Definition of evolution

Marc Roussel mroussel at alchemy.chem.utoronto.ca
Fri Nov 1 17:04:40 EST 1991


In article <1991Nov1.204320.15138 at gpu.utcs.utoronto.ca>
lamoran at gpu.utcs.utoronto.ca (L.A. Moran) writes:
>      Biological evolution is the process of change in the genetic
>      makeup of a population.
>
>I submit that this definition is necessary and sufficient to define evolution.
>It is necessary because there are no known exceptions to the definition.

     This is an abuse of the terminology.  The terms necessary and
sufficient conditions have precise meanings in mathematics.  As Larry
seems to be using them in a similar sense, he should not redefine them
in this implicit manner; either use the terms as they are defined, or
state clearly your definition.  A sufficient condition is one such that
if the condition is satisfied, the result follows.  Larry is therefore
right that his definition is a sufficient condition for evolution: if
the genetic makeup of a population changes, then surely this is
evolution by any reasonable definition of the term "evolution".
     On the other hand, a condition is necessary if it describes the only
way in which the result follows.  Change in the genetic makeup of a
population is thus not a necessary condition for evolution unless one
defines evolution as a change in the genetic makeup of a population.
This is what Larry wants to do (probably justifiably), but then to say
that change in the genetic makeup of a population is a necessary
condition for evolution is a tautology.  We don't normally allow trivial
tautologies to be necessary conditions.  (Since all theorems are
tautologies, it is perhaps a matter of taste as to which ones represent
nontrivial tautologies; I don't think that Larry's statement can be
claimed to be nontrivial however.)  It would have been better to say the
following:

      Biological evolution is the process of change in the genetic
      makeup of a population.

      This is a sufficient condition for evolution.  We believe that it
      is the only mechanism, i.e. it is a law of nature that evolution
      only proceeds by changes in the genetic makeup of a population.

or, better

      Change in the genetic makeup of a population is a sufficient
      mechanism for evolution.  Faced with a lack of counterexamples, we
      currently believe that it is a law of nature that this is the only
      mechanism for evolution.

     I believe that it is important for scientists to express themselves
clearly.  The terminology of mathematics is particularly well defined
and we should be very careful when using it for fear of spreading
inaccurate impressions of one's thoughts.

                                Sincerely,

				Marc R. Roussel
                                mroussel at alchemy.chem.utoronto.ca



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