Rod -
> Thanks for your responses. I haven't done a whole lot of
> reading on this issue but am probably as informed (or
> uninformed) as the average psychologist. However, I have
> heard that some intelligent design theorists make a
> distinction between macroevolution and microevolution.
(snip)
> How would you respond to that position?
Another intuition pump. From alt.talk.origins again, an article on
"macroevolution":
http://www.talkorigins.org/faqs/macroevolution.html
=======================
Conclusion
There is no difference between micro- and macroevolution except that genes
between species usually diverge, while genes within species usually combine.
The same processes that cause within-species evolution are responsible for
above-species evolution, except that the processes that cause speciation
include things that cannot happen to lesser groups, such as the evolution of
different sexual apparatus (because, by definition, once organisms cannot
interbreed, they are different species).
The idea that the origin of higher taxa, such as genera (canines versus
felines, for example), requires something special is based on the
misunderstanding of the way in which new phyla (lineages) arise. The two
species that are the origin of canines and felines probably differed very
little from their common ancestral species and each other. But once they
were reproductively isolated from each other, they evolved more and more
differences that they shared but the other lineages didn't. This is true of
all lineages back to the first eukaryotic (nuclear) cell. Even the changes
in the Cambrian explosion are of this kind, although some (eg, Gould 1989)
think that the genomes (gene structures) of these early animals were not as
tightly regulated as modern animals, and therefore had more freedom to
change.
=======================
In short, one mechanism. _We_ refer to it as microevolution
sometimes, and macroevolution at other times, but remember that evolution
operates on individuals, not on our conceptual categories. The difference
between macroevolution and microevolution is like the difference between a
beautiful blanket of snow covering a field and a damned snowstorm keeping
you from getting to the airport for your trip to Florida. We use different
terms, but as far as nature is concerned, they're one and the same. Once the
creationist admits that it snows (i.e., that microevolution occurs), he or
she has given it all away. It is not incumbent on the evolutionary theorist
to develop separate theories of "snow falling on a field" and "snow falling
on a road" (i.e., "microevolution" and "macroevolution").
That same article points out that "In Theodosius Dobzhansky's
Genetics and the Origin of Species, he began by saying that 'we are
compelled at the present level of knowledge reluctantly to put a sign of
equality between the mechanisms of macro- and microevolution' (1937, page
12)".
1937.
My impression is that the creationists got a lot of mileage out of
this intuition pump for a number of years, but recognized that it was
running out of gas as it had been refuted so effectively. The rise of the
"Irreducible Complexity" argument was simply the next straw to grasp.
Paul Smith
Alverno College
Milwaukee
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