> Consider the molecules in a glass of water. Over time they rearrange
> themselves (if the water is not frozen). This is similar to random mutation
> and drift in a population. So your definition includes changes which have no
> phenotypic result at all. Surely the rearrangements of molecules in a glass
of
> water are not an interesting kind of "evolution". Why not simply call the
> genetic changes 'mutations' and be precise about it? Shouldn't the term
> 'evolution' be reserved for something more important?
You take your analogy too far. The random rearrangement of water molecules may
have no phenotypic effect in a glass of water, but stochastic evolutionary
processes certainly can have important effects on individuals and populations.
Even if they did not, why is this not evolution? You may or may not think
random changes are interesting, but that has no bearing. The definition which
you attack is simple, and defines what biologists call evolution. Which kinds
of evolution are most interesting and which processes are the most important
causes of evolution is debate and study which can only occur once we have
defined evolution. Defining evolution as "any change in the genetic
composition of a population" allows this.
I would also argue that stochastic evolutionary processes can be
extremely interesting and important. Mutations, whether they be single
base-pair changes, non-reduction of gametes, deletions, insertions, etc., play
a special role in evolution, since only mutation introduces new genetic
variation, without which other processes of evolution cannot occur. Mutations
provide the raw material of evolution. The other stochastic evolutionary
process is genetic drift. This refers to random fluctuations in gene
frequencies due to randomness in Mendelian segregation and random changes in
offspring number. In a small population, this process can cause the fixation or
loss of an allele regardless of its effect on phenotype. It can bring together
new allelic combinations which might not occur otherwise. These effects can be
important in later adaptive evolution. Some of the most important theories of
how evolutionary change occurs, like Sewall Wright's shifting balance theory
and Ernst Mayr's founder effect speciation, attribute important roles to
drift. Its actual importance in real populations still is not well known.
>> Tom Schneider
> National Cancer Institute
> Laboratory of Mathematical Biology
> Frederick, Maryland 21702-1201
>toms at ncifcrf.gov
John Bishop, Department of Botany, University of Washington, Seattle, WA
