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Re: CNN article on radical mutation/doomsday genes
---Original Message-- From: Augustus T. White <firstname.lastname@example.org> 30
November 1998 14:04
>On Sunday, November 29, 1998 8:58 PM, John V Jackson
>> --Original Message-- From: Betty Cunningham <email@example.com>
>> 29 November 1998 23:24
>> I was concerned by this paragraph in it:
>> "Evolution is often thought of as incremental," said biologist Andrew
>> Cossins of the University of Liverpool in England. "But the fossil record
>> contains many examples of apparently rapid changes in body form. This
>> mechanism provides, for the first time, a means by which changes in body
>> form can be substantial and stepwise rather than progressive."
>> In fact, if it were true, it would only cause punctuated evolution in
>> response to abnormal heat.
>There is at least one trivial explanation for these results. Can the
>be distinguished from any environmental stress that causes a partial
>in the regulation of meiotic crossing over? In other words, are we looking
>a roughly random assortment of frameshift and unequal cross-over errors?
>a genetic point of view, how can a mechanism that significantly reduces the
>overall fitness of progeny be selectively favored? Sure, there's a chance
>you might produce a line that has some advantage under the new conditions.
> But, much more often than not, this mechanism would simply hasten the
>of an already marginal (for the new environment) species.
> --Toby White
Yes, I was thinking of saying something along those lines. A mess-up in the
cross-over mechanism hadn't particularly occured to me, but I was wondering
whether it could be interpreted as an increase in mutation rate. It's often
tempting to advocate a faster mutation rate as increasing the rate of
evolution, but if a faster mutation rate is "better", why isn't it standard
in the first place? Nature seems to tune the mutation rates quite nicely,
making them lower for large-genomed types.
But then again, two or three years ago there was news of a bacterium that
seemed to up the mutations when conditions became very difficult. Maybe
"faster" is too crude a simplification of "better" when it comes to genetic
evolution; mutations are a mixed blessing, and as you point out, "[such a]
mechanism [might] simply hasten the demise of an already marginal (for the
new environment) species."
In the last couple of weeks (in "Nature"?) it was mentioned that as a genome
got close to its 'optimum' (if we want to talk in those terms), small steps
were more likely to bring further improvement than large steps. Maybe this
is what increasing the mutation rate does - when you've got huge problems,
small steps, even in the right direction, are a waste of time; unless you're
going to make big steps you may as well not bother. Even though they are
more likely to finish you off quickly, they're your only hope - in other
words, just like hitting the hyperspace button in asteroids. (Once we get
into this kind of territory though, I begin to wonder whether my opinions
are worthy of an audience of hundreds!)
But even if that's why bacteria seem to be increasing their mutation rate, I
don't think what is really just failure of the heat shock defence mechanism
can be thought of as "a useful evolutionary ploy", and certainly not "a
central evolutionary process". Whether it's faults in meiosis, or extra
mutation, it's just another reason why animals shrivel up when they're
boiled! And of course, another example of the press making copy out of a
confused story, and I'm sorry to say, somewhat misleading the public, when
they could have printed . . . but that's another story.
John V Jackson firstname.lastname@example.org
"So many professors . . . so little time . . ."
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