On 4/18/2013 11:09 AM, John Clark wrote:
On Thu, Apr 18, 2013 at 1:29 PM, meekerdb <meeke...@verizon.net <mailto:meeke...@verizon.net>> 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.


No because in a sexually reproducing animal the genes that make the error correcting machinery are inherited independently of the very genes that they have corrected, and the vast majority of mutations are detrimental not helpful. So in any generation the offspring of a animal with good error correcting machinery will almost always do better than offspring from a animal with poor correcting machinery.

I think this overlooks the fact that there can be many mutations that are neutral relative to a given environment, but under a change or in combination with another may be advantageous. But I'll look up Dawkins argument.

Brent

And even in the very rare cases where the mutation caused a improvement in a gene the animal will do better if it has the gene for the better error correcting machinery, because otherwise that good gene is likely to mutate again and this time the mutation will almost certainly be bad. As Richard Dawkins said in his wonderful book "Climbing Mount Improbable":

"The predaliction to mutate is always bad, even though individual mutations occasionally turn out to be good. It is best, if more than a little paradoxical, to think of natural selection as favoring a mutation rate of zero. Fortunately for us, and for the continuance of evolution, this genetic nirvana is never quite attained."

  John K Clark








    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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