Evolution vs. De-Evolution

Richard Norman rsnorman at mediaone.net
Wed Sep 20 21:34:02 EST 2000


"Tuphat" <enantiodromiac at my-deja.com> wrote in message
news:8qb70n$i4u$1 at nnrp1.deja.com...
> 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?

Yes, tapeworms have no digestive system of their own.  Parasites are
often highly specialized (i.e. highly "advanced", using an earlier
terminology)
even though their specialization is to become simpler.

If you put very complex organisms like modern humans at this end of
evolution
and obviously less organized single-celled creatures at the start, it does
look
like there is a directionality to it.  But modern flatworms and modern
mosses,
not to mention modern bacteria, have gone through the same several billions
of years of modification and selection and evolution as we humans.








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