On Thu, Apr 18, 2013 at 1:29 PM, meekerdb <[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. > 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. 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 > > > > > > -- > You received this message because you are subscribed to the Google Groups > "Everything List" group. > To unsubscribe from this group and stop receiving emails from it, send an > email to [email protected]. > To post to this group, send email to [email protected]. > Visit this group at http://groups.google.com/group/everything-list?hl=en. > For more options, visit https://groups.google.com/groups/opt_out. > > > > No virus found in this message. > Checked by AVG - www.avg.com > Version: 2013.0.3272 / Virus Database: 3162/6252 - Release Date: 04/17/13 > > > -- > You received this message because you are subscribed to the Google Groups > "Everything List" group. > To unsubscribe from this group and stop receiving emails from it, send an > email to [email protected]. > To post to this group, send email to [email protected]. > Visit this group at http://groups.google.com/group/everything-list?hl=en. > For more options, visit https://groups.google.com/groups/opt_out. > > > -- You received this message because you are subscribed to the Google Groups "Everything List" group. To unsubscribe from this group and stop receiving emails from it, send an email to [email protected]. To post to this group, send email to [email protected]. Visit this group at http://groups.google.com/group/everything-list?hl=en. For more options, visit https://groups.google.com/groups/opt_out.
