http://friam.383.s1.nabble.com/Relaxed-Selection-a-b-level-posting-tp1315075p1317056.html
I think I agree with you. You say "So whether relaxed selection produces
resolidified. The question is if it occurs maybe once in a period of a
million years for each species... and for just one of perhaps thousands of
> -----Original Message-----
> From:
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> Behalf Of Nicholas Thompson
> Sent: Thursday, October 09, 2008 11:37 PM
> To:
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> Subject: [FRIAM] Relaxed Selection, a b-level posting
>
> 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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