Posted by
Nick Thompson on
URL: http://friam.383.s1.nabble.com/Relaxed-Selection-a-b-level-posting-tp1315075p1315474.html
Russell,
Allow me to use CAPS in your text to distinguish my text from yours in the
dialogue below.
Some Santa Fe locals have cautioned me severely that it is impossible to
use CAPS in an email message without shouting; but I am hoping that that
convention does not extend to the southern hemisphere, but if it does, I
apologize in advance. .
Nick
Nicholas S. Thompson
Emeritus Professor of Psychology and Ethology,
Clark University (
[hidden email])
> [Original Message]
> From: Russell Standish <
[hidden email]>
> To: <
[hidden email]>; The Friday Morning Applied Complexity
Coffee Group <
[hidden email]>
> Date: 10/10/2008 7:16:11 PM
> Subject: Re: [FRIAM] Relaxed Selection, a b-level posting
>
> One should not confuse economics with biological selection. It would
> seem plausible that good economic times might lead to rapid evolution
> of economies, such as during the recent Internet bubble for instance,
> but not that it would have any influence on us at the genetic level.
WELL, EVEN IN THE ECONOMIC DOMAIN, I AM TROUBLED BY THE SUGGESTION THAT THE
REMOVAL OF K-SELECTION (YES, FOLKS, i ADMIT THIS IS A B-LEVEL POST) MEANS
THAT ALL SELECTION HAS BEEN RELAXED. OBVIOUSLY, THERE IS STILL R-SELECTION
TO CONTEND WITH. SO EVEN IN A POST EXTINCTION (OR POST RECESSION
ENVIRONMENT), THERE COULD BE INTENSE COMPETITION IN THE SPEED WITH WHICH
FIRMS EXPAND OR ORGANISMS REPLICATE.
>
> The sort of idea that David Green was proposing was that ecosystems
> (aka foodwebs) would cycle between a chaotic and a stable phase. My
> take on this is that immediately after a mass extinction, just about
> any foodweb is stable, because there are not enough connections to
> make it chaotic.
I AM EVEN MORE IGNORANT THAT USUAL IN THIS, HERE, DOMAIN, BUT ISNT IT
POSSIBLE THAT A WEB COULD BE LESS STABLE BECAUSE IT HAD FEWER CONNECTIONS?
DOESNT IT DEPEND ON THE NATURE OF THE WEB ... LIKE WHETHER ITS EDGES (IS
THAT THE RIGHT TERM) ARE MORE SERIAL OR PARALLEL, FOR INSTANCE?
Selection under such circumstances would be fairly
> relaxed.
MY BASIC INTUITION HERE IS THAT IT DEPENDS ON WHICH SORT OF CATASTROPHE
[NEARLY] TAKES OUT THE SPECIES. SELECTION IS JUST DIFFERENTIAL REPLICATION
WITH RESPECT TO SOME HERITABLE PROPERTY OF THE INDIVIDUALS IN THE SPECIES
[OR IN SPECIAL CASES, GROUPS OF THE SPECIES]. FOR INSTANCE, IT HAS BEEN
ARGUED THAT AT THE EXTREME BOTTLENECK WHERE HOMO SAPIENS EMERGED, THERE WAS
TREMENDOUS K SELECTION ON GROUPS. IN A FAMINE SITUATION, THOSE GROUPS
THAT COULD HOLD TERRITORY OR TAKE IT FROM COMPETING GROUPS WERE THE FEW
THAT SURVIVED. HENSE THE EXTREME GROUPISHNESS OF THE HUMAN SPECIES. SO
THAT WOULD BE A POSITIVE INSTANCE FOR YOUR ARGUMENT. BUT IF THE SPECIES
HAD BEEN TAKEN OUT BY SOME OTHER EVENT .... ROCKS FALLING OUT OF THE SKY
.... THEN THERE WOULD HAVE BEEN NO SELECTION. DOES THIS MAKE SENSE, OR AM
I MISUNDERSTANDING THE ARGUMENT?
IS THERE ANY REASON TO BELIEVE THAT FOOD WEB COLLAPSE WOULD BE ANY MORE
SELECTIVE THAN THE CHALLENGES OF RAPID REPRODUCTION????
As evolution proceeds, the foodweb becomes more
> complex until such a time as chaotic behaviour sets in. Extinction
> becomes increasingly likely, and corresponding selection becomes
> "fierce".
> Cycles of mass extinction followed by species radiation _may_ be a
> driving cause of ecosystem complexity.
MY ANSWER WOULD BE, "SOMETIMES". PERHAPS SOMEBODY COULD HELP ME OUT, HERE.
>
> I'm trying a slightly different tack with Tierra, of artificially
> inducing mass extinctions every now and then. I have also tried
> reducing parsimony pressure from time to time (I'm not sure what would
> be the biological world equivalent of this - possibly variation in
> background radioactivity or cosmic rays). But currently my simulation
> code is broken, so I haven't got too far with this to date :(
I OF COURSE KNOW NOTHING OF THE INTRICACIES OF SIMULATION. BUT THIS
INTERESTS ME AND I AM GLAD YOU ARE WRITING ABOUT IT.
AND I PROMISE I AM NOT SHOUTING.
NICK
>
> Cheers
>
> On Thu, Oct 09, 2008 at 09:36:39PM -0600, Nicholas Thompson wrote:
> > Russell Standish offered the following question:
> >
> > > > What do you think of "relaxed selection" ?
> >
> > My inexpert response:
> >
> > Well, I am uneasy about the concept. When I used to be a teacher of
these
> > things, students LOVED the idea that some ages and places are harsh and
> > some are mellow, and that selection is relaxed in the latter. The
metaphor
> > is drawn, I assumed, from human economics, where some decades can be
easy
> > and some difficult. But the metaphor is dangerously misleading ...
> > [thompson loves metaphors but he loves some metaphors a whole lot less
than
> > others, and this one is a terrible one.] The metaphor is terrible
because
> > the time-scale of oscillations of good and bad times in economics is WAY
> > too short for the reproductive capacity of the species to respond. So
the
> > "times" are sort of independent of the reproduction of the species.
> >
> > But in the evolutionary time scale, whether times are good and bad is
> > determined not by how lush the environment but by whether the
environment
> > has been lush long enough for the reproductive potential of the species
to
> > catch up and de-lush it. So rather than think about "good times" in
> > evolution, I would tend to think of periods of rapid expansion of
> > populations (when selection is relaxed) and rapid contraction of
> > populations (when selection is intensified) and periods of stability
(when
> > selection is intermediate.)
> >
> > One of your respondents seemed (sorry, too lazy to go back and look) to
> > confound this issue with the question of how bushy or trunky the
> > evolutionary tree is. I dont think... that the two are related. Bushy
> > phylogenies ... like that of australopithecines (the bipedal apes that
were
> > around as genus homo was coming into being) would seem to be generated
by
> > the distribution of the species over a spatially variant but temporally
> > invariant landscape. Trunky phylogenies are produced by the
distribution
> > of the species over temporally variant and a spacially invariant
> > landscape. This latter pattern characteried the evolution of the genus
> > homo. The attributions of variance and invariance, of course, have to
be
> > made in terms of the longevity of the species and its tendancy to move
> > accross the landscape.
> >
> > So whether relaxed selection produces "exploration of morphology space"
> > will depend on the structure and stability of the environment in terms
of
> > size and longevity of the species.
> >
> > That's what I think of relaxed selection. Apologies if I have been
reading
> > carelessly.
> >
> > NIck
> >
> > Nicholas S. Thompson
> > Emeritus Professor of Psychology and Ethology,
> > Clark University (
[hidden email])
> >
> > > *************************************
> >
> >
> >
> > ============================================================
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> --
>
>
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> A/Prof Russell Standish Phone 0425 253119 (mobile)
> Mathematics
> UNSW SYDNEY 2052
[hidden email]
> Australia
http://www.hpcoders.com.au>
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Meets Fridays 9a-11:30 at cafe at St. John's College
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