What is life? (Spoiler alert: nobody knows)

“Just as the colors of a rainbow merge imperceptibly one into another, the transition to life from nonlife is a seamless continuum”

                                                J.W. Schopf

I teach a variety of classes at my university, General Biology for science majors, my own Pharmacology course for undergraduates and from time to time I also teach graduate courses in my own area (Biochemical Pharmacology and Neurobiology) among others.

However, one of my favorite courses is one that I teach with a physicist colleague: “The origins of Life and the Universe”.  I have no idea why the course was named like that, it was before my time.  Informally, we call it the Astrobiology course.

Our Astrobiology course is targeted to non-science majors; we get people from all over the university (History, Education, Art, etc.).  We enjoy the course in part because it gives us the opportunity to “talk science” to people who in all likelihood would not hear about it otherwise.  We simplify the topics, but we try very hard not to dumb things down or be patronizing.  Personally, I like to follow the example of two of my scientific heroes, Isaac Asimov and Carl Sagan, the master explainers.

Teaching this course is a lot of fun! My physicist friend starts it with the Big Bang, the formation of stars and galaxies, the formation of the elements, solar systems, planets and finally ends up with the pre-biotic Earth itself.

Then yours truly takes over.

I go over the current understanding of what life is, current theories on the origin of life, molecular biology, evolution (gasp!), life as we know it and as we do not know it, artificial life and the search for life and intelligence elsewhere.  And yes, we talk about possible aliens.

I start the very first class by going over a very important topic: “What is life?”

(Spoiler alert: nobody knows)

A friend and fellow scientist and blogger has written quite lucidly on the topic.  From him I learned of a book that lists at least 48 definitions of life, none of them completely satisfactory.  However, it is becoming more and more evident that life is more like a process that an actual “thing” in very much the same way that a person’s portrait can only represent the image of said person at a particular point in time in her or his life and therefore a picture cannot possibly capture what that person “is”.

The funny thing is that in most cases even though we cannot define life itself, we can usually tell whether something is alive.  For example, in the picture below it is really self-evident the “living” part of the picture:


Picture credit: I wish I knew!  I found this for my classes a long time ago and I lost the source.  If this is yours, please let me know so I can immediately credit it properly.

Of course, in the picture above we immediately know that life is represented by the valiant little plant sprouting in the midst of these hard rocks, but  nowadays we know that there must be more “life” in this picture that we cannot see, like bacteria and other microorganisms for example.

Dr. J. William Schopf compares the question of the origin of life with how a reporter goes about writing a news piece about anything.  In essence the kinds of questions that such reporter asks can be summarized as:


Picture credit: Baldscientist

 As far as life is concerned, these questions can be organized like:


Picture credit: Baldscientist

And in our time, we have at least partial answers to some of these questions:


Picture credit: Baldscientist

At our current scientific understanding of life (the “as we know it” phrase is implicit unless I tell you otherwise) two keywords seem to be, well, key: Chemistry and Evolution.

You see, it is pretty hard to seriously deny that Biology is based on two main facts:

  • Life follow the laws of physics and chemistry.
  • All biological processes are a result of evolution (and we’ll talk about evolution -at my own risk- in a future post).

However, in the meantime, just in terms of chemistry, think about the following:

All organisms on Earth (including us), are essentially a mixture of:

Water          Minerals          Proteins            Sugars      Fats

However, living organisms are wonderfully, fundamentally different from an indiscriminate mixture of chemicals.  The very word “organism” is very much related to the concept of “organization”.

what is life

Picture credit: Wikimedia Commons and Baldscientist

One of the remarkable thing about life is  that there are no atoms that are specific for life.  A carbon atom in one of the lumps of coal in the figure above at left is indistinguishable from a carbon atom in the magnificent specimen representing life in the picture above at right.

No, the far right… (:-D).

And carbon, oh sweet, mysterious carbon!  It is the 4th most abundant element in the universe but it does not even make the Earth’s top ten and yet, all life that we have observed so far is carbon-based!

There are five undeniable facts about life in our planet:

  • There is life on Earth.
  • All life on Earth, is essentially made of the same components.
  • Carbon seems to be THE element of life.
  • Life on Earth is very complex.
  • All life on Earth is related

Now, in my view, and I know that I am not alone, the fundamental mystery of the universe has three main aspects, all potentially explainable by a thorough and real understanding of our physical universe:

  • How matter came to be.
  • How that matter organized itself into entities capable of capturing, transforming and using energy from the environment (in essence, to live).
  • How that life, in time, organized itself in such a way that eventually thought, consciousness, sentience whatever you may want to call it came to be.

The emergence of consciousness was a special event in the Universe’s story.  It was then, and only then, wherever and whenever it happened, that the universe started to look at itself.  Will it like what it sees so far?


Picture credit: D. Hillis, D Zwickil and R Gutell of the University of Texas at Austin.

If you want to know more:

JM Smith and E Szathmáry (2000) The Origins of Life: From the Birth of Life to the Origin of Language. Oxford University Press.

AG Cairns-Smith (1990)Seven Clues to the Origin of Life: A Scientific Detective Story (Canto).  Cambridge University Press.

JS Schopf (2002) Life’s Origin: The Beginnings of Biological Evolution. California University Press.



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  1. Pingback: - Hello Spaceboy
  2. Being a Dawkins junky, at least where evolutionary biology is concerned, I scarcely think he has summed up the issue of life in such a succinct way. Your course sounds like it would be an experience worth having.


    1. Thanks man! It is one of my favorite courses to teach. By the way I am humbled by the Dawkins comparison! I love his writings too (when he writes about science, not religion… (;-)…). The angry atheist thing does not appeal to me… One does not need to mock anyone to make a point…Again, thanks!!!


  3. Hi Oné! Thanks for the share! (Oh, and I know! That’s what my theory was all about. And that’s why I got myself into trouble with my colleagues…So it goes. Thanks again.


    1. I know about your theory, though I cannot claim
      to understand it well enough to analyze it in an intelligent way. You know that established science is like a big ship, it takes a very good reason and a lot of effort to make it change its course! Also, I hope you realize that I meant no disrespect when I say that “nobody knows”…

      The Unknown

      As we know,
      There are known knowns.
      There are things we know we know.
      We also know
      There are known unknowns.
      That is to say
      We know there are some things
      We do not know.
      But there are also unknown unknowns,
      The ones we don’t know
      We don’t know.

      Donald Rumsfeld


      1. Love that Rumsfeld quote. Did you notice that he left out the unknown knowns? These are provocative knowns – as they are things we don’t know that we know, as they are staring us right in the face…

        Oh, and it’s all good, I know what you meant. It’s hard to communicate and explain something that only I understand. I’ll keep trying. 🙂 Thanks for all that you do!


        1. You are right… nobody knows what life is… however, check my book from 2010 at my webpage. there is a chapter about life with a definition. for such definition you have to give up to a wrong notion: the “world” (which do not exist). there are epistemologically different worlds, and life is an EDWs than the organism (which belongs to the macro-EW).


          1. Thanks, Gabriel! I will look it up. By the way, a friend of mine alerted me of a Scientific American piece that argues that life does not exist. I have yet to read it, but I imagine that it is the argument of organisms as machines…


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