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What is life?

What are the most important characteristics that we use to define whether something is living and why? It is a difficult border to set because there will always be an exception, but I believe it is an important distinction because once defined (assuming it is possible) it creates a simplifying division to those entities upon which we can apply certain emotions or qualities – plus, I find it interesting.

Here are some conventional characteristics of life to get us started:

  • Growth – stages of development
  • Metabolism – consuming, creating, transforming and storing energy
  • Motion – internal or external
  • Reproduction – ability to create similar, separate entities
  • Response – detect and respond to environmental stimuli

11 Comments

  1. Andrew Hamann

    Jan 7, 21:46

    Ummmm…is this a philosophical or biological question?

    If it is biological, than what you named are the characteristics of what scientists define as life…

    If it is philosophical, then…ah, who am I kidding? I don’t do philosophy… :-p

  2. Tarun

    Jan 8, 02:11

    Perhaps life begins with self-awareness – being aware of your own existence. However, I don’t know if plants or bacteria are self aware. Moreover, consciousness (self-awareness) is specific to central intelligence and doesn’t clearly define consciousness of swarm intelligence.

    Maybe we could define life as anything that has a both a definite structural and functional pattern within it or central bluprint (like DNA or RNA) that directs changes within its basic units and thus controls its existence.

  3. Glen C.

    Jan 8, 10:37

    Don’t forget adaptability as a conventional living characteristic.

  4. Vincenze

    Jan 8, 18:56

    This is a question that has eluded human knowledge and understanding for as long as we know, and my guess is that we will never fully understand what life actually is. We can only make vague predictions based on what we observe, learn and imagine (activities I actively encourage and participate in).

    I think the five points you listed, along with the comments by Tarun, make a very good key for defining what we see life to be. You’re also right in saying that there are always exceptions, such as viruses that only seem to be ‘life’ or living inside a host.

    When you think about it, by the very definitions you have listed, an entity such as a computer virus could be defined as ‘life’ or alive. Now it’s getting interesting, go through each point on the list and you’ll see.

    Vincenze.

  5. Thame

    Jan 9, 06:24

    Andrew: I guess it is a combination of both. Neither seems any easier to get a hold on…

    Tarun: Yes, consciousness would be a major factor of what I would consider life. however, there are varying levels of consciousness – would life be associated with consciousness where the organism recognizes itself as a living organism, or something less complex?

    The reason I am asking this was because I am wondering when life began. There was a point in the early history of earth where small collections of molecules became something with the attributes of life.

    What did they gain or lose that gave them life?

    Glen: Yes, I don’t know if that falls into the catchall of “response” that I put up, but it certainly is a valid characteristic.

    Vincenze: Yes, there are tons of exceptions, even fire seems to – at least minimally – have each of these characteristics. It grows by consuming energy, it moves and is reproducing in it’s growth and responds to it’s environment such as wind or rain.

  6. The Manual's Keeper

    Jan 11, 09:44

    Life is the sum of all the characteristics that have already been described, and yet, as Vicenze said, it has eluded philosophy for centuries and now science.

    Why?

    I believe the point is that we, as a life form, cannot define ourselves the same way a microscope can see the invisible but cannot see itself.

    I believe we, as evolved life forms, are the recently formed sensitive organs of the evolving organism that is the universe. Somehow we can peek into the infinity, but we hardly can grasp ourselves.

  7. Thame

    Jan 11, 19:27

    “Somehow we can peek into the infinity, but we hardly can grasp ourselves.”

    Wonderfully put

  8. Benedict

    Jan 12, 04:30

    Life is a continuum, a family rather than a set. Life is a term whose meaning is too embedded socially to shift in the way it ought to with scientific revelation. Is a virus alive? Is a bacterium? If they are, are they less alive than a frog, or a squirrel, or a human being? Would an artificial intelligence be alive? Is ‘alive’ even a useful term anymore in any field save that of everyday discourse?

  9. Online

    Mar 20, 02:11

    Life is mobile operator in Ukraine(Turksell)
    Life:)

  10. Colleen

    Mar 20, 16:40

    Based on the given definition of life, bacteria and viruses are alive, while robots and computers are not—at least if you’re looking at this from a biological standpoint.

    Now what would be really interesting is if humans could create AI that has the ability to grow and to reproduce on its own. When you think about it, these are the only life chracteristics that separate “natural” life from robotics and AI. Could humans someday create organisms from scratch, distinct from any other current living species that have all of the chracteristics of life? If so, what would that say about the existence of God? I suppose not much, since you are still using “God’s” elements to do the creating. Although you’d be making a new creature, you’d still be using the same building blocks that have been around since the beginning of time. (I put God in quotes because I realize that not everyone agrees that God exists).

    All these questions about autonomous man-made life make me want to go watch The Matrix, and I don’t even like that movie.

  11. Thame

    Mar 20, 17:41

    Although I don’t know if I agree with you on the viruses, I do like the rest of your comment.

    “Could humans someday create organisms from scratch, distinct from any other current living species that have all of the chracteristics of life?”

    Some argue that there is a non-physical component to life and I would imagine that it would be pretty hard to fabricate.

    If not, I think it is only a matter of time before a completely “physical” life is built either from existing organic parts or from scratch.

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