Does life
have a meaning?
Life, it might be argued, is the distinguishing feature of all organisms and
may most usefully be thought of as involving various kinds of complex systems
of organization providing individual organisms with the ability to make use of
those energy sources available to them for both self maintenance and
reproduction. Underlying this deceptively persuasive definition, however, lie those persistent traditional problems inherent in the
search for an essential, distinctive substance characteristic of all forms of
life. Additionally, as evolution theory makes clear, there is the problem of
borderline instances, organisms of which it is not easy to say whether or not
they may be defined as being alive. One such case is that of the virus.
Viruses are the smallest, simplest living things, smaller than bacteria, and
the cause of some of the deadliest diseases known to humanity. They are
composed chiefly of nucleic acid wrapped in a coat of protein and are able to
multiply only from within living cells. As with all other organisms, the virus
depends for its ability to obtain energy and carry out the other processes
necessary to sustain life, upon its stock of DNA, the hereditary material that
makes up the genes, the "instructions" that determine the traits of
every living organism. What is interesting about viruses, however, is that
their genetic stock is very meagre indeed, so much so
that reliance upon it alone cannot enable them to survive. Nonetheless, viruses
do persist from one generation to the next, as if they were alive. How this is
managed, as it clearly is in both plants, animals and
human beings, bears importantly upon the ways in which "life", at
least in the case of viruses, may legitimately be defined.
