Gary,
    Here are my answers to your questions.  I speak only for myself.

>  1. Can microevolution lead to species-level differences in principle?

I have no objection to this possibility, though I do not believe it has been
observed.  I am aware of genetic studies and zoogeographical analyses which
would indicate that this is possible.

>  2. Do you agree that there are observed instances of speciation?
>
>  If your answer is no, look at outline point 5.0 at
>  <http://www.talkorigins.org/faqs/faq-speciation.html> which summarizes
>  cases put forward as observed examples of speciation. Why aren't these
>  cases convincing, and what kind of evidence would you require?

I am unqualified to comment regarding speciation in plants.  The outline did
suggest that speciation through hydridization, etc. may not apply to animals,
except possibly insects.   Though I am skeptical of Mitochondrial DNA studies
(I believe the science is still young and uncertain), I would be persuaded of
speciation of species in isolated populations studied over a period of time
(say 50 -100 years).  I know such might not occur in my lifetime, but such a
detailed study should detect genetic changes in the population(s) due to
changing environment, etc.

>  3. What kind of evidence would convince you that macroevolution occurs?
>
>  The specific case suggested by Doug, a crustacean species arising from a
>  mollusk species is not realistic, because evolution does not suggest that
>  mollusks gave rise to crustaceans, but rather that at some point they had a
>  common ancestor. His more general request for one phylum giving rise to
>  another is also problematic. If I found evidence that one phylum gave rise
>  to another, I would consider the phyla to be synonyms, so the example would
>  evaporate. I think the question has to be phrased as one major group giving
>  rise to another. As soon as ranks get involved, things get slippery.

I suppose I oversimplified macroevolution, but I believe what I suggested is
the concept of macroevolution that most of us adhere to.  Evidence from the
fossil record demonstrating one phyla becoming another phyla would be
persuasive.  I do not consider Archaeopteryx such evidence.  Even
evolutionists are divided as to the placement of Archaeopteryx.  Now suppose
a fossil or fossils demonstrating dinosaurs becoming Archaeopteryx and then
fossil evidence demonstrating Archaeopteryx becoming a bird - that would
cause me to take a closer look at the evidence.

Please explain the lack of such intermediate fossils.  Dr. Patterson (?) of
the British Museum of Natural History has said he does not know of the
existence of any such fossil evidence.

 >  What if something evolved entirely by macroevolution? Blammo, in one giant
>  mutation, something vastly different appeared. How different does it have
>  to be? If I can't find an example of a "phylum" giving rise to a phylum,
>  would an "order" or "family" or "genus" do? What evidence would you accept
>  from the fossil record? What evidence would you accept from the genetics of
>  living animals? I think if we can agree on what kind of evidence is
>  acceptable, we might inch a little closer to understanding, if not to
>  resolution.

Mutations generally do not improve a species.  As for the other questions, I
believe I have already answered them above.

Doug Shelton
Mobile, Alabama