On 4/18/2013 8:15 AM, John Clark wrote:
On Wed, Apr 17, 2013 meekerdb <[email protected]
<mailto:[email protected]>> wrote:
> It's been proposed that the susceptibility to mutation is itself a
characteristic
subject to natural selection.
If a animal is undergoing stress (too hot, too cold, too thirsty, too hungry whatever)
that means there is something about it that is not well adapted to its environment; I
can imagine a gene that in times of stress would switch on and produce a chemical that
increases the rate of random mutation in the genes of the offspring of that stressed
animal. Most of the offspring would have mutated in the wrong direction and die but they
would have probably died anyway because they would have been as poorly adapted as there
parent was, but if the mutational effect was not too strong (even if it's in the right
direction you can change things too far) it could increase the likelihood that at least
one of its children would be better adapted than its parent. However I maintain that
such a stress induced mutation producing gene has had no significant effect on the
history of life, at least not in animals that reproduce sexually.
That's a kind of Lamarckian adjustment of mutability. What I was referring to is simple
Darwinian adjustment of mutability. There are error correcting mechanisms for DNA
reproduction. Suppose they worked perfectly: then there would never be any genetic
variation and when the evironment changed the species would go extinct. But if they had a
slight error rate then there would develop a range of genetic diversity that might, under
environmental change, result in survivors or even new species. So on strictly Darwinian
theory the DNA error correction may be selected to be less than perfect.
Brent
Such a stress-mutation gene has never been found in a sexual animal and it's easy to see
why. In sex all the genes are not inherited in one big package but are shuffled around
with the genes of the other parent, so a animal that was lucky enough to inherit the
good genes produced by the hypothetical stress-mutation gene but not the stress-mutation
gene itself would do just as well or better than a animal that got both the good genes
and the stress-mutation gene that is no longer active because the animal is no longer
under stress. So even if such a stress-mutation gene did occur in one individual in a
population it would vanish in just a few generations from the gene pool. Natural
Selection doesn't figure "I better keep that stress-mutation gene because even though
there is no stress now that could change and such a gene might come in handy in the
future". Evolution has no foresight and can't think and all that matters to it is
what's happening right here right now.
John K Clark
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