>In a message dated 3/30/98 01:39:46 AM, WITTERSJ@ESUVM.
>EMPORIA.EDU wrote:
>>A separate consideration within the "Darwinian scenario"
>>is the issue of speciation. As Gould has argued, the
>>microevolutionary model of change cannot explain what is
>>observed in the fossil record. Would Gould argue that
>>speciation occurs by processes independent of any
>>Darwinian (evolutionary) process?
>
>Jeff,
>
>Of course not. He gives an example in the Natural History
>article of snails from the Bahamas that he studied. He
>found snails on a single mud flat that had gradually
>changed over 10,000-20,000 years. He showed that the snail
>changed gradually from an extinct species to the modern
>species. While he doesn't explicitly spell out the
>Darwinian mechanism he gives no reason to suppose that any
>other mechanisms were involved.
Bob,
Gould does give the Darwinian (hereafter, evolutionary)
mechanism involved in his snail example: reticulate
speciation. Hybridization. There are only two ways for
a species two form: cladogenesis or ret. speciation. That
is, splitting or lumping. In his case yellow and blue made
green.
>But the point...
I must assume you mean your point as what follows was not
Gould's point.
>is that the change only produced another *species* of
>snails, no higher or more general forms. That's the
>point. Microevolution (Darwinian mechanisms) does not
>produce macroevolutionary innovations. If you have
>examples of general, more inclusive organisms arising
>specific ones, let's have them.
"Change" can only produce another species (or not), but
not more than another species in the taxonomically
hierarchical sense. For the sake of arguement, let's
say that Gould's snails had split (cladogenesis) to form a
new genus in addition to the old one, *Cerion*. How could
we know that a new higher taxon (I am presuming higher
taxa than species when you refer to "higher or more
general forms") has been formed? We cannot. Only in
retrospect can we make distinctions at any taxonomic level
above species. This is because species are the only real
entity in taxonomy; the rest are artificial distinctions
for the above reason. Therefore you are asking for a
logical impossibility by dismissing a speciation event and
asking for a "generation" or "classation" event without
the requisite speciation.
So then, having *only* produced a species is NOT the point.
Gould's point is that while the popular idea that evolution
cannot be observed is false ("short-term evolution"),neither
can studies of short-term evolution be directly extrapolated
into an explanation of the "true" rate of evolution as
observed in the fossil record. Before you say, "Ah ha"!,
please take note. They cannot be extrapolated because what
is observed is "stasis [as] a dynamic phenomenon" (p.64 in
the article). To risk beating a dead finch, er..horse :),
I bring up again the Grant's work. It shows precisely
dynamic stasis (or, running nowhere fast). A severe drought
on a little island in the Galapagos produced a strong
directional selection gradient which stuck. Until a
combination of conditions several years later served to
reverse that gradient. The finches were back +/- where they
started. This is the remarkable constancy observed in the
fossil record. Gould pointed out that his 10-20K yr
transition (a puncuation in the equalibrium) would have
composed a single bedding plane in a fossiliferous
sequence -- an otherwise static sequence.
As for those examples you requested...
I remembered while writing this reply that Keith Miller has
an essay on the ASA homepage which if I remember correctly
has a much more eloquent and thorough documentation of
what you have requested. That notwithstanding I shall go
ahead and give you an brief example even though I
have likely already exhausted my daily allotment of time
to be spent rambling.
Yes, the mammal-like reptiles. The mammal-like
reptiles are a good example of the origination of a higher
taxon (Class Mammalia). Synopsis: Synapsida, the
mammal-like reptiles, had the classic (& definitive) jaw
articulation of articular on quadrate. Mammals end up (or
at least may be observed) with a dentary-squamosal joint.
But evolution postulates intermediates, and that is just
what we get. They are not the silly creatures as
caricaturized by some with useless jaws and stone deaf
as they make the "leap". Instead we observe a nice
progression through the fossils of: a-q, a-q & d-s, d-s.
Here is where we see the artificial (or arbitrary)
nature of higher taxonomy. The Class Mammalia appears
(*in retrospect*) with the first presence of a single
jaw joint with the dentary-squamosal articulation. Of
course there is a monumental suite of characters that
also are tagging along, but the joint is the
definitive one. From the perspective of a "bystander"
the emergence of a new class would be unobserveable.
Only a speciation would be observed.
If there is anything in this reply that contradicts
something I wrote last, it is likely because a
committed the inexcusable error of commenting on what
you said Gould thought rather than waiting to comment
on what *I* read Gould to be saying. Or it is
because this late hour seems to be the only time I
have to carry on with this indulgence. No se.
Unless something else really interests or goads me, I
will have to leave this for someone else to pick up
should anyone so desire.
Thanks for the interesting dialogue and a chance to
dust off some neurons.
Respectfully,
Jeff