Tom Jonard's Definition of Life Page

    What is life? is not an easy question to answer.  It seems it was not always so.  When I was growing up I took biology in Junior High and learned that life was defined by ten characteristics.  They went something* like this:
    *I no longer recall the exact ten characteristics we were taught.  Searching the Internet for them has proved fruitless.   Anyhow anything possessing these characteristics was alive by definition.  Everything else was not.  One of the diadactic games this encouraged was to see how each and every living thing we could think of fit these catagories and visa versa.

    I don't know whether our depth of understanding has increased resulting (as as such an expansion always does) in a recognition of the breadth of our ignorance or just that as students we were intentionally sheilded from the complexity and uncertainty of what was known.  I don't think either my teachers or the school system lied to me (despite the fact that I have been assured by my own children that High school is a waste of time which teaches nothing).  And our depth of understanding has increased so that (paranoia aside) biologists themselves have difficulty now agreeing on a definition of life.  In the intervening years since my childhood many discoveries have been made which call into question any neat list of what life is. 

    The first clue that things were not as simple as biology class suggested is the long known fact that sometimes living things act quite dead.  Spores and seeds that can lie dormant for years, decades even centuries and yet are still able to germinate are an example.  We have no problem understanding that such germs of life come from life and possess the potential to become life again.  But what are they in the meantime?  Life otherwise seems to be a process but not for these dormant stages of reproduction.  Such behavior is very like that of a virus when it is not infectious and is one of the reasons for accepting viruses as a form of life or redefining life itself.

    The second was the discovery of the nature of viruses.  Viruses are bits of life (DNA coated with protein) that can't exist by themselves.  They can't reproduce without infecting the cells of another organism and when they do reproducing is all they do.  In the process they usually destroy the cells they infect.  When they are not infecting another organism they are dormant.  They do not participate in any of the other functions of life in the above list whether they are infecting or not.  Viruses turn out not only to be infectious agents problematical for life itself, they are also are problematical for the idea of life.

    The third was the realization after the identification of DNA and genes that proteins also play a curcial role in life.  Not only are they the product of DNA -- the messengers that DNA uses to express it self and direct the operation of cells -- they also control DNA and how it expresses itself.  Beyond this proteins can play a crucial role in an organism as shown by prions.  Prions are proteins gone bad -- abnormal forms of proteins -- that have been identifed as the cause of mad cow disease.  This disease can be transmitted by eating beef from an infected cow or the protein can sponteneously mutate creating disease where there was none before.  Whichever the mechanism of infection the result is the same -- destruction of the nerous system resulting in death.

    The definition of life is clearly not as simple as 10 easily memorized words.  The discovery of DNA and its central role in life provided another handle on the subject.  Now if we wish we can merely think of life as those chemical processes which center around DNA.  All living organisms use this same nucleic acid to control what it is that they do.  The ten characteristics from my biology class are all functions of these chemicals in some way.  Life can even be thought of simply as the manifesting (or reactioning) of these chemicals.  A living organism can be defined as one in which neucleic acids control its processes and characteristics.  Anything else is not living.

    On the other hand if we wanted to hone my Junior High definition of life by revising its original 10 functional  characteristics we might do so by adding these:
    These new functions are evolutionary functions and might generally be covered by saying that living organisms evolve.  Over generations characteristics that enhance an organism's survivibility become promenant while those that do not fade away.  While this is a useful addition to the concept of life it is also worth noting that it is a concept that applies to species and not individuals as the original 10 characteristics do.

    By introducting evolutionary functions we also launch into the midst of controversy for there are many people who do not wish evolution of be taught in schools.  They say that that it is just a theory (by which they mean not true), that other equally valid theories should be taught (which they then make up) or the subject should be presented critically (by which they mean it and only it should be criticized).  Unfortunately if life is whatever evolves then there is no other choice than this:  evolution must be taught in schools so that students may learn what life is.

    Evolutionary functionality is extremely useful for understanding the persistence and ubiquity of life.  Humans are extremely cleaver at being able to extract raw materials from the earth and craft them into all sorts of artifacts.  The one thing we have not mastered is making them persistent in the way life is.  Iron rusts.  Aluminum corrodes.  Even plastic degrades under the harsh ultraviolet rays of the sun.  Yet where this is the end of our creations it is just the beginning of life because life has learned the trick of taking inevitable decay and turning into a new beginning.     
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Created May 1, 2004, 
© 2004, Thomas A. Jonard