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.
Life is self awareness. There you go, just two words.
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.
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.
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.
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.
Oops sorry for the annoying double post. My bad.
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 :).,
The child is yours ! I will win the lawsuit and prove you alive at the same time.
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
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.
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.
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.
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
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.”
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.)
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.
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… 🙂
@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).
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.
My definition of Life is:
“The local minimization of entropy”.
It’s the evolution of structure through time.
Life is a four-letter word.
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Could Edward Trifonov be related to the AMAZING!!! young pianist Daniil Trifonov?
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.
Well, if you want to draw that sort of distinction, we first have to decide whether “you” even exist in the first place…
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…