Evolution vs. De-Evolution

Tuphat enantiodromiac at my-deja.com
Wed Sep 20 15:34:32 EST 2000


In article <39C643B2.EF0D09F5 at unf.edu>,
  jander at unf.edu ("John E. Anderson") wrote:
> "L.A. Loren" wrote:
> >
> > Mutations are
> > almost always bad in that they rarely lead to changes that are helpful.
>
> Is that true?  I agree that most mutations are not helpful, but they are
> not necessarily bad.  What proportion are neutral?
>
>
I dunno, ask Motoo Kimura ;-)

Actually this is a very good question, because people are conditioned to
think in dichotomous terms of beneficial (adaptive) and deleterious
(maladaptive), because popular (mis)conceptions of evolution fail to
delineate between the process of evolution and the mechanism of selection.
Evolution is not wholly selection related or adaptive. There is also the
mechanism of genetic drift where alleles can become fixed in a population or
removed from a population just as a matter of sampling error in small
effective population size.

A basic, bare-bones definition of evolution is "change in allelic frequencies
within a population over time". Selection and drift are known mechanisms
which can result in these allelic frequency shifts. Selection relates to
fitness and adaptation, where drift relates to random sampling errors.

In molecular evolution there is the neutral theory of Motoo Kimura and not
having the requisite theoretical background to present these ideas, I'd
merely say to the interested reader that they should look it up.

The title of this thread, using words like evolution versus de-evolution
reflects some wrong-headed notions about evolution. Evolution is not
equatable or synonymous with progress up a scala naturae or increased
complexity or adaptation. Looking at things in an adaptive light, a loss of
limbs or whatever morphological features can be selected for, just think of
fossorial animals which burrow through sand. Think of snakes, which lost
limbs when compared to legged tetrapod progenitors. Cave fish sometimes lose
full functionality of their eyes, but I'd hardly call this de-evolution. It's
just evolution (whether thought of in an adaptive light or not). I think that
some parasites tend to become simpler when they adapt to their host
environment. Maybe this is a more efficient mode. I'm drawing a blank, but is
it tapeworms or another intestinal parasite which lost or reduced its own
digestive capacities?




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