Since this debate seems at risk of subsiding, I thought I'd try to clarify
a few things. By the way, I think evolution vs creation is an appropriate
topic for Conch-L, since mollusks evolve (but do not play sports) and since
they give some of the best evidence for evolution. The debate so far has
been more productive than most of this sort, perhaps because members of
this group has been talking to each other for a couple of years, so we are
a bit more open than we might otherwise be.
First, if you accept creation or evolution as a matter of pure faith, we
are outside the realm of science, and there is no point debating further.
However, all of us participating in this debate have been used evidential
reasoning, so we are in the realm of science.
Next, let's define some terms. Doing a web search reveals that even among
biologists, there is no consensus as to the definitions of micro- and
macroevolution. Here's some of the variety.
*Macroevolution refers to studies of evolutionary patterns and processes
that manifest themselves on time periods longer than the evolution of
single species
*Macroevolution is the origin of taxonomic groups higher than the species
level.
*Macroevolution = large scale evolution at & above species level
Microevolution = small scale evolution at the population level.]
*Macroevolution refers to large scale patterns, trends and rates of change
among groups of species
*Macroevolution: patterns and processes operating at or above the species
level. Microevolution: patterns and processes operating at or below the
species level.
And the State of South Carolina, 1995: "macroevolution is defined as the
premise that life evolved from nonlife or that randomness and chaos
produced order and design." <http://www.lpitr.state.sc.us/bil95-96/3462.htm>
The creationists participating in the debate seem not to object to
microevolution, but don't think that it accounts for large scale
differences, like those between phyla. As Emilio has noted, some biologists
have the same objection, hence macroevolution. For some interesting
quotations see
<http://id-www.ucsb.edu/fscf/library/origins/quotes/macroevolution.html>.
For the purposes of debate on Conch-L, can we define microevolution as
"gradual genetic change within a species" and macroevolution as "genetic
changes that lead to large scale differences above the species level"? (I
leave out the species level itself for the moment as a zone of ambiguity.
Maybe we should call that mesoevolution.)
I say genetic, because changes that are not genetic are not inheritable.
For example, the snail ^Puperita pupa^ changes from a striped pattern to a
spotted one depending on the salinity. [The genetic changes usually thought
responsible for microevolution are recombination (which brings together new
combinations of existing genes through sexual reproduction), and single
nucleotide mutations, which can create new forms of genes (which are called
alleles). In macroevolution, the genetic changes might be duplication,
deletion or silencing of a gene, duplication of chromosomes, rearrangement
of the order of genes, changes in control regions of genes, transfer of
genes between species, etc.]
Questions for creationists of all stripes (and spots):
1. Can microevolution lead to species-level differences in principle?
If your answer is no, what evidence would you accept to convince you
otherwise? (If the answer is none, then we are outside the realm of science
again.)
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?
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.
If one thinks that microevolution is responsible for all the diversity of
life, then the point at which the line leading to mollusks and the line
leading to crustaceans diverged would look exactly like divergence between
any two garden variety species. If one thinks that a combination of
microevolution and macroevolution occur, there is no reason to expect that
the point at which the mollusk line and crustacean line diverged was
macroevolutionary. Maybe it was a microevolutionary divergence, and then
macroevolutionary changes happened somewhere along the branches.
The fossil record provides many examples of amazing morphological change.
For example, the invasion of land by tetrapod ancestors, and the reinvasion
of the sea by whales and other mammals. (These are the subject of Carl
Zimmer's 1998 book "At the Water's Edge: Macroevolution and the
Transformation of Life" that someone mentioned. See
<http://energion.com/books/science/waters_edge.html> for a review). If this
evidence of change from the fossil record is rejected because we weren't
there to observe the change, then what kind of evidence would be acceptable?
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.
Gary
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Gary Rosenberg, Ph.D. [log in to unmask]
Malacology & Invertebrate Paleontology gopher://erato.acnatsci.org
Academy of Natural Sciences http://www.acnatsci.org
1900 Benjamin Franklin Parkway Phone 215-299-1033
Philadelphia, PA 19103-1195 USA Fax 215-299-1170
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