Re: Hominid fossils FAQ file

Andrew MacRae (macrae@geo.ucalgary.ca)
Tue, 3 Jan 1995 07:22:19 GMT

In article <3e7tu5$qb8@charm.magnus.acs.ohio-state.edu>
bharper@magnus.acs.ohio-state.edu (Brian D Harper) writes:
>
> In article <3e7dk7$snr@nntp1.u.washington.edu>,
> Kathleen Hunt <jespah@u.washington.edu> wrote:
> >>In article <3e1nv9$ouc@newsbf02.news.aol.com>,
> >>Steve ThM <stevethm@aol.com> wrote:
> >>>
> >>>Granted, there are transitional forms within certain species. But
> >>>can you list one clear-cut, completely authenticated transitional
> >>>form between one species and another species? I do not believe you
> >>>can. If so, please file the name of it to me for study.
> >
> >I posted several such examples just LAST WEEK. Perhaps you didn't see
> >them. So here they are again.
> >
> >I particularly recommend you find Gingerich's 1980 paper and look
> ^^^^^^^^^^^^^^^^^^^^^^
> >carefully at the figure that shows *hundreds* of specimens from entire
> >*populations* of fossils, slowly diverging in average morphology until
> >there were two distinct populations, which slowly became two distinct
> >species, which slowly became two distinct genera, etc. [....]
>
> Awhile back, Jim Lippard sent me an article by Donald Prothero on
> punctuated equilibrium. Below is an exerpt which discusses Gingerich's
> papers. I would be interested in your comments.
>
> The complete paper can be obtained by anon. ftp:
>
> //rtd.com/pub/zines/skeptic/01.3.prothero-punc-eq
>
>
=========================================================================
> When the punctuated equilibrium paper first came out, reactions
> were mixed. Since 1972 there have been many traditional
> paleontologists who denied its importance, and trotted out their
> favorite example of gradual evolution. Many of these "classic"
..

> For example, one of the main proponents of gradualism, Philip
> Gingerich (1976, 1980, 1987), showed just two or three examples of
> supposed gradual evolution in early Eocene (about 50-55 million
> years old) mammals from the Bighorn Basin of northwestern Wyoming.
> But a detailed examination of the _entire mammal fauna_
> (monographed by Bown, 1979, and Gingerich, 1989) shows that most of
> the rest of the species do not change gradually through time. Also,
> studies on specific lineages in restricted areas cannot account for
> the possibility that a gradual transition may actually reflect the
> migration of a clinally varying population across a region through
> time. This was documented by Schankler (1981), who showed that some
> of Gingerich's patterns from the northern Bighorn Basin did not
> even hold up in the southern
> Bighorn Basin, just a few dozen miles away!
> -- Donald R. Prothero, "Punctuated Equilibrium at Twenty:
> a Paleontological Perspective", _Skeptic_ vol. 1, no. 3,
> Fall 1992, pp. 38-47.
>
>
> [...]
>

Yes, there are some problems with Gingrich's documentation of the
changes in mammal faunas in the Bighorn Basin. In fact, the possibility
of clinally-varying populations migrating across an area with time is a
potential problem for some other examples of gradual evolution in the
fossil record (including ones I happen to be working on :-)). However, it
can not explain all of them, and it is *very* difficult to document. It
is time-consuming to document detailed changes within a small area, let
alone the regional, sometimes global scale necessary to properly document
the evolution of a group of organisms to the point of excluding all other
possibilities. High-resolution, large geographic area work is difficult.
The pattern Gingerich documents may still turn out to be correct in some
aspects, particularly if there are unforseen geological complications. It
will be a while before the issue is definitively solved. I should check
to see what the latest story is.

An example of one transitional lineage that is unlikely to be
anything but evolution is the brachiopod _Eocoelia_, documented in papers
by Zeigler and other authors. The same succession of four species with
the same morphological trend is observed globally in rocks of Silurian
age. You can find images and references at:

http://www.geo.ucalgary.ca/~macrae/talk_origins.html

I'm sure there may be other potential explanations for this
lineage, but the problems with Gingerich's analysis is not one of them.
There are also plenty of transitional lineages (series of species or
morphoclines within species) that appear to be legitimate, and are
difficult to interpret as anything other than what they appear to be. For
example, the land mammal to whale transitional species are quite
convincing.

--



	-Andrew

	macrae@geo.ucalgary.ca

	home page: "http://geo.ucalgary.ca/~macrae/current_projects.html"