What is “Alive”?

The last post and some recent conversations have really got me thinking about this.  Just what does it mean to be alive?  What is life?

Can this be answered purely in the realm of science?  I’m not totally sure.  If criteria could be defined for life and then measured for things, then yes.  But, I don’t think we can define life in a 100% purely objective sense.  At the very least, there will be massive arguments about the various definitions that could appear.

On the other hand, science (and related systems) give us the only possible route to a robust, coherent, and consistent definition of what life is.

The concept of alive is just so variable.  Most people would have no trouble putting down a beloved pet who was hit by a car and is brain dead.  Brain dead in this case means “can’t think, can’t control voluntary muscles, may or may not have autonomous muscle action”.  Yet those same people will argue that the exact same situation applied to their sister or mother or grandfather is not the same and will keep that person on life support until the heat death of the universe.

I will note here that many governments don’t care what you think and will make the decision to keep a human being on life support indefinitely.  Many doctors will too.

This runs a little afield of my initial question, but it’s something to consider.  I think a requirement for being alive should be “Response”.  Every living thing that we are aware of and every non-organic living thing that we can imagine or build presently has this characteristic.  It responds.  It responds to external environmental ques (mates, food, fear, too hot, etc).  It responds to internal ques (hungry, scared, hurt, etc.). For higher organisms we have to consider both reasoned responses and autonomous responses.

If a dog or a human being can no longer respond, then is it really alive.  And I don’t mean, “it can sense fear, but it can’t make muscles work” lack of response.  Medical technology is perfectly capable of measuring brain and spinal activity.  Open the eye, shine a light in.  Does the pupil respond?  Does an EEG record brain activity in the visual region?  These are the kind of responses I’m talking about here.

Sure, the cells might be using energy, but without medical intervention, there is no way for the cells to get more energy (or proteins or extrude wastes).

Even computers respond.  Presumably, artificial intelligence will respond as well.  If it doesn’t respond, then it might as well be a brick.

Finally, we would need to ask, is there any chance of resuming normal functioning?  This is a good point for science to come in.  Many people will wait for and pray for ‘a miracle’ to save uncle Whatshisface.  They will demand doctors keep their beloved uncle on life support until the deity of their choice restores them to full function (preferably by next weekend so that they can make a chocolate pie for the reunion).  But, how many times has someone who was clinically brain dead returned to life?

None.  I’m not talking about persistent or permanent vegetative state here.  We’re talking about brain death.  The brain is dead.  We get into a whole ‘nother can of worms with vegetative states.

Again, I’m running afield of the intended post, but this is a pretty interesting question in and of itself.

So I think ‘response a stimulus’ is a valid requirement for something to be alive.

Is response all that’s needed?  No, I don’t think so.  But I think it’s a big part.  Computers respond, but I don’t think we’ve create computers that are alive yet.

Does something that is alive have to be made of cells… or even organic?  No, I don’t think so.  We haven’t created strong AI yet, but I suspect that if it is doable, then we will have to rewrite much of what we consider ‘alive’ means.

The requirement that a living thing be made of cells is sort of a classical definition of life.  The good point is that it is a very clear demarcation line.  Cells on one side, no cells on the other.  Life, non-life.  Easy.  I just don’t think that it’s a valid demarcation line.  Very few things (especially in biology) are ever this cut and dried.

I think, pretty soon, we (as a species) will have to make a decision about something being alive that isn’t made of cells.  Will be able to make this call?

What about energy?  One of the hallmarks of living things is the use of energy.  All living things that we are aware of (and all we can imagine) have to have energy.  This is actually an easily provable statement.  It all has to do with thermodynamics.  Living things absorb energy to replace the energy lost in doing the functions of living things.  Without a constant influx of energy, a living thing would run out, and then would not be able to perform its functions anymore.

The maintenance of homeostasis is another classical part of the definition of a living thing and I think this has some merit for organic systems, but may not apply to non-organic systems.

Basically, homeostasis is the act of keeping one’s self at a variety of conditions that are appropriate.  Humans need to be about 98F.  We have a variety of internal systems (and external ones) to help us maintain this temperature.  But homeostasis applies to everything from water content to many, many chemicals, compounds, and elements.  There are many internal conditions to monitor and control (pH, salt concentration, etc.)

A living thing should be able to take care of itself.  I can see some non-organic systems potentially needing a helper for some internal conditions.  So, this one is a maybe.

There are other things to consider.  I suspect that we will revisit this in short order.

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7 Responses to What is “Alive”?

  1. LRA says:

    Ha! Just took an astrobiology class where this was a pertinent question. My answer: metabolism and reproduction. Of course, moving from chemistry to life happened on a continuum. A prion, a virus, and the like are not alive, but they are “proto-life”, IMO.


  2. Sophist says:

    I can simplify this even further. From a scientific sense, life is simply water, DNA, RNA, and protiens. Beyond that there is no evidence that life exists. While we may speculate what life elsewhere may be like, there is no indication that it is anything more than that, and we should stick to a strict definition, at least until there is some hint otherwise. I’m not sure there is any real philosophical debate because those questions all center around quality of life, and that is a purely subjective question to which science can never appropriately answer.

  3. david salako says:

    Alive is a term that is relative to specific circumstances on the basis that the nature of existence is diverse. For example if we say to be alive is the quality of living things, then we must qualify its essence. However one definition in one senario on the basis of characterisation may not be found in another senario of existence. For example is a plant alive? Is growth and response to stimuli features of alive? Notice also that humans also grow and respond to stimuli as well. However we possess sentience which a plant does not. Therefore alive is dependent on the nature of existence. But if alive is dependent on heart, blood, and lungs,(for one cannot be alive without these organs) then it means that to be alive there must be these anatomical and physiological features. But this is only in the context of humanity. Like i said “alive” depends on the nature of existence.

  4. david salako says:

    “What i am about to right now must be connected to what i have written previously”. Why? Because half a story cannot represent things in their perfect state. To be alive in a medical is determined by brain signal. In a clinical setting of emergency a person is not dead when the heart ceases(because the heart can be caused to resume activity) but rather, when there is no brain signal. So we see that in a clinical setting “alive” is dependent on brain signal. Again my point is made. That is “alive” is dependent on the nature of existence. For one existence deffers from another by virtue of their respective essence. Moreover in a clinical setting a person in a coma is not dead until there is a cessation of brain activity. However are they alive? Yes! However it is an incomplete state of “alive”. Or perhaps an artificial state of “alive” because of the use of artificial respiratory equipments without which they will surely die.

  5. OgreMkV says:

    David, that ‘brain death’ raises an interesting point. A person can be brain dead and yet, every cell in their body remain alive for quite a while.

    So why is the organism dead and yet every cell still alive?

    Please note that I don’t know if the brain cells are actually dead or just turned off. I have read of a control region of the brain that regulates all neural activity, so maybe the brain can be ‘rebooted’ in certain cases. My research on this is admittedly minimal, but it raises some interesting questions.

  6. david salako says:

    Again-what i am about to write must be connected to what i wrote before about “alive”. So-is a foetus alive? Does life begin at conception? Or at what point in the gestation period does life occur? Again like i said-“alive” is dependent on the nature of existence. Life begins at conception on the basis of value. For at conception a child begins the process of development. We can say this because there is evidence that it is a child that is developing in the maternal womb of the uterus. The start of this growth and development of a baby occurs at conception and ends when the child is viable in the womb. And during various stages of the gestation period “alive” takes on different forms. E.g-“alive” in the 9th week of gestation period is different from alive during week 20 of the gestation period on the basis of the time gap of development. However the 9th week and the 20 week and all other weeks until week 40(the final week) are all parts of alive that lead to a perfect state of “alive”.

  7. david salako says:

    OgreMkv, i nice addition to what wrote. This has lead to other vital questions. You say, in relation to brain death, why is every other cell in the body still alive? I would say perhaps because by definition a cell is a basic unit of life capable of existing independently under the right conditions. Good question! Research may be able to shed more light on this issue.

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