Posted by
Russell Standish on
URL: http://friam.383.s1.nabble.com/Relaxed-Selection-a-b-level-posting-tp1315075p1315243.html
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.
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. Selection under such circumstances would be fairly
relaxed. 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.
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 :(
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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