"Tim Tyler"  wrote in message
news:c9fpql$19jr$1{at}darwin.ediacara.org...
> Jim Menegay  wrote or quoted:
>
> > But some researchers go farther and claim that mutations
> > leading to alleles that usefully respond to the stress
> > are more likely when the stress is present.  This idea
> > is widely considered to be heresy.  It apparently conflicts
> > with one of the core axioms of neo-Darwinism - that
> > mutation is "random".  Nevertheless, apparently solid
> > empirical results in microorganism systems repeatedly
> > back up this claim of environmentally directed mutation.
>
> [...]
>
> > In any case, results like these have always puzzled me.  What could be
> > the mechanism?
> >
> > Well, I finally ran across a paper that suggests a mechanism.
> >
> > Wright BE.
> > A biochemical mechanism for nonrandom mutations and evolution.
> > J Bacteriol. 2000 Jun;182(11):2993-3001
> > http://jb.asm.org/cgi/content/full/182/11/2993
> >
> > Without endorsing what she says about evolution, I think that
> > I can agree with what she says about mechanism.  Basically,
> > it is that DNA segments that are being actively transcribed
> > are more at risk of mutation than segments that remain
> > continually in double-stranded form.
>
> [...]
>
> > The proposed mechanism is even more powerful in diploid, sexual
> > organisms.  Recombination is also more likely in DNA segments
> > that are actively being transcribed!
>
> How come?  Don't large orgainsims keep their germ-line DNA in
> insulated boxes, well away from the daily toil?
>
> ISTM that this effect would be much reduced in organisms with a
> germ/soma division, since they can take steps to insulate their
> germ line from the environment.

An excellent point.  This mechanism does not apply to the larger
metazoa.  Animal fans will have to come up with a different
mechanism if they wish to be neo-Lamarkian.  Culture has been
suggested as one mechanism.

AFAIK, plants are large organisms that don't generally do
germ line sequestration, though.  Also, I'm not sure to what
extent even germ line DNA gets transcribed for housekeeping
functions in animals.
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