From: Keith Miller (kbmill@ksu.edu)
Date: Wed Aug 13 2003 - 21:11:33 EDT
On Wednesday, August 13, 2003, at 10:18 AM, Walter Hicks wrote:
> I agree that all of these (and ones offered by Terry) affect
> evolution, but I don't see most of them as alternatives to natural
> selection. For the most part they introduce variation and then natural
> selection filters out the ones that are not useful for survival.
> Catastrophic changes are an exception and certainly would represent a
> non-"Darwinian" effect.
Firstly, the issue is not an either/or choice between natural selection
and something else. The question is what is the relative importance of
different processes under different circumstances and at different
heirarchical scales. Natural selection is always operative -
although its impact may be masked by other processes.
Genetic drift and the founder effect are examples where new mutations
can be fixed in a population (usually small) without the filtering
effect of natural selection. These processes may be especially
significant during speciation. Sexual selection is likely another
important driver of evolutionary change.
Another example at a larger scale is species selection. In this case
lineages that have higher speciation rates would displace closely
related lineages with low rates of speciation. The ultimate success of
lineages in this case would not be controlled by natural selection
which operates at the level of the individual.
Major extinction events likely had very important impacts on the
direction of evolution on a large scale. Such effects would be
independent of natural selection.
Keith
Keith B. Miller
Research Assistant Professor
Dept of Geology, Kansas State University
Manhattan, KS 66506-3201
785-532-2250
http://www-personal.ksu.edu/~kbmill/
This archive was generated by hypermail 2.1.4 : Wed Aug 13 2003 - 21:20:25 EDT