Do I Not Live?

By Sean Carroll | January 13, 2012 7:38 am

Can we define “life” in just three words? Carl Zimmer of Loom fame has written a piece for Txchnologist in which he reports on an interesting attempt: biologist Edward Trifonov looked at other people’s definitions, rather than thinking about life itself. Sifting through over a hundred suggested definitions, Trifonov looked for what they had in common, and boiled life down to “self-reproduction with variations.” Just three words, although one of them is compound so I would argue that morally it’s really four.

We’ve discussed this question before, and the idea of reproduction looms large in many people’s definitions of life. But I don’t think it really belongs. If you built an organism from scratch, that was as complicated and organic and lifelike as any living thing currently walking this Earth, except that it had no reproductive capacity, it would be silly to exclude it from “life” just because it was non-reproducing. Even worse, I realized that I myself wouldn’t even qualify as alive under Trifonov’s definition, since I don’t have kids and don’t plan on having any. (And no, those lawsuits were frivolous and the court records were sealed.)

It’s the yellow-taxi problem: in a city where all cars are blue except for taxis, which are yellow, it’s tempting to define “taxi” as “a yellow car.” But that doesn’t get anywhere near the essence of taxi-ness. Likewise, living species generally reproduce themselves; but that’s not really what makes them alive. Not that I have the one true definition (and maybe there shouldn’t be one). But any such definition better capture the idea of an ongoing complex material process far from equilibrium, or it’s barking up the wrong Tree.

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  • http://www.johndanley.com John Danley

    Self-sustaining metabolic process is suitable enough for me.

  • Physicalist

    Only three words? That’s tough.

    Maybe, “Pushing against entropy”?

    Longer: “Life is a property of a system whereby it increases the entropy of its environment so as to lower the entropy within the system itself.”

    Best visualized as a system in an entropy flow propelling itself upstream by pushing entropy even faster downstream.

  • http://twitter.com/NeilWithers Neil

    No way! You can’t take the reproduction out of life! You have the capability to reproduce, you’re just choosing not to do so.

    When it boils down to it, every single living thing is just a little twisty self-replicating molecule with a lot of complex machinery around it. Yours is so complex that you’re able to choose not to let those twisty molecules replicate.

  • http://twitter.com/matt_pitkin Matt

    I assume (having not read the post!) that by self-reproduction they may not necessarily just mean that a complex living thing has to reproduce another entire similar organism, but does at least have to have a capacity for maintenance and self-repair by reproducing some component parts (it would be these component parts that might also have the maximum variation). I would consider you alive without you having to have a child as parts of you are reproducing all the time, both on the level of cells and proteins within cells.

  • Mike

    You might not have plans for reproduction, but your cells are reproducing themselves continuously.

    When they stop reproducing, your continued existence will be exceedingly brief.

    It is fine to imagine a complex system, constructed by an engineer, that could achieve some semblance of metabolism. But all such systems that have been observed (that is living systems) are imperfect and destined to fail.

    It is only through the capacity for self-replication, that overcomes the failure rate, and the process of natural selection that results in more favorable self-replication/failure ratios that we have any examples to study. And that we are here to study them.

    Biochemists for decades have studied cell extracts that carry out “ongoing complex material process far from equilibrium”. Typically not considered to be alive.

    Mammalian red blood cells, that lack a nucleus and the capacity for reproduction are limited in their life spans to a few weeks. It could be argued, that like your fingernails, and outer layer of skin that these are the vestiges of life, functionally important for the organism as a whole, but no longer alive.

  • Bocko

    Before this post, I would have gone with ‘adaptive reproduction’. Sounds moronic, since reproduction itself is not ‘adaptive’, but hey, we only have 3 words.

    One of my teachers, a very theatrical guy, once stated that total thermodynamical equilibrium is DEATH ITSELF, we could reverse this idea as you suggest and try something like ‘a system that resists equilibrium in thermodynamical quantities’, but we must be careful not to include refrigerators. Maybe systems that resist equilibrium with the ability to collect the energy needed by themselves. Too long, but my poor imagination says life cannot exsist deprived of the concept of ‘species’, or at least adaptation. Meh :)

  • Tim

    But you ARE self-reproducing! Some of the cells in your body are dividing right now; even the ones not actively dividing are producing new proteins and nucleic acids, and repairing cellular damage. These processes will stop only when your body is no longer “alive”, by conventional definitions.

    …okay, looks like Matt said it first. So I’ll second.

  • Doug

    If you want to get it in fewer words, you can just go with “von Neumann machine.”

  • http://blogs.discovermagazine.com/cosmicvariance/sean/ Sean Carroll

    Where I come from, “self-repairing” seems pretty obviously distinct from “self-reproducing.” I’d be much more willing to grant the former quality as characterizing “life.”

  • Mike

    Self-repair is miniscule compared to replication (on the cellular level) in living systems.

    DNA replication fidelity may be enhanced several orders of magnitude by repair processes.

    But other “repair” processes (proteins, RNA, membrane components) are really replacement functions and generally indistinguishable from growth that is necessary for replication.

  • http://blogs.discovermagazine.com/cosmicvariance/sean/ Sean Carroll

    I am not trying to be intentionally obscure here. My cells reproducing themselves is different from me reproducing myself. The question is whether I am alive, not my cells.

  • Guest

    A short discussion of What is the meaning of life? By James Lovelock.
    He seems to put a lot more emphasis on metabolism than reproduction.

    http://www.webofstories.com/play/51904?o=MS

  • Jason Dick

    Three words? Not sure I can do that. But the one I like is: “Member of a population whose change through time can be described by evolution through natural selection of random variation of heritable characteristics.”

  • Lonely Flower

    Viruses replicate themselves and are considered by some scientists as non living organisms (I am not a biologist, so if I am wrong please correct me). My point is that self reproduction may not be the only right criteria to define life.

  • Pingback: Defining Life in Three Words « Physicalism()

  • http://none Michael Gorton MD

    Self Organising Matter seems the best 3 word definition I’ve ever heard. Consider the Prion that only reproduces a protein configuation but if it gets into the brain, it corrupts the system as in Mad Cow Disease. The meaning of reproduction varies though all are a part of the self organising concept.

  • JustJim

    My attempt is ‘Reproducing sentient being’.

  • Ben Murray

    Go look at the discussion by David Hillis, and the associated comments, in Sean’s link above (“shouldn’t be one”). For me this is the best discussion I’ve seen of this issue. Briefly, Hillis argues for an ostensive definition of Life, the taxon “(by pointing to it, noting when and where it began, and following its lineages from there)” rather than by arguing about definitions (for which we can always find exceptions). It’s a version of “it is what it is.”

  • Mike

    Since what you set out to explore was a minimal definition of life, it makes sense to consider the proper unit for that definition.

    Cells are the units of life as we know it. There are many control mechanisms established over the eons to coordinate their behavior in complex organisms. But individual cells are the units of life. You are alive because your cells are alive, if they die you die.

    Whether cells in the cutting from a plant, before or after grafting or a cells from a human tumor that can be maintained as an immortal cell line, the life in the thing is not defined in terms of the whole but in minimal units.

    When you consider human reproduction, is it you that reproduces or one particular sperm that finds a receptive ovum, to resurrect a program that was paused in a terminally differentiated state.

    Cells aren’t the units of consciousness certainly, so if that is what you think of as “me” then we are off into philosophy or something else — not biology.

  • Vic

    Independence and temporary self-sustenance?

  • Tintin

    An example on the macro level: all male mules are infertile, but nobody would deny that they are nevertheless alive.

    Which leads to Sean’s question (#11), which by the way as been asked for millennia: “what makes up the “I”?

  • Dan

    I think the requirement that reproduction be included is debatable, at least at the organism level. Mules are certainly alive.

    I think “sustained local lowering of entropy” is closer to the nub. That said, it does seem that some level of reproduction is required for that… even if it is sub-cellular in some cases (thinking of “zombie” or “lazarus” bacteria.) Which actually brings up such basic organisms that can hibernate or enter some kind of spore state.

    So, that leads to something like “local baseline entropy preserving structure via entropy export.” Certainly death, on whatever level you choose, is when the biochemical machinery is no longer able to maintain it’s particular disequilibrium; that holds for large, multicellular organisms (even if cell death does not occur uniformly across the organism) or small.

  • FmsRse12

    even if you don’t want to reproduce you are still a product of reproduction….so it would be “capability of self-reproduction with variations” instead….what’s the difference??…

  • Casey

    Second “local entropic reversal”.

  • Jim Johnson

    I think it’s pretty obvious that “Natural Life” is self-reproducing, and the fact that nature produces aberrant individuals which fail to or are unable to reproduce themselves doesn’t change that – these very individuals are themselves the end product of an unbroken line of reproducers that goes all the way back to the very first organism.

    Or, to put it another way, mules are still self-reproducers, though they are failed ones. (BTW, per Wikipedia, “Since 1527 there have been more than 60 documented cases of foals born to female mules around the world”).

    Artificial life might not have to be self-reproducing, but then we’re not avidly searching the universe for artificial life, and if we do run across it, we’ll have uncovered something a lot more interesting anyway – artifice requires an artificer.

  • lovecraft

    Life is self awareness. There you go, just two words.

  • Magoonski

    Life: The process by which the inanimate becomes animate.

    In otherwords, inanimate things such as rocks, water, etc. going through a process that turns them into something that can move independently.

  • AI

    Add “a product of” in front and it will take care of such aberrant cases as yourself at the cost of another word.

    But there are other problems I see with that definition, for example there are self reproducing patterns which do not constitute life – waves, crystals, fire, chain reactions or even memes are some examples I can think of.

  • mazeRunner

    I think defining life boils down to choosing an arbitrary cut-off point in a continuum of complexity of “objects” that exist. All objects in the universe ultimately follow physical laws and many are complex aggregates of more atomic objects and violate the second law locally. The definition of life, as Sean rightly says, is about how useful it is for us sapient machines and not a basic property of objects in the universe. Some would say reproduction is an essential property, others would say awareness and some others self-maintenance, still others combimations of these. I guess you can mix and match depending on what your own criteria and goals are; there doesn’t have to be a consensus at all levels, since far as I can see such consensus is not useful in any practical way except as an exercise in taxonomy.

    And I think the whole idea of trying to capture what life is unambiguously in essentialist terms smells faintly of baggage from the old days of vitalism, which sought out a distinguishing “life-force” to neatly categorize life from non-life.

  • mazeRunner

    I think defining life boils down to choosing a more or less arbitrary cut-off point within a certain range in a continuum of complexity of “objects” that exist. All objects in the universe ultimately follow physical laws and many are complex aggregates of more atomic objects and violate the second law locally. The definition of life, as Sean rightly says, is about how useful it is for us sapient machines and not a basic property of objects in the universe. Some would say reproduction is an essential property, others would say awareness and some others self-maintenance, still others combinations of these. I guess you can mix and match depending on what your own criteria and goals are; there doesn’t have to be a consensus at all levels, since far as I can see such consensus is not useful in any practical way except as an exercise in taxonomy.

    And I think the whole idea of trying to capture what “life” is unambiguously in essentialist terms smells faintly of baggage from the old days of vitalism, which sought out a distinguishing “life-force” to create neat categories of living and non-living.

  • mazeRunner

    Oops sorry for the annoying double post. My bad.

  • sandia

    If any of you, including the original author were living, you wouldn’t be asking this question. Do I not live? Rather than defining ‘life’ try to define the notion of “I”. Not only is the assumption that life depends on the body horrendously wrong, it is also a fallacy.

    Anyone who is truly ‘living’ knows exactly what life is and the question wouldn’t arise in the first place :).,

  • T.

    The child is yours ! I will win the lawsuit and prove you alive at the same time.

  • http://www.learninglayer.com Steve Flinn

    Generalizing Shannon, biological life as a process (vs. being alive) can be defined as a communications coding process that maximizes the probability of continuity of information propagation through the time-based, unbounded channel over time.

    See:
    http://www.steveflinn.com/Evolution_as%20Communication_MW-AS103%2003-29-06.pdf

  • Tom S

    While you may not think reproduction germaine to defining if YOU or I are alive by any definition, the truth is that every one of us in only alive BECAUSE our species can reproduce.
    Also, the question was to define “life”. I would argue that is completely distint from the question “What makes me alive”. The first is much more generic, and skips over the centric “I” question.

  • George

    Of course, life cannot be defined on the basis of an individual but yet an individual can be alive. I was alway troubled that a virus was considered alive rather than being a toxin. A virus does not meet my definition of being alive.

  • Torbjörn Larsson, OM

    If you built an organism from scratch, that was as complicated and organic and lifelike as any living thing currently walking this Earth, except that it had no reproductive capacity, it would be silly to exclude it from “life” just because it was non-reproducing.

    Since it would be only momentarily alive as an individual system, I don’t think they count for much. Even if eternal organisms would be possible they would be out-competed by populations arising out of the evolutionary process.

    So for all practical purposes, evolution will define most or all life.

    And in that process life is a property of populations, not individuals. It is anthropocentric and egocentric, and in principle mostly exclusive, to define life around consciousness of a few species. Define “alive” as being conscious then, but separate it from the question of what life is.

    But any such definition better capture the idea of an ongoing complex material process far from equilibrium, or it’s barking up the wrong Tree.

    I sincerely used to detest that expression that is thrown about without an, ehrm, stated definition (!) and concomitantly no interest in making it a useful testable thing. In most cases it seems to mean hand waving of “sufficiently far from equilibrium to be interesting for me” or, worse, “my biology teacher used to crib this out of some textbook, it must be important”.

    However, a paper has started to clear that out for me. [“A measure for the distance from equilibrium”, Schindler et al, Eur Biophys J, 1998.] Thermodynamics define “far from equilibrium” as when non-linearities pops up, i,e, when Onsager’s reciprocity fails and we have proper non-equilibrium TD.

    That isn’t how it is defined in biology! Here it can well be partly more or less equilibrium subsystems. The molecular pull-push of many or most metabolic processes comes to mind, where material is transported by consumption further along the chain or by pushing substrates into the system.

    One can use chemical affinity or excess Gibbs energy to measure such systems. And sure, in either of these measures there are subsystems greatly distanced from equilibrium. (Say, molecular machines using many eV of free energy compared to room temperature eV.) Schindler et al proposes to simply use a measure of fluxes, i.e. if material flows it isn’t equilibrium. (In their case, a ratio between normed net and unit fluxes.)

    Then one can see that in biology “far from equilibrium” depends on granularity. The coarse grained carbon cycle is in near equilibrium (net balance between biosphere and atmosphere), while the fine grained system is far from equilibrium (flows between atmosphere, plants, animals and back).

    So the usefulness of this is so-and-so. My take on the NASA diagnosis of life (metabolism/far from equilibrium) is that it is great for capturing individuals, not so much for finding fossils. =D

  • http://www.facebook.com/profile.php?id=100003235694712 Emily Dickinson

    Defining Life in three key words
    Has left deep thinkers stuck.
    Take it from one who’s played it twice,
    It’s simply “lots of luck.”

  • Torbjörn Larsson, OM

    To be more clear, I meant to note that what biologists use as “far from equilibrium” is still thermodynamically sufficiently linear in some cases to not count as TD “far from equilibrium”.

    @ George:

    Anyone can define out viruses. But mind that it now seems, with more sequencing, that many (but not all) viruses were once cellular life forms.

    For example, eukaryotes such as amoeba, or even humans in some cases of lung inflammation, is beset by Megavirus. This newly proposed clade includes such large viruses as Mimiviruses, and have an argued signature of eukaryote ancestry.

    Similarly mass sequencing has discovered virus genomes with archaean relations, and same goes for bacteria I think.

    The proposed ancestry is that an early eukaryote, perhaps still un-nucleated, went parasitic, simplified and its only descendants survived as a virus. A related proposal is based on noting that they grow a “virus factory” inside a host cell that is as complex as some bacteria, that look for all practical purposes like a cell and uses some proprietary metabolic genes. Hence the viral factory is the mature individual and the virions (viral particles) the eggs.

    Now the question for a definition of viruses as non-life is when exactly did the megaviruses loose their “life” property? They are rooted in life, they still look and act like cells. The only difference if the above proposals are accepted is that parasite simplification has made them loose, not the mouth and guts like a tape worm, but the egg metabolism.

    If tape worms are bilaterians (which all have an ancestral digestive system), why can’t such viruses be life? (They probably have to be, if you ask an eager cladist.)

  • Torbjörn Larsson, OM

    Ouch, I need to clarify that too. In the new model, or even before that if I understand biologists correctly, I believe now non-argued diverse ancestry of viruses makes viruses an ecological niche, “a way to ‘live'”, rather than a monophyletic domain with its own common root as the other 3 (Bacteria, Archaea, Eukaryotes).

    @ Steve Flinn:

    Yes, but that the genome is decreasing its mutational Kolmogorov complexity by environmental selection by way of channeling Shannon information is known. Nothing that is described by considering the informational properties of the genome learning process is added to a biologist’s definition of the evolutionary process:

    “Evolution is a process that results in heritable changes in a population spread over many generations.”

    The pity description is “[a process of] differential reproduction”. Both of these are more directly informative of the biology entities and the biological process which is under consideration.

  • Guy

    Prof. Carroll if you don’t mind, I DO have kids (well, one little boy and one girl/boy on the way). It would be REALLY nice of you if you can make an effort for my kids will grow up in a world that has SOME heir of your intellect and science communication skills. If it’s not too much trouble. I can assure you that (statistically) they are completely self-sufficient by the time they’re 30 years old. even 25… :)

  • http://www.learninglayer.com Steve Flinn

    @Torbjörn Larsson responds: “Nothing that is described by considering the informational properties of the genome learning process is added to a biologist’s definition of the evolutionary process: ‘Evolution is a process that results in heritable changes in a population spread over many generations.’”

    I disagree–at a minimum an information-based approach demonstrates that the biologist’s definition is best seen as a special case of a broader phenomenon than would be traditionally considered biological. For example, let’s just pick on some innocuous little words in the biologist’s definition. For example, “many.” Hmmm — is it the next generation? Some arbitrary (i.e., observer dependent) number of generations, or is it unbounded? Seems kind of important to specify or “fitness” has no real meaning. And then there is “population,” which does not necessarily need to be biological as originally intended by biologists (e.g., memes per Dawkins).

  • Sean Peters

    Like Sean, I took one look at “self-reproducing” and said “that’s four words”. But on the second look… what the hell is the difference between “self-reproducing” and “reproducing”? If you’re not reproducing yourself, you’re just producing.

  • Rodolfo Hansen

    My definition of Life is:
    “The local minimization of entropy”.

    It’s the evolution of structure through time.

  • Tintin

    Life is a four-letter word.

  • Pingback: Do I Not Live? | Matteo Rossini()

  • Tintin

    Could Edward Trifonov be related to the AMAZING!!! young pianist Daniil Trifonov?

  • MyName

    I agree that, philosophically, you not only can but should leave out reproduction from the definition. Otherwise, you could have an engineered organism that was complex enough to feel pain or even more than just pain, and if it was engineered to be sterile, you could get away with treating it as not being alive which would open up the door to unethical behavior.

    However, a naturally occurring living organism must be able to reproduce. Otherwise, it would have no way to evolve and may as well not be alive if you are looking at it through an evolutionary timeline.

  • Dunc

    The question is whether I am alive, not my cells.

    Well, if you want to draw that sort of distinction, we first have to decide whether “you” even exist in the first place…

  • new earth

    If this reproducing thing were true then life does not begin until reproduction is successful and complete, which would imply that babies are born dead and remain dead for quite some time. This would lead to all sorts of moral and legal issue, but would resolve the ethical issues surrounding stem cell research and others. This would also explain why many counties have no respect for children…but then they also have no respect for their elderly…

  • http://www.astro.multivax.de:8000/helbig/helbig.html Phillip Helbig

    “I don’t have kids and don’t plan on having any”

    Joining the prestigious company of Steven Pinker. Since you publicly state your wish not to have children, I suppose it’s fair to ask what the reasons for it are. Consider that you are, compared to most people, in a much better position to have children. Also, there are many successful cosmologists (Barrow, Hawking, Sciama, Peebles—probably many more, but I don’t always know how many children people have) who have many children.

  • tsardrosdobrad

    “I don’t have kids and don’t plan on having any”

    Plans are just that plans. Plans are the back-up, there is the surprise factor that only nature controls.

  • Frank

    It seems to me that when you talk about “building an organism from scratch” there is some presupposition that you can separate an organism from its environment. However, from what I understand, such mechanisms as adaptation and selection are functions of the environment, and therefore creating such an organism would not be observationally replicable for all intents and purposes. You would have to identify an organism that is as evolved and sufficiently complex as modern observed organisms, but without reproduction with heritable traits. But the last the time I checked, such mechanisms as adaptation and selection work through the gateway of reproduction with heritable traits, and these are in turn a function of the environment. Has your “from scratch” organism ever been observed and how would you go about identifying it as such? How would such a “from scratch” organism come into existence?

  • http://dylangers.wordpress.com Dylan

    On the cellular level, reproduction is absolutely necessary, but on the larger level you’re right: reproduction cannot constitute life. If it did, mules (combination of horse and donkey that always results in a sterile animal) wouldn’t be considered alive.

  • Zabaleta

    There’s certainly life without reproduction. I therefore conclude by saying this three-letter sentence: “Go fuck yourselves!”

  • amphiox

    I would say that life requires reproduction, and that if it is made up of components that are alive (and reproduce), then it is alive even if it itself does not reproduce.

    Of course, by this definition, societies and civilizations would qualify for being alive, but in my opinion, they are.

  • george briggs

    has anyone noticed that evolving life has the symmetry SU(3)? four DNA building blocks for each parent, or 8 total. this is what Steven Wildberg called the 8 fold way, for the above aymmetry.This is interesting in view of fact that there are 8 basic kinds of non decaying matter (electron, neutrino, proton and dueteron plus their antiparticles}

  • Charles Ames

    “Are you of a kind that has the capacity to reproduce” rather than “have you reproduced” is how I take the definition, so I’m comfortable allowing that Sean is probably alive. However, a thing must die in order to have ever been alive. Any ongoing complex material process operating far from equilibrium that neither stops (dies) nor has the ability to reproduce is… yet to be observed in nature?

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Cosmic Variance

Random samplings from a universe of ideas.

About Sean Carroll

Sean Carroll is a Senior Research Associate in the Department of Physics at the California Institute of Technology. His research interests include theoretical aspects of cosmology, field theory, and gravitation. His most recent book is The Particle at the End of the Universe, about the Large Hadron Collider and the search for the Higgs boson. Here are some of his favorite blog posts, home page, and email: carroll [at] cosmicvariance.com .

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