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Should Science Rethink the Definition of "Life"?

samzenpus posted more than 2 years ago | from the some-kind-of-high-powered-mutant-never-even-considered-for-mass-production dept.

NASA 299

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."

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If it evolves by replicating, it's life. (0)

Corwn of Amber (802933) | more than 2 years ago | (#38669032)

n/t

Re:If it evolves by replicating, it's life. (0)

Haven (34895) | more than 2 years ago | (#38669108)

when rocks fall by gravity and break into pieces?

Re:If it evolves by replicating, it's life. (0)

amicusNYCL (1538833) | more than 2 years ago | (#38669216)

A rock falling and breaking is not evolution.

Re:If it evolves by replicating, it's life. (4, Interesting)

camperdave (969942) | more than 2 years ago | (#38669322)

Actually, a rock falling and breaking IS evolution. Evolution simply means change. What it is not is genetic replication.

Excess sustained negentropy (3, Interesting)

presidenteloco (659168) | more than 2 years ago | (#38669568)

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.

Re:Excess sustained negentropy (1)

presidenteloco (659168) | more than 2 years ago | (#38669598)

more precisely "given the thermodynamic regime and other aspects of the local physical regime (momenta, ranges of other forces)"

Re:If it evolves by replicating, it's life. (5, Informative)

Samantha Wright (1324923) | more than 2 years ago | (#38669246)

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.

Re:If it evolves by replicating, it's life. (1)

Surt (22457) | more than 2 years ago | (#38669484)

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.

Re:If it evolves by replicating, it's life. (1)

Samantha Wright (1324923) | more than 2 years ago | (#38669820)

Yes, I tried to express that, but the lecturer was rather loud and I ended up... well.

Re:If it evolves by replicating, it's life. (-1, Flamebait)

geekoid (135745) | more than 2 years ago | (#38669564)

It's not really a scientific definition if it's filled with exceptions.

1: Fire. It moves to where it is easiest to make new fire
2: Fire: can create copies of it's self. As a side note, I'm not sure why the copies have to be similar to be life.
3: Fire: It can evolve to to burn thing with higher combustion temperatures.

And then there is self replicating molecule. Is that life?

Please, return to you weak ass wikipedia page

Re:If it evolves by replicating, it's life. (0)

Anonymous Coward | more than 2 years ago | (#38669708)

Fire meets the first two criteria, but not the third. A piece of burning paper can set a stick alight, which will burn at a higher temperature: but if you use each of them to set fire to a gas stove, that gas stove will burn the same way in each case. There are no inherent, inheritable changes in the fire: it changes, but it does not evolve.

Re:If it evolves by replicating, it's life. (2, Insightful)

Anonymous Coward | more than 2 years ago | (#38669826)

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.

Re:If it evolves by replicating, it's life. (5, Interesting)

Samantha Wright (1324923) | more than 2 years ago | (#38669914)

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 [wikipedia.org] , 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 [wikipedia.org] , 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.

Re:If it evolves by replicating, it's life. (1)

Oligonicella (659917) | more than 2 years ago | (#38669920)

All you've accomplished is to anthropomorphized fire.

Fire actually does none of those things. Those things can happen to a fire. Big difference.

Re:If it evolves by replicating, it's life. (3, Insightful)

similar_name (1164087) | more than 2 years ago | (#38669690)

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?

Re:If it evolves by replicating, it's life. (5, Interesting)

Samantha Wright (1324923) | more than 2 years ago | (#38669812)

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 [wikipedia.org] 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.

Re:If it evolves by replicating, it's life. (1)

similar_name (1164087) | more than 2 years ago | (#38669950)

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.

I'm not trying to be argumentative I just find that discussions on /. with informed people can lead me to a better understanding of things.

life, from a CS view (1)

bzipitidoo (647217) | more than 2 years ago | (#38669850)

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.

Re:life, from a CS view (1)

Samantha Wright (1324923) | more than 2 years ago | (#38670004)

While that definition certainly encompasses all of what biologists consider to be life (and I've pondered it, too,) it misses several properties of living organisms that we find interesting to study. Life is different from a computer in that it is also partially defined by what functions it computes, not merely that it can compute anything; these functions are those that lead to an increase in its tendency to proliferate and persist in its environment for a longer period of time. For a biologist to consider a glider gun alive... well, I'm a little too tired to ponder that now, but ask me again later and we can see what comes out of it. :)

Re:If it evolves by replicating, it's life. (5, Funny)

R3d M3rcury (871886) | more than 2 years ago | (#38669212)

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.

Re:If it evolves by replicating, it's life. (0)

Anonymous Coward | more than 2 years ago | (#38669258)

Define "replicating". Cuz if it's EXACTLY the same, how can it evolve?

Re:If it evolves by replicating, it's life. (4, Insightful)

Samantha Wright (1324923) | more than 2 years ago | (#38669334)

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.

Re:If it evolves by replicating, it's life. (1)

geekoid (135745) | more than 2 years ago | (#38669590)

That is a really bad definition of evolution.

Re:If it evolves by replicating, it's life. (1)

Samantha Wright (1324923) | more than 2 years ago | (#38669720)

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)

Re:If it evolves by replicating, it's life. (1)

Avarist (2453728) | more than 2 years ago | (#38669342)

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.

Re:If it evolves by replicating, it's life. (2)

Surt (22457) | more than 2 years ago | (#38669500)

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).

Re:If it evolves by replicating, it's life. (1)

Avarist (2453728) | more than 2 years ago | (#38669930)

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.

Re:If it evolves by replicating, it's life. (0)

Anonymous Coward | more than 2 years ago | (#38669518)

Then are fleas and mosquitoes alive? They certainly cannot reproduce without their blood diets... What about other parasitic organisms?

Re:If it evolves by replicating, it's life. (2)

geekoid (135745) | more than 2 years ago | (#38669528)

Fire.
Software.

What about clearly living things that can not replicate? such as a mule.

for the record:
Corwin was a whiny bitch.

It's life, Jim, but not as we know it... (1)

sconeu (64226) | more than 2 years ago | (#38669038)

not as we know it, Captain!

Re:It's life, Jim, but not as we know it... (0)

Anonymous Coward | more than 2 years ago | (#38669122)

http://www.youtube.com/watch?v=OrYbkbWRA2I

@ 45s

Re:It's life, Jim, but not as we know it... (1)

dkleinsc (563838) | more than 2 years ago | (#38669156)

"We come in peace! (shoot to kill, shoot to kill)" - James T Kirk

(reference for those not in the know: Star Trekkin' [youtube.com] by The Firm)

Don't you know what aliens look like? (2)

Toe, The (545098) | more than 2 years ago | (#38669046)

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.

Re:Don't you know what aliens look like? (3, Funny)

Arancaytar (966377) | more than 2 years ago | (#38669080)

All flora looks just like what you find in California.

Some planets resemble forests in British Columbia, or quarries in Wales. :P

Re:Don't you know what aliens look like? (2)

amicusNYCL (1538833) | more than 2 years ago | (#38669230)

There may even be planets that resemble the Tunisian desert, or Norwegian glaciers.

http://www.youtube.com/watch?v=WfwNZO2OqMQ (2)

xigxag (167441) | more than 2 years ago | (#38669336)

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.

Re:http://www.youtube.com/watch?v=WfwNZO2OqMQ (0)

Anonymous Coward | more than 2 years ago | (#38669358)

Neither of your theories account for the Predators, therefore they are useless.

Re:http://www.youtube.com/watch?v=WfwNZO2OqMQ (1)

Surt (22457) | more than 2 years ago | (#38669512)

Predators only showed up in a couple of fringe Trek episodes, they can hardly be considered sci-fi canon.

Is it a cereal, or is it a mathematical game? (1)

davidwr (791652) | more than 2 years ago | (#38669058)

I guess that depends on whether you ask Mr. Conway or Ms. Nooyi.

Dumb article (5, Informative)

Anonymous Coward | more than 2 years ago | (#38669076)

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.

Re:Dumb article (5, Informative)

Black Parrot (19622) | more than 2 years ago | (#38669090)

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.

Mod up. Biologists have indeed told me that life is defined by a collection of properties such as metabolism and reproduction. Maybe NASA needs to change its definition, but not "Science".

Re:Dumb article (1)

Anonymous Coward | more than 2 years ago | (#38669132)

From wikipedia:

Metabolism (from Greek: "metabol", "change" or Greek: metabolismos, "outthrow") is the set of chemical reactions that happen in the cells of living organisms to sustain life. These processes allow organisms to grow and reproduce, maintain their structures, and respond to their environments.

So basically, your comment is saying that for life to happen, there needs to be a set of chemical reactions that makes life happen? Mod parent up +6 insightful.

Re:Dumb article (1, Interesting)

MozeeToby (1163751) | more than 2 years ago | (#38669130)

Life is defined as something that feeds and reproduces.

So... fire is alive by your definition and a bumble bee drone isn't.

Re:Dumb article (1)

jc42 (318812) | more than 2 years ago | (#38669178)

So... fire is alive by your definition and a bumble bee drone isn't.

Huh? A (bumble)bee drone reproduces. Essentially, that's the only thing it does, and then it dies. But its descendants live on, starting from the fertilized eggs inside the drone's mate(s).

Fire does sorta throw water on the definition, though. It definitely "feeds", and reproduces in the sense of expanding. So do crystal formations, which aren't considered alive.

Methinks this definition needs a bit of revision. Maybe some actual biologists could chime in with something with better wording.

Re:Dumb article (0)

Anonymous Coward | more than 2 years ago | (#38669224)

Life includes inherited genetic material.

Re:Dumb article (3, Informative)

amicusNYCL (1538833) | more than 2 years ago | (#38669320)

Fire does sorta throw water on the definition, though. It definitely "feeds", and reproduces in the sense of expanding. So do crystal formations, which aren't considered alive.

I'm not a biologist.

I think you can distinguish fire vs. life by metabolism. With metabolism, chemical processes inside the organism occur to fuel the organism. With fire, those processes do not happen within the flame, they happen inside the fuel. I can't think of an organism which fuels itself by chemically transforming fuel outside of its "body". This may be shaky, because you could argue that the chemical processes would not happen were it not for the presence of the flame. Fire doesn't sound like it fits the definition of metabolism though, unless you view the flame as simply the result of the metabolism and the organism itself which produces the fire through metabolizing the fuel is unknown.

With crystals growing in a liquid, matter which is dissolved in the surrounding liquid gets added to the crystal. There is no real chemical change that takes place, the dissolved particulates just coalesce on something else. When the liquid and its particulates is removed the crystal no longer grows, but the crystal itself does not take the particulates out of the liquid. The particulates simply adhere to the crystal (or any other structure on which the crystal starts).

Re:Dumb article (1)

geekoid (135745) | more than 2 years ago | (#38669478)

Combustion.

Re:Dumb article (1)

MachDelta (704883) | more than 2 years ago | (#38669520)

External digestion does exist; fungii are a good example of this (heterotrophy II).

Re:Dumb article (0)

Anonymous Coward | more than 2 years ago | (#38669588)

Show fire to an animal that hasn't seen it before. (Do you remember the first time your puppy saw fire?) The animal will often react to fire as if it's alive.

Re:Dumb article (0)

Anonymous Coward | more than 2 years ago | (#38669236)

... a bumble bee drone isn't.

FYI Drones are the males, which exist solely to allow the colony to reproduce. I think you meant workers. Even then, a worker bee can in some cases lay eggs, though as I understand it such eggs only hold drones.

Re:Dumb article (1)

mark-t (151149) | more than 2 years ago | (#38669184)

Can something be considered alive that does not reproduce? What about mules?

Re:Dumb article (1)

amicusNYCL (1538833) | more than 2 years ago | (#38669324)

A mule is alive because it was created though reproduction. Sterility does not mean that something is not alive.

Re:Dumb article (1)

xigxag (167441) | more than 2 years ago | (#38669378)

Something which is comprised of living things is by class inheritance alive. Hence mules via their cells. And corporations via their "citizens united."

Re:Dumb article (0)

Anonymous Coward | more than 2 years ago | (#38669210)

Life is defined as something that feeds and reproduces.

Regular slashdot readers only score one out of two.

Re:Dumb article (0)

Anonymous Coward | more than 2 years ago | (#38669244)

I didn't know we had so many anorexics on Slashdot.

Re:Dumb article (0)

Anonymous Coward | more than 2 years ago | (#38669326)

From what I hear, they don't score at all.

Perhaps it's not a discrete concept (1)

Tablizer (95088) | more than 2 years ago | (#38669862)

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.

Re:Perhaps it's not a discrete concept (1)

timeOday (582209) | more than 2 years ago | (#38669940)

Yup, these discussions are dumb, like debating whether Pluto is a "planet" or not. Life is an ascribed property, so of course it has no crisp boundaries in nature. Some things clearly are, others clearly not, and a few things are very debatable. Find new phenomena on earth or other planets first, then we can judge how interesting they are and whether they alter our notion of "life."

self-reproduction with variations (4, Interesting)

JoeMerchant (803320) | more than 2 years ago | (#38669078)

FTA: Simply, Life is "self-reproduction with variations" - like mutating computer viruses?

Re:self-reproduction with variations (0)

Anonymous Coward | more than 2 years ago | (#38669580)

FTA: Simply, Life is "self-reproduction with variations" - like mutating computer viruses?

Yes - and science (including science done at NASA) has done a good job of defining this already;

Christoph Adami: Finding life we can't imagine (Oct'11) [ted.com]
How do we search for alien life if it's nothing like the life that we know? At TEDxUIUC Christoph Adami shows how he uses his research into artificial life -- self-replicating computer programs -- to find a signature, a 'biomarker,' that is free of our preconceptions of what life is.

From the transcript:

One day a NASA manager comes into my office, sits down and says, "Can you please tell us, how do we look for life outside Earth?" And that came as a surprise to me, because I was actually hired to work on quantum computation. Yet, I had a very good answer. I said, "I have no idea." And he told me, "Biosignatures, we need to look for a biosignature."

[...]

So I'm highlighting just a few words and saying definitions like that rely on things that are not based on amino acids or leaves or anything that we are used to, but in fact on processes only. And if you take a look at that, this was actually in a book that I wrote that deals with artificial life. And that explains why that NASA manager was actually in my office to begin with. Because the idea was that, with concepts like that, maybe we can actually manufacture a form of life.

[...]

So the first thing that we learn is that it is possible to define life in terms of processes alone, without referring at all to the type of things that we hold dear, as far as the type of life on Earth is. And that in a sense removes us again, like all of our scientific discoveries, or many of them -- it's this continuous dethroning of man -- of how we think we're special because we're alive. Well we can make life. We can make life in the computer. Granted, it's limited, but we have learned what it takes in order to actually construct it. And once we have that, then it is not such a difficult task anymore to say, if we understand the fundamental processes that do not refer to any particular substrate, then we can go out and try other worlds, figure out what kind of chemical alphabets might there be, figure enough about the normal chemistry, the geochemistry of the planet, so that we know what this distribution would look like in the absence of life, and then look for large deviations from this -- this thing sticking out, which says, "This chemical really shouldn't be there." Now we don't know that there's life then, but we could say, "Well at least I'm going to have to take a look very precisely at this chemical and see where it comes from." And that might be our chance of actually discovering life when we cannot visibly see it.

Speaker: Christoph Adami [ted.com]
Christoph Adami researches the nature of living systems, using 'artificial life' -- small, self-replicating computer programs. His main research focus is Darwinian evolution, which he studies at different levels of organization (from simple molecules to brains). He has pioneered theapplication of methods from information theory to the study of evolution, and designed the "Avida" system that launched the use of digital life as a tool for investigating basic questions in evolutionary biology. He is Professor of Applied Life Sciences at the Keck Graduate Institute in Claremont, CA, and a Visiting Professor at the BEACON Center for the Study of Evolution in Action at Michigan State University. He obtained his PhD in theoretical physics from the State University of New York at Stony Brook.

Note that his TED video includes his life definition also - his work is an excellent piece of science.

Sure... (4, Insightful)

hipp5 (1635263) | more than 2 years ago | (#38669100)

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.

Re:Sure... (5, Insightful)

Canjo (1956258) | more than 2 years ago | (#38669304)

Exactly this--there might well be other forms of life, but we only really know how to look for life like our own. You may say that it's dumb for NASA to look for carbon-based life, or for SETI to look for life that uses radio wavelengths like us, but if you do so you're misunderstanding their logic. If there is enough life out there, some subset of it will be carbon based, some subset will use radio communication, and some subset will be interested in communication. That subset is the ONLY subset that we have the tools to look for. There may be non-carbon-based life, sure, but since we've never seen it we don't know exactly what its properties are or how to detect it. We may be able to theorize, but those are only theories; whereas we KNOW how life works here. It's not that researchers have a narrow definition of life, it's that we have limited resources and can only hope to detect the subset of life that is like life here on Earth.

Re:Sure... (1)

geekoid (135745) | more than 2 years ago | (#38669442)

Fact: We know carbon based life forms exist
Fact: we know they need water.

So it makes sense to start looking where you know for a fact life COULD exist withing know parameters.

Re:Sure... (1)

jamvger (2526832) | more than 2 years ago | (#38669900)

And also, water is way more abundant than any of the alternative solvents. It's also way better - chemically stable, high heat capacity, more stuff dissolves in water than in anything else, the heat of vaporization keeps things cool if needed, ice floats, etc. Water has already been seen on Mars, it would be silly to look for alternative mechanisms. Not to say that liquid methane wouldn't work, i.e. on Titan, which in fact should be investigated some day. Why a solvent? Life requires complex chemistry, which requires removal of by-products, which requires a liquid. Water is the best such liquid.

energetics, of course (1)

ronpaulisanidiot (2529418) | more than 2 years ago | (#38669134)

life obeys the laws of thermodynamics, no matter where it occurs. hence it needs an energy source in order to sustain itself; regardless of whether it is oxygen, sulfur, vespene, or unobtanium. find the consumption of energy and you will likely find life.

Re:energetics, of course (1)

viperidaenz (2515578) | more than 2 years ago | (#38669202)

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.

Re:energetics, of course (1)

WillHirsch (2511496) | more than 2 years ago | (#38669298)

In fairness, one definition of "consumption" of energy follows from the second law.

You can't look for everything (1)

nedlohs (1335013) | more than 2 years ago | (#38669148)

so you pick things that at least you can work out how to look for and that you know can exist.

Distinction between life form and machine? (1)

Nanosphere (1867972) | more than 2 years ago | (#38669154)

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?

Re:Distinction between life form and machine? (1)

Jamu (852752) | more than 2 years ago | (#38669222)

Nothing. Life forms are machines.

Of course we should. (1)

unity100 (970058) | more than 2 years ago | (#38669162)

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.

Re:Of course we should. (0)

Anonymous Coward | more than 2 years ago | (#38669408)

Of course, we start getting into a problem of permutations in our explorations is we can be overly broad in what we look for. So missions to specific planets must be somewhat targeted to what we understand of that planet. We don't exactly have the technology to create the one-size-fits-all plot device probes of Star Trek.

Curiosity is targeted based on what we understand of the planet up to this point. Which isn't a huge amount since we've only had a few decades of study by a handful of people, using very limited payloads. However, we know that the planet likely has a good supply of carbon compounds, that water exists, and that the water very likely flowed in the geological past of the planet. That means a planet that was at one point warm enough for liquid water, which tells us a lot about the likely other states of various other compounds that would make them more unsuitable for the life systems than water. So with the abundance of simple carbon compounds and the evidence of liquid water, what else would we look for that can fit on the rover? What do we give up? Do we buy another mission to run in parallel or wait for the results of the first one before we try a different tack? Really the key thing we haven't seen is complex organic compounds, although we have only been able to scratch the surface, quite literally. A surface blasted by radiation other fun stuff that tends to disintegrate what we are looking for.

However, I don't think NASA would be silly enough to send something like Curiosity to Titan. Instead, they would send something to investigate the methane and see if there is a way to detect if there are processes using the methane. Either via chemical combustion or some other process.

I agree that looking for Earth-like life everywhere is narrow minded. However, I don't think we have much choice but have targeted searches like this at this point, especially when we are at least following the evidence available to target the missions.

Re:Of course we should. (0)

Anonymous Coward | more than 2 years ago | (#38669416)

You should credit whoever you plagiarized those first two paragraphs from.

Thermodynamic definition of life (5, Interesting)

idbedead (2196008) | more than 2 years ago | (#38669164)

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.

Re:Thermodynamic definition of life (1)

hazem (472289) | more than 2 years ago | (#38669362)

> but life could generally be defined as the ability to actively resist entropy

Indeed, that's what I thought of too - I think it was in Heinlein's Stranger in a Strange Land that he used a phrase something like "phenomena of localized negative entropy".

Re:Thermodynamic definition of life (1)

hazem (472289) | more than 2 years ago | (#38669422)

Here it is:
Three of them were big enough, as planets go, to be noticeable; the rest were mere pebbles, concealed in the fiery skirts of the primary or lost in the black outer reaches of space. All of them, as is always the case, were infected with that oddity of distorted entropy called life~, in the cases of the third and fourth planets their surface temperatures cycled around the freezing point of hydrogen monoxide-in consequence they had developed life forms similar enough to permit a degree of social contact.

He also referred to Mike (the computer in The Moon is a Harsh Mistress" as a "pocket of negative entropy".

Throw in something about metabolism and you probably have a pretty good set of parameters for identifying life. Including "negative entropy" eliminates fire from being a life form, since while it does reproduce and energy is metabolized, it is also increasing the entropy around itself.

Re:Thermodynamic definition of life (1)

geekoid (135745) | more than 2 years ago | (#38669428)

You mean like fire?

We should rethink the false dichotomy first. (3, Insightful)

Anonymous Coward | more than 2 years ago | (#38669174)

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.

Re:We should rethink the false dichotomy first. (3, Insightful)

mark-t (151149) | more than 2 years ago | (#38669226)

The dichotomy isn't false. Death is simply defined that way. If it's not alive, it's dead. If it's not dead, it's alive.

You may as well say that it's a false dichotomy to only have 0 and 1 as valid significant figures in binary.

Conjecture (2)

bigg_nate (769185) | more than 2 years ago | (#38669190)

For any reasonably concise definition of life, it's possible to come up with a hypothetical example that clearly shows the definition is wrong.

It's Mars though. (2, Interesting)

Anonymous Coward | more than 2 years ago | (#38669208)

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.

That's not how science works (2)

Hentes (2461350) | more than 2 years ago | (#38669248)

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.

MSL won't enter Mars orbit (0)

Anonymous Coward | more than 2 years ago | (#38669292)

I'm pretty sure MSL would not brake to orbit but do a direct landing from interplanetary trajectory like all recent Mars landers (Pathfinder,MERs,MPL; the old Vikings probes entered orbit first, though).

Definitely Yes. (0)

forkfail (228161) | more than 2 years ago | (#38669302)

After all, we've made corporations citizens. So, life no longer even really needs to have physical existence. At least, under our rather convoluted legal system.....

Re:Definitely Yes. (0)

Anonymous Coward | more than 2 years ago | (#38669420)

Who says that citizens need to be alive. (see chicago voting records for more info.)

What a load of... (0)

Anonymous Coward | more than 2 years ago | (#38669338)

bull, "Equipped with a 'sky crane,' the lander will gently lower the one-ton Curiosity rover on the surface of Mars."

That thing is going to splat on the ground like a watermelon at a Gallagher show.

If it isn't very much like us.. (4, Interesting)

landofcleve (1959610) | more than 2 years ago | (#38669354)

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.

Re:If it isn't very much like us.. (2)

geekoid (135745) | more than 2 years ago | (#38669418)

Just because it's not like us, doesn't mean it's technology wont be the same. We might end up using oscillating radio waves to communicate.

News flash (3, Interesting)

geekoid (135745) | more than 2 years ago | (#38669414)

You have to be able to define life before you can redefine it. Turns out to be pretty tricky.

"Howler" alert (5, Interesting)

jc42 (318812) | more than 2 years ago | (#38669440)

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.

We have two choices. (2)

pclminion (145572) | more than 2 years ago | (#38669492)

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?

Why "rethink"? (5, Interesting)

jd (1658) | more than 2 years ago | (#38669496)

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.

The best definition I've found ... (1)

dankasak (2393356) | more than 2 years ago | (#38669508)

By far the most insightful discussion I've seen on this topic is this book: http://books.google.com.au/books/about/Autopoiesis_and_cognition.html?id=nVmcN9Ja68kC&redir_esc=y [google.com.au] Basically, it argues that life can be identified by it's circular organisation. It dismisses listing properties of living things. It also dismisses the idea that life must replicate or even evolve. Life is simply a particular kind of organisation. If it evolves and replicates, great. If it consumes something and expells something, great. But it's important not to list these as requirements of life, or we risk staring life in the face and not recognising it.

Silly humans... (1)

benjamindees (441808) | more than 2 years ago | (#38669596)

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!

If at first you don't succeed... (1)

mschaffer (97223) | more than 2 years ago | (#38669608)

expand the definition and hope you get lucky.

Obviously not a scientist. (2)

WrongMonkey (1027334) | more than 2 years ago | (#38669616)

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.

Life Simplified. (0)

andydread (758754) | more than 2 years ago | (#38669618)

My definition of life
Anything that can replicate whether through copulation or cell division is life. everything else in the universe need not apply.

Let me get this straight... (0)

Anonymous Coward | more than 2 years ago | (#38669626)

They are looking for signs of life in a hole in the ground created by the obliteration of anything that sat there before the meteor struck?

Life? (1)

Anonymous Coward | more than 2 years ago | (#38669824)

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 is perfectly good reason (1)

Osgeld (1900440) | more than 2 years ago | (#38669958)

how many lifeforms have you seen not on earth?

changing the question to fit your answer is not science, its religion

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