From: rowe@pender.ee.upenn.edu (Mickey Rowe)
Newsgroups: k12.ed.science
Subject: Re: evolution
Date: 5 Jan 93 23:45:53 GMT
Organization: University of Pennsylvania

In article <33650.2B3F16C0@puddle.fidonet.org>
     Jim.Maroon@f33.n214.z1.fidonet.org (Jim Maroon) writes:

...

>        Two thoughts.  One, there are many examples of transitional change.
> Witness Hyeracotherium  to equus, the modern horse, among a myriad
> of others.

I think you did a reasonably good job for the most part, but a couple
of points need to be clarified.  In the above passage, you leave the
impression that horse evolution is a line leading from hyracotherium
(eohippus) to equus.  Perhaps this is a result of poor wording on your
part, but I'd like to make it clear that this chain of descent is not
predicted by evolution nor supported by the facts.  Evolution proceeds
by anagenesis (a single population whose features change over time)
and cladogenesis (a single population splits into two populations
whose features change independently of each others).  If only the
former mechanism existed, a straight chain from hyracotherium to equus
would be reasonbly expected.  However, because of the latter
mechanism, the tree of life (the begats of the fossil record if you
will :-) looks like a bush, not a ladder.  If anyone wants a synopse
of the history of horse evolution, I have a wonderful article
describing the various horse fossils and how they relate to each
other.  It was posted to talk.origins by Kathleen Hunt.

> Two, you are arguing with the rather old fashioned notion of how natural
> selection occurs.  It was once thought that species evolve slowly, over
> millions of years, and while they do to an extent, that is not the driving
> mechanism behind evolution.  Natural selection works best during times of
> trauma... 

Here you may have gone a bit astray.  Natural selection has been
turned on its head somewhat by modern biologists.  Some have gone so
far as to say that evolution proceeds in spite of selection rather
than because of it.  While that sentiment may be extreme, this is a
hot topic in biology today.  I hope everyone recognizes that I'm *not*
saying that there is controversy over the fact that evolution
occurred.  There is, however, controversy over how.

In the late 70's or early 80's, a man named Motoo Kimura proposed the
neutral theory of the evolution of species.  Under this framework,
populations evolve by picking up mutations that do not affect the
survival of the bearers of those mutations (i.e. the mutations are
selectively neutral).  In this scenario anagenesis is "propelled" not
by selection, but rather by genetic drift and other non-selective
mechanisms. 

Cataclysmic events ("times of trauma" like the asteroid that hit near
Chixculub and wiped out the dinosaurs 65 million years ago) do have
large effects on populations.  However, it seems that animals that
survive these cataclysms don't do so because they're well adapted
(adapted for a cataclysm is somewhat oxymoronic), and subsequent
radiation of species into the niches emptied by the cataclysm may well
not be driven primarily by selection either.

I also think that you waved away too many of Bruce's statements about
geology.  There are good explanations for Bruce's "facts", but they
require more than one line (i.e. "Earthquakes and plate tectonics, as
well as normal, minor shifting.")  However, I don't have the time nor
inclination to go through all of them (people would probably hate me
if I tried anyways :-)

>Internet: Jim.Maroon@f33.n214.z1.fidonet.org

Mickey Rowe     (rowe@pender.ee.upenn.edu)