Why science can’t define ‘LIFE’

Science defines most things in the world, but do you know that science has no proper definition for life?

World religion including Hinduism, Christianity or Islam adheres to the ‘meaning’ of life more than the definition of life. Many early western philosophers used the similar notion ‘soul’ or vitality elements to define life. However, as much as we see life flourishing in abundance, modern day scientists are still finding the proper definition of life as a staggering act. The spiritual aspects regarding life remained despite the scientific approaches supporting the origin of life (e.g Haldane, Oparin, Urey and Miller etc).

I will present some of the definitions of life and their contradictions in this post. Firstly, its important to know that the definition itself can be broken down in many ways in terms of physiological, metabolic, biochemical, genetic and thermodynamic forms (C.E Cleland, 2002). All of them had/have strong counter arguments.

For example, NASA’s working definition is: “Life is a self sustained chemical system capable of undergoing Darwinian evolution” (Joyce, 1994ab). Despite being ‘considerably’ accepted within the astrobiological community, Darwinian evolution requires the ability to reproduce. Consequently, a conclusion can be drawn that worker ants or mules should be considered as non-life although we know otherwise intuitively.

A second example, Guimaraes defines “The functions, which are called life are metabolism, growth, and reproduction with stability through generations” (Kolb, 2006).  If we look at ‘growth’ as a criteria, the same is also validated for inorganic crystals, which could grow with the right nutrients. Development in organism get adjusted to regulated trajectory, the similar happens when local surface trajectory influence the course of metal oxides crystals (Cairns-Smith, 1982). Even clouds ‘grow’ and become numerous, depending on the weather patterns.

In terms of thermodynamics, life have a low entropy system. This means life maintains a high degree of order. On close examination, life is very selective, for example; only left handed amino acid (protein builders) and right handed sugar (DNA) are utilized to perform life’s activities. This is referred to as homochirality. Even the simplest bacteria Mycoplasma pneumonia when studied in detailed is highly complex. However, a chemical system criteria alone is not enough since many non-living entities do those as well (i.e formation of stars).

Don’t you think it’s rather awkward that we only know life intuitively (on earth at least) but can’t properly define it. The importance of defining life would be very useful since we can streamline all our technical approaches to promisingly identify alien life forms in space (Titan, Europa), unless the green man himself decides to land on earth and say ‘こんにちわ’ (hello in Japanese), millions of dollars could be saved.

On the contrary, the unpopular term “autopoiesis” to define life is slowly making a comeback, despite several misconception and misgauge of the term within science (Boden, 2000). The word ‘autopoiesis’ was first coined by the Chilean duo Humberto Maturana and Francisco Varela in the early 1970’s. (By the way Francisco is the father of Leonor Varela). 

Their definition of life was ill received from mainstream scientist because it was not in tandem with Darwin’s theory of evolution and also DNA making its entry as an important aspect in biology during that time.

Autopoiesis literally means self-producing in Greek. The authors described that life is defined as a unity with a network of producing component (Maturana et. al 1974), in other words an autopoiesis system is capable of organizing the production of its own components that is within a boundary (a membrane is a boundary of a cell) (Luisi, 2003) The term deliberately down plays the importance of genetics (DNA and/or RNA) and focuses on the boundary which holds life’s system. This is simply because Darwinian theory reflects more on the general populations than on the individuals. Before his death in 2001, Varela expressed autopoesis in the following ways: verifying (1) whether the life’s system has a semipermeable boundary that (i.e cell membrane) (2) life is produced from within the system (i.e metabolism) and (3) that encompasses reactions that re-generate the components of the system (i.e transcription) (Varela 2000). Autopoiesis is gaining popularity and few are already using it for synthetic biology (i.e Luisi’s group) and the origin of life field specifically to recreate the proto-cell (Morowitz‘, Deamer‘, Szostak‘ groups).

As mentioned earlier, the specific definition of life is important if we are to understand our origins and to find aliens (i am being real here). But, with the latter, we can’t really rely on earth’s life definition (even if have one) itself since there is a possibility that aliens may be define in other ways beyond our current state of biology.

Ps: I would advice readers who don’t have a formal biology/chemistry background to click on the hyperlinks if they find it difficult digesting the post. I have included wikipedia pages, youtube links and journals (you can download some of it). So do take your time understanding it. Also do give some thoughts on what you think the definition of death might be. 

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49 thoughts on “Why science can’t define ‘LIFE’

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  3. With regards to your criticism of Nasa’s definition, Darwinian evolution doesn’t happen to individuals. Is a lone human no longer alive if they cannot reproduce? Worker ants can reproduce, but they experience a hormonal environmental which stops them from doing so. Mules might be able to with IVF…


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  5. Well, it’s not that hard, really.
    If it has ribosomes, it has life.

    Also, by any definition even when we have drawn our last breath, we are still mostly alive. With having more bacterial cells than human cells, death just cannot be immediate for a human symbiont, unless one invokes spontaneous combustion… … but that’s a whole another story.


      1. I was thrown for a loop for aabout an hour here, but it turns out that arenaviruses as they bud out of cells bring with them some of hosts material, including ribosomes. However, not their own ribosomes, stolen ones.
        So let me amend my original statements:
        If it has its OWN ribosomes, it has life.

        Naturally one can go back in event chain to say if that it has genes for ribososomes it has life, etc., but ribosomes do fulfill the operational criterion.

        Enjoy life!


  6. Ironically enough i just wrote a paper about evolution, and in the process i found i needed to briefly discuss that it’s very hard to define life. I honestly don’t believe we as humans will be able to ever come to a finite definition. A better idea would be to categorize certain characteristics of life and put different things that fit in those categories. Viruses do possess some of these characteristics, and yet most people don’t consider them quite alive. Which i find to be unfair.

    If you really want to get a nice page or two of some really good insights into this, then i suggest you get a copy of Robert Hozen’s “Genesis: the Scientific Quest for Life’s Origin”. Check out pages 28, 29; 30. They are a gold mine!

    Here’s are two nice quotes from that book:

    “Attempts to formulate an absolute definition that distinguishes between life and nonlife represent a similar false dichotomy.”

    “…scientists in the early twenty-first century are in no position to define life.”


  7. Really enjoying your blog.
    Your presentation of this topic is really fascinating.
    Great intellect! Keep writing.


  8. Your first sentence has a strange omission: ” World religion including Hinduism, Christianity or Islam adheres to the ‘meaning’ of life more than the definition of life.”
    Of course Judaism predates all three – and Christianity is new Judaism that follows the ‘Messiah Yeshua Yoina’ (Joshua John) currently referred to as Jesus, and Islam follows that stream of conciousness approximately 670 years later. Shared belief in the oneness of humanity is what unites us.


  9. THe NASA definition needs a bit of expanding to be sure, but worker ants and mules as a refutation? Not convincing. After all, that would mean that all organisms which die before reproducing would then be, after the fact, reclassified as non-life. But, sterile hybrids and non-reproducing social insects are simply a dead-end of sorts, for life, of which they are obviously a product. Perhaps the issue here is that irritating prevalence of discontinuity. Their cells are “reproducing”, replicating, even when as a whole, the organism cannot. So, on a cellular level, they satisfy the NASA definition, at least it appears to this non-biologist history major… in the end, this becomes more about semantics and philosophy rather than hard science in my mind.


    1. I think NASA uses it for cellular level, i agree with you there. But do you really think hard science can answer this (philosophy certainly can..lol).. as for now i don’t think so.


  10. As you aptly point out, depending upon the scientific view there are a variety of definitions or descriptions of life. If we concentrate just on human life then of course we are dealing with a very complex bio-chemical-physical array each of which contributes to the definition. On the other hand when we consider the most elemental cellular life form then we are looking at basics. The problem is do those basics appear in all life forms? I think they do, and Thomas’s marvelous book Lives of A Cell enforce my opinion. I think that common factor is the still underfined “bio-chemical spark” that moves an ordinary chemical compound into the realm of the living. What we have still not fully come to understand is just how that happens.

    Good article, but I firmly believe science rather than philosophy will ultimately arrive at the answer and it will be quite stunning, awesome, or breathtaking. It will also be inspiring and reassuring about the purpose and value of human life here and throughout the Cosmos.


  11. Definitely enjoyed the article and followed this Blog!

    I find this kind of difficulty definitively defining life a somewhat frustrating endeavor. I am a philosophy major, and am currently in a class studying Epistemology. we have the same problem definitively defining “knowledge” as well. Just as you pointed out in this article in regards to a definition of life, we can grasp intuitively what knowledge is, but that doesn’t mean we can pin down a definition that doesn’t have flaws.

    As pointed out by previous commentators, we do not need to have this definitive definition in order to work with the topic at hand, but that sort of final definition would definitely go a long way in aiding and clarifying the subject matter, whether it be life, or knowledge, or any other area of understanding with an elusive subject.

    I will have to ponder what I would use as a definition for life, (or death for that matter) and will let you know if I think I discover anything fruitful.

    BTW, I am glad to see you enjoyed my blog enough to follow it! I should hopefully have a few more posts going up in the next couple of days. Let me know what you think of any of my articles, and feel free to comment and hopefully spark some discussions


    1. Thanks for the feedback, i didn’t knew that ‘knowledge’ has the same problem as well. I was browsing on blogs which share the similar view of life and origins and your’s popped right out. Looking forward for your new posts.


  12. If panspermia theory is right, still the question arises how life was formed somewhere else. After all, the universe is also just 13.5 billion years.
    And if we can accept life to be forming somewhere else, why is it not possible that life formed on Earth itself?


    1. actually, we have no answers on how life is formed, panspermia is a theory just like the rest. Even the part you mentioned “why is it not possible that life formed on Earth itself?” comes under the same category.


  13. Life can be scientifically defined then as a set of organised (physical or chemical) processes which can self-replicate under favourable conditions.
    Life, as we know it, is around 4 billion years old; over 500 million years after Earth formation. So current self-replicating systems might appear a primitive form of life within the next 200 years or so considering the rapid technological achievements.


    1. “Life can be scientifically defined then as a set of organised (physical or chemical) processes which can self-replicate under favourable conditions.”

      Doesn’t this definition rule out certain types of animals, such as the Mule and the Worker ant (as pointed out in the article)?


      1. Thats why I mentioned “under favourable conditions”.
        Suppose we activate the gene (“a chemical process”) for fertility in worker ants by changing the environment. Then they also will replicate. 🙂


  14. That was a post worth waiting for 🙂 Hmm…well…my mobile 😉 defines life as “the quality which people, animals, and plants have when they are not dead, and which objects and substances do not have.” (Collins Advanced Dictionary of English) It also states that death “is the permanent end of the life of a person or animal.” Which of course circles back round to the original issue of defining…or not…life!

    Even if we do manage to accurately define life, we will only be doing so within the boundaries of human experience. Our “laws” and theories are potentially meaningless outside our own little world. What’s to say we haven’t already encountered alien life/intelligence (a necessity for life or not?) only for it to be so far beyond our human comprehension of what defines life that we remain still in ignorance?

    As to death…that would seem to be only as definable as the definition of life…currently non-definable! Quite a quandary 😉 Thing is as well…I believe all life is sacred…and therefore existing on both a scientific level and also a spiritual level. That being the case it may well be that we were never intended to be able to define life though it likely enhances our life experience by attempting to decipher it’s meaning and it’s definition…thereby perhaps answering the all consuming question for many…Why are we here? What is the purpose of our lives?

    One other thing…love the photo you chose for this post!! Those kittens are just so cute!! 🙂


    1. Good point europasicewolf – “within the boundaries of human experience”. But that goes with any definition. Until we discover microbial life in the glacial lakes of Europa or on Mars, or that fabled green martian, our definition has to be confined to earth experience.

      Unless you believe that life was sown on our planet by panspermia? In which case…

      I think definitions do constrain research, taxonomy being a prime, futile example.


      1. Looks like you are saying a possible “YES” to shadow biosphere theory. Panspermia will remain a theory, but there are evidence that earthly microbs can survive UV for a long time in space. I just can’t remember the authors name to give you the link.


      2. Nevermind microbial life on Europa or the “fabled green martian”…! There’s IceWolves on Europa!!! Or did you think they were a figment of my overactive imagination? 😉
        I keep an open mind as regards panspermia…never rule anything out till you’re certain! 🙂


  15. Why didnt I think about this? I hear exactly what youre saying and Im so happy that I came across your blog. You truly know what youre talking about, and you made me feel like I ought to learn much more about this. Thanks for this; Im officially a huge fan of your blog


  16. Though i liked the article in general, but the justification of the need to define life could have been done away with. I do not think researchers stick to strict definitions when they look for aliens or for that matter when they look for anything in particular. Though definitions may serve as guidelines, they seem extremely overrated in this article. Research should be and actually is generally carried out with much more open minds and never stays confined by such pseudo boundaries.


    1. Sandeep, Thanks for the comments and criticism. However, scientist need to justify why they use a certain criteria for finding aliens. That’s when the definition comes into play.


  17. Mmm very good point, life is almost to diverse and wonderful to encapsulate. Great point actually.

    I’m not sure the “meaning” and “definition” of life in this case can be disseminated to be honest. The purpose to reproduce, or to support the interests of genes. Definitely some Richard Dawkins Selfish Gene kind-of-answer should be considered!

    NASA’s definition is perhaps the best you presented.


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