Re: [asa] Two questions

From: D. F. Siemens, Jr. <>
Date: Wed Apr 15 2009 - 14:22:10 EDT

I'm not a master of history or genetics, but I have ideas relative to
your questions. First, Darwin was Lamarkian, which specifically required
small changes from generation to generation. This mirrors what George
noted. Second, drift is essentially without benefit. A change may be
deleterious. This would be taken out if it were not balanced against some
benefit. I think of the cost of fancy feathers on male birds, balanced by
sexual selection. If, on the other hand, the change is beneficial, it
would be subject to positive selection. In other words, drift contributes
nothing relevant to an evolutionary sequence. The only place I can think
of where it might be relevant is something neutral. This may be the
situation with the blackbirds I encounter. Some are black, but there are
a number of dark brown ones also. I'll be embarrassed if these turn out
to be sexual variations.
Dave (ASA)

On Wed, 15 Apr 2009 00:00:03 -0400 "Nucacids" <>
Let me quote from Eugene Koonin’s recent paper, “Darwinian evolution in
the light of genomics” (Nucleic Acids Research, 2009, 1–24). These are
twp excerpts from where he is outline the principal concepts of the
Modern Synthesis.

“Evolution proceeds by fixation of the rare beneficial variations and
elimination of deleterious variations: this is the process of natural
selection that, along with random variation, is the principal driving
force of evolution according to Darwin and the Modern Synthesis. Natural
selection which is, obviously, akin to and inspired by the ‘invisible
hand’ (of the market) that ruled economy according to Adam Smith, was the
first mechanism of evolution ever proposed that was simple, plausible,
and did not require any mysterious innate trends. As such, this was
Darwin’s second key insight. The founders of population genetics, in
particular, Sewall Wright, emphasized that chance could play a
substantial role in the fixation of changes during evolution not only in
their emergence, via the phenomenon of genetic drift that entails random
fixation of neutral or even deleterious changes. Population-genetic
theory indicates that drift is particularly important in small
populations that go through bottlenecks (6,16). However, the Modern
Synthesis, in its ‘hardened’ form (13), effectively, rejected drift as an
important evolutionary force, and adhered to a purely adaptationist model
of evolution (17).”
“The beneficial changes that are fixed by natural selection are
‘infinitesimally’ small, so that evolution proceeds via the gradual
accumulation of these tiny modifications. Darwin insisted on strict
gradualism as an essential staple of his theory: ‘Natural selection can
act only by the preservation and accumulation of infinitesimally small
inherited modifications, each profitable to the preserved being . . . If
it could be demonstrated that any complex organ existed, which could not
possibly have been formed by numerous, successive, slight modifications,
my theory would absolutely break down.’ [(1), chapter 6]. Even some
contemporaries of Darwin believed that was an unnecessary stricture on
the theory. In particular, the early objections of Thomas Huxley are well
known: even before the publication of the Origin Huxley wrote to Darwin
‘‘You have loaded yourself with an unnecessary difficulty in adopting
Natura non facit saltum so unreservedly’ (18).”
Here are my two questions:
Why did Darwin insist on strict gradualism as an essential staple of his
Why did most proponents of the Modern synthesis reject drift as an
important evolutionary force, and adhered to a purely adaptationist model
of evolution?
- Mike
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Received on Wed Apr 15 14:26:35 2009

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