Re: Nei's "new mutation theory" resurrects William Bateson


<arlin.stoltzfus@xxxxxxxxx> wrote in message news:fjumub$22ta$1@xxxxxxxxxxxxxxxxxxxxxx
On Nov 3, 12:29 pm, j...@xxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxx (Joe
Felsenstein) wrote:
In article <fgd4qr$fe...@xxxxxxxxxxxxxxxxxxx>,
forsdyke <forsd...@xxxxxxxxxxxxxxx> wrote:
The idea that "natural selection is of secondary importance" in
evolution has recently been recalled by Masatoshi Nei in "The New
....
I think two other people in present-day biology have similar views to what
Nei is saying, if I it correctly. Arlin Stolzfus, and um, er, Donald Forsdyke.
Or do I misunderstand?

Yes. First, there are not just a few, but MANY biologists today who
hold a mutationist view. Most of them (probably including yourself,
Joe) don't know it-- they don't accept the label, out of ignorance,
misinformation, or fear. Second, neither Nei nor I (don't know about
Donald) is proposing to go back to the views of 1906.

What is mutationism? Unfortunately, the only version most people know
is the false version propagated by *opponents* of mutationism such as
Ernst Mayr. Would anyone out there learn Darwinism from a
creationist? So why do so many people think they know what
mutationism is because they have read Mayr? I learned it by reading
the mutationists themselves-- Morgan, Punnett, Shull, et al.

The actual historical version of mutationism was the Old Synthesis (of
genetics and selection) that preceded the "New" or Modern Synthesis
(MS). Mutationists saw evolution as a two-step process of mutation
followed by acceptance/loss. It would be more accurate to call this
the mutation-selection view, but don't blame this on the
mutationists-- they didn't invent the label. A harmless mutation might
be accepted by chance (i.e., neutral evolution), but the probability
of acceptance would be increased if the mutation had a beneficial
effect (i.e., adaptation). This gave a new twist to the concept of
"selection" or "survival", a significance not apparent in Darwin's
theory, which invoked a fuzzy continuous process of variation, and
rejected any role for distinctive sports or mutants.

The MS argued instead that adaptation occurs by shifting the
frequencies of alleles (with infinitesimal effects) already present in
the "gene pool". They redefined "evolution" as "shifting gene
frequencies". Of course, they knew that the origin of new alleles by
mutation had to be included SOMEWHERE, but they forced it to enter
through the back door (so to speak), not as part of evolution, but via
the precondition that "evolution" (= shifting...) can't happen unless
there is heritable variation; they insisted that mutation had no
direct or controlling influence on what happens in evolution, due to
the buffering capacity of the "gene pool".

Today, the two-step view of the mutationists is the framework of
adaptation implicit in cutting-edge work in evolutionary genetics such
as Orr's models of adaptation: a mutation is introduced, and it faces
acceptance with some probability. This two-step view is the basis for
the novelty of the Neutral Theory (not the same as mutationism, since
the NT focuses only on neutral changes) and for many subsequent
advances in molecular evolution. We now know that evolution depends
on the rate of mutation in a way that the architects of the MS
rejected outright. The dependence is so sensitive that just a few-
fold difference in rates of mutation (e.g., transition:transversion
bias) shows up in the pattern of evolutionary divergence.

I would like to explain more implications, but I've said enough. The
next step is for a bunch of know-nothings to jump in and tell me that
I'm a century out of date and that I just need to read a textbook to
get straightened out on how evolution really works.

Arlin, I also would like to thank you for posting here. (Thx also to JF
and DF). I am strictly an amateur myself, but nothing you have written
here on how evolution really works strikes me as particularly unorthodox.
Your take on the intellectual history is mildly out of the mainstream,
though I think you are right to claim that people of the 'synthesis'
generation were at least surprised by and in some cases hostile to the
new results produced by Kimura and Nei. As to whether Nei's
(correct) viewpoint is closer to the classical mutatationists like
Bateson than to 'synthesists' like Dobzhansky - well, I don't know
enough history to judge.

It is obvious that mutation provides the 'fuel' for adaptive evolution,
and that it may, in some situations, hold the speed of adaptive
evolution "on a leash". It is not clear to me how common this
kind of situation is.

It is also clear that that for some attributes (such as G+C / A+T
ratio) that mutation provides direction to the evolutionary
trajectory.

I'll even agree about the "synthesists" that you quoted elsewhere
in this thread to the effect that mutation rate cannot be an
important determinant of the rate of evolution because it is
only supplies a trickle into the pool of variation - those guys
are either being silly or else they are addressing a slightly
different issue than the one your quotation made it seem
that they were addressing. (They are right if they are saying
that short-term fluctuations in mutation rate are not the cause
of short-term fluctuations in allele fixation.)

But I am not aware of any other reasons for placing mutation
up there with selection as a major player in evolution. Your
comments that "... just a few-fold difference in rates of mutation
(e.g., transition:transversion bias) shows up in the pattern of
evolutionary divergence" intrigues me. What are you saying
here? Do you have a cite?



.

Relevant Pages

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