On 4/18/2013 8:15 AM, John Clark wrote:
On Wed, Apr 17, 2013  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.

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itself would do just as well or better than a animal that got both the good genes and the stress-mutation gene that is no longer active because the animal is no longer under stress.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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