Posted by
Nick Thompson on
URL: http://friam.383.s1.nabble.com/Relaxed-Selection-a-b-level-posting-tp1315075.html
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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