In article <Pine.SUN.3.91.950614115747.25439H at castor.cc.umanitoba.ca> gordonr at cc.UManitoba.CA (Richard Gordon) writes:
>Is natural selection sufficient to explain progressive evolution, or is
>there something about the structure of the genome that enables the latter?
>>-Dick Gordon, U.Manitoba[Jun14,95]
What, precisesly, is meant by the term "progressive" evolution? Is this
the same thing as "adaptation," or is it something else? Adaptation
resulting from the action of natural selection on heritable variation
need not be progressive. The fitness of an individual is a function of
its environment. Natural selection can increase the frequencies of certain
alleles, perhaps raising them to 100%. This population could be doomed
if the environment changes. In fact, wasn't this one of the early
arguments against Darwinian evolution: that it did not guarantee
progressive evolution to some "higher" organism (e.g., humans)?
Perhaps an analogy to Darwinian evolution would be a radio with
quartz-lock tuning that seeks the nearest station on the dial that "comes
in" over a certain threshold level. It doesn't guarantee that you'll
progress up the dial, or down the dial, but it should do a pretty good
job of finding *something* to listen to (unless there's just nothing out
there).
Rich Kliman
Dept. of Biology
Radford University
