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NASA Science

Should Science Rethink the Definition of "Life"? 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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Should Science Rethink the Definition of "Life"?

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  • Sure... (Score:5, Insightful)

    by hipp5 ( 1635263 ) on Wednesday January 11, 2012 @07:55PM (#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.
  • by Anonymous Coward on Wednesday January 11, 2012 @08:04PM (#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.

  • 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.

  • Re:Sure... (Score:5, Insightful)

    by Canjo ( 1956258 ) on Wednesday January 11, 2012 @08:23PM (#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.
  • by Samantha Wright ( 1324923 ) on Wednesday January 11, 2012 @08:29PM (#38669334) Homepage Journal
    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.
  • by similar_name ( 1164087 ) on Wednesday January 11, 2012 @09:25PM (#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?

  • by Anonymous Coward on Wednesday January 11, 2012 @09:43PM (#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.

  • by Maljin Jolt ( 746064 ) * on Thursday January 12, 2012 @03:39AM (#38671438) Journal

    According to your definition of life, all my hard disks are alive!

    What you have missed: 1. perception of proximity, sensing 2. behavioral intent

  • Re:Dumb article (Score:5, Insightful)

    by Maritz ( 1829006 ) on Thursday January 12, 2012 @04:47AM (#38671648)
    A mule strikes me as a cheap argument. They may be unable to reproduce, but their ancestors stretching back 4 billion + years were able to. By that argument you could castrate a man and say 'look, your definition of life is invalid'.

Lend money to a bad debtor and he will hate you.