life is a great grim grayness, and it inflicts fright and pain and loneliness upon all who experience it. And you want to know how to destroy it? Well, I don't think you can. But I'll tell you the best way to fight life—with laughter. As long as we can fight it that way, it can't overcome us."
THE SOFTWARE, IT NO WORKY!!!
Life is a monosyllabic morpheme consisting of a fronting diphthong followed by a labio-dental voiceless fricative.
That's easy for you to say.
To have a right to do a thing is not at all the same as to be right in doing it
"Did you lose your keys here under the streetlight?"
"Nope, but this is where the light is."
Porquoi?
So, the rocks falling fit. Rocks that fall into areas where they are more likely to generate derbris create more derbris to fall into areas that will create more derbris...
But did we have a definition for life? That is news for me.
Rethinking email
People like you make me fear for my unborn grandchildren. I see folks with no understanding of how computers work thinking that they're "thinking machines", like idiots in the media have been calling them since ENIAC, which was less powerful than a Hallmark greeting card.
A computer is nothing more than an electric abacus. It works on exactly the same principle as an abacus. IT DOES NOT THINK, IT IS NOT ALIVE! I made a pseudoautonomous program thirty years ago on a machine with only 16k of memory and no disk drive. You'd have sworn it could think, but I assure you it's only David Copperfield trickery, not Merlin Magic.
But you people will have a "machine rights" movement anyway, if history is any indication.
However, I do tend to think that we might find life, even intelligent life, and not realise it's alive.
If we took all the culture/religion and all the technology away , what makes US humans different from animals?
We are animals. We're not different from animals, we're different from other animals. I'm sure bonobos think they're life's superiors and consider us less than bonoban, and probably dolphins as well (Douglas Adams comes to mind here).
If you would replace many of your organs with inorganic components and you weren't capable of reproduction through SEX , would you still consider yourself life?
I'm a cyborg, and although I can reproduce I wouldn't be able to if I were female, because I'd be past menopause. I do know post-menopausal female cyborgs, and yes, they're human as well as alive; their cells still reproduce. Are you trying to say that a eunuch isn't alive? That's just silly.
Many life forms don't reproduce through sex, but they do reproduce. Asexual reproduction doesn't mean an organism isn't alive.
I don't really care what the definition of life is because it surely is WRONG.
Words are defined by consensus. "Life" is whatever we say it is.
Free Martian Whores!
I can't define it, but I know it when i see it.
You may have meant to reply to someone else. The quote you included isn't from my post.
"Who is the Journal of Quantum Physics going to believe?" --Stephen Hawking
Sorry for the double post, but specifically, I think you probably meant to reply to the parent post of mine.
"Who is the Journal of Quantum Physics going to believe?" --Stephen Hawking
Fragmentation is not considered a form of reproduction. The pieces do not reproduce the "parent"--they are smaller and never grow to be like the original rock
I think we need the term self-sustaining somewhere in the definition.
Is 1563649 a prime number?
Mules come from crossing a donkey with a horse. Any time you want a mule, you have to cross a donkey and a horse.
Evolution simply means change.
No it doesn't. If evolution simply meant change then we would call it change instead of evolution.
Evolution is any change across successive generations in the heritable characteristics of biological populations.
Notice that definition does not stop after the fourth word.
The gradual development of something, esp. from a simple to a more complex form.
A piece of a rock is no more complex than the whole rock. When something goes from a complex to a simple form we typically refer to that as devolution. Which is still not what the rock is doing. What the rock is doing is referred to as "breaking". If I crash my car and the doors fall off I don't claim that my car has just evolved. It's broken now, it's less than it was, it's not a higher being.
"Our two-party system is like a bowl of shit looking at itself in a mirror." - Lewis Black
Why not just give the biological definition of life?
http://en.wikipedia.org/wiki/Definition_of_life#Biology
No where does it mention water or carbon. In regards to the moronic title over TFS, there is no need to change this.
Self proclaimed typo king, and inventor of the bear destroying coffee table (patent not pending).
I am a Biologist, and the GP missed 4 of the 7 criteria
http://en.wikipedia.org/wiki/Definition_of_life#Biology
Self proclaimed typo king, and inventor of the bear destroying coffee table (patent not pending).
Naked mole rats do this too -- mammals.
3/7, you fail.
http://en.wikipedia.org/wiki/Definition_of_life#Biology
I've see the same seven criteria listed on the wikipedia page for 20 years now, at least.
*Homeostasis - The ability to keep an internal environment different from the external environment
*Organization - use of cells in the Wikipedia page is bad, it would be better to say regions or compartments that keep their own specialized environments (organelles and even regions in/around enzymes count for this)
*Metabolism - Doesn't have to be carbon/oxygen based, just the use of chemical energy storage. I've heard this extended to use of any energy mechanism, which almost makes it a redundant criteria
*Growth - Needed, if nothing else, to repair injuries
*Adaptation - Adapts over time to changes the environment, considered long term / evolutionary change.
*Responds to stimuli - Short term changes in an organism to deal with short term environmental changes
*Reproduction - Given sufficient energy and materials, the creature must be able to reproduce on it's own volition. I've heard this extended to creatures that fit the previous definition as well as their descendants (thus, sterile descendants are still alive).
Self proclaimed typo king, and inventor of the bear destroying coffee table (patent not pending).
There really is no accepted "biological definition of life." Indeed, the wikipedia page you reference offers numerous candidates.
Note: that could be misread. I've seen the 7 criteria that are listed on the wikipedia page, listed in many other places (particularly textbooks) for at least 20 years now. Wikipedia hasn't been around that long, so I"m sure some someone would love to read that in a completely different manner...
Self proclaimed typo king, and inventor of the bear destroying coffee table (patent not pending).
There are numerous candidates, but that is the one generally accepted by biologists. The only "biologist" I've seen use anything different (and not, effectively synonymous) in 20 years or so, was here on slasdot. Quotes since I can't confirm he/she is a biologist
Self proclaimed typo king, and inventor of the bear destroying coffee table (patent not pending).
I am speaking as a biologist
Though how someone defines "life" comes down to an issue of semantics, it has very real consequences monetarily. Not to say it is good for any kind of scientific community to attempt to dupe the laymen of the country, but if people see headlines exclaiming that scientists have found life on Mars, they will be more likely to support continued funding of the space program or other areas of biological inquiry. The exact definition can be bent around to suit the political end of receiving funding. I do not necessarily advocate for the idea but think it could be at least relatively effective in practice as taxpayers and venture capitalists become more excited about what science has to offer.
I think a better way to put it is: Does it inherit traits when reproducing?
In other words, fire may have the basic characteristics of life, but can you breed a race of tiny green fires, or is fire always dependent on it's fuel for traits?
Then why not just call it change? I mean from the principle of maximum laziness (an "inside" Physics definition of Newton's laws), change is one sylabble and ev-uh-loo-shuhn is 4, just too much for a person to say....
My point is evolution has a specific interpretation, not a word used to generalize a process... Otherwise, you'll have me saying this year: "vote for hope and evolution"...
See my response to the post above yours. A parasite is not a self-sufficient living system to be evaluated under this metric.
The parasite species + its host species together is the correct definition of the parasite living system. Don't stop at the physical
single organism body boundary when trying to find the boundary of the most fundamental living system to be evaluated.
In a parallel example. You can't look at the individual ant and say "this is the most significant self-sufficient living system
around here." You have to define the colony as a whole as the most significant (most self-sufficient for the long-term) living system,
and measure the excess sustained negentropy of the ant colony. The individual ant can only maintain its form and function
(its integrity) for some relatively short time period (even shorter without its supporting colony.) The colony as a whole can maintain
its core form and function (more precisely its genomic information which is the essence of the thing) essentially in near perpetuity
(assuming we allow wiggle room in the definition of "maintaining the information" to allow for "maintenance of the same
information or closely related and derived and more adaptive information i.e. evolved information).
Where are we going and why are we in a handbasket?
No, because the crystal has sustained negentropy, but not a huge amount of EXCESS sustained negentropy
"given the thermodynamic regime and other aspects of the local physical regime (momenta, ranges of other forces)"
But on the other hand, it could be that simple crystal forms are in fact the lowest end of the self-maintaining or self-promoting, self-expanding
ordered pattern spectrum, whose more extreme end we call life.
Where are we going and why are we in a handbasket?
It should be noted that reproduction is too specific for the second criterion.
2. Maintenance of its form (or essential information) through time, longer than the physics of its environment would stochastically permit.
is the actual second requirement.
It so happens that for straightforward "essentially material" lifeforms, reproduction (or more precisely, repeatedly restarting the organism-building process
from its simplest and smallest form) is the only practical way to do my version of 2, because of the entropy tendency that acts on each physical form
with the passage of time.
However, for more "essentially informational" life forms, like, for example "The Roman Catholic Church" meme, we may not have to say that
it reproduces itself. It is enough if it is able to sustain itself (its core informational form) through replacement of some of its physical parts (adherents, books, paraphenalia), and through repeated embodiment of some of its informational form in new human adherents over time.
But since the "instance" of the church meme never disappears through all of this, it is not reproducing itself (only its tiny parts), it is maintaining itself.
Are there not sponge colonies or something that do this "maintenance rather than reproduction of whole self" as well?
Where are we going and why are we in a handbasket?
While it may be controversial whether a virus (species/strain whatever) constitutes life, it cannot be controversial
that a viable "virus-host" system is a living system, of alternate form, definition, extent, essential core information and destiny compared to just the host system or just the virus subsystem.
Where are we going and why are we in a handbasket?
It seems interesting to me that we have little difficulty in deciding whether or not a particular thing is alive;
1) People - yes
2) Rocks - no
3) Fire - no
4) Viruses - in a sense but not really
But we seem to have extraordinary difficulty in actually writing down a definition of life.
Congratulations on being late to the party; I already apologised for the abbreviated and dehydrated list. And cited the Wikipedia article. "Fail" may be a bit harsh.
Bio questions? Ask me to start a Q&A journal. Computer analogies available for most topics!
3. Evolution. Its offspring must be able to adapt to changes in the environment through to natural selection.
I'm a clone, you insensitive clod!
diphthong
Heheheh. He said "diphthong". Heheheheh.
Maybe! But there's room for your offspring to evolve. And you might not be a perfect clone!
Bio questions? Ask me to start a Q&A journal. Computer analogies available for most topics!
Nope; I'm afraid you're more inclusive than biology currently is. The livingness of the virus-host system is under debate; a virion (the particle itself) is simply an inert lump of organic molecules. For similar reasons, transposons are also considered non-living.
Bio questions? Ask me to start a Q&A journal. Computer analogies available for most topics!
Usually when we talk about reproduction as a requirement for being alive, we're talking about unicellular organisms. Multicellular organisms are thought of more as colonies—and in that sense, just like sponges, the genus Volvox, and many kinds of fungi, organisations like the Roman Catholic Church do reproduce, as ideas in the minds of their followers. The church as an entity is (at one level) an abstraction, just like the multicellular organism itself.
Bio questions? Ask me to start a Q&A journal. Computer analogies available for most topics!
Not a bad suggestion—but the point is that just because successive generations of something vary, that doesn't contribute to their life-worthiness. Elsewhere I gave an example about successive generations of photocopies: they may change, but that change is only relevant if someone actually looks at the photocopies; i.e. it must be able to change in a way that is subject to evolutionary pressure. May seem not super-important, but that detail shouldn't be left out.
Bio questions? Ask me to start a Q&A journal. Computer analogies available for most topics!
The problem is that if you define a sufficiently sophisticated AI as "not life", it might define you as being "not life". You might be nothing more than a sophisticated abacus, or something which could in principle be simulated on one. We honestly don't know.
Having said that, your last sentence is 100% absolutely correct.
sub f{($f)=@_;print"$f(q{$f});";}f(q{sub f{($f)=@_;print"$f(q{$f});";}f});
That's a pretty good way of viewing it—another trick that makes the definition easier to swallow is to consider multicellular organisms as colonies of single-celled organisms doing the same thing.
Bio questions? Ask me to start a Q&A journal. Computer analogies available for most topics!
To perform homeostasis, your car would also have to seek out gas, oil, windshield washing fluid, radiator fluid etc., avoid bad weather and bad roads on its own, and (ideally) also drive itself to the auto mechanic when necessary. You're kinda on the right track, though. :)
Bio questions? Ask me to start a Q&A journal. Computer analogies available for most topics!
That's a much better way of putting it—which I've used in a few other responses here. :) We do need to still explain away non-reproductive organisms like skin cells and worker ants. They, instead, act to further their groups' reproduction, which is, well, close enough since they're the same species.
Bio questions? Ask me to start a Q&A journal. Computer analogies available for most topics!
Ah-ah-ah—there are many species that include unnecessary (and quite elaborate) error production processes to enhance certain types of mutation (especially the favourite of us higher animals, chiasmata.) Most species are in a position where they easily could reduce their error rates, but because of the evolutionary benefits of not doing so, such mechanisms and imperfection remain. To evolutionary biologists, that's close enough to intention that we're comfortable with making that particular personification for the sake of convenience. There's no need to let the blatant mental dysfunction of creationism influence a perfectly harmless and well-understood categorical error made in good confidence between rational people.
Bio questions? Ask me to start a Q&A journal. Computer analogies available for most topics!
I think that the current definitions are too hung up on the most obvious physical boundaries of these things. The distinction between the phenotype and the extended phenotype should be minimized, if both are required for continuation through time of the particular genotype.
The most fundamental thing (and the thing that is carried forward through time) in living systems is the particular information in the genome.
- If there is some embodied information somewhere - e.g. (but not exclusively) information embodied in DNA/RNA
- and if that information in conjunction with a small kernel transcription machine (which can also be produced with the information) can cause/influence surrounding matter and energy to form patterns (forms, processes)
- and if those forms/patterns can among other things lead ultimately to the conservation (often but not necessarily by reproduction) of the information that was at the heart of all this, then:
There is a living system going on around here.
What that system's most meaningful physical (as opposed to informational) boundary should be considered to be should depend on the extent of stuff in the surroundings of the embodied information which really has to be there for the whole process of continuing the localized embodiment of that information through time. Use a functional physical boundary definition rather than the "skin" boundary of what may just be a part in a viable living system.
Yes. That's abstract, but so should the essence of life be considered to be if we want to understand how it might be elsewhere, or how it came to be here.
Where are we going and why are we in a handbasket?
So I, guilty as I am of being a multicellular organism, am an abstraction then?
Or just because my cells are kind of wedged together and thus constrain each other, shape each other communicate with each other, support each other in very direct physical way, I am am somehow fundamentally different than that embodied meme? Or than the ant colony?
The constituent units of these slightly more loosely physically connected multicellular "lifeforms" also constrain each other, shape each other, communicate with each other, and support each other, for their own sake, but also as constrained and guided by the "rules" of (or paths of least resistance created by ) the overall composite (emergent?) form or process.
If the whole is a significant player in constraining and sustaining the parts, then it has to be considered a real and perhaps an equally significant entity. We wouldn't say that human's don't have a human/mammal identity as living systems, nor should we say that of more loosely connected but still essentially connected composite living systems.
Where are we going and why are we in a handbasket?
"The maintenance of an internal environment (homeostasis) is considered the most important, and the primary reason scientists have hesitated to consider transposons and viruses to be alive."
But many species have spore or dormant phases in their lifecycle. Also, the definition of homeostasis should be flexible. You only need to maintain your internal state within the bounds that allow you to survive (to do more interesting things, like reproduce, later). If your internal state is "solid" and "simple" enough that it doesn't need, for example, temperature regulation, but it can still recover into a more lively form later, then by george you are a lifeform.
Viri are just a component of a virus-host system. The virion outsources (the more conventional kind of homeostasis) to the host component of its living system.
Where are we going and why are we in a handbasket?
I'm afraid you are indeed an abstraction. Of course, so is everything else—but don't let that make you feel bad. You and everything else are all still real. The thing is, pretty much every known biological cell—even E. coli—forms colonies when left to their own devices. Some human cells, like spermatozoa and certain leukocytes, can even survive reasonably well on their own, and it's only in the absence of the right chemical environment that most human tissues won't survive.
The idea you're describing has all but been admitted by biologists who study chemical evolution, however, in that we now believe an unprotected proto-DNA molecule (specifically, one made of RNA) was the first life form, and that it later built what we call a cell around it. Still, we biologists do love us some metabolic processes (we studied them first), so we're kinda stingy about letting go of them as a core element of the definition of our field.
Bio questions? Ask me to start a Q&A journal. Computer analogies available for most topics!
Replied to this in my other reply (#38685130). Because two conversations is possibly excessive.
Bio questions? Ask me to start a Q&A journal. Computer analogies available for most topics!
Your dog is sentient. It thinks, it feels. A sophisticated simulation by a big enough computer to model every subatomic particle in a human brain inreal time would still have no more real thought than a computer simulation of an atomic explosion produces real radiation; its radiation, too, is only a simulation.
If we were computers we' be a lot better at logic and a lot worse at playing frizbee. Even a dog can play frizbee, but no robot can.
Free Martian Whores!
"Perfect replication + deliberate error mechanisms = evolution"
You don't necessarily need deliberate error mechanisms.
As long as the error rate & type is in a usable range (for having a reasonable chance at adaptive changes among perhaps many more maladaptive/destructuve ones).
A way I would put it is that physical replication systems are likely to have an error level just due to the vagaries and complexities of physical reality (thermodynamics, entropy increase in systems etc). There is a sweet spot (or sweet range) somewhere in that error level, where evolution gets to test alternative designs/life strategies at a pace sufficient to successfully adapt to and survive and outcompete in a given environment.
There is no doubt evolutionary competition between replication mechanisms (or mechanism tweaks) just like there is between other traits.
And which error rate and reproduction rate is better no doubt depends somewhat on the niche, and on the general life strategy of the general kind organism.
Where are we going and why are we in a handbasket?
Yes. That being said, all known living organisms are more error-prone than they need to be. See this comment.
Bio questions? Ask me to start a Q&A journal. Computer analogies available for most topics!
(And also this comment, too.)
Bio questions? Ask me to start a Q&A journal. Computer analogies available for most topics!