On 18 Apr 2013, at 22:05, Craig Weinberg wrote:
On Thursday, April 18, 2013 1:29:29 PM UTC-4, Brent wrote:
On 4/18/2013 8:15 AM, John Clark wrote:
On Wed, Apr 17, 2013 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.
How does a deterministic universe invent something which is
intentionally less than perfect? I'm not saying that it couldn't, or
didn't, but why would there really even be any possibility of
volatility built into physics in the first place? What, in a
deterministic universe, constitutes an 'error'?
A deterministic reality might be unable to make an error at the
"bottom level", but if it can emulate high level complex processes,
like running some complex software, and such software can make an
error with respect to the goal (like "survive"). Look at some youtube
"crash investigation" showing why today some plane crash are due to
computer errors. The error can have multiple origin, hardware or
software.
Likewise it is reasonable for a biologist to say that when a DNA
polymerase introduces an unwanted supplementary nucleotide, it is
making an error. In fact living cells contains a lot of error
correction code to handle such cases, with 'error' taken in a sense
similar to the one used in computer science. This illustrates that
some errorless low-level can support higher level errors.
Bruno
Craig
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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