-----Original Message-----
From: Chris Cogan <ccogan@telepath.com>
To: evolution@calvin.edu <evolution@calvin.edu>
Date: 17 August 2000 06:54
Subject: Macro, Shmacro
>This is one of Stephen Jone's tagline quotations:
>
>>--------------------------------------------------------------------------
>>"The changes within a population have been termed microevolution, and
>>they can indeed be accepted as a consequence of shifting gene frequencies.
>>Changes above the species level-involving the origin of new species and
the
>>establishment of higher taxonomic patterns- are known as macroevolution.
>>The central question of the Chicago conference was whether the
>>mechanisms underlying microevolution can be extrapolated to explain the
>>phenomena of macroevolution. At the risk of doing violence to the
>>positions of some of the people at the meeting, the answer can be given as
>>a clear, No." (Lewin R., "Evolutionary-Theory Under Fire: An historic
>>conference in Chicago challenges the four-decade long dominance of the
>>Modern Synthesis," Science, Vol. 210, pp.883-887, 21 November 1980,
>>p.883).
>
>
>Regardless, the empirical fact is that, genetically and morphologically,
>many species differ from each other in ways that amount to collections of
>microevolutionary changes, in the same kinds of ways we'd expect them to
>differ if one species evolved via microevolutionary steps from the other
>(or from a close common ancestor). This does not *prove* microevolution, of
>course. It just makes ID theory pointless until there is some *positive*
>evidence that macroevolution is not simply another word for multiple
>microevolutionary steps. In short, it has to be shown that the idea of
>macroevolution can be *relevantly* distinguished from microevolution. So
>far, all we have are *assertions* to this effect. If macroevolution simply
>*is* microevolution repeated a few times, ID theory loses its primary
>alleged reason for being.
>
>Since repeated (*cumulative*) microevolution is readily observable in the
>lab and in Nature, just what *is* the point of ID theory? Are ID folk
>claiming that there is some *limit* on the number of times microevolution
>can occur on one genetic subtree? If so, what is the *evidence* that there
>is any such limit, and just how many times *can* a genetic subtree exhibit
>microevolution before microevolution comes to a halt? And just what is it
>that forcibly prevents *further* steps of microevolution from occurring?
>What *keeps* populations of one species from evolving into other species if
>environmental conditions are favorable to such evolution? Why don't we see
>horrendous and insurmountable *stoppages* of further genetic variations as
>microevolutionary steps accumulate, and *regardless* of the biological
>advantages that such further steps would provide for the organism and the
>genomes involved? Why were humans able to breed (mostly by chance) broccoli
>*and* cauliflower *and* brussels sprouts *and* cabbage from the same
>initial plant? Why didn't the limitation on microevolutionary steps prevent
>this from happening?
>
>And, of course, if this can happen simply because people in different
>places and times preferred to grow plants with more of some features and
>less of others, why can't similar "selection" occur in nature, via climate,
>predation, nutrient availability, and so on? Since pleiotropism and genetic
>cross-linkages are obviously not enough stop microevolution in its tracks,
>just what *does* prevent microevolution from going that one more step and
>becoming macroevolution?
>
>Without strong answers to the core questions here (such as what evidence
>there is that there *is* a real limit on microevolutionary steps), ID
>remains just another scientifically superfluous crackpot theory promoted
>almost entirely for religious reasons.
Chris, you're overlooking an important point. Speciation (and hence
macroevolution in the sense that it's used by Lewin) *has* been observed.
And even ID proponents have accepted this. (I seem to remember seeing a
statement to that effect by Phillip Johnson--I'll try to find it.) So our
knowledge of macroevolution is not based on extrapolation alone, but on
direct evidence.
As we know, creationists/IDers use the term macroevolution differently, to
mean major changes well above the species level. But that has nothing to do
with Lewin's statement above, and no additional mechanisms are needed when
going from small changes at or above the species level to larger changes.
In other words, any *apparent* problem posed for evolution by Lewin's
statement above is purely an artefact of the anti-evolutionists' equivocal
use of the word "macroevolution".
Richard Wein (Tich)
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